Colloids Interfaces, Volume 8, Issue 1 (February 2024) – 13 articles

Gas-enhanced oil recovery (EOR) through huff-n-puff (HnP) is an important method of recovering oil from fracture-stimulated reservoirs. HnP productivity is hampered by fracture channeling, leading to early gas breakthroughs and gas losses. To mitigate these issues, foam-generating surfactants have been developed as a method of reducing injected gas phase mobility and increasing oil recovery. This work investigates foam generation and propagation by a proprietary surfactant blend in high-temperature, high-pressure, high-permeability, and high-shear conditions that simulate the environment of a proppant-packed fracture. Bulk foam tests confirmed the aqueous stability and foaming viability of the surfactant at the proposed conditions. Through several series of floods co-injecting methane gas and the surfactant solution through a proppant pack at residual oil saturation, the effects of several injection parameters on apparent foam viscosity were investigated. The foam exhibited an exceptionally high transition foam quality (>95%) and strong shear-thinning behavior. The foam viscosity also linearly decreased with increasing pressure. Another flood series conducted in an oil-free proppant pack showed that swelling of residual oil had no effect on the apparent foam viscosity and was not the reason for the inversely linear pressure dependency. An additional flood series with nitrogen as the injection gas was completed to see if the hydrophobic attraction between the methane and surfactant tail was responsible for the observed pressure trend, but the trend persisted even with nitrogen. In a previous study, the dependence of foam viscosity on pressure was found to be much weaker with a different foaming surfactant under similar conditions. Thus, a better understanding of this important phenomenon requires additional tests with a focus on the effect of pressure on interfacial surfactant adsorption. Full article

Coarse-grained molecular dynamic simulations are employed to investigate the spatiotemporal evolution of vesicles (polymersomes) via self-assembly of randomly distributed amphiphilic diblock copolymers PB-PEO (Poly(Butadiene)-b-Poly(Ethylene Oxide)) in water. The vesiculation pathway consists of several intermediate structures, such as spherical/rodlike aggregates, wormlike micelles, lamellae, and cavities. The lamella-to-vesicle transition occurs at a constant aggregation number and is accompanied by a reduction in the solvent-accessible surface area. Simulation predictions are in qualitative agreement with the mechanism of vesicle formation in which the unfavorable hydrophobic interactions between water molecules and polymer segments, along the edge of the lamella, are eliminated at the expense of gaining curvature energy. However, rod–lamella–vesicle transition is accompanied by an increase in copolymer packing density. Hence, the change in the surface area accompanying vesiculation predicted by the simulations is significantly lower than theoretical estimates. Changes in information entropy, quantified by the expectation of the logarithm of the probability distribution function of the segmental stretch parameter s, defined as the difference between the maximum and instantaneous segmental extension, are statistically insignificant along the vesiculation pathway. For rods, lamellae, and polymersomes, s follows a log normal distribution. This is explained based on the configurational dynamics of a single diblock chain in water. Full article

Different oils can be homogeneously dispersed in the network junctions of the separated bicontinuous micellar phases. Upon dilution, these dispersions spontaneously form nanoemulsions. The possibility of a micellar sponge phase formation in the case of mixtures with three anionic and two zwitterionic surfactants in the presence of divalent and monovalent salts is studied. The best results are obtained using sodium lauryl ether sulfate with 1 ethylene oxide group (SLES-1EO) and both cocamidopropyl betaine (CAPB) or N,N-dimethyldodecylamine N-oxide (DDAO) in the presence of an appropriate small amount of MgCl₂ and CaCl₂. Bicontinuous micellar phases can be produced also in high-salinity NaCl solutions. The bulk properties of these phases are independent of the concentration of the initial solutions from which they are separated, and their Newtonian viscosities are in the range from 0.3 Pa·s to 0.8 Pa·s. Both 8 wt% CAPB- and DDAO-containing sponge phases engulf up to 10 wt% limonene and spontaneously form nanoemulsion upon dilution with droplet sizes of 110–120 nm. Vitamin E can be homogeneously dispersed only in CAPB-containing saturated micellar network, and upon dilution, these dispersions spontaneously form nanoemulsions with smaller droplet sizes of 66 nm for both 8 diastereomers and 2 diastereomers mixtures of vitamin E. Full article

Colloidal particle self-assembly into higher-ordered structures has been of great interest due to the promise of creating metamaterials with novel macroscopic properties. The physicochemical properties of these metamaterials can be tailored to achieve composites with tunable functionalities, either by controlling the assembly morphology and/or chemistry of the colloidal building blocks. This work describes a strategy of developing microparticles with a hybrid configuration that have an inorganic and an organic part. The inorganic part comprises functional nanoparticles, which are embedded within an organic polymer particle composed of diethyl methylene malonate polymer [p(DEMM)] prepared using anionic emulsion polymerization. DEMM polymerization is initiated entirely by the presence of hydroxyl anions and the resulting particle diameter can be tuned between 300 nm and 1 micrometer by reaction pH. Inorganic nanoparticles with varying chemistry (TiO₂, CdTe, ZnO) can be loaded into the p(DEMM) particle with a controlled weight fraction, as confirmed by thermogravimetric analysis. The colloidal stability of the composite microparticles is seen to be dependent on the ligand coating attached to the inorganic constituent. These results provide a synthetic groundwork for creating hybrid, stimuli-responsive microparticles. Full article

