Liquids, Volume 4, Issue 2 (June 2024) – 8 articles

Swallowing disorders, or dysphagia, can lead to bolus aspiration in the airway, causing serious adverse health effects. Current clinical interventions for dysphagia are mainly empirical and often based on symptoms rather than etiology, of which a thorough understanding is still lacking. However, it is challenging to study the swallowing process that involves sequential structural motions and is inaccessible to standard visualization instruments. This study proposed an in vitro method to visualize swallowing hydrodynamics and identify the fundamental mechanisms underlying overflow aspirations. An anatomically accurate pharynx–epiglottis model was developed from patient-specific CT images of 623 µm isotropic resolution. A compliant half-pharynx cast was prepared to incorporate dynamic structures and visualize the flow dynamics in the mid-sagittal plane. Three locations of frequent overflow aspiration were identified: the epiglottis base, cuneiform tubular recesses, and the interarytenoid notch. Water had a consistently higher aspiration risk than a 1% w/v methylcellulose (MC) solution. The contracting–relaxing pharynx and flapping epiglottis spread the liquid film, causing a delayed esophageal entry and increased vallecular residual, which was more pronounced with the MC solution. Dispensing the liquid too slowly resulted in water aspiration, whereas this was not observed with the MC solution. An incomplete epiglottis inversion, such as horizontal or down-tilt 45°, aggravated the aspiration risks of water. This study suggests that it is practical to use anatomically accurate respiratory–digestive models to study the swallowing process by incorporating varying physiological details. Full article

Density, viscosity, refractive index, and ultrasonic velocity were measured for the pure materials anisole, methanol, and toluene, and for the binary mixtures: methanol—anisole and methanol—toluene. Excess molar volume V^E, isobaric thermal compressibility α, excess Gibbs activation energy for fluid flow ΔG^E*, and excess isentropic compressibility κ_S^E were calculated from the measured quantities. For both binary mixtures V^E and κ_S^E were <0 while Δn > 0 and ΔG^E* > 0 over the entire mole fraction composition range. Anisole mixtures exhibited more negative values for V^E and κ_S^E while more positive values were displayed for Δn and ΔG^E* compared to toluene mixtures. For Δη, negative values were observed at low alcohol concentrations but positive values at high alcohol concentrations for both systems. Full article

We have kinetically estimated the enzymatic redox reaction at the horseradish peroxidase (HRP)-modified electrode combined with ionic liquids by adding N-(2-methoxythethyl)-N-methylpyrrolidinium bis(trifluoromethane sulfonyl)imide (MEMPTFSI) to HRP/carbon paste (CP)/Ketjenblack EC600JC (EC). The fluctuation of the steady-state reduction current of HRP at the HRP/CP-modified electrode progressively increased as the applied potential was lowered. The enzymatic redox reaction with hydrogen peroxide as a substrate at the HRP/CP/EC/MEMPTFSI-modified electrode and the HRP/CP-modified electrode could be correlated by the Michaelis–Menten equation. The Michaelis constant of the enzymatic redox reaction at the HRP/CP/EC/MEMPTFSI-modified electrode was the same as that at the HRP/CP-modified electrode. On the other hand, the turnover number of the enzymatic redox reaction at the HRP/CP/EC/MEMPTFSI-modified electrode was six times larger than that at the HRP/CP-modified electrode. Consequently, the specificity constant of the enzymatic redox reaction at the HRP/CP/EC/MEMPTFSI-modified electrode was much higher than that at the HRP/CP-modified electrode. Full article

In this article, the particle concentration of finely dispersed copper(II) oxide nanosuspensions as precursors for reductive laser sintering (RLS) is optimized on the basis of rheological investigations. For this metallization process, a smooth, homogeneous and defect-free precursor layer is a prerequisite for adherent and reproducible copper structures. The knowledge of the rheological properties of an ink is crucial for the selection of a suitable coating technology as well as for the adjustment of the ink formulation. Different dilutions of the nanosuspension were examined for their rheological behavior by recording flow curves. A strong shear thinning behavior was found and the viscosity decreases exponentially with increasing dilution. The viscoelastic behavior was investigated by a simulated doctor blade coating process using three-interval thixotropy tests. An overshoot in viscosity is observed, which decreases with increasing thinning of the precursor. As a comparison to these results, doctor blade coating of planar glass and polymer substrates was performed to prepare precursor layers for reductive laser sintering. Surface morphology measurements of the resulting coatings using laser scanning microscopy and rheological tests show that homogeneous precursor layers with constant thickness can be produced at a particle–solvent ratio of 1.33. A too-high particle content results in an irregular coating layer with deep grooves and a peak-to-valley height ${\mathrm{S}}_z$ of up to $7.8$ μm. Precise dilution control allows the fabrication of smooth surfaces with a ${\mathrm{S}}_z$ down to $1.5$ μm. Full article

