Colloid Journal
ISSN (print): 0023-2912
Media registration certificate: № 0110217 от 08.02.1993
Founders: Russian Academy of Sciences, Institute of Physical Chemistry of RAS
Editor-in-Chief: Boinovich Ludmila Borisovna, academician RAS, Doctor of Sc.
Frequency / Access: 6 issues per year / Subscription
Included in: White list (2nd level), Higher Attestation Commission list, RISC
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Vol 87, No 4 (2025)
- Year: 2025
- Published: 15.08.2025
- Articles: 15
- URL: https://journal-vniispk.ru/0023-2912/issue/view/21422
Articles
Theoretical and numerical methods for studying surface phenomena and surface forces
Colloid Journal. 2025;87(4):277-280
277-280
Modeling the influence of convective flows through an ion-selective area on electric current regimes in binary electrolyte solutions
Abstract
The paper presents the results of numerical simulations of a cell containing an ion-selective area in a one-dimensional statement. The mathematical model takes into account non-ideal selectivity of the ion-exchange area, and the presence of a convective electrolyte solution flow through it. The flow has been proven to influence the eventual selectivity of the ion-exchange area; the electric current through the system can both increase and decrease depending on the resulting current regime: underlimiting or limiting. The understanding of this effect will be useful in applications, including analyte preconcentration systems in microlaboratories for chemical analysis of biological liquids and electrobaromembrane separation systems for metal ions.
Colloid Journal. 2025;87(4):281-288
281-288
A study of electroconvection during uniform electrolyte solution flow through an ion-selective area
Abstract
The results of a theoretical investigation of electroconvection emergence and development near an ion-selective area under a uniform electrolyte solution flow through this area are presented in the paper. The linear stability analysis of a stationary solution has allowed obtaining the dependence of the critical electric potential difference (that triggers electrokinetic instability) on the external flow rate. Two-dimensional numerical simulation has revealed the peculiarities of nonlinear electroconvection regimes. The research has proven the stabilizing effect of the external flow: electroconvection occurs at larger potential differences, whereas its regimes change each other faster with increasing the potential difference. Understanding these effects is useful in applications like the development of analyte preconcentration systems in microlaboratories for chemical analysis of biological liquids.
Colloid Journal. 2025;87(4):289-298
289-298
Relaxation phenomena and electromagnetic emission of oscillating cloud droplets
Abstract
A theoretical study of the effect of relaxation processes in water on the intensity of electromagnetic radiation of an oscillating charged drop of water, which is accepted as viscous and incompressible, was carried out. A theoretical analytical expression of the dispersion equation of an oscillating and radiating drop having the form of a complex algebraic expression of the fifth degree is derived. The charge relaxation effect in an oscillating charged water droplet affects the intensity of electromagnetic radiation by it through the conductivity of the water. The greatest intensity of electromagnetic radiation is characteristic of a drop of an ideally conductive liquid. It is an order of magnitude higher than the radiation intensity of a drop of liquid with finite conductivity. The lowest radiation intensity will be for a drop of dielectric liquid with a frozen charge. The surface tension relaxation effect affects the electromagnetic emission of the charged oscillating droplet by disrupting the order of the surface water molecules and changing the magnitude of the surface tension coefficient. The water viscosity relaxation effect does not have a noticeable effect on the decaying capillary oscillations and electromagnetic radiation of cloud droplets.
Colloid Journal. 2025;87(4):299-319
299-319
Supercooling of evaporating water droplets on superhydrophobic surfaces at low temperatures
Abstract
A theoretical analysis of the temperature change of an evaporating droplet on a superhydrophobic surface is performed taking into account heat fluxes of various types. The results show that the additional cooling effect of evaporation can lead to significant cooling and even crystallization of sessile droplets at positive temperatures. However, with a decrease in the ambient temperature, the efficiency of this additional cooling decreases. A method for continuous monitoring of the temperature of an evaporating droplet based on the measured thermodynamic parameters of sessile droplets is proposed. Experimental studies conducted at temperatures slightly above and below zero degrees Celsius demonstrated a satisfactory correlation between the results of the theoretical analysis and the experimentally measured supercooling of water droplets.
Colloid Journal. 2025;87(4):320-331
320-331
Extension of the inverse “dry” micelles model to disk-shaped aggregates
Abstract
This paper presents a molecular thermodynamic model of formation and growth of nonionic aggregates from surfactant molecules in a nonpolar solvent in the absence of water. which allows fluctuating coexistence of micelles of different shapes without activation barriers between them. The work of micelle aggregation is derived for in heptane using molecular dynamics data. In the considered model, for any aggregation numbers, the minimum aggregation work depends not only on aggregation numbers and surfactant monomer concentration, but also on two independent shape parameters characterizing the deviation from the spherical shape of the aggregate. This approach provides a common description for both disk and cylindrical micelles.
