Liquids, Volume 5, Issue 1 (March 2025) – 8 articles

Ionic liquids exhibit distinctive solvation and reactive properties, making them highly relevant for applications in energy storage, catalysis, and CO₂ capture. However, their complex molecular interactions, including proton transfer and physisorption/chemisorption, necessitate advanced computational efforts to model them at the atomic scale. This review examines key molecular dynamics approaches for simulating ionic liquid reactivity, including quantum-mechanical methods, conventional reactive force fields such as ReaxFF, and fractional force fields employed in PROTEX. The strengths and limitations of each method are assessed within the context of ionic liquid simulations. While quantum-mechanical simulations provide detailed electronic insights, their high computational cost restricts system size and simulation timescales. Reactive force fields enable bond breaking and formation in larger systems but require extensive parameterization. These approaches are well suited for investigating reaction pathways influenced by the local environment, which can also be partially addressed using multiscale simulations. Fractional force fields offer an efficient alternative for simulating significantly larger reactive systems over extended timescales. Instead of resolving individual reaction mechanisms in full detail, they incorporate reaction probabilities to model complex coupled reactions. This approach enables the study of macroscopic properties, such as conductivity and viscosity, as well as proton transport mechanisms like the Grotthuß process—phenomena that remain inaccessible to other computational methods. Full article

Based on data from broadband dielectric spectroscopy (BDS) and a molecular model based on the Landau–de Gennes concept, the effect of confinement on the structural, dielectric, and dynamic properties of 4-n-pentyl-4′-cyanobiphenyl (5CB) in the nematic phase is studied. The dielectric permittivity and relaxation times were previously obtained by the BDS technique in a wide frequency range ($1\mathrm{MHz}\le \mathrm{f}\le 1\mathrm{GHz}$) in the nematic phase composed of 5CB molecules confined to Anopore membranes with pore sizes of 0.2 $\mathsf{\mu }$m. The distance-dependent values of the order parameter $P_2\left(r\right)$, the relaxation time $\tau \left(r\right)\equiv {\tau }_{00}^1\left(r\right)$, the rotational diffusion coefficient $D_{\perp }\left(r\right)$, and both rotational viscosity coefficients ${\gamma }_i\left(r\right)$ ($i=1,2$) as functions of the distance r away from the bounding surface are calculated by a combination of existing statistical-mechanical approaches and data obtained by the BDS technique. Reasonable agreement between the calculated and experimental values of ${\gamma }_i(i=1,2)$ for bulk 5CB is obtained. Full article

Dimer and trimer acids are interesting viscous liquids produced from fatty acids derived from renewable sources. The chemical structures of dimer and trimer acids are known and quite complex and are presented here, discussed and further elucidated through electronic absorption spectroscopy, FT-IR and Raman spectroscopy. Dimer and trimer acids have a number of applications in their original form or in the form of derivatives. In the present study, a series of esters of dimer and trimer acids with alcohols from renewable sources were synthesized for use as plasticizers for rubber and plastics. The polarity of the dimer and trimer acids as well as their esters with alcohols from renewable sources (dimerates and trimerates) were systematically studied using a Nile red solvatochromic probe. The resulting E(NR) values were compared with the E(NR) values of the most common types of rubber and plastics. Compatibility and other physical properties expected from the E(NR) scale were studied and successfully confirmed in tire tread rubber compound formulations and in nitrile rubber and PVC matrices, confirming once again the sensitivity and the validity of the Nile red solvatochromic polarity scale for the development of new plasticizers. The validity of the liquids polarity measured with the Nile Red dye is supported by the correlation found between the E(NR) scale and the dielectric constants (ε) of carboxylic acids (including dimer and trimer acids, hydrogenated dimer acids and isostearic acid) and alcohols. A correlation was even found linking the E(NR) values the with the ε values of thin solid films of rubbers and plastics. In the case of the esters the correlation of their E(NR) values was found with the length of the aliphatic chains of the alcohols used in the esterification. Full article

Utilizing the shake-flask technique under atmospheric pressure (101 kPa) within the temperature range of 293.2 to 313.2 K, the experimental solubility and density values of deferiprone were determined in binary mixtures of polyethylene glycol 400 and 1-propanol. The mole fraction solubility of deferiprone exhibited an augmentation with elevated temperature and increased polyethylene glycol 400 mass ratio in polyethylene glycol 400 + 1-propanol compositions. A subsequent regression analysis of the solubility data was conducted employing the van’t Hoff, λh, Yalkowsky, modified Wilson, Jouyban–Acree and Jouyban–Acree–van’t Hoff models upon the comprehensive evaluation of the entire dataset; the van’t Hoff equation demonstrated the most favorable regression. Furthermore, the findings of this study hold significance for advancing the understanding of the basic thermodynamic data pertinent to the crystallization and industrial separation processes of deferiprone. Full article

