The article presents the results of experimental studying the hysteresis of water contact angles at crystalline surfaces. Receding and advancing contact angles and their hysteresis at hydrophilic and hydrophobic substrates with different surface structures (silica, mica, and calcite) have been studied under the action of an external pressure applied to the three-phase contact line of a sessile air bubble. Hysteresis of the contact angles has been observed on hydrophobized samples of silica and mica. The anchoring of the three-phase contact line (pinning) facilitates a change in the contact angles under the applied external pressure. When the three-phase contact line moves along the hydrophilic surfaces of silica and mica no marked changes in the advancing and receding contact angles are observed, and the hysteresis is actually absent. The stable pinning observed on the polished surface of a calcite crystal brought in contact with water leads to the appearance of contact angle hysteresis and hydrophilization of the calcite surface, with the hydrophilization being related to structural displacements in the crystal lattice.

Capillary electrokinetics has been employed to measure the streaming current in solutions of alkali metal chlorides at electrolyte concentrations of 0.1 and 1 M. The results obtained have confirmed the earlier conclusion that there are no hydrodynamically immobile layers near a solid molecularly smooth surface. It has been shown that the magnitudes of the current and the calculated electrokinetic potential decrease in a series LiCl, NaCl, KCl, RbCl, and CsCl. In this series, the crystallographic radius increases and the radius of a hydrated ion decreases. The obtained dependences have led to a conclusion that the cations located near a negatively charged surface are unhydrated.

The microheterogeneous model makes it possible to describe the main transport properties of ion-exchange membranes using a single set of input parameters. This paper describes an adaptation of the microheterogeneous model for describing the electrical conductivity and diffusion permeability of a track-etched membrane (TEM). Usually, the transport parameters of TEMs are evaluated assuming that ion transfer occurs through the solution filling the membrane pores, which are cylindrical and oriented normally to the membrane surface. The version of the microheterogeneous model developed in this paper takes into account the presence of a loose layer, which forms as an intermediate layer between the pore solution and the membrane bulk material during track etching. It is assumed that this layer can be considered as a “gel phase” in the framework of the microheterogeneous model due to the fixed hydroxyl and carboxyl groups, which imparts ion exchange properties to the loose layer. The qualitative and quantitative agreement between the calculated and experimental concentration dependencies of the conductivity and diffusion permeability is discussed. The role of the model input parameters is described in relation to the structural features of the membrane. In particular, the inclination of the pores relative to the surface and their narrowing in the middle part of the membrane can be important for their properties.

Measurements of zeta potential of membranes is usually treated based on Smoluchowski equation. However, in the case of membranes with sufficiently high porosity and permeability it is necessary to introduce a correction taking into account the influence of the fluid flow and charge transfer inside the membrane itself and its influence of measurements of the zeta potential. Equations for calculations of modified zeta potential were deduced for both cases of measurements of streaming potential and streaming current considering flow and charge transfer inside the membrane.

Porosity, permeability, and conductivity of PTMSP membranes in ethanol-water mixtures were determined by analyzing the impedance characteristics. The critical volume fraction of porosity at which through conductivity channels are formed was calculated. When the alcohol content in the solution increases, it was 0.29; when it decreases, it was 0.17. The obtained dependencies indicate that the transfer of matter in the membrane occurs the liquid phase elements, forming a percolation cluster as the amount of sorbed liquid increases. The hysteresis effect was observed in the measured values of porosity, permeability, conductivity, and capacity. The porous structure of a dry PTMSP membrane consists of free volume elements that are unconnected to each other. At ⁓30% alcohol concentration, through channels, begin to form, connecting both sides of the membrane. In this case, both permeability and electrical conductivity increase as a power function, in contrast to the porosity that increases linearly. Lichtenecker and Rother’s formula helped to calculate the volume fractions of the conducting and non-conducting phases in the system. The obtained values of the amount of liquid in the membrane at various spatial arrangements of the channels made it possible to establish the structure of the liquid-filled channels. The best agreement with the experimental values was obtained for the chaotic structure. This is consistent with the existing ideas about the structure of the studied membranes and confirms the assumption that the percolation cluster is formed from free volume elements filled with the liquid phase. The observed low values of the zeta potential and, consequently, the low values of the electrostatic component of the wedging pressure indicate that the increase in the size or the number of transport channels is associated with non-electrostatic forces.

The kinetics of adsorption of two polylysine samples with different molecular weights from aqueous solutions on the surface of fused quartz has been studied by the capillary electrokinetics method. It has been found that the adsorption of positively charged polylysine on the negatively charged quartz surface decreases the absolute value of the initial ζ potential; moreover, in the case of polylysine with the higher molecular weight, it leads to the reversal of the surface charge. The constant values of the ζ potential and the times for which these values are reached depend on the molecular weight and concentration of polylysine. The rate of variations in the ζ potential is highest during the first several minutes of the solution contact with the surface. A decrease in the electric conductivity during polylysine adsorption has, for the first time, been observed, thus leading to a hypothesis that large aggregates are formed on the quartz surface. The measurement of the deformability of the layers has shown that, under our experimental conditions, dense undeformable layers are formed. Polylysines are irreversibly adsorbed on the quartz surface.

