Colloid Journal最新文献

This work is devoted to studying electrophoresis of conducting and nonconducting particles in a polar electrolyte solution under the action of a strong electric field. Numerical simulation results are presented for both types of particles, including distributions of cation and anion concentrations, charge densities, and total concentrations and fluxes of ions near the particle surface. It is shown that an extended spatial charge region arises near a dielectric surface at a sufficiently high surface charge. This region is formed due to a high surface conductivity in the electrical double layer and intense tangential ion fluxes. Qualitative differences are revealed between the the mechanisms of extended spatial charge formation for ion-selective and dielectric particles. The results obtained facilitate understanding the nonlinear electrokinetic processes and can be useful for designing microliquidic systems and colloidal technologies.

The article discusses the deposition of a gas onto a crystalline substrate in the presence of a permeable membrane between the substrate and the gas. The membrane repels gas particles; however, the repulsive potential has a finite maximum force, thus allowing gas particles to penetrate through this membrane when their velocity exceeds a certain value. It is shown that, depending on the maximum repulsive force of the membrane (repulsion intensity), the system acquires absolutely different final states: a single crystal, polycrystals with different degrees of porosity, or no crystallization occurs in the system at all.

A molecular thermodynamic model has been considered for the formation and growth of nonionic aggregates of surfactant molecules in a nonpolar solvent in the absence of water. The model implies fluctuating coexistence of micelles having different shapes without activation barriers between them. The work of micelle aggregation has been derived for a ({{{text{C}}}_{{{text{12}}}}}{{{text{E}}}_{{text{4}}}}) solution in heptane using molecular dynamics data. In the considered model, it is assumed that, for any aggregation numbers, the minimal aggregation work depends not only on the aggregation numbers and surfactant monomer concentration, but also on two independent shape parameters characterizing the deviation from the spherical shape of an aggregate. This approach provides a unified description for both disc-shaped and cylindrical micelles.

The article presents the results of the molecular dynamics simulation performed for thermoinduced structural transformations in four-component Cu–Au–Pt–Pd nanoalloys using the tight-binding potential. The following configurations have been chosen as initial ones: a core–shell (Cu₂₀₀–Au₆₀₀–Pt₈₀₀)@Pd₂₄₀₀ system, in which the core is a multicomponent alloy with uniformly distributed components; an onion-like Cu₂₀₀@Au₆₀₀@Pt₈₀₀@Pd₂₄₀₀ structure, a Cu₂₀₀–Au₆₀₀–Pt₈₀₀–Pd₂₄₀₀ alloy with a uniform distribution of the components, and Janus structures with asymmetric (Cu₂₀₀/Au₆₀₀/Pt₈₀₀/Pd₂₄₀₀) and symmetric (Cu₁₀₀/Au₃₀₀/Pt₄₀₀/Pd₂₄₀₀/Pt₄₀₀/Au₃₀₀/Cu₁₀₀ and Pd₁₂₀₀/Pt₄₀₀/Au₃₀₀/Cu₂₀₀/Au₃₀₀/Pt₄₀₀/Pd₁₂₀₀) distributions of the components. The analysis of the temperature dependences of the potential component of the internal energy has been employed to determine the temperatures corresponding to the onset of the melting–crystallization phase transition and to estimate the value of the temperature hysteresis. The regularities have been found for variations in these values as depending on the thermal action rate. The regularities of the structure formation have been analyzed, the dominating role of the local fcc environment has been revealed, and the cases of the formation of other crystalline structures (hcp and bcc) have been observed. The regularities of chemical segregation have been described confirming that different scenarios of the segregation behavior of the components may take place. An original technique has been used to estimate the specific surface energy for multicomponent metal nanoparticles (final configurations resulting from a cycle of a thermal action including the melting–crystallization phase transitions). The values of the specific surface energy correlate with the stability of the final configurations corresponding to different initial configurations.

The goal of this work is to determine the possibilities to synthesize stable latex with a narrow particle size distribution by homogeneous polymerization of methyl methacrylate in an aqueous solution. For the first time, methyl methacrylate is polymerized under static conditions in an aqueous solution of a hydroquinone–potassium persulfate redox system. It is assumed that semiquinone radical anions formed at the intermediate stage of hydroquinone oxidation can participate in the termination of growing radicals and affect the process of formation of latex particles by changing parameters of polymer molecules. The article presents the results of studying the colloidal parameters of the obtained latex, which show that the selected polymerization conditions make it possible to reproducibly synthesize monodisperse stable latexes.

