*Article* **Flexible Sample Environments for the Investigation of Soft Matter at the European Spallation Source: Part III—The Macroscopic Foam Cell**

**Matthias Kühnhammer 1, Tobias Widmann 2, Lucas P. Kreuzer 2, Andreas J. Schmid 3, Lars Wiehemeier 3, Henrich Frielinghaus 4, Sebastian Jaksch 4, Torsten Bögershausen 5, Paul Barron 5, Harald Schneider 5, Arno Hiess 5, Peter Müller-Buschbaum 2,6, Thomas Hellweg 3, Regine von Klitzing 1,\* and Oliver Löhmann 1,5,†**


**Abstract:** The European Spallation Source (ESS), which is under construction in Lund (Sweden), will be the leading and most brilliant neutron source and aims at starting user operation at the end of 2023. Among others, two small angle neutron scattering (SANS) machines will be operated. Due to the high brilliance of the source, it is important to minimize the downtime of the instruments. For this, a collaboration between three German universities and the ESS was initialized to develop and construct a unified sample environment (SE) system. The main focus was set on the use of a robust carrier system for the different SEs, which allows setting up experiments and first prealignment outside the SANS instruments. This article covers the development and construction of a SE for SANS experiments with foams, which allows measuring foams at different drainage states and the control of the rate of foam formation, temperature, and measurement position. The functionality under ESS conditions was tested and neutron test measurement were carried out.

**Keywords:** foams; small angle neutron scattering; sample environment; instrumentation

#### **1. Introduction**

Neutrons play an important role for current fundamental science. Investigation of soft matter in the submicrometer range relies on neutron science due to the possibility of an unique contrast variation based on hydrogen–deuterium exchange. The European Spallation Source (ESS), which is under construction in Lund (Sweden), will be the leading neutron source in terms of flux and brilliance in the future [1,2]. This high flux will lead to decreasing measurement times and, therefore, will reduce the amount of beam time allocated to the individual users. This benefit also comes with a challenge, since the installation of sample environments (SEs) and the time required for preparation of the

**Citation:** Kühnhammer, M.; Widmann, T.; Kreuzer, L.P.; Schmid, A.J.; Wiehemeier, L.; Frielinghaus, H.; Jaksch, S.; Bögershausen, T.; Barron, P.; Schneider, H.; et al. Flexible Sample Environments for the Investigation of Soft Matter at the European Spallation Source: Part III—The Macroscopic Foam Cell. *Appl. Sci.* **2021**, *11*, 5116. https://doi.org/ 10.3390/app11115116

Academic Editor: Antonino Pietropaolo

Received: 30 April 2021 Accepted: 25 May 2021 Published: 31 May 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

experiment will become a crucial factor for an efficient use of the beamtime. Consequently, the design of SEs should have a strong emphasis on the reduction of down time during sample and SE changes. The FlexiProb project (funded by the Federal Ministry of Education and Research of Germany, BMBF) is a collaborative effort of three research groups to design and construct three SEs in the field of soft matter research for implementation at the two small angle neutron scattering (SANS) instruments at the ESS, namely LoKI [3] and SKADI [4,5]. The SEs include an in situ SANS/DLS setup [6], a GISANS setup [7], and a SE for SANS experiments on aqueous foams, which is presented in this paper. In principle, the SEs are also compatible with beamlines at other neutron sources. However, the carrier system was designed to specifically fit into the sample areas of the instruments mentioned above. Every SE is assembled on an optical breadboard, which will be mounted on the kinematic mounting system, which is currently developed by the ESS. The whole setup is then transferred to the sample area of SANS instrument with a pallet truck. This approach allows preparing the experimental setup outside the instrument before the actual experiment. In addition, the ESS is planning offline alignment stations at which prealignment can be done within the ESS Universal Sample Coordinate System (USCS) [8]. All of this will allow for an exchange of the whole SE in a single step. This should enable fast and easy changes between different SEs and, therefore, should reduce down time between different experiments and users.

Foams are ubiquitous in everyday life in detergents, cosmetics, and food. In addition, foams are used in industrial processes such as mineral flotation, oil recovery, and fire fighting. Given their large abundance in everyday life and industrial processes, foams are the subject of numerous scientific studies and books [9–15]. However, some fundamental parameters such as foam stability or foamablity (foaming capability) are still difficult to predict [16]. The reason for this lies in the complexity of the foam structure and the vast variety of foam stabilizers ranging from surfactants, ionic and nonionic, to polyelectrolyte/surfactant mixtures, inorganic particles, and proteins. Depending on the system, different parameters seem to govern the overall properties of the resulting macroscopic foam. These parameters include surface elasticity and viscosity [17,18], maximum disjoining pressure in individual foam films [19,20], the formation of aggregates [21,22], and the composition at the interface [23]. The reason for this broad variety of parameters associated with macroscopic foam properties lies not only in the distinct differences between foam stabilizers, but also in the complex structure of the foam itself. All of the above mentioned parameters were studied at single air/water interfaces, bubbles, or foam lamellae, which is a drastic simplification of the complex structure of foams. Although they are challenging, measurements on entire foams can address the structural complexity and dynamics. The dynamics inside of nanoparticle stabilized foams were studied by diffusing wave spectroscopy [24,25]. Here, two dynamic processes were observed: a fast one caused by the nanoparticle diffusion and a slow one reflecting the foam dynamics. The internal structure of foams can be investigated by SANS [26–31]. The main measurable feature here is the thickness of foam lamellae inside of the foam. In this context, specific salt and pH effects [29], the chemical nature of the surfactant [31,32], and different drainage states of the foam [26,29,32] were studied. Furthermore, it is possible to detect objects inside the foam such as micelles [26,27], solid nanoparticles [30], or polymer sufactant complexes [33]. In such experiments, contrast variation is especially powerful, because it allows to selectively mask or unmask objects or structures inside the foam [30]. Since foams are thermodynamically unstable by nature and, with the specific example of aqueous foams, are highly dynamic at a timescale of minutes, SANS experiments were limited to rather stable foams.

Different cell designs for SANS on foams were reported in literature [26,28,29,31]. In all of these cells, foam formation is realized by bubbling gas through a porous plate either made of steel or sintered glass. The first cell of this type was designed by Axelos et al. and consists of a Plexiglas cylinder with a single quartz window for the neutron beam [26]. Taking into account the changing liquid volume fraction along the height of a foam column,

Micheau et al. used a cell with three plane parallel windows at different positions along the foam cylinder [29]. This made it possible to probe the foam at different (gravitational) drainage stages. Following this approach, we designed a foam cell that allows SANS measurements at any desired height along the foam cylinder. Since the foam formation before each SANS experiment takes several minutes, the presented SE includes a sample changer for up to three foam cells, allowing foaming the next sample during the measurement of the previous one. As stated above, this is especially important for highly brilliant neutron sources such as the ESS in order to reduce the downtime between sample changes. The high flux and reduced measurement time at the ESS will also enable measurements with more dynamic and less stable foams and will allow studies with high time resolution, which is especially appealing for highly dynamic foams. In order to use the full potential of the ESS from day one, it is crucial to design and test SEs for various experiments before the start of operation.

In this article, we present the design and construction of the FlexiProb SE for SANS experiments on foams. Detailed technical aspects of the measurement cell itself and the peripheral components such as temperature control, gas flow control, and sample positioning, as well as first benchmarks for measurements with neutrons, are shown.

#### **2. Instrumental Concept and Performance**

#### *2.1. General Construction*

The main parts of the sample environment are three foam cells, in which the foam will form. Figure 1a,b show an engineering drawing and a photograph of a single foam cell. Each cell consists of a 250 mm long quartz glass cylinder with an inner diameter of 30 mm and a wall thickness of 2 mm. Quartz is almost transparent to neutrons and the circular design avoids the rupture of lamellae at edges. A porous quartz glass plate (pore size 10–16 μm, porosity P16 (ISO 4793)) is fused to the bottom of the cylinder. The whole cylinder is mounted to a gas-inlet socket via an O-ring in a crimp connection. From below, a gas (e.g., air or nitrogen) is pressed through the porous plate, which breaks the continuous gas flow into small bubbles. This results in the formation of foam, when an appropriate foaming solution is poured into the cylinder. Finally, the gas exits the cylinder at the open top, which ensures pressure equilibrium. For temperature control, two thermostating jackets are fitted to each foam cylinder, using titanium screws from the bottom of the gasinlet socket. One of the main features and advantages of this foam cell is the possibility to measure at any position along the height of the foam cylinder. Therefore, the thermojackets are designed in a way to leave a slit-shaped gap between them. The width of this gap governs the maximum scattering angle accessible. Figure 1c shows a sketch in top view for the estimation of the maximum scattering angle at the geometrically least favorable position. For a scattering event occurring at the edge of a 10 mm wide primary neutron beam (highlighted in orange) at the side facing the primary beam, the scattering angle limit 2*θlim* is 13.8°. Assuming a neutron wavelength of *λ* = 5 Å, the maximum scattering vector *qmax* is calculated by

$$q\_{\max} = \frac{4\pi}{\lambda} \sin(\theta\_{lim}) \approx 0.3 \,\text{\AA}^{-1} \tag{1}$$

This corresponds to a minimum measurable size of 2 nm in real space, which is sufficient to resolve structures such as foam films or incorporated objects such as micelles or nanoparticles. It is worth noting that the SANS instruments LoKI and SKADI at the ESS will be operated with a predicted neutron wavelength band of 2 Å to 22 Å and 3 Å to 21 Å, respectively [2]. We expect an accessible *<sup>q</sup>* range of 0.005–0.6 Å−<sup>1</sup> for our foam cell at these ESS instruments. The lower limit is governed by the instrument's design and the upper limit by the cell geometry. This will lead to a range of measurable sizes of ca. 1–125 nm. The gas-inlet socket and thermostating cylinder are made of AlMg4.5Mn0.7, a special aluminum alloy that is easy to process and not activated by neutrons. The hose connectors are made of AlMg4.5 and, therefore, are also not activated by neutrons. All three foam cells are placed in a folded AlMg4.5 socket.

**Figure 1.** Individual foam cell. (**a**) Explosion-view drawing and (**b**) photograph in front view. (**c**) Schematic top view. The individual foam cells consist of a quartz glass cylinder, thermojackets, and a gas-inlet socket. The neutron beam (highlighted in orange) passes the cell perpendicular to the thermojackets in variable height. For the estimation of the minimal range of scattering angles accessible, a scattering event at the (geometrically) least favorable position is considered (green arrow).

The side facing the primary neutron beam is protected by an aluminum plate covered with 1 mm B4C including rectangular slits at the respective positions of the foam cells. Since the cells are open to the top, an aluminum cover was placed above the cells to avoid dust incorporation. A backview of the mounted cells is shown in Figure 2a. The setup is placed on a translation stage (travel range 508 mm), which allows remote controlled sample changes between the different foam cells as shown in Figure 2b,c. The entire setup is mounted on a breadboard (900 × 1200 mm2, Newport Spectra-Physics GmbH, Darmstadt, Germany). Later on at the ESS, the entire setup will be mounted on a lifting table, which is also part of the unified carrier system used by all FlexiProb SEs. This will ensure fast setup changes by removing the entire setup including the board. The lifting table installed at LoKI and SKADI will have a vertical displacement range of >300 mm with a 0.1 mm positional accuracy, which is sufficient for the foam cell SE.

**Figure 2.** Overview of the sample environment (SE). (**a**) Backview of three foam cells on folded aluminum construction. (**b**) Technical drawing of the complete SE mounted on the breadboard. (**c**) Front view of the SE (technical drawing) without shielding.

#### *2.2. Gas Flow Control*

The flow of the foaming gas is controlled by a FG-201CV mass flow controller (Bronkhorst, AK Ruurlo, The Netherlands) operating at an upstream pressure of 3 bar. The gas flow rate can be adjusted between 0–30 mL min−1. The three foam cells have separate gas circuits with individual mass flow controllers. This opens the possibility to prepare foams while another is measured or to define different foam states with a fast shift between different columns. The devices are connected via RS232 connections to a serial device server (NPort 5450, Moxa, Taipei, Taiwan). Here, the RS232 signal is converted into an Ethernet signal, which is transmitted via LAN to the instrument control. Communication is realized on a dynamic data exchange (DDE) server implemented in the supplier's FlowDDE software (Version 4.81). With this connection established, the devices are controlled using the DDE client program FlowView (Version 1.23) also distributed by the supplier.

Figure 3 shows the results of a foaming experiment in which 12 mL of tetradecyltrimethylammonium bromide (C14TAB) (*c* = 3.5 mM) surfactant solution were foamed with synthetic air at a flow rate of *V*˙ = 30 mL min<sup>−</sup>1. Pictures of the foam column were taken in a time interval of 80 s and the respective foam heights extracted by image analysis. Neglecting foam decay, a theoretical foam height *hth*(*t*) was calculated using Equation (2) for comparison, which is based on the volumetric gas flow rate and the cross-sectional area of the foam cell.

**Figure 3.** Test of the foaming procedure and tightness of the gas flow system. (**a**) Three pictures of a foaming C14TAB (*c* = 3.5 mM) solution at different times. (**b**) Foam height as a function of time (black squares) and the theoretical height (red line) according to Equation (2).

$$h\_{th}(t) = \frac{\dot{V} \cdot t}{A} \tag{2}$$

Here, *V*˙ is the volumetric gas flow rate, *t* is the foaming time, and *A* is the crosssectional area of the foaming cylinder.

The measured values are in good agreement with the theoretical foam height as shown in Figure 3b. This shows that the gas flow system works and the foam is formed as intended.

#### *2.3. Temperature Control*

Temperature change of the foams is achieved by two AlMg4.5Mn0.7 thermostating jackets at both sides of each foam cylinder. The thermostating jackets of all three sample cells are connected via appropriate distributors to a Julabo FP50-HL circulating thermostat (Julabo GmbH, Seelbach, Germany) with a temperature range of −50 °C to 200 °C when the appropriate thermofluid is used. For studying aqueous foams, however, an achievable temperature range of 10 °C to 80 °C is typically sufficient, allowing the use of water as thermofluid. To validate the performance of the heat input by the thermostating jackets, tests with a foam stabilized by C14TAB at its critical micelle concentration of *c* = 3.5 mM were performed [34]. Therefore, 12 mL of the surfactant solution were foamed at ambient temperature with a synthetic air flow of 15 mL min<sup>−</sup>1. After the foam reached the top of the quartz cylinder, the gas flow was stopped and the setpoint of the water bath thermostat was adjusted to 50 °C. The evolution of the temperature was monitored by three Pt-100 temperature sensors (model PT-102-3S-QT, Lake Shore Cryotronics, Inc., Westerville, OH, USA) at different positions at a height of 11.5 cm inside of the foam cylinder. The positions were chosen in a way to reflect the asymmetric shape of the thermostating jacket around the foam cylinder as indicated by A, B, and C in Figure 4. One sensor was put in the center of the cylinder (C), while the remaining two sensors were placed on the rim of the foam column, one in close proximity to the thermostating jacket (A) and one right behind the neutron window slit (B). The evolution of the temperature and a schematic sketch of the different positions are shown in Figure 4a.

Following an initial increase, the temperature reaches a plateau at all three positions after around 20 min. The final temperatures were 48 °C at position A (close to thermostating jacket), 42 °C at position B (behind neutron window slit), and 45 °C at position C (center). This temperature gradient is explained by the asymmetric shape of the thermostating jacket around the foam cell and the low heat conductivity of foams. As explained in Section 2.1, this asymmetric shape was chosen to allow SANS measurements at any height along the foam cylinder, accepting the drawback of a potential temperature gradient. The temperature jumps observed at every position are most likely due to air bubbles passing by the sensors, changing the heat conductivity next to them.

