Liquids, Volume 6, Issue 1 (March 2026) – 10 articles

The research on nonaqueous two-phase systems, i.e., ternary nonaqueous systems with a liquid–liquid phase split induced by a solid component, is discussed. Previous scattered reports are reviewed and summarized. The first systematic studies are described in detail. These included qualitative testing of numerous ternary systems (a solid component and two liquid solvents, significantly different in polarity) to determine whether a liquid–liquid phase split occurred. Some correlations between this occurrence and the Hofmeister series were suggested. The liquid–liquid equilibrium was determined experimentally in a few systems, and the problems encountered during this determination are discussed. Possible applications and further topics of investigation are suggested. Full article

Experimentally, adsorption is usually described by adsorption isotherms, which present a saturation effect at high enough concentration or pressure of the adsorbate fluid. This well-known saturation effect was first theoretically discussed by Langmuir, and it is commonly attributed to the finite number of adsorption sites on the substrate surface. Here, we propose an alternative approach to introduce saturation via a repulsive interaction potential, $\varphi$, among the adsorbate particles, in addition to the attractive potential between the adsorbate particles and the substrate. Using the proposed toy model for a semi-infinite sample, we calculate adsorption isotherms for a typical van der Waals interaction potential. The concentration profile of the adsorbate as a function of the distance from the surface is calculated for several bulk concentrations. The functional dependence of the saturation concentration on the strength of the repulsive inter-particle interaction is extracted by fitting numerical data. Our results are compared to those of the Langmuir model. No assumption of a finite predefined number of adsorption sites is required to obtain saturation. Full article

The energies, structures, and vibrational frequencies of [Fe(H₂O)_n]³⁺, n = 0–6, 18 have been calculated at the Hartree–Fock, second-order Møller–Plesset, and density functional (B3LYP) levels of theory using the 6−31G* and 6−31+G* basis sets. The metal–oxygen distances and stretching frequencies were compared with each other, with related crystal structure and solution measurements and with previous calculations. The Fe-O distances and stretching vibrational frequencies were well reproduced with an explicit model for the second hydration shell. Full article

We present the design and characterization of a fully automated free-standing liquid crystal (FSLC) film holder, enabling remote and precise control of liquid crystal (LC) volume release, wiping speed, and temperature. Using 4-octyl-4′-cyanobiphenyl (8CB) as a test material, we systematically investigated the influence of formation parameters on the resulting film thickness and temporal evolution. Thickness measurements performed by monitoring the difference in optical path lengths of two arms of a standard optical intensity autocorrelation setup reveal that the wiping speed is the dominant factor determining both the initial film thickness and the subsequent annealing dynamics, while temperature becomes relevant only at the highest wiping speeds. Faster wiping speeds consistently produce thinner and more uniform FSLC films on the order of 3 µm, due to reduced LC mass deposition. Time-resolved optical and X-ray scattering measurements confirm the presence of an annealing phase following film formation, which can last for between 1 s and 10 min time scales, until a stable smectic configuration is reached. The holder provides a reliable and fully remote tool for generating high-quality FSLC films at rates up to 1 Hz, suitable for optical to hard X-ray experiments where direct access to the sample environment is limited. Full article

An upgraded GAFF2 force field has been used to simulate two fluorinated alcohols, TFE and HFIP, in aqueous solutions at several concentrations. The same force field has also been employed to simulate a 26-residue amphiphilic peptide in several cosolvent/water mixtures to verify and clarify its efficacy in stabilizing the secondary structure. The calculated thermodynamic and structural properties are in agreement with experimental findings. The force field allows a correct description of the secondary structure and affords an accurate characterization of the spatial organization of cosolvent molecules around the peptide. Full article

Solubility studies are an essential requirement for the development of more efficient industrial processes. In this context, the use of cosolvents is a relevant strategy in pharmaceutical sciences, especially when dealing with green solvents such as water (W (2)) and Polyethylene glycol 400 (PEG 400 (1)). The objective of this study is to thermodynamically analyze the solubility of isoniazid in {PEG 400 (1) + W (2)} cosolvent mixtures at seven temperatures (288.15 to 318.15 K). The study was conducted by calculating thermodynamic functions from experimental solubility data determined using the flask shaking method, employing UV spectrophotometry as the quantification technique. The dissolution process was shown to be endothermic and entropy-driven. Although maximum solubility would be expected to be achieved in a cosolvent mixture, given that the solubility parameter of isoniazid (30.54 MPa^1/2) has an intermediate value between the two pure solvents (PEG 400 ≈ 22.5 MPa^1/2; Water $\approx 47.8$ MPa^1/2), maximum solubility is achieved in pure PEG 400 and the lowest solubility is achieved in pure water. Full article

Filtration of emulsions is an important operation in multiple processes of chemical, environmental, and petroleum engineering. The primary concern of the present study is cleaning of water produced from a petroleum reservoir. The produced water is filtered from the oil droplets before being dumped into the sea or reinjected into the reservoir. Efficiency of filtration is determined, in particular, by the droplet size distribution and interfacial properties. We have developed a new population balance model of emulsion filtration, based on the Boltzmann–Smoluchowski approach. The model accounts for the droplet size distribution, as well as for the different mechanisms of the droplet capture: attachment to the surface and straining in the pore constrictions. The model can not only be applied to filtering of the produced water, but also to more general emulsion processing. It is capable of reproducing experimental data on the droplet production history and dynamic permeability decline. The sensitivity study indicates low sensitivity of the permeability decline curves to the model parameters. The production histories or other kinds of experimental data are necessary to discriminate between the different parametrizations of the model. Full article