One of the practical problems in the oil and gas industry is the formation of oil–acid emulsions and asphaltene sludge when well stimulation fluids come in contact with oil. The key to solving these problems lies in understanding the processes occurring at the interfaces between oil and these agents, with these processes being qualitatively studied in this work. This research investigates the processes occurring between sensitive oil and two types of well stimulation fluids based on hydrochloric acid and ethylenediaminetetraacetic acid (EDTA) in the presence and absence of a surfactant. Three following methods have been employed: simple mixing (“bottle-test”), simultaneous flow of fluids in a capillary, and simultaneous flow of fluids in a micromodel simulating a porous medium. Using the simple mixing method, it has been shown that the addition of the surfactant to a 15% hydrochloric acid solution can prevent sludge formation but does not hinder emulsion formation. Additionally, it has been found that EDTA-based fluids with neutral pH values are compatible even with sensitive oil. Experiments on the simultaneous flow have shown the role of capillary walls in creating sludge and the cleaning ability of the chelating agent. The simultaneous flow in the micromodel has revealed the distinctive features of hydrochloric acid as compared with the chelate, i.e., the discrete flow, emulsion formation in the near-wall layer, and precipitate formation on pore walls. The results of this study may be useful both for further fundamental studying interfacial processes in oil reservoirs and for practical applications.

A composite based on a cross-linked ionic polymer containing functional groups [–N(CH₃)₃]⁺ and a Cr³⁺ cation was obtained and studied. As a result of the contact of the polymer with the KCr(SO₄)₂ solution, the jarosite mineral-type composite is formed: R₄N[Cr₃(OH)₆(SO₄)₂], in which R₄N⁺ is the polymer group. Considering that the composite can be used as a sorbent with selective properties, its stability in solutions of KCl, Na₂CO₃, Na₂SO₄, NaNO₃, NaF and Na₂S was investigated. In concentrated NaCl solutions, the original composite is transformed into another, as a result of the replacement of  ({text{SO}}_{4}^{{2 - }}) with Cl^– ions. The regenerated polymer is capable of forming a composite again. Using FTIR, SEM EDX and thermogravimetry methods, the changes that occur in the polymer phase during composite formation and its regeneration were studied. It has been shown that the composite has selective sorption properties.

It has been found that, when an aqueous 5% poly(vinyl alcohol) solution is subjected to vacuum ultraviolet (VUV) radiation at a wavelength of 172 nm, the solution structure changes to form crosslinked fragments of the polymer despite the fact that VUV radiation penetrates into the solution to a small depth.

This work is devoted to studying mechanical durability of a superhydrophobic coating obtained on the basis of commercial EP-140 epoxy enamel. To achieve the superhydrophobic state, the applied coating is modified by pulsed laser texturing and fluorosilane chemisorption. The goal of the research is to assess the coating resistance to various mechanical actions typical for outdoor service, namely, long-term contact with water, exposure to high-speed water jet, abrasive wear under the action of falling sand, and multiple detachments of an adhesive tape. It has been shown that the combined approach used for the superhydrophobization provides coatings not only with pronounced water-repellent properties but also with significant resistance to degradation. For example, the performed experiments have revealed only a slight decrease in the wettability characteristics with retaining the heterogeneous wetting regime, thereby confirming that the coating retains its functionality even under extremal mechanical impacts. The data obtained have indicated the promise of applying the developed coating in industry fields that require a combination of high wear resistance and economic efficiency.

Mushroom polysaccharides are biologically active substances with strong reduction, capture, and stabilization capabilities. They have great potential in the synthesis of metal nanoparticles. This study developed a method for the electrochemical synthesis of silver nanoparticles from polysaccharide extracts (AgNP-AcPOLY) of the Amanita pantherina mushroom. Silver nanoparticles (AgNPs) were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), electrophoretic light scattering (ELS), UV-vis spectroscopic (UV-Vis), and laser diffraction spectroscopy (LDS) methods. XRD and TEM studies showed that the silver nanoparticles are spherical with a size of about 11.6 nm. The electrochemical performance of AgNP-AcPOLY nanoparticles was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results indicate that AgNP-AcPOLY exhibits outstanding electrochemical properties, significantly enhancing the performance of screen-printed electrodes (SPE). In addition, the antibacterial activity of nanosilver was evaluated through the methods of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against two strains of bacteria, Staphylococcus aureus and Escherichia coli. The results of this study indicate that the silver nanoparticles synthesized from the polysaccharide extract of A. pantherina are clean and environmentally friendly and have broad-spectrum antibacterial ability.