In order to reduce this temperature gradient, the experiment was repeated with the foam cylinder wrapped in aluminum foil (see Figure 4b). Again, the temperature reaches a plateau after around 20 min with final temperatures of 49 °C at position A, 47 °C at position B, and 48 °C at position C. Wrapping the cylinder in aluminum foil decreases the temperature gradient inside the foam because of the improved thermal contact between the quartz cylinder and the thermostating jackets. In addition, aluminum is almost transparent to neutrons and is also often used as a material for neutron windows. A drawback of this approach is that it is no longer possible to observe the foam during a SANS experiment with a camera. Detecting the formation of holes at the measuring position is sometimes beneficial, especially when dealing with rather unstable foams where holes may form randomly. Depending on the requirements regarding the accuracy of temperature control, one of the two methods described can be used.

**Figure 4.** Evolution of the temperature of a tetradecyltrimethylammonium bromide (C14TAB, *c* = 3.5 mM) foam in the foam cylinder without (**a**) and with (**b**) aluminum foil cover. The temperature was monitored using three Pt-100 temperature sensors at positions depicted by the inset. The setpoint of the water bath thermostat was adjusted to 50 °C at the beginning of the experiment and was reached after ca. 8 min.

#### *2.4. Sample Positioning*

Horizontal sample alignment is achieved with a linear translation stage (LS-180, Physik Instrumente GmbH & Co. KG, Karlsruhe, Germany) with a maximum load of 100 kg, an operating displacement of 508 mm at a maximum speed of 150 mm s<sup>−</sup>1, and a bidirectional repetition accuracy of ±0.1 μm. The linear stage is driven by a two-phase bipolar halfcoil stepper motor (model PK-258-02B, Oriental Motor, Tokyo, Japan). The position is monitored with a linear optical encoder with RS-422 quadrature signal transmission (LIA-20, Numerik Jena, Jena, Germany). The entire setup will be placed on an optical breadboard based on a lifting table, which ensures the vertical sample alignment. The control unit was built according to ESS specifications ensuring compatibility with ESS control standards. Figure 5 shows the corresponding circuit diagram for the custom built crate. The translation stage is labeled with "AXIS 1". For testing purposes, a two-axis goniometer was also integrated (motor top, motor bottom, encoder top, and encoder bottom). However, in the framework of the foam cell SE, this goniometer is not used.

**Figure 5.** Circiut diagram of the motion control crate. Beside the translation stage, a two-axis goniometer is also controlled by this crate.

The custom built 19-inch crate is equipped with 24 V (BLOCK Transformatoren-Elektronik GmbH, Verden, Germany) and 48 V (Mean Well Enterprises, New Taipei City, Taiwan) power supplies. The latter one provides power for the motors while the first one provides the power for the control unit. The control unit is based on an Ethernet fieldbus system (EtherCAT, Beckhoff Automation GmbH & Co. KG, Verl, Germany). An embedded PC (CX5130) is connected to a potential distribution terminal (EL9189) and a stepper motor terminal (EL7041), which ensure the motor movement. A digital input terminal (EL1808) and a digital output terminal (EL2819) are connected, sending and reading the motor positions. Additionally, an incremental encoder interface terminal (EL5101) is added to read the encoder signal out.

The embedded PC communicates with the hardware of the linear stage via the Twin-CAT 3 software. This signal is forwarded to the Experimental Physics and Industrial Control System (EPICS) [35], which will be the unified control software for beamline devices at the ESS and is able to control the devices and monitor their state. The EPICS is used by the Networked Instrument Control System (NICOS) [36], which offers a graphical interface for users and is the outermost layer of the instrument control structure at

the ESS. Further details regarding instrument control and data streaming are described elsewhere [37].

From 2015 until 2019, the ESS operated a dedicated testbeamline at the Helmholtz-Zentrum Berlin, also known as V20 [38,39]. Here, a fully workable environment, mimicking a future ESS instrument, was built up for testing and development. The linear stage was successfully tested at this instrument, proving the compatibility with the ESS standards in terms of control, interaction with other devices, and data logging.

The integration of the peripheral SE components into NICOS also allows programmable measurements with automated changes between the three foam cells and the measurement height along each cell, varying temperature, and gas flows.

#### **3. Neutron Test Measurements**

Test measurements with a single foam cell were carried out at the KWS-1 small angle scattering diffractometer at the Heinz Maier-Leibnitz-Zentrum (MLZ, Garching, Germany) [40,41]. Figure 6a shows the foam cell at the beamline. All measurements were performed at a wavelength of 4.92 Å with a 10% wavelength resolution (FWHM), a squared neutron beam of 10 × 10 mm, and a data acquisition time of 5 min. Scattering patterns were recorded with a 6Li-scintillation detector with photomultiplier tubes and a spatial resolution of 5.3 × 5.3 mm2. All measurements were background corrected due to dark current. The foam measurements were also corrected for the scattering by the empty cell. The sample–detector distance was determined using an optical theodolite. Figure 6b shows the 2D detector image of the empty foam cell recorded at a sample–detector distance of 7.615 m. As expected, the empty quartz cylinder provides a low background with no significant secondary scattering.

**Figure 6.** (**a**) Single foam cell installed at the KWS-1 beamline at the MLZ. (**b**) 2D SANS data of an empty quartz foam cylinder. (**c**–**e**) 2D SANS data of a steady-state foam produced from a 25 g L−<sup>1</sup> SDS solution at 16 cm (**c**), 9.5 cm (**d**), and 2 cm (**e**) foam height above the foaming solution. All experiments were carried out at a sample–detector distance of 7.615 m. Data acquisition time was 5 min.

Test measurements were conducted with a foam stabilized by 25 g L−<sup>1</sup> (86.7 mM) sodium dodecyl sulfate (SDS), which is well above the critical micelle concentration of 8 mM [42], at different foam heights. This system was chosen because of the high foam stability and the fact that the first study ever performed on SANS on foams also used a SDS foam at this concentration, making it a reference system [26]. 12 mL of the surfactant solution were initially foamed with a nitrogen gas flow rate of 10 mL min<sup>−</sup>1. After the foam level reached a height of around 18 cm, the gas flow was reduced to 1 mL min<sup>−</sup>1. At this flow rate the foam height does not change anymore, meaning that the foam formation at the

bottom and the foam decay at the top of the column are balanced. This results in a steadystate foam, in which the foam height corresponds to the age of the foam (i.e., the time passed after its formation at the bottom of the cylinder) and therefore its drainage state.

Figure 6c–e shows the corresponding 2D detector images recorded at 16 cm, 9.5 cm and 2 cm above the foaming solution. All images exhibit an isotropic scattering signal around the primary beam. This reveals that the neutron path length through the cell is long enough to average over all orientations of the foam structure, namely the liquid films, within the measuring window. The scattered intensity decreases with increasing measurement height. This is explained by the decreasing liquid volume fraction of the foam with increasing foam age (or height) and proves that different states of the foam can be accessed with a steady-state foam in one experiment.

Axelos et al. studied the same system using a similar foam cell with a single quartz window for the neutron beam in the lower third of the cylinder and the reported values are shown for comparison (closed squares in Figure 7) [26]. They performed two types of measurements. The first type of measurement was a continuous foaming experiment, in which the SANS data were recorded while nitrogen was continuously bubbled through the foaming solution. This resulted in a wet foam at the measuring position. The second type of measurement was a drainage experiment, in which the gas flow was stopped after foam formation. After some time, this led to a dry foam at the measuring position at the bottom of the foam column. These two types of foams are related to different foam heights in a steady-state foam. Here, a wet and fresh foam is observed at the bottom while a dry and aged foam is observed at the top of the steady-state foam.

**Figure 7.** Radial averaged scattering data from a 25 g L−<sup>1</sup> SDS foam (86.7 mM) at three different foam heights in a steady-state foam (open symbols) and comparison with reference data of a wet continuous foam and a foam after drainage [26].

The measured radial averaged scattering curves are plotted in Figure 7 (open squares). The data were shifted in intensity for better comparison. Normalization of SANS data of foams is still challenging and was not an aim of this experiment. The determination of the foam's liquid volume fraction based on the neutron transmission is prone to errors, since most foams show a high transmission close to 1 [26,29]. In general, the trend of measured scattering curves are in good agreement with the literature data, showing that there are no intrinsic artefacts caused by the foam cell. Data recorded at a height of 2 cm are similar to the one of a wet foam reported in literature and the data recorded at a height of 9.5 cm are in good agreement with the one of a drained foam. The data measured at a height of 16 cm correspond to a foam in an even more drained state. The shoulder at *<sup>q</sup>* <sup>≈</sup> 0.08 Å−<sup>1</sup> is attributed to surfactant micelles present in the liquid foam films. Consequently, the intensity

of this shoulder decreases with increasing foam height, as the liquid drains out of the foam films over time. The shoulder at *<sup>q</sup>* <sup>≈</sup> 0.02 Å−<sup>1</sup> occurs due to scattering at the liquid foam films and is related to their thickness [26]. The fact that this shoulder was not observed by Axelos et al. in their wet continuous foam could be explained by an even lower measuring position or higher gas flow rate in the steady-state. Both factors would results in a wetter foam, leading to a less ordered foam structure with a higher polydispersity regarding the film thickness and, therefore, in a smearing out of the corresponding scattering feature. Since it was possible to reproduce two different experiments reported in the literature by scanning along the foam height of a steady-state foam, the presented approach is valid for accessing the foam in different drainage stages with varying liquid volume fractions in one experiment.

#### **4. Conclusions**

We successfully designed, constructed, and tested a sample environment (SE) for SANS measurements on liquid foams. The SE allows the control of the gas flow rate used for foam formation and offers the possibility to control the temperature. The complete foam cylinder is made from neutron-transparent quartz glass, which enables SANS measurements at any position along the foam height and the possibility to study different drainage stages in a single experiment. Additionally, a sample changer on the basis of a linear stage was constructed and completely integrated into the foreseen ESS control structure at the ESS test beamline V20 at the HZB. Finally, SANS test measurements were successfully performed at the KWS-1 beamline at the MLZ with a model foam already reported in literature.

The presented SE is well-suited for studying liquid foams with SANS and should meet the special requirements of neutron sources with high brilliance such as the ESS, where an efficient use of the allocated beamtime becomes more important and the time required for sample changes should be reduced to an absolute minimum. This is accounted for by the sample changer for up to three foam cells and the possibility to access different states of the same foam in a single measurement cell. In return, a neutron source such as the ESS will allow new and/or more detailed SANS experiments using foams. The high neutron flux at the ESS will reduce the data acquisition time for a similar experiment as presented above at least by one order of magnitude to below 1 min. This will enable experiments with less stable foams or studies investigating structural changes in foams caused by external stimuli.

**Author Contributions:** Conceptualization, T.H., P.M.-B., and R.v.K.; planning and discussion of setup components, M.K., O.L., T.W., L.P.K., A.J.S., L.W., S.J., H.F., H.S., and A.H.; construction and test of setup components, M.K. and O.L.; software integration, M.K., O.L., T.B., and P.B.; SANS measurements, M.K., O.L., and H.F.; writing—original draft preparation, M.K.; writing—review and editing, O.L., T.W., L.P.K., A.J.S., L.W., S.J., H.F., T.B., P.B., H.S., A.H., T.H., P.M.-B., and R.v.K.; visualization, M.K.; supervision, O.L. and R.v.K.; project administration, T.H.; funding acquisition, T.H., P.M.-B., and R.v.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the German Federal Ministry for Education and Research (BMBF) within the project "FlexiProb" sample environment grant number 05K2016.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Derived data supporting the findings of this study are available from the corresponding author upon reasonable request.

**Acknowledgments:** We thank Judith Houston (ESS) for valuable discussions and Dirk Oppermann (TU Darmstadt) for help with constructing the foam cell. Furthermore, We thank Ibrahim El-Idrisi (TU Darmstadt) and Konstantin Quoll (HZB) for wiring and testing the motion control crate. We would also like to acknowledge Robin Woracek (ESS) and Peter Kadletz (ESS) for the help at the ESS test beamline.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


## *Review* **Soft Matter Sample Environments for Time-Resolved Small Angle Neutron Scattering Experiments: A Review**

**Volker S. Urban 1,\*, William T. Heller 1, John Katsaras <sup>1</sup> and Wim Bras 2,\***


**Featured Application: This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes.**

**Abstract:** With the promise of new, more powerful neutron sources in the future, the possibilities for time-resolved neutron scattering experiments will improve and are bound to gain in interest. While there is already a large body of work on the accurate control of temperature, pressure, and magnetic fields for static experiments, this field is less well developed for time-resolved experiments on soft condensed matter and biomaterials. We present here an overview of different sample environments and technique combinations that have been developed so far and which might inspire further developments so that one can take full advantage of both the existing facilities as well as the possibilities that future high intensity neutron sources will offer.

**Keywords:** soft matter; neutron scattering; time-resolved; sample environments

#### **1. Introduction**

The use of neutron scattering in soft materials research has a long tradition. Neutrons scatter from atomic nuclei and neutron scattering lengths depend unsystematically on the atomic number, and in the case of hydrogen-rich soft materials, the scattering lengths of protium and its isotope, deuterium, are very different. This ability to vary neutron contrast in hydrogen-rich materials with H/D isotopic labels has made neutron scattering an important tool in elucidating some of the basic concepts of polymer dynamics, phase behavior, and molecular conformation, both in solution and in the bulk.

There are a limited number of neutron sources and user facilities, which limits the number of experiments that can be performed relative to those possible using X-ray scattering techniques. Yet neutrons remain vital for materials research, owing to the unique information provided by their unique atomic and isotopic sensitivity, magnetic moment, and highly penetrating nature. An excellent opportunity exists to develop time-resolved experiments and the sample environments needed for these experiments. Related developments have taken place in X-ray synchrotron radiation facilities, in part due to the abundance of beamlines [1–3]. Despite the limitations due to the limited number of neutron scattering beamlines, the scope for developments of time-resolved experiments and the required sample environments is much wider than often is perceived.

The impact that neutron scattering can have on soft matter research can be increased when the capabilities of neutrons as applied to static structure determinations can be extended to the time-resolved domain. Apart from the data acquisition systems needed to

**Citation:** Urban, V.S.; Heller, W.T.; Katsaras, J.; Bras, W. Soft Matter Sample Environments for Time-Resolved Small Angle Neutron Scattering Experiments: A Review. *Appl. Sci.* **2021**, *11*, 5566. https:// doi.org/10.3390/app11125566

Academic Editor: Sebastian Jaksch

Received: 13 May 2021 Accepted: 7 June 2021 Published: 16 June 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

enable such experiments, it is also required to provide sample environments capable of perturbing samples in a controlled and homogeneous manner.

For soft matter studies, it is not only important to control sample parameters, such as temperature, pressure, pH etc. accurately, but it is also necessary to control the parameter history. For instance, the different thermal histories for a given material can lead to very different morphologies. This is particularly relevant when using complicated sample environments that try to mimic the conditions in which a material is exposed to processing conditions. Here, the combination of temperature, volume, pressure, shear force etc. has to be accurately controlled in order to be able to obtain meaningful insights into the material behavior during the process.

