Liquids, Volume 5, Issue 4 (December 2025) – 6 articles

This study presents a quantum electrodynamics (QED) framework that explains the anomalous behavior of liquid water. The theory posits that water consists of two coexisting phases: a coherent phase, in which molecules form phase-locked coherence domains (CDs), and an incoherent phase that behaves like a dense van der Waals fluid. By solving polynomial-type equations, we derive key thermodynamic properties, including the minima in the isobaric heat capacity per particle (IHCP) and the isothermal compressibility, as well as the divergent behavior observed near 228 K. The theory also accounts for water’s high static dielectric constant. These results emerge from first-principles QED, integrating quantum coherence with macroscopic thermodynamics. The framework offers a unified explanation for water’s anomalies and has implications for biological systems, materials science, and fundamental physics. Future work will extend the theory to include phase transitions, solute interactions, and the freezing process. Full article

Droplets sliding down a partially wetted surface are a ubiquitous phenomenon in nature and everyday life. Despite its apparent simplicity, it hinders complex intricacies for theoretical and numerical descriptions matching the experimental observations, even for the simplest case of a drop sliding down a homogeneous surface. A key aspect to be considered is the distribution of contact angles along the droplet perimeter, which can be challenging to include in the theoretical/numerical analysis. The scenario can become more complex when considering geometrically or chemically patterned surfaces or complex fluids. Indeed, these aspects can provide strategies to passively control the droplet motion in terms of velocity or direction. This review gathers the state of the art of experimental, numerical, and theoretical research about droplets made of Newtonian and non-Newtonian fluids sliding down homogeneous, chemically heterogeneous, or geometrically patterned surfaces. Full article

The rheological properties of aqueous solutions of wormlike micelles (WLMs) of cationic surfactant erucyl bis(hydroxyethyl)methylammonium chloride (EHAC) in the presence of hydrotropic salt sodium salicylate (NaSal) and inorganic salt sodium chloride (NaCl) have been studied. The conditions for maximum zero-shear viscosity at fixed surfactant concentration were investigated. It has been shown that charged WLMs in the presence of NaSal have higher viscosities than well-screened micelles in the presence of NaCl. This is because the adsorption of hydrophobic salicylate ions onto the micelles increases their length more significantly than the presence of a large amount of sodium ions in the solution. It was discovered that the effect of temperature on the rheological properties depends on both the type of salt used and the salt/surfactant molar ratio. An unusual increase in zero-shear viscosity and elastic modulus was observed at a NaSal concentration that corresponds to the maximum zero-shear viscosity when the WLMs are linear, charged, and “unbreakable”. These results expand the possibilities of using hydrotropic salts to create stable, highly viscous systems in various fields, and opening up new horizons for applications in oil production, cosmetics, and household chemicals. Full article

Liquids like water are not expected to produce a thermal change under shear strain or flow (away from extreme conditions). In this study, we reveal experimental conditions for which the conventional athermal hydrodynamic assumption is no longer valid. We highlight the establishment of non-equilibrium hot and cold thermal states occurring when a mesoscopic confined liquid is set in motion. Two stress situations are considered: low-frequency shear stress at large strain amplitude and microfluidic transport (pressure gradient). Two liquids are tested: water and glycerol at room temperature. In confined conditions (submillimeter scale), these liquids exhibit stress-induced thermal waves. We interpret the emergence of non-equilibrium temperatures as a consequence of the solicitation of the mesoscopic liquid elasticity. In analogy with elastic deformation, the mesoscopic volume decreases or increases slightly, which leads to a change in temperature (thermo-mechanical energy conversion). The energy acquired or released is converted to heat or cold, respectively. To account for these non-equilibrium temperatures, the mesoscopic flow is no longer considered as a complete dissipative process but as a way of propagating shear and thus compressive waves. This conclusion is consistent with recent theoretical developments showing that liquids propagate shear elastic waves at small scales. Full article

This study investigates the formation of hydroxyl radicals (OH radicals) in cavitation bubble plasma-treated water (CBPTW) using a chemical probe method. CBPTW samples were prepared with different electrode materials (W, Fe, Cu, and Ag), and the chemical scavenger was added two minutes after the completion of cavitation and plasma treatments. The concentrations of metal ions and hydrogen peroxide (H₂O₂) generated in the CBPTW were also measured over time. This study reveals a novel mechanism whereby metal nanoparticles and ions released from electrodes catalyze the continuous generation of hydroxyl radicals in CBPTW, which has not been fully addressed in previous studies. The results suggest a continuous generation of OH radicals in CBPTW prepared with W, Fe, and Cu electrodes, with the amount of OH radicals produced in the order Cu > Fe > W. The study reveals a correlation between OH radical production and electrode wear, suggesting that the continuous generation of OH radicals in CBPTW results from the catalytic decomposition of H₂O₂ by metal nanoparticles or ions released from the electrodes. It should be noted that cavitation bubble plasma (CBP) is fundamentally different from sonochemistry. While sonochemistry utilizes ultrasound-induced cavitation to generate radicals, CBP relies on plasma discharge generated inside cavitation bubbles. No ultrasound was applied in this study; therefore, all observed radical formation is attributable exclusively to plasma processes rather than sonochemical effects. However, the precise mechanism of continuous OH radical formation in CBPTW remains unclear and requires further investigation. These findings provide new insights into the role of electrode materials in continuous OH radical generation in cavitation bubble plasma treated water, offering potential applications in water purification and sterilization technologies. Full article

A new method is presented for the estimation of contributions to solvation free energy from dispersion, polar, and hydrogen-bonding (HB) intermolecular interactions. COSMO-type quantum chemical solvation calculations are used for the development of four new molecular descriptors of solutes for their electrostatic interactions. The new model needs one to three solvent-specific parameters for the prediction of solvation free energies. The widely used Abraham’s LSER model is used for providing the reference solvation free energy data for the determination of the solvent-specific parameters. Extensive calculations in 80 solvent systems have verified the good performance of the model. The very same molecular descriptors are used for the calculation of solvation enthalpies. The advantages of the present model over Abraham’s LSER model are discussed along with the complementary character of the two models. Enthalpy and free-energy solvation information for pure solvents is translated into partial solvation parameters (PSP) analogous to the widely used Hansen solubility parameters and enlarge significantly their range of applications. The potential and the perspectives of the new approach for further molecular thermodynamic developments are discussed. Full article