A. M. Emel’yanenko

Hydrophobic properties of composite fluoropolymer coatings on titanium

The results of studies of the hydrophobicity of composite coatings on titanium formed using the method of plasma electrolytic oxidation (PEO) with further treatment by superdispersed polytetrafluoroethylene and its low-molecular fractions are presented. The chosen regimes of application of fluoropolymer materials of different fractional composition onto oxide coatings allow enhancing significantly hydrophobic surface properties (the contact angle reaches 131°).

Analysis of wetting as an efficient method for studying the characteristics of coatings and surfaces and the processes that occur on them: A review

The use of a method of studying wetting both for the research of fundamental problems of surface physicochemistry, such as obtaining information on the structure and properties of the interface and the processes that occur with its participation, and for technological applications related to the preparation of new materials and coatings is analyzed. The fundamental relationships between the contact angle and the thermodynamic and geometric characteristics of the surface are discussed; the factors that have an effect on the contact angle value on nanocomposite surfaces are analyzed. It is shown that recent advances in digital processing of video images provide a qualitatively new level of measurement of contact angles and make the analysis of surface wetting one of the most efficient experimental methods for studying the processes that occur at interfaces. In some cases, the accumulated basic knowledge about the relationship between the measured contact angle and the properties of the surface under study makes it possible to rapidly and reliably obtain detailed information about the roughness, chemical composition, and topology of the surface without using expensive equipment; in other cases, it provides additional information that makes it possible to reveal the mechanisms of the surface phenomena under study. As a case in point, we describe the use of techniques of analysis of wetting for determining the surface porosity and surface topology, for estimating the pattern of interaction between polymer materials and aqueous media, and for revealing the efficiency of anticorrosion coatings on metal surfaces.

Interaction between Hydrophobic and Superhydrophobic Materials with Aqueous Media

Interactions between hydrophobic materials and aqueous media was studied using the analysis of specific surface resistance. Methods for measuring surface resistance are developed for both samples exposed in vapors and those in direct contact with liquid. As a result of the measurements performed, it is confirmed that water molecules penetrate the matrix of the material under prolonged contact with hydrophobic and superhydrophobic materials with aqueous media. The processes of formation on the surface of hydrophobic and superhydrophobic materials of the wetting/adsorption films are observed and the method of estimation their thickness is suggested.

Interactions of silicone rubbers designed for electrical engineering applications with aqueous media

Interactions of a number of electrical engineering silicone rubbers with water and aqueous salt, weakly acidic, and weakly basic solutions were studied by measuring contact angles. A mechanism for leakage currents along the surfaces of silicone insulators was proposed.

The development of coatings that give superhydrophobic properties to the surface of silicone rubber

Hydrophobizing agents on the basis of functional silanes with fluorohydrocarbon substituents have been synthesized. Using these agents and Aerosil nanoparticles, textured coatings were developed that give superhydrophobic properties to the surface of electrotechnical rubbers. Specific features of interaction between the hydrophobic surfaces and water were studied based on analysis of contact angles. For all the hydrophobic materials and coatings studied, even during short-term contact with water, the change in the state of the material surface is shown to be taken into account, with the proposed superhydrophobic coatings demonstrating the most long-term water resistance.

Features of the occurrence of electrochemical processes in contact of sodium chloride solutions with the surface of superhydrophobic coatings on titanium

A joint analysis of the results of electrochemical studies and the evolution of the parameters of a sodium chloride solution droplet in contact with the coating under test reveals the pattern of changes in the surface state which result from the electrochemical reactions and adsorption-desorption processes at the coating/electrolyte interface. Features of the corrosion process are studied on titanium samples with different protective layers on the surface: (1) a natural oxide, (2) a coating prepared via plasma electrolytic oxidation (PEO coating), (3) a PEO coating with a hydrophobic layer, and (4) a PEO coating with a superhydrophobic nanocomposite layer. The best protective properties in a chloride-containing electrolyte are exhibited by the superhydrophobic nanocomposite coating. The mechanism of corrosion protection of this coating is formulated.

Application of contact angle analysis and surface-assisted laser desorption/ionization mass spectrometry to studying the surface state of AMg-6 and Ad-0 aluminum alloys

Surface- and matrix-assisted laser desorption/ionization mass spectrometry and analysis of contact angles have been employed to examine the surfaces of structural materials (Ad-0 and AMg-6 aluminum alloys). The combination of methods used has been shown to enable one to compare the degrees of nonuniformity of different surfaces and determine the effect of the chemical composition of surface impurities on surface properties. Owing to the high sensitivity and informativity, the proposed combination of the methods can be used to determine the nonuniformity of surfaces subjected to the action of rocket fuel components.

Superhydrophobization of low-carbon steel with conversion coatings

Hydrophobization of a surface by fluorosilanes is proposed for protection of low-carbon steel with conversion coatings from atmospheric corrosion. The effect of the heterogeneity of conversion coatings on their hydrophobicity is shown. Employment of superhydrophobization processing increases the angle of wet- ting of the surface by a water droplet up to 160° and significantly enhances the anticorrosion properties of such a composite coating.

Delay in the Freezing of Supercooled Water Drops on Superhydrophobic Surfaces of Silicone Rubber at Negative Temperatures

A method is proposed for fabricating textured superhydrophobic surfaces of silicone rubber with mechanical resistance toward liquid or freezing aqueous solutions. The anti-icing characteristics of silicone rubber samples that differ in the wetting characteristics and mechanical stability of their micro- and nanotextures are derived by analyzing the delays in the freezing of supercooled sessile water drops deposited on the sample surface. The longest delay in freezings are observed for sessile water drops on superhydrophobic surfaces prepared by laser texturing with subsequent application of a layer of a hydrophobic agent to consolidate the textural elements. Delay in freezings can be as long as tens of hours on such surfaces at T = −18°C. The prepared superhydrophobic surfaces exhibit greater anti-icing ability with respect to aqueous salt solutions than to deionized water.

Triple point in spatially limited systems: Small particles and pores

A general thermodynamic approach is presented towards a triple point shift in arbitrary spatially limited systems with a curvilinear interface, including interfacial phases, small particles, and matter in pores. The suggested approach is based on using the coupling equations for vapor pressure over the bulk and spatially limited media together with the Clausius-Clapeyron relationships, and allows one to explain the effect of different physical-chemical parameters on the value and sign of the shift in the phase transition temperature. Besides, an explanation was offered within the developed theory for the difference in the melting points of different crystal faces, the presence of a nanometer melt layer for the substance in fine pores, and the formation of premolten or presolidified shell about nanoparticles.