Neutron scattering is rarely the sole tool used to obtain an understanding of samples in out-of-equilibrium conditions and is often used in combination with data sets obtained from other experimental techniques where each technique addresses different length scales or thermodynamic aspects of the problem. If the sample environment is complicated enough and if the time-resolution is so fast that it becomes difficult to combine the data sets from individual experiments at a later stage, it makes sense to combine such experiments in a single multimodal experiment. This adds to the experimental complexity, but the benefit of obtaining complementary data, knowing that the sample is in the same physical state, outweighs the extra required efforts in developing and implementing such sample environments, and represents an excellent growth opportunity for novel neutron scattering instrumentation. Importantly, the availability of multi-modal experiments can increase the productivity and scientific impact of the large-scale neutron scattering facilities in a more cost-effective way than projects aimed solely at increasing neutron flux.

This article provides an overview of what sample environments and experimental techniques have been developed for soft matter research on neutron scattering beamlines with an emphasis, but not exclusively, on time-resolved small angle neutron scattering experiments, where one wants to follow the evolution of structure from an equilibrium state to one that is out of equilibrium, and vice versa.

#### **2. Time Resolution**

From a technical point of view, the raw neutron flux that a beamline can produce is an important parameter in defining the time-resolution that is achievable, but it is certainly not the only relevant instrumental parameter. Intrinsic background in the scattering pattern arising from the instrument, scattering contrast and sample chemical composition, sample size, detector efficiency, and associated electronics all play a role. Although the technical differences between experiments on a pulsed neutron source vs. a continuous source must be considered, in some ways they are less relevant than the type of sample environments used to carry out experiments, which can have a profound effect on the quality of the resultant data.

From a practical point of view, the time-scale over which the sample transforms from one physical state to another is the most important. However, equally important is how uniformly the sample can be perturbed. For instance, in a temperature jump experiment, temperature gradients are bound to develop. With the relatively large beam sizes produced by neutron scattering beamlines, one is detecting structural information over a thermal range. The faster the temperature jump, the larger the gradients, and the more complicated the data interpretation becomes.

The data quality per frame in a time-resolved experiment depends on the data collection time, which in turn depends on the progress in time of the process being studied. For different applications, different degrees of statistical accuracy are required. For example, if the goal is to perform a detailed structural analysis, the statistical quality of the data has to be very high. However, if one is satisfied with understanding how the radius of gyration of a particle in solution or the growth of a lamellar peak in a polymer crystallization experiment changes with time, the counting statistics requirements can be lowered and the experiments can be performed in a much more expeditious manner.

With the above points in mind, one can conclude that there is no definitive answer as to how fast a process one can resolve in a neutron scattering experiment. However, one should determine how fast a reasonable quality dataset can be acquired in order to address the problem and then assess whether or not the pertinent experiment is feasible to perform. New 'event mode' data acquisition will to some degree allow experimenters to have more leeway to carry out the experiment and afterwards decide on which time-resolution is feasible. 'Event mode' data acquisition involves retaining the position and time of each neutron detected, in contrast to traditional histogramming of detector data. Doing so makes it possible to parse a single data set collected into arbitrary time bins after data collection, which is extremely valuable for studies of time-dependent processes. It improves upon fast-frame data collection (i.e., a series of snapshots taken in quick succession) because it is not limited by the performance of the detector read-out, such as might be encountered with detectors used at synchrotrons.

For time-resolved experiments where a trigger is used to initiate a non-reversible process and the data are collected in individual time frames, this capability was available in the early 1990s with time-resolutions of between 2 and 3 min/frame to study late stage spinodal decomposition in polybutadiene-polyisoprene blends, where one of the blocks was deuterated [4]. Similar time resolutions have been reported for polystyrene-polyisoprene diblock-copolymers [5]. Nearly a decade later, a researcher studying micelle-to-vesicle transformations in D2O was surprised about what was feasible and wrote: 'A measurement time of 60 s already results in astonishingly good statistics, although the total surfactant concentration is less than 1 mg/mL to avoid interparticle interaction effects' [6]. A decade later, in an experiment on the growth of mesoporous silica nanoparticles, using deuterium contrast variation, a time-resolution of 10 s/frame was reported. See Figure 1 [7].

**Figure 1.** Time-resolved SANS data from the surfactant templated formation of mesoporous silica nanoparticles. This is one of the fastest neutron scattering experiments reported so far. A timeresolution of 10 s/frame rendered analyzable data (reproduced with permission from [7], American Chemical Society, 2012).

One may get the impression that every 10 years one gains a factor of 10 in timeresolution, but in reality, it demonstrates how strongly time resolution depends on the system being studied. Even though progress in instrumentation has been considerable, the quality of samples, to a great extent, still determines the achievable time-resolution. For example, in the case of a lysozyme crystallization experiment carried out in 1995, a time

resolution of hours/frame was mentioned [8]. Similarly, 10 min/frame was reported for the growth kinetics of lipid-based nano-discs to unilamellar vesicles [9]. When not making full use of selective deuteration, one can still expect 20 min/frame of low statistical data quality in a demixing experiment of incompatible crude oils [10].

Improving the achievable time resolution by increasing the neutron flux is a very expensive process. The European Spallation Source (ESS) being constructed in Lund, Sweden and the proposed Second Target Station (STS) of the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory in the USA will be the next generation of neutron sources offering increased neutron fluxes. However, both will require some years and large budgets until they are completed and ready for experiments. In the meantime, there are experimental methods currently available that significantly improve time-resolved experiments.

For experiments where cycling is an integral part of the study (i.e., oscillatory shear), or the periodic deformation used in simulations of the behavior of rubber tires, one can use a series of repeated short time frames and then merge the data series on-line. In principle, if the sample survives, one can collect for extended periods of time to obtain the required statistics and thus obtain a very high time-resolution. This method has been used for large oscillatory shear measurements (LAOS) on triblock copolymer micelles [11] and the effects of start-up and cessation of flow [12] using a commercial stress-controlled rheometer in the Couette geometry, where the rheometer generates an analog I/O signal that can be used to synchronize with the neutron scattering data acquisition system. In the case of the these strongly scattering systems, 300 cycles were sufficient to achieve 100 ms time-resolved data.

If an experiment that is not intrinsically cyclic can be accurately repeated, then one can follow the same procedure. Such a strategy can work if the sample can be recycled or if the synthesis/preparation is not too costly or time-consuming. Whether this is practically feasible depends on the length of the interval between experiments. In a temperature quench or pressure jump experiment, the dead time would be the required time to heat the sample up again before the next quench or to release/built up the pressure. A recent example of this is a series of pressure jumps that were used to study the phase transition kinetics of smart N-n-propylacrylamide microgels [13]. The jumps (200-40-200 bar) were performed with a frequency of approximately 23 Hz and repeated 5400 times. A time-resolution of 10 ms/frame was obtained (2 Hz frequency) over a period of 1.5 h of experimentation.

Another approach used to obtain good quality time resolution data of a continuous process is to translate the distance from the point where the perturbation takes place (e.g., mixing, extrusion, temperature change) to the point where the neutron beam interacts with the sample and translating this into time. By varying the time between the initiation point and the beam intercept, one can construct a timeline. An excellent example of this method is the (X-ray) study of polyolefin crystallization using an extruder [14]. Such experiments could easily be used on neutron beamlines as well. This translation method in combination with SANS was applied in studies of phase-separating systems, such as the cellulose nitrate/methyl acetate/isopropanol/deuterium oxide mixture, where the sample environment mimics the relevant conditions for industrial casting evaporative processes. See Figure 2 [15].

Better resolved time data are possible with the TISANE technique [16], and the first condensed matter results using this technique were reported in 2006 [17]. The technique can either be used on a pulsed neutron source or a steady-state source SANS beamline equipped with a timing chopper. Since this technique also requires periodic modulation of the sample, it therefore has a somewhat limited range of applications. Even though the TISANE technique offers great potential for the acquisition of very high-quality timeresolved data, it appears it is available to facility users, and it remains to be utilized to its full potential for time-resolved studies. The TISANE technique can, however, be improved through the use of time-of-flight techniques and event-mode data collection [18]. This can push the boundaries to 0.1 ms/frame but, again, only for experiments where cyclic data collection is feasible, and the samples scatter sufficiently strongly.

**Figure 2.** A flow-through cell used to study the liquid-liquid demixing process, which is the preliminary stage before casting the material to form a porous membrane. The degree of phase separation and the composition of the different phases determines the membrane structure to a large degree. The stirred reaction vessel is connected to the measuring cell, and the reacting mixture can be pumped through the neutron beam (reproduced with permission from [15], AIP Publishing, 2017).

We should point out that the above-mentioned examples are not intended to be a comprehensive list of what is feasible with time resolved neutron scattering experiments. Instead, the intention is to show that even though neutron beams are not as intense as X-ray beams, this is not a reason why one should not develop and carry out time-resolved studies. Although beyond the scope of this manuscript, one should also consider a change in mindset regarding time-resolved data. If the purpose of the experiment is to obtain insights into the evolution of the structure, instead of the accurate structural determination, a lower threshold for counting statistics data is acceptable as long as one properly analyzes the data and applies the appropriate error bars to the derived parameters.

#### **3. Sample Environments**

A sample environment can be a basic piece of equipment that is used to bring a sample to a steady state in order to measure the material properties and morphology or it can be used to bring the material out of equilibrium and in the experiment follow the structural evolution on the pathway to equilibrium. The latter can be of pure fundamental nature or a process mimicking an industrial process where several parameters like pressure, temperature, shear force, and tensile load are all varied simultaneously.

While many hard-condensed matter neutron scattering experiments use cryogenics, vacuum, and high magnetic fields, soft matter research has its own specialized sample environment requirements. Cryogenic conditions convert soft matter in general to hard matter, which is only in rare circumstances of interest in soft matter research.

Although neutron facilities historically were the first to develop sample environments for non-equilibrium studies, the advances in sample environments at synchrotron sources have in recent times taken place at a quicker pace than those at neutron sources. This does not imply that there is less demand for such developments, but it is more a reflection of the fact that it is more difficult to develop and implement novel sample environments at neutron sources, as a result of the size and intensities of the available neutron beams and the limited number of available instruments. While in the 1990s, X-ray beam sizes on the order of 300 μm were quite common, specialized beamlines currently can produce sub-micron size beams. Neutron beam sizes usually vary between 1 and 10 mm.

Traditionally, one key advantage that neutrons have over X-rays is their penetrating ability through different sample environment materials, making it possible for neutrons to study in a more facile manner materials under extreme conditions, such as elevated pressures, for example. However, the present generation of upgraded high energy storage rings generates high brilliance even in the photon energy range where the penetration is strongly enhanced and can be foreseen to encroach upon this neutron monopoly.

#### *3.1. Temperature*

Temperature is one of the basic parameters that can be varied during an experiment. This was already remarked upon by André Guinier in the proceedings of the first small angle scattering conference organized in 1965 [19]. For soft matter, research temperature control is important since the thermal history of a sample can dictate the material's ultimate properties. The main technical issue for neutron scattering is that neutron beam sizes are relatively large, making it more difficult to minimize sample environment temperature gradients. In the case of sample environments for static experiments, there are good commercial solutions to this problem. However, when there are special requirements, like the need to rotate the sample during a crystallization experiment, where the possibility of sedimentation is a real possibility, temperature control becomes somewhat more complicated, but in the range of between −10 and 80 ◦C, there are solutions [20,21]. In these cases, temperature control can be achieved using halogen light bulbs as the heating source and an infra-red sensor as thermal sensor, with an accuracy of approximately ±2 ◦C. Also, accurate control can be achieved by using water baths.

For soft matter, however, the sample's thermal history can determine its final morphology and it is thus important to accurately control both heating and, especially, cooling rates. As such, a logical development is to combine neutron scattering with differential scanning calorimetry (DSC), a development that was implemented at X-ray facilities in 1995 [22,23]. The engineering difficulties due to the requirement to have access to the sample with larger neutron beams is evident since it took until 2014 before this was implemented on neutron beamlines [24] with an instrument that can operate in the temperature range −150 ◦C to 500 ◦C.

The larger beam size also implies that for time-resolved experiments involving temperature jumps, the situation is more complicated due to the low thermal conductivity of the samples. Fast quench rates, combined with the larger sample sizes required for neutron experiments, increases the problem of thermal gradients over the sample so that one does not obtain a realistic correlation between temperature and structure at a given temperature, but over a bandwidth of temperatures. However, compared to X-rays, there is the advantage that metallic window materials can be used which, when connected with the heating/cooling elements, can mitigate the gradient problem to some degree.

For jumps at higher temperatures, one could contemplate the use of microwave radiation [25], which can provide more uniform heating of the sample. However, for quenches to a lower temperature, material thermal conductivity remains the rate-limiting parameter. For liquids, one can perform temperature jump (T-jump) experiments by injecting the fluid into a pre-heated/cooled cell using, for instance, a syringe pump [26]. A temperature jump device specifically designed to operate on a SANS beamline, using two furnaces between which the sample is shuttled, can operate in the range 150–600 K with heating rates up to 19 K/s and cooling rates 11 K/s [27]. One can also adapt a stop-flow cell to operate as a T-jump device. This was done to understand the kinetics of the collapse, transition, and subsequent cluster formation in a micellar solution of P(S-b-NIPAM-b-S) [28]. See Figure 3. Approximately 100 s were required for a modest temperature jump of 6 ◦C.

**Figure 3.** (**a**) Left hand panel, SANS curves obtained during a temperature jump on a micellar solution of P(S-b-NIPAM-b-S), from 29 to 35 ◦C, where the first structural changes were observed 7 s after initiation of the experiment. (**b**) The right-hand panel shows the structural models determined from the data, where micelles collapse and subsequently aggregate into clusters (reproduced with permission from [28], Wiley, 2012).

The latter example shows that it is not always necessary to use world record Tjump speeds to obtain the desired information with respect to the scientific question to be answered.

#### *3.2. Pressure*

Pressure is the thermodynamic parameter that is relatively easy to change homogeneously. For the larger sample volumes routinely used in neutron scattering, this allows the reduction/elimination of large pressure gradients over the sample, allowing for a better controlled experiment producing more robust results. Most high-pressure experiments use hydrostatic pressure, which is not directional. An example of uni-axial pressure exerted on a sample in combination with a SANS experiment can be found in soil- or geo-mechanics [29]. The pore size distribution in bentonite clay was investigated as a function of pressure whilst simultaneously loading the cell with dry CO2 and water in order to elucidate the role that intercalation of these two components play in the complicated pore-pressure diagram. Pressures up to 10 MPa at ambient temperature were applied.

An example where hydrostatic pressure was applied was in research to determine if CO2 could be stored in porous shales. Here, CO2 was not only the object of study but also the neutron contrast variation medium [30]. Pressures of 25–40 bar were achieved over a temperature range of 20–60 ◦C. This type of study can be relevant to soft matter where, for example, the porosity of a material must be characterized to understand the impact of processing conditions.

Not only does the static characterization of pores attract attention, but also the combination of hydrostatic and uniaxial pressure is relevant for understanding flow in porous materials [31]. In the fracking of oil-containing shales, water is used as the pressurizing agent. In the case of neutron scattering experiments, this allows one to exploit the difference in scattering length between light and heavy water, in addition to the natural air-matrix scattering length difference. Uniaxial stresses, σax, in combination with the hydrostatic pressure inside the pores, p, allows to generate an effective stress σ<sup>e</sup> = σax-p of 600 Bar.

An example of the effects of hydrostatic pressure is surfactant solutions of SDS in D2Oforming microemulsions, as shown in Figure 4. Here, a static pressure was applied and the effect of pressure is the continuous transformation of spherical particles to elongated micelles [32]. The pressure cell used was capable of a maximum pressure of 10 kbar and a maximum temperature of 80 ◦C.

**Figure 4.** The effects of hydrostatic pressure on a micellar SDS solution as observed in a SANS experiment. At increased pressures, there is a continuous transformation from spherical to elongated micelles as evidenced by the gradual peak shift to lower angle. Figure provided by author [32].