It has been shown for the first time that in the case of a pressure flow of a Newtonian fluid in a circular pipeline, the influence of forces of rheological origin, ion electrostatic and Van der Waals nature on the radius of the undeformed flow core is described by a third-degree polynomial with respect to the thickness of the layer, where the suspension structure is destroyed and its shear flow occurs. In this polynomial, the contributions of rheological forces and the influence of the hydraulic size of the solid-phase particles in the suspension enter as linear terms; ionic electrostatic and Van der Waals forces enter as quadratic and constant terms, respectively. For conditions typical of water–coal fuel, we demonstrate that the hydraulic (size) term is several orders of magnitude smaller than the leading terms and may be neglected, and that the quadratic term is negligible compared with the constant (free) term, so that the limiting value of the undeformed core radius is obtained as the real root of a cubic equation containing cubic, linear and constant terms. At DLVO equilibrium, the constant term vanishes, and the limiting relative core radius reduces to the rheological–hydraulic expression; away from equilibrium, the constant term becomes positive or negative, thereby altering the admissible interval of the relative core radius. Using Cardan’s method, we show analytically that (i) when the cubic discriminant is positive, a single real root exists and physically admissible solutions occur only for a negative constant term; (ii) when the discriminant is negative, three real roots exist and the maximum relative radius at which the suspension structure is preserved shifts above or below the rheological-only radius depending on the sign of the constant term. Numerical evaluation of the proposed lyophobicity model for proportionality coefficients k₁ in the range 1–10 yields a lyophobicity function varying approximately from 0.67 to 1.06, confirming the modest but non-negligible role of interparticle interaction energy in modifying the undeformed core size under water–coal fuel conditions. These results quantify the competing roles of rheology and interparticle forces in determining the stability and extent of the undeformed core in pipeline transport of structured suspensions. Full article

Arid zones, such as the MENA regions and the Sahara countries, are experiencing significant water stress. To address this global challenge, desalination technologies provide a crucial solution, particularly the reverse osmosis (RO) technique, which is widely used to treat Seawater or Brackish water. Mauritania is among the countries facing a scarcity of potable water resources and relies on desalination technologies to meet its water demand. In this work, a numerical and experimental study was carried out on the functional and productive parameters of the Nouadhibou desalination plant in Mauritania using MATLAB/Simulink (R2016a). The study considered two operating scenarios: with and without the energy recovery unit. The objective of this paper is to perform an analytical study of the operating procedures of the Nouadhibou RO desalination plant by varying several parameters, such as the pressure exchanger, and the feed water mixing ratio in the pressure exchanger unit, etc., in order to determine the system’s optimal operating point. This paper analyzes the system’s performance under different conditions, including recovery rate, feed water temperature, and PEX splitter ratio. In Case No. 1 (without a pressure recovery unit), and with a recovery rate of 20%, doubling the plant’s productivity from 400 to 800 m³/d requires 400 kW of power. In contrast, in Case No. 2 (with a pressure recovery unit), achieving the same productivity requires only 100 kW, with a 75% of energy saving. When the desalination plant operates at a productivity of 400 m³/d@40%, the SPC decreases from 6 kWh/m³ (Case No. 1) to 2.7 kWh/m³ (Case No. 2), resulting in a 55% specific power consumption saving. The results also indicate that power consumption increases with both feed water temperature and PEX splitter ratio, while variations in these parameters have a negligible effect on permeate salinity. Full article

Over the past two decades, terahertz (THz) spectroscopy has demonstrated remarkable potential for the investigation of liquids, including studies of living organisms and biological components in their natural, aqueous environments. The main advantages of THz radiation lie in its ability to interact with collective and low-energy vibrational modes of macromolecules and microorganisms, while being non-harmful due to the low photon energy involved. These characteristics make THz spectroscopy particularly valuable for research in liquids compared to other well-established techniques such as Raman and infrared spectroscopy. In this study, we offer a concise overview and comparison of two case studies from our earlier publications, highlighting how Ultrabroadband THz spectroscopy and Intense THz Spectroscopy serve as complementary methods for advancing research in liquids. Ultrabroadband THz spectroscopy enables simultaneous probing of both intermolecular and intramolecular interactions in a single experiment. On the other hand, intense THz spectroscopy greatly simplifies the determination of the optical constants of liquid solutions, eliminating the need for additional assumptions or prior knowledge. Moreover, it offers high sensitivity, allowing the detection of dilute solutions and subtle spectral variations. Currently, these two techniques typically rely on different THz sources, as achieving both broadband coverage and high intensity in a single setup remains challenging. In fact, the experimental results reviewed here were obtained at two different times and within two distinct scientific collaborations. In particular, the intense source was accessed through a collaboration with Prof. Novelli at Ruhr University in Bochum. Integrating both capabilities into a single apparatus would be highly desirable. Therefore, we also present a theoretical investigation of a novel experimental approach that could enable combined ultrabroadband and intense THz spectroscopy, merging the strengths of both methods. Full article