Aqueous phase pH is a critical metric with significant importance in understanding reactive transport processes in porous media. At the microscale, however, traditional pH detection methods face challenges in capturing dynamic pH due to limited sample volume and sensing time. To overcome these limitations, we leveraged micro/nanofabrication techniques to create a microfluidic porous medium coated with polyaniline (PAni) on its surface. Using this innovative microfluidic design, we achieved colorimetric delineation of pH spatial distribution with fast response and robustness in porous media. By conducting coinjection tests with hydrochloric acid (pH = 2) and DI water (pH ≈ 5.8, equilibrated with air) at various flow rates and relative flow rate ratios in a sandstone-patterned microfluidic device, we observed dynamic pH changes in porous media and obtained a comprehensive understanding of the acid advection-diffusion dynamics. The results highlighted the capability of PAni to enable microscale pH sensing. This research contributes to the development of advanced porous media microfluidics and applications, particularly in mass transfer limits during reactive transport of carbon dioxide sequestration and geological hydrogen storage. Full article

Although the potential of natural minerals for purification of liquid radioactive wastes (LRW) from radionuclides has been widely studied, the use of hybrid polymer composites made of zeolite is still rather scarce. This article reports on the preparation of zeolite-based hybrid polymer composites using the in situ polymerization technique in the body of mineral matrix and its intercalated with copper ferrocyanide (CuFC) forms. This hybrid polymer composites have shown unique and enhanced properties for the removal of micropollutants from wasted water as compared to the individual mineral. The change in conventional properties of two mixed minerals, such as zeolite and bentonite, and their intercalated with CuFC forms were probed using techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and FT-IR analysis. The totality of analysis showed a coexistence of intercalated and percolated zeolite phases. The hybrid polymer composites exhibited both adsorption and ion-exchange properties in the removal of ^134,137Cs⁺, ^57,60Co²⁺ and ⁸⁵Sr²⁺ radionuclides from LRW. Full article

Dispersed phases like colloidal particles and emulsions are characterized by their particle size distribution. Narrow distributions can be represented by the monodisperse distribution. However, this is not the case for broader distributions. The so-called quadrature methods of moments assume any distribution as a bidisperse one in order to solve the corresponding population balance. The generalization of this approach (i.e., approximation of the actual particle size distribution according to a bidisperse one) is proposed in the present work. This approximation helps to compress the amount of numbers for the description of the distribution and facilitates the calculation of the properties of the dispersion (especially convenient in cases of complex calculations). In the present work, the procedure to perform the approximation is evaluated, and the best approach is found. It was shown that the approximation works well for the case of a lognormal distribution (as an example) for a moments order from 0 to 2 and for dispersivity up to 3. Full article

This study provides valuable insights into biobased surfactant systems, shedding light on their behavior and potential applications in cleaning and oil recovery processes. By combining the alkyl polyglycoside Triton^® CG-110 with C₁₂OH fatty alcohol, a promising strategy emerges, enhancing the efficiency of surfactant-based formulations. This innovative approach paves the way for sustainable solutions in diverse industrial applications. A rheological analysis of the formulations containing C₁₂OH demonstrated a Newtonian-like behavior of up to 3.2 v/v% of Triton, while a viscoelastic response was observed in a system containing 6.4 v/v% of Triton. Self-diffusion nuclear magnetic resonance revealed the formation of larger aggregates with C₁₂OH, diverging from the classical spherical micellar solution. Moreover, cleaning efficiency tests highlighted C₁₂OH’s significant enhancement of the surfactant system’s oil-uptake capacity. This study identified the optimum formulation point, corresponding to the Winsor III microemulsion phase, in samples containing C₁₂OH. This pivotal discovery showcases the potential of tailored surfactant blends, indicating a path toward greener and more effective industrial practices. Full article

The onset and early stages of dynamic wetting on different hydrophobic surfaces is investigated experimentally for aqueous solutions of two commercial trisiloxane surfacants of similar chemical structure, one of which exhibits superspreading behaviour, in order to investigate the spreading dynamics independently of the surface activity. Superspreading, or the ability of a surfactant solution to spread on a surface beyond the state determined by thermodynamic equilibrium, has been investigated for more than 30 years however its physical mechanism remains poorly understood to date despite its important applications in the formulation of agrochemicals. Surfactant solutions were prepared by dissolving S233 and S240 surfactants (Evonik Industries AG, Essen, Germany) into de-ionised water at a weight concentration of 0.1%. Drops of surfactant solutions and pure water were deposited on three horizontal substrates with different wettability (equilibrium contact angle of water ranging between ${55}^{\circ }$ and ${100}^{\circ }$), and observed from below with a high-frame rate camera to visualise the advancing contact line. The spreading ratio of drops as a function of time was extracted from high-speed videos by digital image processing. Results reveal that the superspreading solution exhibits an intermittent spreading rate, as well as peculiar features of the contact line, which are not observed for the non-superspreading solution, and confirm the superspreading effect becomes less significant when the surface energy of the substrate is decreased. Full article