Colloid Journal. 2025;87(4):332-345
332-345
Convection in a small hemispherical drop of binary solvent: Analytical solution and applications
Abstract
A new analytical solution of the linearized Navier–Stokes equations and the diffusion equation is proposed that allows to relate the intensity of Marangoni flow to the surface tension gradient in a droplet of binary solvent and to study the associated mass transfer and self-organization of solvated solutes (nanoparticles, molecules). When deriving the equations, the smallness of the Reynolds number was assumed, which corresponds to the smallness of the drop size and the liquid flow velocity. Evaporation was assumed to be slow enough for the quasi-stationary approximation to be valid. The smallness of the Peclet number was also accepted, which corresponds to relatively small velocity of convective flow in relation to the velocity of diffusion transfer of the impurity. In this case, the Marangoni number can have a value in the range from 1 to several tens. The model was tested on water–ethanol and ethanol–hydrogen peroxide systems. The streamlines of convective flows were visualized, and the conditions for their occurrence were considered.
Colloid Journal. 2025;87(4):346-360
346-360
The role of the hydrate layer in nanobubble stability
Abstract
The factors determining the stability of a nanobubble with a hydrate layer 1 nm thick and a permittivity of about 3 are considered. Two stability hypotheses are compared: electrostatic and mechanical (ice-effect or “electrofreezing”). In the first case, the Laplace pressure is compensated by the electrostatic pressure at its boundary, and in the second – by the effect of electrofreezing of its Δ-layer in a high electric field. It is shown that in salt-free water, a smaller nanobubble charge is required for the formation of an ice shell than with the Coulomb stabilization mechanism. In seawater, on the contrary, the Coulomb mechanism is more efficient, since icing is counteracted by ions of the dissolved salt. The sizes and charge of the nanobubble are determined for two stability mechanisms.
Colloid Journal. 2025;87(4):361-368
361-368
Microscopic modeling of magnetorheological properties in magnetic elastomers
Abstract
This paper introduces a microscopic model explaining the magnetorheological properties of magnetic elastomers, which are composed of micron-sized magnetizable, without own magnetic moment, particles within a polymer. The study examines composites that are initially isotropic (made without a magnetic field) and anisotropic (polymerized under a magnetic field). Applying an external magnetic field to the composites causes internal anisotropic structures to form (or expand), leading to a notable increase in the material’s shear modulus. The theoretical findings are in good agreement with experimental results.
Colloid Journal. 2025;87(4):369-386
369-386
Numerical Simulation of Stationary Nucleation Taking into Account Thermal Effects in a Wide Range of Supersaturations
Abstract
The problem of stationary vapor–liquid nucleation with a constant number of particles interacting via the Lennard-Jones potential is solved by the molecular dynamics method for both isothermal and non-isothermal nucleation, over a wide range of vapor supersaturations. A special simulation approach is used, in which clusters that reach a certain size are removed from the system, and their particles are returned as monomers. The temperature distribution over cluster sizes is determined. It is found that the temperature, starting from the monomer level, decreases somewhat but as the cluster size approaches the critical value, returns to its initial level and then increases rapidly. This temperature distribution over cluster sizes governs the distribution of their number densities, controlling the vapor non-ideality and significantly affecting the nucleation rate. The critical importance of knowing the cluster temperature for analytical models is demonstrated, as it enables accurate determination of vapor supersaturation and the actual non-isothermal nucleation rate. The nucleation rates and critical cluster sizes obtained for the isothermal and non-isothermal cases show satisfactory agreement with a theoretical model predicting a decrease in the nucleation rate under non-isothermal conditions.
Colloid Journal. 2025;87(4):387-397
387-397
On the Relationship Between Spontaneous Segregation of Components in Ternary Pt–Pd–Ni Nanoparticles and the Stability of Core–Shell Nanostructures: Molecular Dynamics Study
Abstract
We have performed a comparative study of stability of the core-shell nanostructures Pd5000Ni5000@Pt5000, Pt5000Ni5000@Pd5000, and Pt5000Pd5000@Ni5000 during uniform heating them from 300 to 2200 K. For this purpose, the isothermal molecular dynamics and the LAMMPS software were employed. We have found that all three above homotops keep their core–shell morphology until the onset of melting. However, the ternary Pt5000Ni5000@Pd5000 nanoparticles are found to be more stable: their melting begins at a higher temperature, and they partly inherit the core–shell morphology even after the completion of melting. A conclusion is made about the relationship between the higher stability of PtNi@Pd nanostructures and the effect of the Pd surface segregation in ternary Pt–Pd–Ni nanoparticles. In turn, the pronounced surface segregation of Pd in Pt–Pd–Ni nanoparticles is explained by the fact that just this component is characterized by the lowest value of the specific surface energy.