A detailed design for a temperature-controlled high-pressure cell developed for biological applications, specifically protein denaturation studies, was described by Teixeira et al. [33]. The sample cell was capable of a low temperature of −18 ◦C with a pressure of 2 kbar. Because of the cell's large thermal mass, which is required for mechanical strength at these elevated pressures, it required 1 hour for sample equilibration. When working at sub-zero temperatures, one stands the risk of ice crystal formation. Down to about −20 ◦C, ice formation can be inhibited by anti-freeze agents, but this will alter the biologically relevant environment of the proteins. By using pressure, the freezing point can be lowered, and the use of anti-freeze agents is avoided. There are several other sample cell designs available [34].

Pressure jumps can perturb a sample over the whole volume exposed to the neutron beam without any pressure gradients and can be relatively simply and accurately repeated. This makes it possible to perform such experiments with a reasonably high time resolution using the 'cyclic' procedure mentioned in the section on temperature jumps.

An example is the phase transition from swollen chains to polymer mesoglobules of an aqueous solution of poly(N-isopropylacrylamide) with pressure jumps across the coexistence line [35]. This was investigated with kinetic small-angle neutron scattering with a 50 ms time resolution. The pressure jumps were on the order of Δp ≈ 200 bar. The interesting variation here is that the data acquisition time per frame was not constant but starting with a time frame length of 0.05 s that was elongated by a factor of 1.1× for each frame, thus anticipating that events evolved fastest immediately after the pressure jump. Obviously, this has some consequences regarding the statistical quality of the data, but the experiment only had to be repeated five times. This is another area where 'event mode' data collection will allow the experimenter more freedom to postmortem decide how to time-slice the data set.

A similar development was used to study the volume phase transition kinetics of N-npropylacrylamide microgels [13]. A jump sequence of 200 → 40 → 200 bar was performed using a time frame length of 5 ms over a total time period of 350 ms. However, in this case, the experiment had to be repeated 5400 times before satisfactory data sets could be obtained.

It should be noted that pressure jump experiments, as those described above, are not only interesting for fundamental research purposes, but also understanding industrial processes. However, to do so, the apparatus should be capable of jumping both pressure and temperature simultaneously, preferably with the application of a shear force [36,37]. This type of experiment has been implemented for X-ray scattering, but it is probably still beyond the limits of what is feasible for neutron scattering due to beam size limitation and neutron flux.

#### *3.3. Shear and Rheology*

The flow of materials is a research area of interest to both the fundamental as well as the applied/industrial research communities, and one that lends itself to neutron scattering experiments. The cell walls of conventional Couette cells commonly used in neutron scattering experiments can be easily penetrated by neutrons and the amount of material required is small, which keeps deuteration costs to a minimum. Couette cells have a long history of commercial development and as such, are a mature technology able to keep a stable flow over the entire time required for the acquisition of data with good signal to noise ratio; one of the first mentions of the use of a Couette cell in a scattering experiment was in 1984 [38].

Rheology, however, is a complicated subject in which the observed components of a flow profile depend on the configuration of the cell or in which direction one probes the flow profile within the cell. In Figure 5, the different flow planes are defined and further discussions about the terminology can be found in an extensive review [39]. For the directions where one can probe the desired flow field whilst keeping the Couette cell axis vertical, i.e., the 1–3 and 2–3, radial and tangential directions, respectively, it is feasible to perform quantitative rheological experiments with neutron scattering [40,41]. However, a cell for the 1–2 direction, where one has to align the neutron beam in the gap parallel between the two Couette cylinders, has proven more difficult to design [42]. With the Couette cylinder axis horizontal, the material must be confined, otherwise gravity will force low viscosity materials out of the cell.

**Figure 5.** The different configurations in which a Couette type shear cell can be used. The different flow fields are indicated with v indicating the flow direction, ∇v the flow gradients, and ω the vorticity direction (**a**). In neutron scattering experiments, the 1–3 (**b**) and 2–3 (**c**) directions can be probed with a cell having a vertical rotation axis. On the other hand, the 1–2 (**d**) direction requires a cell with a horizontal rotation axis. Figure provided by J. Vermant [43].

For the conventional Couette geometry where the cylinder axis is vertical, one can rely on commercially available rheometers. Since the topic of shear and rheology is rather popular, there have been numerous in-depth reviews on the subject [39]. These reviews include oversights of other available shear geometries that have been used on X-ray and neutron beamlines. Measuring the axis torque allows quantitative measurements of shear stress simultaneously with macroscopic strain gradients imposed by the frequency of rotation and microscopic deformation observed in the SANS data [42]. As mentioned, for most neutron scattering experiments there are commercially available instruments, where the replacement of the commercial Couette cylinders by cylinders made out of neutron transparent materials like quartz and titanium can be straightforward.

The literature contains a wide range of subjects that have been studied using Rheo-SANS methods. They range from investigations into the shear banding mechanism in a fluid comprised of cetyltrimethylammonium bromide wormlike micelles [44], to detailed studies of polymer chain conformations composed of polyethylene-polypropylene blends with Si particles nanocomposites [45], to the shear-induced formation of rod-like entities in metallo-supramolecular gels based on a multitopic cyclam bis-terpyridine [46]. The Couette geometry can also be used to probe material relaxation properties by using an oscillatory flow protocol, which is mentioned in the section on time-resolution.

The 1–3 and 2–3 Couette geometries are now fairly standard for neutron scattering experiments. Progress in instrumentation in the coming years will most likely be incremental and most developments will focus on the analysis of neutron-rheology data sets [47]. Some developments were recently reported on the implementation of the technically more challenging case, where one wants to probe the 1–2 plane [42,48] by directing the neutron beam through the gap between the two cylinders that make up the Couette cell. With a small enough beam, it is possible to probe the different flow profiles as a function of the position within the gap [48]. Such spatial mapping is not commonly associated with neutron scattering since the neutron beams tend to be rather large and can only be reduced in size by sacrificing intensity. For stable flow rheological applications, this is a problem only limited by the available beam time and neutron flux, and not by any technical aspects. From an experimental point of view, it should be remarked that it is often necessary to obtain scattering data along all three shear planes [49]. Unfortunately, this requires the use of two different Couette cells capable of covering the same temperature and shear range. Designs for a cell that can accommodate experiments in all three shear directions are available, but rare [42], and still require substantial reconfiguration when changing between geometries.

In addition to the above-mentioned shear flow geometries, there is the less popular but useful plate-plate geometry [50] used in a range of SANS experimentation, such as studies on the self-assembly of nanofibers composed of fibronectin mimetic peptideamphiphiles [51].

The design for a cone-plate geometry instrument for use in reflectometry is discussed in the framework of test experiments involving polystyrene/deuterated polystyrene, with the flat bottom plate modified to be transparent to neutrons [52]. A modified commercial instrument, for example, was used for the study of asphaltenes in the reflectometry configuration [53]. However, placing the neutron beam in the gap between the cone and plate, like what has been successfully done with X-rays, requires that very tight neutron beam collimation be used, which impacts data rate and quality. An interesting development is the use of Grazing Incidence SANS or GISANS. The feasibility of this technique in combination with a cone-plate rheometer was demonstrated in experiments on bolaamphiphilic arginine-coated peptide nanotubes [54]. However, data collection took about 5 h per sample, indicating that this method still requires further development.

The more difficult problem of how one goes about studying elongational flow appears to still be out of reach of real time neutron scattering experiments. The methodology of flash freezing a material that has been subjected to elongational/extensional flow off-line and then using the frozen samples to carry out a static measurement was reported in 1990 [55], and the method was still regarded as recently as 2016 as being the best method to study dendritic polymer blends with linear chains [56]. Here, the main issue remains that the time-resolution of the physical process does not match the time-resolution that can be reasonably achieved on SANS beamlines.

Whilst the examples being discussed above fall under the 'drag flow' category, there are also configurations that allow 'pressure flows' to be studied [57]. Capillary- or Poiseuilleflow and slit-flow are examples of pressure flow. This type of flow is important to understand the fundamental behavior of chain molecules in conditions relevant for industrial processing. For instance, in injection molding, the predominant physical processes are Poiseuille flow and thermal quenches. Not only is flow in an unrestricted path relevant, but studies of the behavior of the material as it flows around obstructions and restrictions are also required. Such information provides firstly, insights into material properties, and secondly, these results can be used to validate computational models as to how entangled polymers behave under elongational flow or when encountering a change in flow geometry. In other words, such physical results provide predictions on how to process materials [58,59]. When run in an 'open' configuration, these set-ups require considerable amounts of material, which with deuterated samples tends to be prohibitively expensive. Hence, efforts have gone into recirculating flow cells, which require relatively small amounts (~200 g) of material [60–63]. This cell is equipped with non-birefringent sapphire windows that are strong enough to resist pressures of up to 10 MPa, and also allow for birefringence measurements to be carried out, thus creating a set-up which can deliver structural and orientational information over a wide range of length scales. See Figure 6.

**Figure 6.** 2D scattering patterns from a material encountering an obstruction using a pressure-driven slot flow cell (**a**,**b**). The neutron beam is directed at right angles with respect to the flow direction (**c**). The numbered boxes correspond to the different SANS patterns. The anisotropy is due to the deformation of the backbone of the comb-shaped polymer seed in this experiment (reproduced with permission from [63], ROYAL SOCIETY OF CHEMISTRY, 2009).

A recent design based on developments in microfluidics [64], which itself was based upon a larger scale design by G.I. Taylor from 1934, allows for a variety of different flows to be applied within a single sample environment. The Fluidic Four Roll Mill, so named because it uses four rolling cylinders [65], is a device consisting of 4 × 2 orthogonal channels in which flow patterns can be generated by opening/closing a series of valves [66]. See Figure 7.

**Figure 7.** A schematic of the fluidic Four Roll Mill device in which different flows can be generated. The flows can be created by applying a pressure flow in the channels marked with closed dots and opening the valves in the channels marked with the open dots. The neutron beam is directed along the white path between the flow channels with a diameter of 1 mm. The flow channels have dimensions of 2 <sup>×</sup> 3 mm2 (reproduced with permission from [66], Springer, Nature, 2018).

#### *3.4. Mechanical Deformation*

Uniaxial mechanical deformation studies on soft materials are relatively easy to implement and are extensively used by academics and in industrial materials testing laboratories. Several small-scale deformation stages are commercially available, but these are in general, only suited for qualitative tensile data involving local molecular conformations. To obtain quantitative tensile results simultaneously with the neutron scattering data, one has to make sure that the sample is uniform over its entire volume and not only at the point of intercept with the neutron beam. With the exception of ambient or near ambient temperatures, one encounters the issue of how to uniformly heat the sample. This obviously can be achieved by placing the entire deformation load frame in a temperature-controlled chamber, but in doing so, any temperature changes will be slow to equilibrate, thus limiting the technique's application with neutron scattering instrumentation.

Since polymeric materials exhibit a wide variety of materials properties, the type of required load frame depends on the maximum tensile force and elongation required. Elastic rubber samples require little stress but a high strain, i.e., elongation [67], whilst the reverse is true for High Density Polyethylene (HDPE) [68]. For such samples, the required mechanical performance (i.e., stresses between 10 and 200 N) required of the load frames is easily covered by commercially available equipment from a variety of suppliers.

Early on, mechanical deformation experiments were performed in a quasi-static fashion, i.e., deform-hold-collect data. This deformation protocol works well for some materials where the molecular relaxation times are long. Otherwise one has to revert to continuous stretch protocols where the data collection time can be problematic. This is often the situation when the materials are unclamped and allowed to molecularly relax [69]. Relaxation of isotopic blends of linear polyethylene and ethylene copolymers with butyl and hexyl was studied, but due to the relatively small amount of material in the neutron beam (intrinsic to this type of deformation experiments), data could only be obtained at 30 min time intervals. An extensive discussion on how the anisotropy manifests itself in scattering patterns, due to the molecular and domain orientation induced by applying the deformation, can be found in experiments of elastomeric polypropylene [70].

A method to increase the information content of on-line deformation experiments is the use of Digital Image Correlation (DIC) [71]. This optical method is easy to install on a neutron scattering instrument and allows one to probe the homogeneity of the deformation process over the entire sample and also provide macroscopic material parameters. See Figure 8. When combined with neutron scattering experiments, one obtains a more complete picture of the material's deformation behavior. Simultaneous DIC furthermore supplies additional validation of the reliability of the experimental results since mechanical problems, such as slippage at clamps, will be noticed earlier.

**Figure 8.** An experimental X-ray/neutron scattering set-up incorporating optical digital image correlation. This combination of experiments can increase considerably the information content of experiments and is relatively simple to implement. Figure made available by authors [71].

Although homogeneous temperature control on samples that require large elongation is somewhat more complicated to achieve, other parameters like humidity can be relatively easy controlled. This requires the construction of a solid chamber around the moving parts. An example of this is the stress-induced long range ordering in spider silk [72]. Here a combination of finite element modelling and SANS data were used to elucidate the role that crystalline domains play in the ordering of silk when extended. The crystalline domains are less susceptible to water uptake compared to the amorphous domains, and this physical characteristic allows for contrast variation to be used. By placing the tensile load frame in a 100% D2O relative humidity environment, it was possible to selectively deuterate the amorphous parts of the silk.

One of the issues that one might encounter due to beam intensity and the samples becoming thinner when elongated is that the statistical quality of the scattering patterns is rather poor. One might be tempted to use a stop-start technique where the material is not continuously stretched but instead, after a short stretch, a pause is taken to allow data to be collected. Of course, this has the problem that the sample is allowed to relax and the results will not necessarily be the same as with a continuous stretch. The differences between the results obtained with these two approaches when deforming polypropylene are discussed in the literature [73].

#### *3.5. Stop Flow/Chemistry On-Line*

To be able to follow structure formation due to chemical reactions requires reaction cells that are resistant to the chemistry being carried out and also capable of attaining the desired temperature and pressure range. In the case of low viscosity solutions, the reaction products can sediment out and therefore change the composition of the sample as 'seen' by the probe beam [74]. This can be overcome by the use of a tumbling cell, which rotates the sample solution around the beam axis, preventing sedimentation. These cells are routinely used in all neutron scattering facilities. As an alternative, a cell of sufficient thickness with a mechanical stirrer can also be used. As with any equipment that contains moving parts, this leads to a more complicated temperature control system. One design that contains an array of four tumbling cells, makes use of air cooling/heating, is capable of a limited temperature range of 10–50 ◦C, and is suitable for slow reaction kinetics without thermal variations [20]. By placing the equipment on a translation stage and triggering the chemical reactions at different times, it is possible to alternate between the samples and map out the kinetics over extended time scales, also making effective use of the allocated beamtime.

For faster experiments, sedimentation is less of a factor and here one can consider the use of conventional stop-flow cells. Due to the required beam size, the sample volume will be rather large, and thus there are constraints on the achievable mixing- and dead-times, but workable solutions do exist. A review on the use of stop flow cells in SAXS and SANS experiments was written by Isabelle Grillo [75], who pioneered such experiments on SANS beamlines. A practical example of such experiments is the formation of microgels due to the precipitation and subsequent polymerization of N-Isopropylacrylamide [76]. Here the early stage of gel formation was the point of interest, which is often the most difficult part since structural changes tend to develop faster than in later stages. A commercially available stop-flow cell was used at a fixed temperature. Data were collected over a period of 20 min with a time framing rate of 5 s/frame. However, in order to obtain sufficient quality data, the experiments were repeated three to four times and the results were averaged. The data yielded the total particle volume and the number density of particles. A similar home-built device was used to report on cationic liposomes complexes with DNA. However, instead of temperature, a pH jump was induced by the stopped flow to trigger the reaction [77].