When examined at the nanometer length scale, metallic liquids exhibit extensive ordering. Bonding enthalpies are balanced against entropic tendencies resulting in a rich complicated behavior that leads to clustering that depends on temperature but evolves on picosecond time scales. The structural organization of metallic liquids affects their thermophysical properties, such as viscosity and density, thus influencing the ability of a metallic liquid to form useful technological phases, such as metallic glasses. The time-dependent pair correlation function (the Van Hove function) was determined for metallic-glass forming Cu₄₉Zr₄₅Al₆ at 1060 °C from time-of-flight inelastic neutron scattering measurements made using the Neutron Electrostatic Levitation facility at the Spallation Neutron Source. The time for changes in local atomic connectivity, which is the timescale of atomic ordering, was determined by examining the decay of the nearest neighbor peak. The results of rigorous statistical analyses were used to distinguish between competing models of ordering, suggesting that a stretched exponential model of coordination number change is valid for this system. Full article

The behavior of the energy of the peaks of the first UV/Vis absorption band and the presence or absence of isosbestic points in this band with changing temperature for all-trans-DPH and all-trans-β-carotene, dissolved in 1-chlorobutane or hydrocarbon solvents, allows us to show conclusively whether these compounds transform their all-trans-molecular structures into a structure of their conformers. From these analyses, it is concluded that in these solvents, all-trans-DPH is not thermally transformed to its conformer s-cis-DPH in a temperature range from 133 K to 350 K. On the other hand, all-trans-β-carotene, as a model-compound, does show changes in its molecular structure in these solvents with changing temperature. We also show that a portion of all-trans-DPH dissolved in cis-Decalin, at room temperature, slowly transforms into its conformer s-cis-DPH. Full article

The relation between the pressure and molar concentration (in mol/L) of real gases in a low- to medium-pressure range is precisely described by a logarithmic two-parameter equation. Increasing the concentration caused an increase in pressure and also the weakening of the effect due to intermolecular interactions, forming the basis for an equation with an adjusted parameter. Exceeding a critical concentration by a further increase caused a switch to another set of parameters in the same equation. At high pressure, a second switch to an exponential term was observed. This equation of state, defined segment by segment, was attributed to three different structures of the medium. The validity of the equations found was verified with experimental data reported in the literature for helium, neon, argon, krypton, and xenon and is discussed in more detail for argon. The temperature dependence of the parameters of the equations is reported and the formation of a liquid phase is discussed. Full article

Raman scattering measurements were performed on 1 mol dm⁻³ aqueous calcium nitrate (Ca(NO₃)₂) and sodium nitrate (NaNO₃) solutions containing 4% (w/w) D₂O in a temperature range from 25 to 350 °C and pressure of 40 MPa. As the temperature increased, the N–O symmetric stretching vibrational band (ν₁) of NO₃⁻ at 1045–1047 cm⁻¹ shifted to a lower wavenumber by 5~6 cm⁻¹. The band analysis using one Lorentzian component showed that the full-width at half maximum (FWHM) did not change significantly below 175 °C but increased rapidly above 200 °C for both solutions. The peak area for an aqueous Ca(NO₃)₂ solution showed a breakpoint between 225 and 250 °C, suggesting a change in the coordination shell of NO₃⁻ at 175~250 °C. The OD symmetric stretching vibrational band of HDO water was deconvoluted into two Gaussian components at 2530 and 2645 cm⁻¹; the former component has high temperature dependence that is ascribed to the hydrogen bonds, whereas the latter one shows less temperature dependence due to the non-hydrogen bonds of water. X-ray scattering measurements were performed on a 1 mol dm⁻³ aqueous Ca(NO₃)₂ solution at 25 to 210 °C and 40 MPa. Empirical potential structure refinement (EPSR) modeling was used to analyze the X-ray scattering data. Ca²⁺ forms a rigid coordination shell consisting of about seven water molecules at 2.48 Å and one NO₃⁻ at 25~170 °C, with further water molecules substituted by NO₃⁻ at 210 °C. NO₃⁻ is surrounded by 13~14 water molecules at an N–Ow distance of 3.6~3.7 Å. The tetrahedral network structure of solvent water pertains from 25 to 170 °C but is transformed to a dense packing arrangement at 210 °C. Full article