Colloid Journal. 2025;87(4):398-413
398-413
Atomistic simulation of thermally induced structural transformations in quaternary Cu–Au–Pt–Pd nanoalloys with different morphologies
Abstract
The results of molecular dynamics simulation of thermally induced structural transformations in four-component Cu–Au–Pt–Pd nanoalloys using the tight-binding potential are presented. The following initial configurations were chosen: a core–shell system in which the core corresponds to a multicomponent alloy with a uniform distribution of components (Cu200–Au600–Pt800)@Pd2400, an onion structure Cu200@Au600@Pt800@Pd2400, an alloy with a uniform distribution of components Cu200–Au600–Pt800–Pd2400, Janus structures with asymmetric Cu200/Au600/Pt800/Pd2400 and symmetric distributions of components (Cu100/Au300/Pt400/Pd2400/Pt400/Au300/Cu100 and Pd1200/Pt400/Au300/Cu200/Au300/Pt400/Pd1200). Based on the analysis of temperature dependences of the potential part of the internal energy, the temperatures corresponding to the onset of the melting-crystallization phase transition were found, and the value of temperature hysteresis was estimated. Regularities in the change of these quantities depending on the rate of thermal action were established. Regularities of structure formation were analyzed, the dominant role of the fcc local environment was established, cases of occurrence of other crystalline structures (hcp and bcc) were revealed. Regularities of chemical segregation are described, confirming the possibility of existence of various scenarios of segregation behavior of components. Based on the original technique, estimates of the specific surface energy for multicomponent metallic nanoparticles (final configurations after a cycle of thermal action, including the melting-crystallization phase transition) were carried out. The value of the specific surface energy correlates with the stability of the final configurations corresponding to different initial configurations.
Colloid Journal. 2025;87(4):414-427
414-427
Capillary forces between rough surfaces produced by the micro/nanotechnology methods
Abstract
Capillary forces are one of the main sources of adhesion between the elements of microtechnological devices. This phenomenon manifests itself during the fabrication or operation of a device and plays a negative or positive role. The paper describes a method that makes it possible to estimate the capillary force between hydrophilic rough surfaces as a function of the relative humidity and the nominal contact area. The method is based on counting the number of roughness asperities, which are able to form capillary bridges spontaneously. To implement the method, detailed information about the roughness of the contacting surfaces is required, which can be obtained using an atomic force microscope (AFM). The idea of the method is illustrated, using as an example, deposited gold films of different thickness that come into contact with a smooth silicon surface. AFM scans of a surface with an area of 20×20 µm2 and a resolution of 4096 pixels per line are used. The developed theory reproduces the basic patterns observed experimentally. In particular, it is shown that the relative role of capillary forces decreases with an increase in the nominal contact area, and dispersion forces begin to play a major role in adhesion. The results of the work are important for the design of microsystems and experiments measuring dispersion forces.
Colloid Journal. 2025;87(4):428-442
428-442
The Effect of a Permeable Membrane on the Crystallization of a Simple Liquid
Abstract
The article discusses the deposition of gas onto a crystalline substrate provided there is a permeable membrane between the substrate and the gas. The membrane repels gas particles, but the repulsive potential has a finite maximum force, which allows gas particles to penetrate through this membrane if their velocity exceeds a certain value. It is shown that, depending on the maximum repulsive force of the membrane (the intensity of repulsion), the system comes to completely different end states: a single crystal, a polycrystal with varying degrees of porosity, or no crystallization occurs in the system at all.
Colloid Journal. 2025;87(4):443-452
443-452
Electrophoresis of conducting and non-conducting microparticles in a polar electrolyte under a strong electric field
Abstract
This work focuses on the study of electrophoresis of conducting and non-conducting particles in a polar electrolyte solution under a strong electric field. Numerical modeling results are presented for both types of particles, including distributions of cation and anion concentrations, charge density, total ion concentration, and ion fluxes near the particle surface. It is shown that, for a dielectric surface with a sufficiently high surface charge, an extended space-charge region can form. The emergence of this region is driven by high surface conductivity in the electric double layer and by intense tangential ion fluxes. Qualitative differences in the mechanism of extended space charge formation are revealed when comparing ion-selective and dielectric particles. The findings enhance our understanding of nonlinear electrokinetic processes and can be useful in designing microfluidic systems and colloidal technologies.
Colloid Journal. 2025;87(4):453-466
453-466