By using continuous flow methods, a larger variety of experiments is feasible even though much larger quantities of materials are required. In some cases, it is even feasible to use a recirculating flow and gradually change the conditions without incurring the penalty of requiring large volumes of sample. This is especially relevant when dealing with deuterated materials. A purposely designed sample environment meeting these requirements was reported. See Figure 9 [78].

**Figure 9.** Schematic of an experimental set-up that allows structure formation due to chemical reactions to be followed in real time by SANS. The system consists of a reaction vessel where the reactions can be initiated using remotely controlled syringe pumps. A peristaltic pump is used to bring the mixture to the measuring cell. The system has the option to be used in open or closed loop configuration. In a closed loop system, one can, for instance, observe the effects of a gradual change in pH. Here, 'Nomad' is the name of the central control computer (reproduced with permission from [78], Springer Nature, 2018).

For test experiments, aqueous solutions of polyoxyethylene alkylether carboxylic acids, a class of surfactants with strong pH-responsive properties, were used. During the experiments, the pH was changed by titration. As the authors remarked, these time-resolved experiments, down to 1 s/frame, were made feasible in recent years by more efficient detectors and increased neutron flux thanks to improvements in neutron guide technology.

Pressurized CO2 gas can be used as a neutron scattering contrast agent in porous materials like lignite and shale [79], and SANS/USANS experiments are part of the toolset

that can be used to determine pore distribution size and morphology for pores that are accessible to the CO2. However, when introduced in its supercritical state (ScCO2), it is a good solvent, primarily for nonpolar low-molecular-weight compounds. For polar higher molecular weight compounds, it is a rather poor solvent. Thanks to the fairly benign conditions at which criticality occurs (7.39 MPa, 31.1 ◦C), ScCO2 is a fairly attractive option for performing chemical synthesis of surfactants, polymers, and biomaterials [80]. On-line neutron scattering investigations of poly(dimethylsiloxane) polymer-ScCO2 solvent phase diagrams were performed and fundamental applications demonstrated [81]. Time-resolved scattering experiments where the ScCO2 to CO2 transition was used as a foaming agent to create micro and nano foams allowed the kinetics of foam formation to be studied as a function of pressure and pressure modulation [82]. The use of fluorinated surfactants in CO2 microemulsions is widespread but not desired for environmental reasons. In a systematic pressure and contrast variation study, it was shown that partial substitution of ScCO2 by cyclohexane reduced the required amount of fluorinated surfactants considerably [83]. Contrast variation through the use of D2O exchange was crucial in this case and the only way this kind of structural information could be obtained.

Performance of on-line chemical synthesis experiments has so far not been widely explored, although it appears that neutron scattering could play an important role, as the above example has shown. When used for structure forming on-line chemical processing, temperature control and homogenization of the reaction mixture is of the utmost importance. The designs for such cells used in on-line experiments should take this into consideration, as well in allowing for the possibility of siphoning off small amounts of the reaction mixture (for off-line chemical analysis) during the course of the experiments without perturbing the pressure/temperature conditions [84].

The use of on-line size-exclusion chromatography to deliver well-defined and nonaged samples for scattering experiments has become feasible, although here one has to keep in mind the restrictions on the amount of available material. This method requires beamlines that can deliver high intensity and small beam sizes. However, when these conditions are met, the experimental accuracy can be considerably improved. For example, proteins that have a tendency to aggerate in solution can still be studied in their nonaggregated state [85].

#### *3.6. Electromagnetic Fields*

Sample environments generating electric fields have not been extensively developed for use at neutron beamlines. AC fields that can be used to (partially) align relatively short rigid polymeric molecules in solution in order to perform fiber diffraction experiments have been used for biological molecules. The main problem with this approach is that the frequencies used should be such that the sample does not heat up and that the fields are high enough that they are not shielded by the salts in the buffer solution [86].

The main problem with using static electric fields is that the voltage required as function of sample thickness is considerable. When using too high a field, one risks electric breakdown damaging the sample. To induce domain alignment in thin films of symmetric diblock-copolymer of polystyrene and poly(methylmethacrylate), (PS-b-PMMA) fields of 40 V/μm were used in a sample cell consisting of an aluminumized Kapton film used as an electrode and a similar electrode that is isolated from the sample by a thin layer of poly(dimethylsiloxane) [87]. The alignment process could be followed by time-resolved SANS experiments. As to be expected, the interplay between the sample thickness and the interfacial interactions between the electrode and the sample plays an important role. For thin samples, where the interfacial interactions are most important, the structure can evolve over periods of hours. On the other hand, for thicker films, complete alignment takes only minutes. Static electric-field-induced deformation of bulk poly(styrene-block-isoprene) lamellar phases, swollen in toluene or tetrahydrofuran, has been studied with SAXS and with SANS. Capacitor cells with 3–5 mm electrode gaps and typically 5 mm beam path length were used to apply up to 60 kV, reaching electric fields up to 12 kV/mm [88]. See

Figure 10. Electric breakdown is a common limitation under these conditions, sufficient stability for the duration of experiments can however be reached with careful control of experimental conditions, paying very careful attention to drying polymer and solvent to remove any traces of water.

**Figure 10.** Electric field setup used for on-line SANS experiments [89]. Schematic drawing of experimental setup (**a**). Capacitor dedicated for small-angle neutron scattering experiments of polymer solutions (**b**). The capacitor consists of gold electrodes and its interior parts are mantled in Teflon.

Dielectrophoresis uses the intrinsic polarizability of objects/molecules to be manipulated in a gradient or AC electric field. When this method is applied in combination with SANS, it is possible to follow the development of molecular ordering due to different field strengths and frequencies. A model system, polystyrene particles in H2O (diameter 195 nm and 530 nm), and an applied AC field formed colloidal crystals consistent with the space groups P6mm and C2mm [90]. A schematic overview of the cell is shown in Figure 11. The AC field was applied in transverse direction to the neutron beam and depending on the experiment, a range of 0 < ω < 100 kHz and 0.62 < E<1.4 kV was used with a cell thickness in the neutron beam direction of 130 microns. The cell thickness was limited in this design due to the requirement of exposing the sample to a reasonably homogeneous AC field; a thicker cell would contain field gradients.

**Figure 11.** Top view of an electrophoresis cell used for on-line SANS experiments (panel (**a**)). The AC field is applied perpendicular to the beam direction and induces the formation of a colloidal crystal. Panel (**b**) shows a representative diffraction result. Figures not to scale (reproduced with permission from [90], The Royal Society of Chemistry, 2010).

Where the formation of colloidal crystals by the application of an AC electric field is maybe somewhat counterintuitive, the formation of oriented bundles of rather stiff fibrous molecules of the conjugated polymer poly(3-hexylthiophene) (P3HT), with a persistence length of several nm, is less surprising [91]. The authors are also describing parallel optical experiments where the data were Fourier transformed to provide an estimate of the degree of orientation.

One of the surprising findings is that on-line strong magnetic fields have so far rarely been used as a sample environment in soft matter-related neutron research. In most neutron scattering laboratories, there is an abundance of resistive and superconducting magnets available for research on magnetic materials. One would have expected that several potential user groups would have taken advantage of this opportunity and used these magnets for soft matter experiments as well. For soft matter, one clearly requires higher sample temperatures than the cryogenic temperatures most commonly used in magnet research and most often a configuration where neutron beam and magnetic field are at 90 degrees, thus requiring a split coil magnet over a simpler solenoid.

In liquid crystal and liquid crystalline polymer research, the study of material response to magnetic fields is common, but often only moderate fields (<2 T) are required. An example of this is the interplay between ordering and microphase separation of liquidcrystal polystyrene-poly(methyl methacrylate) block copolymers bearing a chiral biphenyl ester side group linked to the backbone by a dodecyloxy spacer [92]. The applied magnetic field causes the polymer backbone to partially orient. Experiments on another liquid crystalline block copolymer to map out the temperature-magnetic field phase diagram have also been reported [93]. When doped with lanthanides, lipid membranes can also be oriented [94].

Since the interaction of soft matter often is via diamagnetism, the required fields to be able to observe a relevant alignment interaction are >5 T, i.e., greater than the fields produced by permanent and electromagnets. The requirement to use superconducting magnets is a severe complication. Some static on-line X-ray experiments are published [95,96] and even some dynamic studies, where the sample was rotated inside the magnetic field and observed whilst rotating back [97,98]. For neutron experiments, occasionally an off-line magnet was used to produce aligned samples from fibrous biological macromolecules [99,100] and more recently the use of an on-line 8 T magnet to measure alignment by SANS of bicelles complexed with lanthanides was reported [101].

Transportable higher field on-line superconducting solenoids (17 T) have been used, but so far, no results on soft matter samples have been published [102]. For higher continuous fields, one has to resort to more permanent installations like Bitter magnets, very large superconductors, or hybrids of these two. Pulsed magnetic fields using capacitor banks are often transportable and split coils can reach up to 30 T [103–105] and solenoids up to 40 T [106], but the short pulses (msec) and the slow repetition rates (several shots/hour) make these magnets unrealistic options for soft matter research.

#### *3.7. Light*

The use of visible or UV light to modify samples on-line has found some applications in chemistry and in biological systems. An example is the use of UV light in a solution with a UV photo-destructible anionic sodium 4-hexylphenylazosulfonate (C6PAS) surfactant in combination with an inert surfactant hexaethylene glycol monododecyl ether (C12E6). Upon exposure to the UV light from a high-pressure Hg lamp, the C6PAS fell apart and released the content of its micelles to react with the inert surfactant. Hg lamps produce a high light intensity so care should be taken in controlling sample temperature [107]. Similar experiments on reversible phase separation systems using narrow bandwidth light sources have also been reported. Here two different UV wave lengths (350 and 450 nm respectively) were used to initiate phase separation and to reverse it [108]. Photorheological studies, where the rheological material properties are influenced by the exposure to UV light, have also been reported, but it should be noted that the UV irradiation was not performed on-line with the SANS experiments [109].

Visible light produced by a 'white' halogen lamp was used in SANS experiments to gain insight into the gelation process of the conjugated optoelectronic polymer poly(3hexylthiophene-2,5-diyl) (P3HT). Here the effect of the exposure to light was found to retard the growth of microstructures [110,111]. Although the authors mention that they monitored the light intensity, no information about differences in growth of microstructures as function of dose rates was provided.

The conformation of biological molecules involved in the photosynthesis process as a function of exposure to light is a research subject that is well-suited for study by SANS. Not only because of the advantages that contrast variation via deuteration can bring, but also due to the fact that one does not have to worry about the interactions of photoelectrons, which invariably are created in X-ray-based experiments. Here, the issue is not so much recognizable radiation damage, but instead, the less recognizable effects of the direct interaction of X-ray photoelectrons possibly causing conformational changes [112]. Using live cells that were, both on- and off-line, exposed to 'cool white LED light' with an intensity of ≈ <sup>20</sup> <sup>μ</sup>mol of photons m−<sup>2</sup> <sup>s</sup>−1, the structural organization of membrane systems in cyanobacteria were investigated [113]. An illustrative example of the results is shown in Figure 12. It should also be mentioned that quasi-elastic neutron scattering experiments were performed under similar illumination conditions.

**Figure 12.** SANS data from the membranes of live cyanobacteria cells in both light and dark conditions. WT, CB, CK, and PAL indicate data from different cyanobacteria mutants. The panels marked (**A**,**B**) show data obtained under light and dark conditions, respectively. There are subtle differences apparent between the two illumination conditions. The numbers indicate the different peaks visible in the spectrum. For a full explanation, one is referred to the original manuscript. Figure adapted and provided by the authors [113].

Similar experiments, using SANS and Quasi Elastic Neutron Scattering (QENS), were used to determine the volumetric changes of the light sensitive biological pigment rhodopsin, although the experimental details with respect to the exact illumination conditions are somewhat vague in the manuscript [114].

Microwave radiation can be used for sample heating, but an alternative use is to influence chemical reactions, although the exact way that microwaves influence chemical reactions is not entirely clear. It can change the rate constants, but the reaction pathway may also change. Preliminary neutron scattering experiments with an on-line microwave generator were performed, but these experiments were inconclusive [115] and have not received much follow-up. This may be a missed opportunity since in a later work using X-ray scattering, it was shown that by adding microwave-interactive chemical species it was possible to perform targeted annealing of specific molecular regions [116]. Such a use of microwaves, in combination with the advantages that selective deuteration can impart, may allow one to gain insights in chemical pathways.

#### *3.8. Container-Less Measurements*

In some cases, contactless or container-less experiments are carried out to minimize the interaction of the sample with the sample cell or to reduce the background scattering due to window materials. This is particularly important for very high temperature experiments, where the sample–wall interaction can change the chemical composition of the sample [117]. So far, aerodynamic levitation, where a vertical gas stream keeps a droplet of material in the beam, is most commonly used to study materials at high temperature. Powerful lasers are used as a heating source [118]. For soft matter research, aerodynamic levitation appears to be less popular and acoustic levitation is used, instead [119]. A test experiment on the drying of lysozyme solution droplet has been reported [120]. Although this experiment was intentionally aimed at drying and thus increasing the protein concentration, it also highlights one of the method's shortcomings, namely solvent evaporation. The authors also noted that the strong 22 kHz soundwave, which helps to maintain internal mixing, also has the unwanted side effect of denaturing the protein.

Independent of which levitation method one uses, a drawback is that one can only levitate droplets that are smaller than the average neutron beam, thus reducing the scattering intensity as well as possibly introducing parasitic scatter from the sample-air interface. Even if using a jet of liquid shooting through the beam, one will still be restricted to small sample sizes since it is difficult to create large, stable laminar flows. Another ingenious approach to contact-free measurements that mitigates the problem of size mismatch between sample and neutron beam is to create a free liquid film by flowing a solution between two wires [121]. See Figure 13.

**Figure 13.** Container-less measuring device. A continuous stream of liquid is spread out by a nozzle between vertical wires. The free-standing film can be approximately matched to the size of a conventional neutron beam. Not shown is the bag filled with inert gas surrounding the system that is used to avoid the sample interacting with air moisture, resulting in an altered H-D ratio [121].

A rather specialized container-less measurement is the formation of soot particles in a combustion process. Here the flame is placed on a vertical translation stage so that the distance between the flame-neutron beam interception point and the flame mixer can be varied. This method has been used at a number of synchrotron and neutron facilities [122]. Just as in similar SAXS experiments, the data quality remains low and suitable caution is required when fitting the data.

Whatever the method used, one should be aware of the fact that container-less measurements do not mean that there is no sample-environment interaction. Oxidation, denaturing of protein, and exchange of deuterated for protiated water have been reported. It is also well-known that elongated molecules can orient themselves around air–water interfaces.

#### *3.9. Ultrasound*

Ultrasound used in aqueous solutions, or other solvents, creates cavitation bubbles that cause local agitation, affecting a variety of processes. Depending on the frequency used and physical system under investigation, ultrasound can be destructive. For example, it is used extensively for cleaning objects (20–40 kHz), but it can also help materials to crystallize (20 kHz) [123], or used as a diagnostic tool. Another application of ultrasound at a frequency around 1 MHz is to create a time-dependent mechanical perturbation. This was demonstrated in SANS experiments on sodium dodecyl sulfate (SDS) surfactant micelles in aqueous solution. Here the application of ultrasound allowed for the reversible observation of deformation of micelles as a function of time exposure to ultrasound [91].