Two open issues on the measurement of the dilational modulus (E) for an adsorbed protein film during the adsorption process have been unacknowledged: how E varies during the adsorption and the length of time needed to attain a stable E value. A new approach for detecting the E variation from a clean air–water interface to saturated film and estimating the time needed to reach a saturated state was proposed. A pendant bubble tensiometer was utilized for measuring the relaxations of surface tension (ST) and surface area (SA), and the E was evaluated from the relaxation data of minute distinct perturbances. The data showed a clear variation in E during the BSA adsorption: E sharply decreased to a minimum at the early stage of BSA adsorption; then, it rose from this minimum and oscillated for a while before reaching an E corresponding to a saturated BSA film after a significant duration. The adsorbed BSA film took ~35 h to reach its saturated state, which was much longer than the reported lifetime of the adsorbed film in the literature. A rapid surface perturbation (forced bubble expansion/compression) could change the E, causing a significant drop in E followed by a slow increase to the original stable value. Full article

Every year, millions of foodborne illnesses with thousands of deaths occur worldwide, which is why controlling foodborne pathogens is sought. In this study, nanoemulsions of phytochemicals extracted from Plectranthus hadiensis var. tomentosus (PHT) were obtained, and their antioxidant and antimicrobial capacities were evaluated. PHT extracts were obtained by maceration, ultrasound, and Naviglio methods, and their antimicrobial activity against Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Salmonella enterica was determined by the microdilution method. The extract with the highest antimicrobial activity was obtained by Naviglio with a minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 12.5 and 25 mg/mL, respectively, for all bacterial strains. The nanoemulsion (o/w) made with Tween 40, 5% extract, and 50% ultrasonic amplitude had a globule size of 4.4 nm, a polydispersity index of 0.48, and a surface charge of −0.08 mV and remained stable for 30 days. This nanosystem presented significantly higher antimicrobial and antioxidant activity than the free extract. Thus, the nanoencapsulation of the phytochemicals in the PHT extracts is an alternative to protect and enhance their biological activity against pathogenic microorganisms. Full article

Evaporating a liquid sessile drop deposited on a horizontal surface is an important object of applications (printing technologies, electronics, sensorics, medical diagnostics, hydrophobic coatings, etc.) and theoretical investigations (microfluidics, self-assembly of nanoparticles, crystallization of solutes, etc.). The arsenal of formulas for calculating the slow evaporation of an axisymmetric drop of capillary dimensions deposited on a flat solid surface is reviewed. Characteristics such as vapor density, evaporation flux density, and total evaporation rate are considered. Exact solutions obtained in the framework of the Maxwellian model, in which the evaporation process of the drop is limited by vapor diffusion from the drop surface to the surrounding air, are presented. The summary covers both well-known results obtained during the last decades and new results published by us in the last few years, but practically unknown to the wider scientific community. The newest formulas, not yet published in refereed publications, concerning exact solutions for a number of specific contact angles are also presented. In addition, new approximate solutions are presented (total evaporation rate and mass loss per unit surface area per unit time in the whole range of contact angles $\theta \in [0, \mathsf{\pi })$, drop lifetime in constant contact radius evaporation regime and constant contact angle mode), which can be used in modeling without requiring significant computational resources. Full article

The release of drugs from core/shell nanoparticles (NPs) is a crucial factor in ensuring high reproducibility, stability, and quality control. It serves as the scientific basis for the development of nanocarriers. Several factors, such as composition, composition ratio, ingredient interactions, and preparation methods, influence the drug release from these carrier systems. The objective of our study was to investigate and discuss the relationship between modifications of core/shell NPs as multifunctional drug delivery systems and the properties and kinetics of drug release using an in vitro drug release model. In this paper, we prepared four core/shell NPs consisting of a superparamagnetic iron oxide NPs (Fe_3−δO₄) core encapsulated by a biocompatible thermo-responsive copolymer, poly(2-(2-methoxy) ethyl methacrylate-oligo (ethylene glycol) methacrylate) or P(MEO₂MAx-OEGMA_100−x) (where x and 100 − x represented the molar fractions of MEO₂MA and OEGMA, respectively), and loaded with doxorubicin (DOX). Colloidal behavior measurements in water and PBS as a function of temperature showed an optimization of the lower critical solution temperature (LCST) depending on the molar fractions of MEO₂MA and OEGMA used to form each NPs. In vitro studies of doxorubicin release as a function of temperature demonstrated a high control of release based on the LCST. A temperature of approximately 45 °C for 60 h was sufficient to release 100% of the DOX loaded in the NPs for each sample. In conclusion, external stimuli can be used to modulate the drug release behavior. Core/shell NPs hold great promise as a technique for multifunctional drug delivery systems. Full article