A relatively new term of colloid science, “pinning,” characterizes the phenomenon when a drop or bubble, spreading over a solid surface, suddenly stops its movement at its base. Usually pinning is observed with an increase in the drop or bubble volume by pumping substances into them. In this paper, small but macroscopic air bubbles were studied at the water–silicon interface, and their volume increased in a non-contact way by increasing temperature. The observed phenomenon can be called temperature pinning. The experiments were carried out both on the natural hydrophilic surface of silicon wafers and on their surfaces artificially hydrophobized to various degrees in the temperature range of 20–75°C. In all cases, temperature pinning was observed in the initial temperature range from 20°C, but was also observed at other temperatures. The general conclusion is that temperature pinning is common and has various manifestations.

The goal of this work is the experimental verification of a recently formulated thermodynamic theory of the temperature dependence of sessile bubble contact angle [Rusanov, A.I., Colloid J. , 2020, vol. 82, p. 303]. In particular, the possibilities of an increase in small contact angles and a decrease in large ones (larger than 90°) are tested. The experiments are carried out with a bubble at a water–silicon interface using two types of polished silicon plates: clean plates with a water contact angle of 12° and plates with a hydrophobized surface and the water contact angle of 104° within a temperature range 20–80°C. In both cases, the experiments have confirmed the theory. In addition, a temperature pinning effect (anchoring of the three-phase contact line) has been revealed for the sessile bubble.

The bactericidal activity of copper and copper alloys is well appreciated and was already exploited in medical practice in 19th century. However, despite of being an essential nutrient required by organisms to perform life functions, excess copper is extremely toxic and detrimental to health. Recent studies have shown that superhydrophobic surfaces have a significant antibacterial potential for reduction of nosocomial infections. At the same time, the prolonged contact with biological liquids may cause a degradation of the superhydrophobic copper surface and corrosion with increasing egress of toxic copper ions. These aspects are poorly studied so far. In this paper, we analyze the evolution of the properties of both the superhydrophobic copper surface and the suspension of Escherichia coli bacteria during their prolonged contact and study the impact of such contact on the bactericidal activity of the surface. It is shown that by controlling the corrosion resistance and the wettability of the superhydrophobic copper substrate, it becomes possible to sustain the bactericidal action of copper substrates for a long time, simultaneously avoiding the excessive corrosive degradation and release of copper ions in the environment.

Although usual pressures have typically a weak effect on the properties of condensed phases and their surface layers, a parameter has been found in the surface physical chemistry—a contact angle at a three-phase contact line—that is rather sensitive to hydrostatic pressure. Experiments with an air bubble adhered to a solid surface immersed in water have shown that an increase in the hydrostatic pressure by less than two times causes a growth of the contact angle by more than 10°, if the angle is markedly smaller than 90°. Therewith, the three-phase contact line remains immobile, and only the liquid−gas interface changes its orientation. If the angle (no matter, acute or obtuse) is close to 90°, the three-phase contact line acquires mobility as an alternative way to reach an equilibrium . A thermodynamic theory has been developed on the basis of the generalized Young equation to explain these phenomena. It has been shown that, when the three-phase contact line is fixed, a growth of the pressure in a liquid always leads to a rise in the contact angle.

The electrokinetic properties and selectivity of an acetyl cellulose membrane with respect to 0.0001 mol/L sodium chloride solutions in water–ethanol mixtures have been studied. The electrical conductivity, streaming potential, and filtration and selectivity characteristics of the membrane have been measured. It has been found that, in solutions with alcohol contents of 4 and 12%, the membrane selectivity with respect to sodium chloride is increased and decreased relative to that in an aqueous solution, respectively. No correlation between the membrane selectivity and its surface charge has been observed. The membrane has been found to possess a slight selectivity (20–26%) with respect to ethanol. It has been hypothesized that the solvation enthalpy of electrolyte ions changes differently in a free solution and membrane pores at different contents of ethanol in the mixtures, thereby affecting the membrane selectivity.

Nanoparticles are particles with a characteristic dimension below 100 nm. The properties of nanoparticles differ substantially from those of “big” colloidal particles (size bigger than 1 μm) because radius of surface forces, which is around 100 nm, is greater than or comparable with the nanoparticles size. The latter means that each nanoparticle could be completely covered by the surface forces of the neighbouring particles at small enough separation. It also means that the well-known Derjaguin approximation cannot be applied directly and some modifications are required. Pairwise interaction between nanoparticles can be used only at an extremely low volume fraction of nanoparticles (below some critical volume fraction, which is ~0.02%), and above this concentration a new theory based on many-particle interactions should be applied, which is yet to be developed. Some recent progress in the area of interaction between nanoparticles is reviewed and the properties of nanosuspensions based on interaction between nanoparticles are described. The authors have not attempted to cover all available literature in the area but instead have tried to underline the fundamental problems in the area which need to be addressed.

Streaming current has for the first time been measured in solutions of salts with double- and triple-charged cations at high electrolyte concentrations by the method of capillary electrokinetics. It has been shown that the streaming current is proportional to an applied pressure. At an electrolyte concentration of 1 M, the diffuse layer is completely absent. In this case, the existence of the streaming current indicates that there are no hydrodynamically immobile layers near a smooth solid surface.

Electrokinetic properties of an asymmetric nanofiltration membrane modified with a cationic polyelectrolyte (styrene–dimethylaminopropylmaleimide copolymer) and the selectivity of the membrane with respect to solutions of differently charged electrolytes have been studied. The modification has been carried out by filtering the polyelectrolyte from the side of the selective layer and the opposite side of the membrane. It has been found that the membrane selectivity to sodium sulfate and magnesium chloride solutions increases with polyelectrolyte concentration in the solution used for membrane modification from the side of the selective layer. A decreased selectivity to sodium sulfate and an unchanged selectivity to magnesium chloride have been observed for the membrane modified from the substrate side.