A more elaborate ultrasound system that operates in the 1.25 MHz range, uses two spherically focused acoustic transducers and an acoustic cavitation detection system. The latter can be used to decouple changes observed due to cavitation versus changes that occur as a result of the propagation of non-cavitating acoustic waves [124]. In these experiments, a neutron absorbing aperture was used in order to match the dimensions of the neutron beam to those of the acoustic field. Even though the size of acoustic bubbles was within the detection range of the SANS experiments, it was found that due to their short half-lives they did not affect the data analysis to any appreciable extent. Several suggestions for future developments, beyond those in this manuscript, are given by the authors.

#### *3.10. Humidity Control*

In a range of fields, the control of humidity is important. For biological materials that have to be studied in their natural state, this is an obvious requirement, but industrial processes and the filling of the pores of porous materials to influence the scattering contrast should also be mentioned.

The simplest method is to place the samples in a closed environment with a reservoir containing a saturated salt solution. However, to change the relative humidity one has to use different salt solutions, which makes this method somewhat cumbersome for on-line experiments [125].

An elaborate system using mass flow controllers with the possibility to mix two different vapors to control the relative humidity between 0 and 90% has been used to study semicrystalline polymers, porous materials, and polyelectrolyte membranes [126]. The advantage of having two independent streams of vapor that can be mixed is that it offers the possibility to vary the H2O/D2O ratio, which in the case of porous materials, allows one to find the matching point for contrast variations very rapidly. The same system can be used to create a vapor pressure of organic solvents.

Developments in commercial humidity generators allow for the construction of rather simplified humidity-controlled cells, which were used in studies of forest products [127] where structural changes as function of moisture were observed. A commercial humidity generator was also used to study novel phases of lipid bilayers that are important for membrane fusion [128].

Relative humidity control of membranes in fuel cells during SANS experimentation was reported. However, in order to gain insights into the performance of nafion membranes in fuel cells under normal operating conditions, a total immersion of the membranes in H2O/D2O, whilst the material was uniaxially deformed, was required. To avoid a complicated experimental set-up with multiple mechanical feedthroughs to the liquid reservoir, U-shaped load beams were used, allowing for the material of interest to be immersed in a temperature-controlled D2O reservoir [129]. See Figure 14.

**Figure 14.** A load frame with U-shaped load beams that allow the sample to be deformed, whilst being completely immersed in water. The temperature-controlled reservoir containing H2O/D2O can be placed around the sample (reproduced with permission from [129], AIP Publishing, 2013).

#### *3.11. Devices*

Given the high penetration power of neutrons in combination with the possibility of highlighting different parts of a material or the distribution of water via the use of deuteration, one would guess that neutron scattering techniques would be a prime tool for the investigation of devices, like batteries, liquid/gas separating membranes under operando conditions, and soot formation by combustion of hydrocarbons in engines, to name a few. However, this kind of research does not currently have a widespread following. This might be due to a combination of the relatively low neutron fluxes available currently and a certain bias that neutron facilities are somewhat inaccessible to the general user. However, there are examples of the above-mentioned systems studied with neutrons. There also is somewhat of a bias against more engineering-oriented or applied applications that can be found in many beam line access panels. Most of the experiments using simulated devices can be found in energy storage and generation-related materials.

The device that was studied using neutron scattering and imaging techniques was a polymer-electrolyte fuel cell [130]. The interest here is the distribution and transport in the fuel cell and the two techniques, SANS and imaging, were combined in a single experiment where the neutron imaging system could be moved out of the beam during the acquisition of the SANS data. This is particularly interesting since the two techniques might not give the same type of information, but the accessible length scales are complementary, and relevant information over length scales from nano- to milli-meters can be obtained in a single experiment. It can be pointed out that this cell was a realistic model where metal components were illuminated by the neutron beam. Using SAXS experiments, where the electron densities of H2O and polymers are not sufficiently different to generate a contrast that can make aluminum, H2O and polymer all visible, no information about the distribution of water can be obtained. Importantly, the above-mentioned experiment emphasizes the ability to study materials under operando conditions. It is noteworthy that data acquisition time for SANS was 80 s/frame and for imaging 210 s/frame. In a

later publication, infrared spectroscopic data were also used to evaluate the physical and chemical events inside the fuel cell [131,132].

Another energy-related application is the study of Li-ion batteries. The concentration of Li-salt and the type of electrode material used has consequences for the operation of the battery and its longevity. By using a half-cell, i.e., a single electrode surrounded by an electrolyte solution, it enables one to follow the events at the solid–electrolyte interface. In the case where one uses an ordered mesoporous carbon electrode, mesoporous events take place in the range where small angle scattering (SAXS/SANS) can yield information. Here again there is a lack of electron density contrast between the Carbon and the Li compared to the pores, which indicates that neutron scattering is better suited to gain insights into the effects of the use of different Li-salts and concentrations during the duty cycle for in-operando cycling/discharging [133]. Similar experiments, but with greater emphasis on the analysis of the scattering results and the role of the scattering contrast in the analysis of the data, were also published [134].

Supercapacitors, hybrid devices with characteristics between a capacitor and a battery, rely on a high internal surface for redox reactions to take place. The most promising materials are porous nitrides of vanadium and molybdenum, which strictly speaking, do not classify as soft matter, but in the context of this review are relevant as they are materials known to have some of the highest storage capacities [135]. By performing the required electrochemistry on-line, it was shown that the smallest pores in these materials allow for the increased adsorption of OH− ions. These experiments would also benefit from on-line X-ray spectroscopy experiments in order to obtain insights about what is driving the charge storage mechanism.

#### **4. In-Situ Technique Combinations**

In most research, neutron scattering is only one of the tools in the experimental toolbox required to obtain the knowledge of the material properties that one is investigating. In certain circumstances, it is beneficial if one can combine neutron scattering experiments with complementary on-line auxiliary techniques, as has become a fairly routine approach at synchrotron radiation facilities [136,137]. The advantages of being able to simultaneously collect complementary data sets at the same time, using the same sample, outweigh any disadvantages due to the increased experimental complications regarding synchronization of the data sets and access of different probe beams, which cannot always use the same window material. Conditions in which one can consider the use of a multimodal approach are when dealing with spatially inhomogeneous materials or when the time resolution in an experiment is too fast to be able to stitch the data sets in a reliable way that does not create uncertainties in the time-correlation between the different experiments. In both cases, one should try to interrogate the same sample volume with the different probes.

The use of on-line Differential Scanning Calorimetry (DSC) with X-ray measurements is a good example where the data quality of the DSC signals suffers somewhat but where the synergy of having two simultaneous data sets outweighs the loss of quality [22]. When the strong peaks in a DSC curve can be correlated to the X-ray frame number, one can correlate the real thermodynamic temperature of the sample with the appropriate X-ray structure. Hence, the correlation can be made with an accurate DSC curve obtained with a well calibrated off-line instrument. The design problems for constructing a similar set-up for neutrons are somewhat larger than those for X-rays, since the beam access window needs to be considerably larger. However, this engineering issue can be overcome as was shown in phase separation experiments on partially deuterated alkanes, CnH2n+2:CmH(D)2n+2. A commercial instrument with an operation range from −150 ◦C to +500 ◦C was successfully modified to enable neutron beam access. A slight drawback is that it was not feasible to use commercially available DSC pans but instead special pans had to be custom designed and machined [138]. The time resolution that could be achieved in this experiment was 2 min/frame.

The combination of Raman scattering with different neutron scattering techniques has been reported over the years [139,140], including for the protein lysozyme, but these experiments were all carried out at cryogenic temperatures, which is of limited use in soft matter research. However, it was only recently that the cold deformation, i.e., ambient temperature, of low-density polyethylene was followed by both SANS and polarized Raman spectroscopy [141], where the experiments were performed using the same tensile stage but not simultaneously. By combining the different data sets, one can investigate the interplay between chain stretching (SANS) and the transition from amorphous to all trans conformers (Raman). Although these experiments were done separately, with the present generation of portable Raman spectrometers, there is no reason why this could not be carried out simultaneously if the required time-resolution would make this beneficial [142].

Dielectric spectroscopy can provide information at the molecular level about a variety of soft matter processes. For instance, chemical changes, segmental relaxation in polymers, and phase transitions are among the physical phenomena where dielectric spectroscopy can render complementary information to X-ray [143] and neutron scattering [144]. Such experiments were carried out in combination with a strain controlled Couette shear cell on a SANS instrument [145]. The Couette cylinders were constructed of titanium with thin mylar windows, allowing access to the neutron beam as well as for impedance measurements between the inner and outer cylinders (See Figure 15 for a schematic layout of the experiments). Crucial for this type of experiment is the synchronization of the different techniques, which can be readily achieved using 'event-mode' data collection [146]. Data were successfully obtained on the self-assembly of conjugated polymer melts and shear sensitive ionic liquids.

**Figure 15.** Schematic of a Couette rheology cell that allows for the simultaneous collection of rheological, dielectric spectroscopy, and neutron scattering data. The electrical impedance is measured between the Ti cylinders. Temperature control is achieved by using a forced convection oven that surrounds the cell (reproduced with permission from [145], AIP Publishing, 2017).

In order to investigate how high a molecular weight of polyethylene glycol dimethyl ether (PEGDME) can be incorporated in the crystalline region of syndiotactic polystyrene, one requires both the structural information provided by neutron scattering and vibrational spectroscopy. This was done by combining Fourier Transform Infrared Spectroscopy (FTIR) with SANS [147,148]. Here one encounters the issue that the optimum sample thickness required by both techniques is not the same. This can be partially overcome by using an FTIR sample cell and Attenuated Total Reflection, where the infrared beam makes multiple passes through the sample material [149]. However, a better solution is to place the IR and neutron beams co-parallel to ensure that one is studying the same part of the sample. This can be achieved by coupling the IR beam with an elaborate system of KBr crystals that act

as mirrors for the IR beam but are relatively transparent to neutrons. As a compromise, the sample thickness was chosen to be 50 μm, just sufficiently thick for neutron scattering but thin enough for infra-red measurements. The combined data sets showed a distinct difference between the PEGDME conformation in the amorphous and crystalline regions of the polystyrene.

In experiments where the materials exhibit (partial) orientation and are transparent to visible light, birefringence is widely used to determine orientational effects. Neutron and X-ray scattering are also sensitive to orientational order, albeit on different length scales than birefringence. Scattering is mainly sensitive to the alignment of molecules, whilst birefringence is sensitive to bulk material properties [150]. Although such a capability seems to be very useful, it is somewhat surprising that this has not been applied more often [62,150,151].

Even though it is understood that having combined neutron and X-ray scattering data is highly beneficial in understanding a system, these techniques are not combined as often as they should [152–154]. In an ideal world, one would be able to use parallel beams of X-rays and neutrons, but an orthogonal combination is technically easier to realize. The achievable time-resolution, i.e., the length per time frame in which useable data can be collected, for the two experiments should be of the same order of magnitude. Until recently, such a combination was not feasible, but developments in X-ray generation and detector technology have allowed the first steps in allowing such a combined scattering instrument to be developed. Specifically, the two probe beams were placed at right angles to one another, making the system less useful for samples that are anisotropic, but it can serve as a proof of principle [155]. The complication that one faces with the development of such an instrument is that one invariably tries to mount an X-ray system on an existing neutron scattering beamline. Hence, one encounters space and shielding issues that make things more complicated (but not impossible).

The combination of neutron scattering with light scattering or birefringence should be more straightforward to achieve and would extend the length scales over which information can be obtained. However, this also seems to be an area waiting to be developed since few publications can be found. A combination of SANS with diffuse wave spectroscopy (DWS) was reported. DWS can be used in high concentration colloid solutions and can be used to obtain information about the ensemble dynamics of particles, while SANS provides the structural information [156].

An example where an industrially relevant testing method, Rapid Visco Analysis (RVA), was combined with SANS experiments was used to determine the nature of the structural changes in starch during pasting. This combined mechanical and thermal treatment of materials plays an important role in process- and quality-control in the food industries. By combining the neutron scattering data with the viscosity, as measured with an adapted RVA system, the abrupt changes in viscosity could be correlated with the changing morphology of the starch and the starch derivative network [157].

#### **5. New Directions**

One of the disadvantages of neutron scattering experiments is the size of the neutron beam. Due to the abundance of available photons and the development of optical systems that take advantage of this abundance, X-ray beam sizes on the submicron scale are common. This is not the case with neutrons. A smaller neutron beam is achieved at the expense of available flux, and hence of the attainable time resolution. Although one cannot reasonably expect sub-micron neutron beams, it is still feasible to obtain spatially resolved data where the (inhomogeneous) sample is probed with a small beam of around 100 microns at different positions [48] or to use microfluidic devices [157].

The promise of a higher effective flux that will be made available by the new generation of spallation sources will obviously have an impact on how fast data can be collected. However, this increase in intensity will not bring many orders of magnitude of improvement. Therefore, if one wants to increase the potential time-resolution, one should also

look at better ways to perform experiments and at innovative ways of processing the data, and where the emphasis is placed on which parameters one would like to measure instead of trying to obtain the best statistical quality data. Certainly, for non-isotropic scattering samples there are improvements possible in what kind of time-resolution can be achieved.

The combination of neutron scattering, or spectroscopy data and complementary techniques is quite common. Less common, however, are approaches to analyze the data simultaneously, for example, using multidimensional correlation spectroscopy [158,159]. This method has already been applied in X-ray scattering experiments to elucidate events at the early onset of crystallization, where the nascent signals of the new phases are very weak [160,161], and the impact of radiation damage on proteins and the assembly in nanomaterials [162], and can be considered reminiscent of the low statistical data quality one would encounter in fast time-resolved neutron experiments.

So far, we have not mentioned the use of computational modelling, but it is not unreasonable to assume that this can in the near future become a virtual on-line technique combination. Modeling can become an inroad for new approaches to neutron experiments, which are optimized to provide just sufficient data quality to resolve whether the modeling result can be confirmed or disproven. This would require a 'pipeline' that feeds from modeling to defining neutron experiments.

An interesting development is the advances in ray-tracing simulations for instrument designs, e.g., McStas [163] or McVine [164]. These programs have expanded to include sample scattering kernels and sample environments [165]. It is now possible to simulate accurate sample geometries, instrument resolution, and counting statistics [166,167] to determine if planned experiments are feasible.

The importance of thin polymer films and grazing incidence studies characterizing the structure and structure formation of materials has increased in recent years [168]. In the case of X-ray studies, complicated on-line experiments, like roll-to-roll printing of polymers, have been reported. Neutron-based grazing incidence studies undoubtedly can play a bigger role in elucidating more complex morphologies. Data collection times, however, are still on the order of hours for a single static measurement [169], although in favorable cases, this can be reduced to minutes and can be further improved when dealing with cyclic processes [18]. It should also be noted that these results were obtained on non-dedicated beamlines. With a specialized design, further improvements could be made.

With the higher flux that one can expect from the new neutron sources that are being developed, obviously the situation for 'neutron hungry techniques', like time-resolved, spatially-resolved, and grazing incidence scattering experiments will improve. However, one cannot expect the many decades in improvement, which was the signature of the successive generations of X-ray sources, to be achievable. Still, there is substantial scope for increasing the experimental sophistication in soft matter research using neutron scattering techniques.