An overview of solvent replacement strategies shows that there is great progress in green chemistry for replacing hazardous di-polar aprotic solvents, such as N,N-dimethylformamide (DMF), 1-methyl-2-pyrrolidinone (NMP), and 1,4-dioxane (DI), used in processing active industrial ingredients (APIs). In synthetic chemistry, alcohols, carbonates, ethers, eucalyptol, glycols, furans, ketones, cycloalkanones, lactones, pyrrolidinone or solvent mixtures, 2-methyl tetrahydrofuran in methanol, HCl in cyclopentyl methyl ether, or trifluoroacetic acid in propylene carbonate or surfactant water (no organic solvents) are suggested replacement solvents. For the replacement of dichloromethane (DCM) used in chromatography, ethyl acetate ethanol or 2-propanol in heptanes, with or without acetic acid or ammonium hydroxide additives, are suggested, along with methanol acetic acid in ethyl acetate or methyl tert-butyl ether, ethyl acetate in ethanol in cyclohexane, CO₂-ethyl acetate, CO₂-methanol, CO₂-acetone, and CO₂-isopropanol. Supercritical CO₂ (scCO₂) can be used to replace many organic solvents used in processing materials from natural sources. Vegetable, drupe, legume, and seed oils used as co-extractants (mixed with substrate before extraction) can be used to replace the typical organic co-solvents (ethanol, acetone) used in scCO₂ extraction. Mixed solvents consisting of a hydrogen bond donor (HBD) solvent and a hydrogen bond acceptor (HBA) are not addressed in GSK or CHEM21 solvent replacement guides. Published data for 100 water-soluble and water-insoluble APIs in mono-solvents show polarity ranges appropriate for the processing of APIs with mixed solvents. When water is used, possible HBA candidate solvents are acetone, acetic acid, acetonitrile, ethanol, methanol, 2-methyl tetrahydrofuran, 2,2,5,5-tetramethyloxolane, dimethylisosorbide, Cyrene, Cygnet 0.0, or diformylxylose. When alcohol is used, possible HBA candidates are cyclopentanone, esters, lactone, eucalytol, MeSesamol, or diformylxylose. HBA—HBA mixed solvents, such as Cyrene—Cygnet 0.0, could provide interesting new combinations. Solubility parameters, Reichardt polarity, Kamlet—Taft parameters, and linear solvation energy relationships provide practical ways for identifying mixed solvents applicable to API systems. Full article

The results of a photothermal spectroscopy technique that effectively images convective and conductive heat flow in liquids via a thermal lensing effect are described. Pure water; sodium chloride solutions at salinities of approximately 5, 15, 25, and 35 g/kg; and an artificial seawater of 35 g/kg were studied across a range of temperatures. This system was studied because of the importance of thermal pluming in seawater. ‘Frustrated’ thermal starting plumes were observed near the temperature of maximum density. The physical characteristics of these thermal starting plumes are reported. Full article

The energies, structures, and vibrational frequencies of [Sb(H₂O)_n]³⁺, n = 0–9, 18 have been calculated at the Hartree–Fock and second-order Møller–Plesset levels of theory using the CEP, LANL2, and SDD effective core potentials in combination with their associated basis sets, or with the 6-31G* and 6-31+G* basis sets. The metal–oxygen distances and totally symmetric stretching frequency of the aqua ions were compared with each other and with related crystal structure measurements where available. Full article

After a survey on polymer plasticization theories and conventional criteria to evaluate polymer–plasticizer compatibility through the solubility parameter, an attempt to create a polymer–plasticizer polarity scale through solvatochromic dyes has been made. Since Reichardt’s E_T(30) dye is insoluble in rubber hydrocarbon polymers like polyisoprene, polybutadiene and styrene–butadiene copolymers and is not useful for the evaluation of the hydrocarbons and ester plasticizers, the Nile Red solvatochromic dye was instead used extensively and successfully for this class of compounds. A total of 53 different compounds were evaluated with the Nile Red dye and wherever possible also with Reichardt’s E_T(33) dye. A very good correlation was then found between the Nile Red scale E(NR) and Reichardt’s E_T(30) scale for this class of compounds focusing on diene rubbers and their typical hydrocarbons and new ester plasticizers. Furthermore, the E(NR) scale also shows a reasonable correlation with the total solubility parameter calculated according to the Van Krevelen method. Based on the above results, some conclusion was made about the compatibility between the diene rubbers and the conventional plasticizers, as well as a new and green plasticizer proposed for the rubber compounds. Full article