#### **6. Conclusions**

This article gives an overview of diverse sample environments that can be used in neutron scattering techniques applied in the area of soft condensed matter. We have focused on the small angle neutron scattering technique. Even though we have covered many different areas of sample environment control, such a survey can never be all-encompassing. However, we hope to have demonstrated with this overview that neutron scattering is not only suitable for static structure determination but can be implemented in a greater number of studies than what is being used presently. We suggest that more emphasis should be placed in SANS applications on observing the time-evolution of selected structural parameters during the response of materials to external perturbances. In this way, neutron scattering has the potential to make impactful contributions to the understanding of complex systems, such as soft materials, even when a complete structural analysis is out of reach. Importantly, observing parametrized changes in materials often does not require the highest statistical data quality, and therefore improvements in time resolution can be

found by carefully optimizing to the minimum counting statistics level that is necessary, rather than following traditional optimization rules that were developed for obtaining best data from static structures.

**Author Contributions:** W.B. carried out the literature investigation, all authors contributed equally to the manuscript writing. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** We would like to acknowledge input from our colleagues Ralf Schweins, Steve King, Paul Butler, Sai Venkatesh Pingali, Frank Bates, Bin Wu and Gary Lynn. A special acknowledgement is due for our sadly missed colleague Isabelle Grillo. T. Plivelic, J. Vermant and R. Winter have made original figures available. The anonymous reviewers have made some valuable suggestions and are acknowledged for their careful reading of the manuscript. W.B.'s contribution is based upon work supported by Oak Ridge National Laboratory, managed by UT-Battelle LLC, for the U.S. Department of Energy. A portion of this research used resources at the High Flux Isotope Reactor and the Spallation Neutron Source, DOE Office of Science User Facilities operated by the Oak Ridge National Laboratory. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan http://energy.gov/downloads/doe-public-access-plan (accessed on 13 May 2021).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


## *Article* **A Unified User-Friendly Instrument Control and Data Acquisition System for the ORNL SANS Instrument Suite**

**Xingxing Yao, Blake Avery, Miljko Bobrek, Lisa Debeer-Schmitt, Xiaosong Geng, Ray Gregory, Greg Guyotte, Mike Harrington, Steven Hartman, Lilin He, Luke Heroux, Kay Kasemir, Rob Knudson, James Kohl, Carl Lionberger, Kenneth Littrell, Matthew Pearson, Sai Venkatesh Pingali, Cody Pratt, Shuo Qian \*, Mariano Ruiz-Rodriguez, Vladislav Sedov, Gary Taufer, Volker Urban and Klemen Vodopivec**

> Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA; xingxingyao@gmail.com (X.Y.); averybe@ornl.gov (B.A.); bobrekm@ornl.gov (M.B.); debeerschmlm@ornl.gov (L.D.-S.); geng@ornl.gov (X.G.); gregoryrd@ornl.gov (R.G.); guyottegs@ornl.gov (G.G.); harringtonml@ornl.gov (M.H.); hartmansm@ornl.gov (S.H.); hel3@ornl.gov (L.H.); herouxla@ornl.gov (L.H.); kasemirk@ornl.gov (K.K.); knudsoniroiv@ornl.gov (R.K.); kohlja@ornl.gov (J.K.); calionberger@lbl.gov (C.L.); littrellkc@ornl.gov (K.L.); pearsonmr@ornl.gov (M.P.); pingalis@ornl.gov (S.V.P.); prattcl@ornl.gov (C.P.); ruizmm@ornl.gov (M.R.-R.); sedovvn@ornl.gov (V.S.); tauferga@ornl.gov (G.T.); urbanvs@ornl.gov (V.U.); vodopiveck@ornl.gov (K.V.) **\*** Correspondence: qians@ornl.gov; Tel.: +1-865-241-1934

**Abstract:** In an effort to upgrade and provide a unified and improved instrument control and data acquisition system for the Oak Ridge National Laboratory (ORNL) small-angle neutron scattering (SANS) instrument suite—biological small-angle neutron scattering instrument (Bio-SANS), the extended q-range small-angle neutron scattering diffractometer (EQ-SANS), the general-purpose smallangle neutron scattering diffractometer (GP-SANS)—beamline scientists and developers teamed up and worked closely together to design and develop a new system. We began with an in-depth analysis of user needs and requirements, covering all perspectives of control and data acquisition based on previous usage data and user feedback. Our design and implementation were guided by the principles from the latest user experience and design research and based on effective practices from our previous projects. In this article, we share details of our design process as well as prominent features of the new instrument control and data acquisition system. The new system provides a sophisticated Q-Range Planner to help scientists and users plan and execute instrument configurations easily and efficiently. The system also provides different user operation interfaces, such as wizard-type tool Panel Scan, a Scripting Tool based on Python Language, and Table Scan, all of which are tailored to different user needs. The new system further captures all the metadata to enable post-experiment data reduction and possibly automatic reduction and provides users with enhanced live displays and additional feedback at the run time. We hope our results will serve as a good example for developing a user-friendly instrument control and data acquisition system at large user facilities.

**Keywords:** SANS; neutron scattering; instrument control; data acquisition; user facility; GUI

#### **1. Introduction**

Small-angle neutron scattering (SANS) is a powerful technique to resolve structures from a few to hundreds of nanometers in a wide range of materials. The SANS instrument suite at the Oak Ridge National Laboratory (ORNL) neutron scattering facilities—including the biological small-angle neutron scattering instrument (Bio-SANS), the general-purpose small-angle neutron scattering diffractometer (GP-SANS), and the extended q-range smallangle neutron scattering diffractometer (EQ-SANS)—serve many different research communities, including biology, soft matter, quantum materials, and metallurgy [1].

The three instruments are custom-developed and built with similar yet different components at two different neutron sources, the spallation neutron source (SNS) and

**Citation:** Yao, X.; Avery, B.; Bobrek, M.; Debeer-Schmitt, L.; Geng, X.; Gregory, R.; Guyotte, G.; Harrington, M.; Hartman, S.; He, L.; et al. A Unified User-Friendly Instrument Control and Data Acquisition System for the ORNL SANS Instrument Suite. *Appl. Sci.* **2021**, *11*, 1216. https:// doi.org/10.3390/app11031216

Received: 4 January 2021 Accepted: 25 January 2021 Published: 28 January 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

the high flux isotope rector (HFIR) at ORNL. While there is much overlap among the instrument specifications, each of these instruments has unique advantages for different types of experiments. Thus, there is considerable overlap in their user bases, who use multiple instruments for different experimental needs, such as specific performance or sample environment equipment needs. The SANS instrument suite has had very different instrument control and data acquisition systems (IC-DASs) over the past decade for historical reasons. EQ-SANS, located at the SNS, relied on PyDAS, a Python extension of the original home-developed SNS DAS [2]. Bio-SANS and GP-SANS, both located at HFIR, were served by a customized graphic user interface (GUI) extension based on the Spectrometer Instrument Control Environment (SPICE) software built on LabView [3].

At the SNS, the original SNS DAS played a critical role in the commissioning and operation of early instruments. It also laid the foundation of the data format for timestamped event mode data coming from the pulsed neutron source, which is required to record the time-of-flight of each neutron for further data process and reduction [4,5]. Later instruments with higher data throughput were commissioned at the SNS and exposed the data acquisition bandwidth limitations of the original SNS DAS. Years of operational experience also highlighted the need to improve the reliability and usability of the original SNS DAS. As a result, a series of significant software and hardware upgrade projects have taken place at the SNS [6–9], using the Experimental Physics and Industrial Control System (EPICS) toolkit and Control System Studio (CS-Studio) [10–12] that are used by the SNS accelerator control system. EQ-SANS at the SNS was the first among the SANS suite to be upgraded to the EPICS-based IC-DAS.

Over time, significant upgrades at Bio-SANS and GP-SANS, including upgrades allowing them to use the same type of 3He linear position-sensitive detectors used at EQ-SANS [13], neutron collimation systems, and additional sample environment equipment [1], have challenged the existing capabilities of SPICE and DAS. For example, the timestamped event mode data from the detector system have been converted to histograms to be handled by SPICE, losing valuable temporal information for neutron detection at Bio-SANS and GP-SANS. Moreover, given the growing suite of sample environment equipment shared among the SANS instruments and the need for a unified user experience, it is imperative that Bio-SANS and GP-SANS follow suit to upgrade to the EPICS-based system. This unification of the IC-DAS also will make system management and operation easier without splitting resources on what otherwise might be two separate development efforts.

This article shares our user needs and requirements analysis results, key methods we relied on, and new features of the EPICS-based SANS IC-DAS. Besides basic instrument control and data acquisition features, our new system is ready to be deployed for other similar SANS instruments, offering accurate and intuitive metadata handling, sophisticated experiment planning tools, and different user operation interfaces catering to different user communities.

#### **2. User Needs and Requirements Analysis**

#### *2.1. Diverse User Needs*

The users of the SANS IC-DAS are quite diverse. Categorized by different roles, they can be external facility users, instrument scientists, and supporting teams including sample environment teams, detector teams, and so forth. In addition to the rudimentary instrument control functionality, each role has more specific requirements of the system. For example, supporting teams require in-depth control of instrument components, clear status indication, and sufficient logs for monitoring and diagnostic troubleshooting. Instrument scientists have a good overall knowledge of the whole instrument system and are highly experienced in configuring an instrument for specific scientific requirements. However, they need to be freed from tedious hands-on operations to focus on scientific aspects of user experiments. The largest and most important group are external neutron scattering facility users. We want to empower them to successfully conduct experiments and collect useful measurement data with minimum effort expended on instrument oper-

ation. As the SANS instrument suite covers a large span of scientific communities with different skill sets; different experience levels with neutron scattering instruments; and, most crucially, different ways of conducting experiments suited for their sciences, our IC-DAS must make it easy for all of those communities to be productive during the short period of time they spend at an instrument. For example, users from the experimental condensed matter physics community usually have a single sample, but require various sample environment conditions in a particular experiment. They need to be able to easily visualize and interpret the reduced data to decide on the next condition to explore. They usually spend more time on a sample and require quick, flexible manipulation of many instrument and sample environment parameters. On the other hand, biochemists or biologists conducting solution SANS experiments usually use highly standardized instrument configurations for a series of samples with small variants. They need an effortless way of setting up their experiments, while they focus primarily on preparing fresh samples on-site. For these two extreme cases and others between them, a variety of user interfaces reflecting different workflows need to be designed and developed.

Our analysis of previous usage data further supports the above requirements. For example, the wizard-like GUI extension (Figure 1) previously developed within SPICE served 99.4% of Bio-SANS experiments and 7.8% of GP-SANS experiments over the 2 years since its deployment in 2016 (HFIR was in a long outage from late 2018 to late 2019). The rest of the experiments during that period were served by SPICE macros similar to scripting interfaces. Based on these findings, the new system implements and improves on both of these tools, offering wizard-like Panel Scans and Scripting Tool based on Python, in addition to the simple start/stop button-click GUI and Table Scan feature that were part of the previous EPICS/CS-Studio system.

**Figure 1.** The Spectrometer Instrument Control Environment (SPICE) graphic user interface (GUI) extension with a wizard-like tool to set up scans for small-angle neutron scattering (SANS); highlighted in purple is the currently selected function group.

#### *2.2. Complex Data and Metadata*

During a neutron scattering experiment, an extensive amount of data and metadata are collected. The data are mainly events detected by the large two-dimensional (2D) position-sensitive neutron detectors with timestamps of each neutron event referring to a reference time. Such event mode data provide convenience for post-collection time-slicing or synchronizing with sample environment parameters for time-resolved studies or a stroboscopic method. The metadata, also recorded with timestamps, include inherent instrument parameters such as hardware component positions, health conditions, and sample environment equipment readouts, and user-input supplementary information such as sample and background details. All of those parameters are critical for setting up the correct instrument measurement configuration, and many of them are required for correct data reduction and interpretation.

Most inherent parameters are motor positions and other equipment readouts (Figure 2). They can be grouped in relation to (1) beam characteristics (e.g., status of neutron guides, source aperture, attenuator, beam trap); (2) the Q-range (the momentum transfer, Q, is the most important factor in a small-angle scattering experiment, representing the size range to be probed in the reciprocal space within which SANS measures; e.g., velocity selector rotation speed and tilt angle, sample aperture size, detector motor positions); (3) sample environment devices and conditions (e.g., temperature, magnetic field, pressure, rotating cell speed); and (4) sample changer and slot number. Individual motor position and other readings are difficult for both expert and non-expert users to comprehend; therefore, it is necessary to associate and display them with more meaningful configuration descriptions. In addition, a higher-level collective setup can be used to configure an instrument without setting those parameters individually.

**Figure 2.** (**A**) An overview of a SANS instrument system. (**B**) The collimation system used at the biological small-angle neutron scattering instrument (Bio-SANS) and the general-purpose small-angle neutron scattering diffractometer (GP-SANS) with interchangeable neutron guide and aperture systems. There are eight sections of almost identical units with independent motor control.

> User-input supplementary information is needed for users to keep track of different parameters such as slight variations in composition, concentration, matching background, and so on. Some of this information can be pulled from the centralized sample management database, inventory tracking of equipment, material and sample (ITEMS), whereas some can be provided only by users manually during an experiment. Moreover, the system needs to provide an expandable pathway for adopting emerging standards for metadata, such as Information System for Protein crystallography Beamlines (ISPyB) used by the biological small-angle scattering community [14] and the collective action for nomadic small-angle scatterers (canSAS, www.cansas.org) community.

#### *2.3. Integrated Experiment Planning Tool*

Our instrument scientists and users have been using simple calculating tools such as Excel spreadsheets to plan experiments, including Q-range and measurement time, and manually convert that information into actual instrument parameters to use. Given the increasing complexity of instruments—e.g., multiple detectors, different sample changers, multiple beam stops, sample environment devices—an integrated experiment planning

tool that can take advantage of the known constraints of the parameters, and then easily save the planned configuration for use and reuse, is valuable. Clearly defined instrument configurations will also enable the implementation of automatic data reduction and provide coarse real-time data reduction, which is very helpful to guide users during measurements.

#### **3. Methods**

#### *3.1. Needs-Driven and User-Centered Design*

The developers initialized a thorough user experience–focused study on the existing SPICE and other relevant software environments. The study was guided by the principles from the latest user experience and design thinking research (e.g., references [15–17]), and based on effective practices from previous EPICS upgrade projects, such as using a beginner mindset, maintaining operational flexibility, and balancing between overall performance and individual process optimization. With help from database administrators, the previous metadata from SPICE (already ingested into the catalog database) were used to mine useful usage data to quantify the findings of our study. This effort not only helped clarify the required functionality but also helped prioritize the requirements based on evidence rather than impressions. The study further helped frame a shared vision of delivering an IC-DAS that is both functional and easy-to-use and helped build a relationship of trust between instrument scientists and control system developers.

Based on a goal of minimizing the physical, mental, and emotional efforts required of users in carrying out their tasks, the study identified four focus areas that could potentially be improved for a better user experience. These four focus areas are (1) the Q-range configuration representing the instrument configuration, including many component settings; (2) a user interface including both wizard-like Panel Scans and a Python-based Scripting Tool; (3) customizable detailed sample and buffer information tracking; and (4) detector geometry handling with various viable offsets and motor positions. With these in focus, we co-designed all main components of our high-level user-oriented tools; the details are provided in the results section.

#### *3.2. Automation Based on Process Knowledge*

Following the principle of "first make it work, then make it better," we built on the team's expertise and experience to create shared process knowledge regarding how the different parts of the SANS instruments are interwoven with one another. For example, as mentioned earlier, setting an instrument to a specific Q-range configuration requires coordinating the establishment of the beam characteristics with the settings for other hardware motors. For instance, the collimator guides and apertures used to define the incident beam are coupled with several pieces of distance metadata for Q-range calculation and other settings. This interwoven nature of the instrument parameters should be considered in aspects including instrument control, experiment planning, and metadata handling.

Another challenge is effectively managing instrument Q-range configurations with small variations that are sample- and proposal-specific. Improved understanding of the process knowledge in actual operation enabled us to differentiate between configurations that are standard or are changed infrequently, and those that are changed often. We did so by creating a sample- and proposal-dependent layer that allows a user to save Q-range configurations with only minor modifications, while still sharing the parameter files (e.g., flood, beam center, and dark current files) associated with the standard configurations. We designed our tools with as much automation as possible and set the order of development based on shared process knowledge.

#### **4. Results**

Within the user needs and requirements scope identified earlier, built on the EPICS system architecture (Figure 3), we developed and delivered a distributed IC-DAS customized for the SNS and HFIR SANS instruments. We added customizations and improvements to already developed features and building blocks, significantly reducing the user experience

gaps encountered among the three SANS instruments at ORNL. This system is built on the abundant base of EPICS drivers that interface with different items of physical hardware, such as motors, temperature controllers, and magnets. Among modular applications (also referred to as input–output controllers) and different user interfaces, a scan server application serves as the "brain" and controls the overall instrument state while maintaining a "command queue" for future measurements. Various user interfaces (including Panel Scans and Scripting Tool) cater to different needs and preferences and enable users to plan and conduct their experiments efficiently. This architecture ensures a sound and flexible system that can meet the requirements of complex instruments such as the SANS instrument suite.

In this section, we detail a few novel aspects of our system and discuss how they provide users with an improved instrument control and data handling experience. Additional screenshots of the new system are exhibited in the Supplementary Materials.

#### *4.1. Intuitive Motion Control with Reliable Metadata*

Following a good practice implemented in the previous SPICE software, we grouped the control of multiple devices into pseudo-motors. For example, for collimator motion control with eight different sections of guide motion control, a single "nguides (NGuides)" (number of guides) command can coordinate the control of guide motions in and out to keep a specific number of guides in the beam, along with apertures in the beam configuration. Note that the number of guides usually define the apparent source-to-sample distance (the flight path from the end of last guide to sample position). The distance needs to be coordinated with the sample-to-detector distance, various aperture sizes, and detector pixel resolution to provide optimal scattering geometry in SANS [18]. We included additional enhancements such as the newly defined 20 mm aperture in the beam configuration (aka, NGuides = "−1" in Figure 4); automated motor homing procedures; and logic embedded within the collimator motion control software to consistently compute and update the source aperture diameter and the metadata for the source-to-sample distance, based on motor positions. Similarly, detailed detector distance calculation logic is also integrated within the motion control to simplify or automate various offsets (e.g., sample-to–silicon window offset and detector motor position, see Figure 5) with a combined pseudo-motor total sample-to-detector distance. The latter matches the typical convention employed by SANS users in detector geometry and is critical in experiment planning and data

reduction. The pseudo-motor is controllable like any physical motor, and the corresponding actual motor position is calculated based on offset values that can be changed according to different experiment setups. Note that all individual values and combined pseudomotor values are captured in metadata redundantly in case they need to be cross-checked. The development and testing effort in motion control has been rewarded by a clean, simplified interface with enhanced functionalities, tighter integration with high-level tools, and more reliable metadata.


**Figure 4.** An example of motor grouping, the pseudo-motors for guide operation in the collimation system.

**Figure 5.** The diagram shows that the sample-to-detector distance combines the sample-to–silicon window offset and the actual detector motor position to form a controllable pseudo-motor.

#### *4.2. A Customized and Fully Integrated Q-Range Planner*

Instrument-specific experiment planning is important for the success of an experiment. For SANS experiments, Q-range is one of the most critical factors, as it determines the size range of a measurement. Previously, instrument scientists developed spreadsheets or other calculation tools independently to do their planning without much instrument-specific information or constraints. The integration of the Q-Range Planning tool within the IC-DAS enables the direct transfer of the Q-range configuration from the planning stage to the measurement stage. In addition to the benefit of imposing the physical constraints (e.g., motor limits) of a specific instrument, this implementation reduces the number of Q-range configurations that are due to small, unnecessary inconsistencies.

Once we understood these requirements, a customized Q-Range Planner was developed based on instrument scientists' spreadsheet calculators, as well as previous work on other instruments. The SANS Q-Range Planner helps users specify/update factors such as wavelength, attenuation factor, number of guides, aperture sizes, detector distance/rotation, distance offsets, and beam trap configuration for both scattering and transmission measurements. The factors then are converted into actual hardware settings such as motor positions. The planner then calculates the minimum Q at the beam stop rim, depending on the beam

stop chosen, maximum Q values at corners and edges on each detector, and direct beam size on the detector; and, when applicable, it calculates the overlapping ratios between different detectors. Users can easily save a Q-range configuration to use and reuse in actual measurements. The saved Q configuration is in a human-readable text file format.

The SANS Q-Range Planner is deployed among the instrument suite. At different instruments, the calculation incorporates different instrument component details (e.g., detector, collimator, and beam trap details) but with an almost identical high-level interface for users (Figure 6). We also added beam center enhancement so users could more accurately calculate Q-ranges based on the specified beam center on the 2D display, instead of always pretending the beam center is at the previous physical detector center. The beam center coordination and calculated Q-range details are captured in each Q configuration file, reused at the run time for live displays (see Section 4.4), and saved in each data file to be used by the data reduction software. To meet the different needs and access privileges of external users and instrument scientists, two instances of the Q-Range Planner are running on each instrument. One is dedicated to use by instrument scientists to establish new standard configurations. The other is embedded within Panel Scans (see Section 4.3) to flexibly deal with sample- or experiment-dependent minor modifications, as well as to collect data with more than one Q-range configuration. Q-range configurations can also be easily set like a simple variable by using other user operation interfaces such as Scripting Tool and the generic Table Scan. With Q-Range configurations generated by the planner, a soft matter simulator (Figure S7) has been developed for generating typical model scattering curves with realistic instrument factors such as flux at different neutron guide numbers, Q resolutions, etc., to further aid users to plan an experiment.

**Figure 6.** The Q-Range Planner.

#### *4.3. User Operation Interfaces: Panel Scans and Scripting Tool*

The previous EPICS/CS-Studio system included a generic Table Scan feature that used a spreadsheet to set up a list of scans for batching measurement. However, the intuitiveness and ease of use of the generic Table Scan was limited. To provide more functional and straightforward interfaces to different users, we implemented a wizard-like GUI-based tool, Panel Scans, and a Scripting Tool with an improved scripting middle-layer library. Both can use the Q-range configurations generated from the Q-Range Planner introduced in the previous section.

The SANS Panel Scans tool was designed based on earlier development of the SPICE GUI extension and other EPICS high-level scanning tools. It uses one instance of the Q-Range Planner and a six-step workflow (Figure 7) to guide users through the complex measurement planning process. This includes (1) checking or modifying individual Q-range configurations; (2) selecting up to four Q configurations in any order; (3) configuring sample environment variables; (4) keeping track of sample- and buffer-related variables for each sample changer slot; (5) specifying the exposure time for each combination of sample changer slot/Q configuration/sample environment variables; and (6) expanding the entire batch with all the details into a tabulated scan list. The scan list can then be simulated and tested before execution, submitted to the scan server to execute, and saved as a file for future reference.


**Figure 7.** The workflow laid out by different tabs in the Panel Scans interface (details on the workflow tabs are presented in the Supplemental Materials).

The guided workflow and clear steps of Panel Scans not only make the complex process more manageable and less overwhelming for even new users, but also encapsulate many thoughtful features and improvements within an appropriate sub-task context. These features include a user-friendly table view and visualization of Q-ranges (see Figure 8), generation of scripting snippets with Q-range configurations selected (Figure 8), support for both pre-configured and ad-hoc sample environment variables for routine and innovative experiments, standardized sample- and buffer-related metadata variables (still with customizable tags for automatic background association), and accommodation of flexible expanding orders. The system also provides a high degree of freedom for users to set up and change their measurements. For example, if users choose to submit each table row as a separate scan job, they can use the upgraded scan monitor to reorder or delete and resubmit queued scan jobs. In addition, the "load sample" step provides customizable sample information to obligate users to keep track of variants among different samples, which encourages good practices for accurate supplementary information and enables future automatic background matching in data reduction.

Similarly, in Scripting Tool, the Scan Tools helper library also incorporates lessons learned from the legacy PyDAS, SPICE macros, and several early generations of homedeveloped EPICS Python middle layer libraries. It supports all Python features and additional scan-specific commands to be executed by scan server. The scientists worked together with the developers to ensure that the scripting library is easy to use for users

with different levels of programming experience (see Figure 9). Other improvements that come with this implementation include converting other existing high-level scanning tools to use the same helper library, simplified and enhanced device configuration (including limits checking), and a simple screen for submitting scripts.


**Figure 8.** Friendly table view and visualization of Q-ranges (highlighted by the upper red rectangle box), scripting snippets generating with Q-range configurations selected (lower red box). The example shows up to four Q setups at the same time.

**Figure 9.** An example of the Python script used in Scripting Tool to control the magnet, cryostat temperature, and polarization for a highly flexible experiment.

#### *4.4. Event Data Mode and New Features Related to Live Displays*

One of the results of this upgrade is that it enables the production of event mode data for the whole DAS, especially the detectors at HFIR. Event mode imposes timestamps on neutron events detected and on other instrument systems, such as fast sample environment devices, enabling convenient post-data collection filtering. This is very useful in experiments that involve time-resolved kinetic studies, stroboscopic methods, setting up a time-of-flight source at HFIR with choppers, or simply detecting sample deterioration over time. At SNS, "event mode" refers to the pulsed accelerator timing signal; however, as a continuous neutron source, HFIR did not have an inherent timing signal as a reference. Therefore, a time server was set up for HFIR instruments; and Network Time Protocol [19] is used to synchronously timestamp events at an instrument, including neutron events and fast sample environment data, at a precision of within 1 ms. The system was made compatible with SNS event-based acquisition, which uses a timestamping rollover of 16.6667 ms, corresponding to the 60 Hz pulse rate. In other words, the events are grouped by their occurrence in the 16.6667 ms windows, and as such are saved in data files in Nexus format. For reactor-based instruments such as Bio-SANS and GP-SANS, the event timestamps are merely additional information about the neutron events and can be ignored if only the histogram of the data is used. No other changes or additions at HFIR SANS instruments are needed for event-based acquisition, as the relevant features had already been developed and tested on the SNS instruments. In Figure 10, an example of event mode data shows the rapid precipitation that occurs in a novel high strength, high ductility alloy that occurs as the sample was heated from room temperature to 700 ◦C from an experiment on GP-SANS [20]. The size and number density of the precipitates mediates the balance between strength and ductility in this family of alloys. The SANS data can detect such precipitates in-situ. This data was collected in the event mode in a single data set and was processed post-experimentally to split it up by 60-s interval during the temperature ramp and ten 300-s intervals for the annealing temperature. Moreover, the post-experiment process can be flexible depending on samples and sample conditions. The new capability also allows the visualization of sequential defined-time snapshots of the event mode data to aid real-time experimental evaluation and planning.

We have been using EPICS area detector driver for neutron event data (ADnED) and dynamicMapping (a Python tool for live data conversions) [9] to provide meaningful 2D and 1D live displays on other instruments. There are three related new features on SANS that may be worth mentioning. First, an ImageSnapshot Python tool has been deployed on the SANS instruments (and a few other instruments), which saves snapshots of histogrammed 2D detector images at the end of a run. These images are further parsed and ingested in the data catalog database for a quick view of measurement data. They can also be used for quick data reduction without reading the large HDF5 files if event mode data is not needed. Second, by updating dynamicMapping and saving and reusing beam center information in Q-range configurations, we were able to fully automate dynamicMapping to update mapping files for live d-spacing and Q conversions and for cursor display on the histogrammed 2D detector images. Third, a prototype Python tool, SANS-AutoRebin, has been developed to bin the data integrated by ADnED into log bins using default Q-range configurations, normalize log-binned data according to the number of pixels contributing to each log bin, and then scale the normalized data to beam monitor counts or run time. This prototype tool is part of our effort to provide users with live, coarsely reduced data for better steering of their experiments during the run time.

**Figure 10.** The SANS data processed over the time course of an experiment showing the rapid precipitation in a novel alloy under heating. On the left side, each slice along Q is a traditional Intensity vs. Q curve in SANS (the intensity is in cm<sup>−</sup>1). On the right side is the temperature of the sample environment over time, also recorded as the event mode data.

#### **5. Conclusions**

Our new IC-DAS is based on EPICS, an open source distributed control system environment that has been widely adopted by other large scientific facilities. The systems completed commissioning at all SANS instruments by early 2020; an example data using the event mode is shown in Figure 10. With carefully designed and developed features to meet the needs of the SANS user communities, our new system provides a uniform user experience across the ORNL SANS neutron scattering instrument suite. Collaboratively, we designed and delivered a system that reflects a deeper understanding of our diverse user needs, instrument configurations, and complex experiment processes. Easy-to-use tools and more automation result in less cognitive load, confusion, stress, and human error for novice users, and more efficient use of beam time with higher-quality measurement data. The flexible architecture of the new system can handle the ever-increasing complexity of modern instruments. It also provides a manageable solution for integrating existing and new sample environment equipment across all SANS instruments. We hope the enhanced capabilities of our new system and the improved user experience it enables can also benefit other, similar instruments by improving operation for more productive scientific discovery.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/2076-3 417/11/3/1216/s1, Figure S1: Check Q Setups tab in the Panel Scans interface. The yellow outline highlights buttons are required to be clicked to ensure the output parameters to be calculated. Figure S2: Select Q Setups tab in the Panel Scans interface. Figure S3: Sample Environment Devices tab in the Panel Scans interface, for selecting specific sample environment for the current experiment. "Use other device combination:" will reveal the text input box to type a comma separated parameter

names or aliases. Figure S4: Load Samples tab in the Panel Scans interface, for more specific sample information. Figure S5: Specify Exposure Time tab in the Panel Scans interface to setup measurement time or detector count at different configurations and samples. Figure S6: Expand and Submit tab in the Panel Scans interface. It expands the scans in different ways with all conditions from previous setups (such as samples, sample environment, configurations, measurement type (transmission, scattering or both)), only part of the columns are shown in the screenshot. Figure S7: The soft matter simulator with instrument specific parameters

**Author Contributions:** Conceptualization, X.Y., L.D.-S., R.G., G.G., S.H., L.H. (Lilin He), R.K., K.L., S.V.P., S.Q., and V.U.; funding acquisition, G.T.; investigation, M.B., L.D.-S., X.G., R.G., G.G., M.H., S.H., L.H. (Lilin He), L.H. (Luke Heroux), K.K., J.K., C.L., K.L., M.P., S.V.P., C.P., S.Q., M.R.-R., V.S., and K.V.; methodology, B.A., M.H., R.K., J.K., K.L. and, M.R.-R.; project administration, X.Y. and R.K.; resources, L.H. (Luke Heroux) and R.K.; software, X.Y., B.A., M.B., X.G., R.G., G.G., K.K., M.P., M.R.- R., V.S., G.T., and K.V.; supervision, S.H.; writing—original draft, X.Y. and S.Q.; writing—review and editing, X.Y. and S.Q. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by US DOE Office of Science.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors thank all beamline teams and external users with whom we worked, database administrators Jeff Patton and Peter Parker, beamline scientists Changwoo Do, William T. Heller, Mark Lumsden, and all SPICE developers, all EPICS and CS-Studio developers, and all previous and current developers in the SNS Instrument Data Acquisition and Controls group. This project used resources at HFIR and SNS, DOE Office of Science User Facilities operated by ORNL. The Bio-SANS instrument is supported by the DOE Office of Biological and Environmental Research.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

