Colloid Journal最新文献

The water-repellent properties have been studied for the surface of a protective metal–ceramic coating based on titanium dioxide. It has been shown that the water-repellent properties of the coating surface can be efficiently changed by varying the technological parameters of spraying. When producing the coatings, technological parameters, such as the distance between a substrate and a detonation gun barrel (spraying distance) and the speed of barrel movement, have been varied. Regularities have been derived to relate the technological parameters of the detonation spraying of the coating and its contact angle. It has been found that, under certain conditions, the dependence of the contact angle on the spraying distance obeys a parabolic law. Parameters have been calculated for the phenomenological equation that adequately describes the observed parabolic dependence. The optimal values of the detonation spraying parameters necessary to achieve the maximum hydrophobicity of the produced coatings have been determined.

The Poisson–Boltzmann equation has been employed to consider the electrostatic interaction between two charged dielectric spherical particles in a solution of a symmetric electrolyte. The interaction forces between the particles of the same radius have been calculated by the finite element method under the condition of uniform charge distribution on their surfaces in the absence of an external field. The dependence of the electrostatic repulsion forces between the particles on the magnitude of the particle charges and the dielectric permittivities of the particle materials and the ambient medium has been analyzed.

The surfaces of solids (gold, silver, and polymers) have been modified with adsorption layers of various compounds. Optimal modification conditions have been determined using the methods of contact angle measuring and quartz crystal microbalance. The degree of surface coverage with the adsorption layer has been calculated and the data obtained have been compared with the results of the direct measurements of adsorption. The surface energy of the modifying layers has been determined and the potential application fields of the modified solids as functional materials have been demonstrated.

Modern power industry widely uses high-voltage overhead lines to transport electrical energy, with these lines encountering the problems of corona discharge and leakage currents, especially under the conditions of rain and snowfall. One of the approaches to solving these problems is the creation of protective coatings that can diminish corona discharge under adverse weather conditions. This paper reports the results of studying a hydrophilic organosilicon coating based on aminopropyltriethoxysilane and poly(ethylene glycol) for aluminum wires. The study of the coating resistance to a long-term contact with water, UV radiation, and ozone-saturated atmosphere has shown that the hydrophilicity of the coating increases under the influence of these factors, thus improving its anticorona properties. Thus, the durability of the developed coating under the operating conditions opens prospects for its use in the power engineering.

It is well known that super-hydrophobic materials have a wide application prospect. However, many methods for preparing super-amphiphobic coatings are too complicated or have poor stability, which limits the practical application of super-amphiphobic materials. In this paper, a stable and durable super-amphiphobic coating is prepared on the fabric surface via a simple sol-gel method. The water and vegetable oil contact angles of this coating are 160.5 ± 0.8° and 154.8 ± 2.6°, respectively. Specifically, the super-amphiphobic coating is prepared by grafting nano-silica on the surface of the fabric by a simple sol-gel method, and then grafted 1H, 1H,2H,2H-perfluorodecyltrimethoxysilane (FAS-17) as a hydrophobic modifier. After various chemical and mechanical stability tests, including concentrated ammonia solution soaking, saturated sodium hydroxide solution soaking, concentrated salt solution soaking, and THF soaking with stirring, the coating still maintains hydrophobicity. And the coating has excellent air permeability, which is expected to have great potential in the field of special protection.

The self-cleaning effect of titanium dioxide coatings is based on the photocatalytic oxidative ability and the phenomenon of photoinduced superhydrophilicity. Doping with metals is used to enhance the photocatalytic activity; however, its influence on the surface hydrophilicity remains to be studied. In this work, the effect of the heterovalent doping of titanium dioxide anatase on its hydrophilic properties has been investigated in detail. Thin xM–TiO₂ films, where the M symbol denotes Nb⁵⁺, Sc³⁺, and Al³⁺, with dopant concentrations of 0.0–1.0 at % have been obtained on glass substrates from solutions of corresponding sols by the deep coating method. The phase composition, surface dopant content, lattice microstress, surface acidity, and electron work function values have been determined and analyzed for three series of doped samples as functions of dopant concentrations. The surface hydrophilicity of xM–TiO₂ nanocoatings has been estimated by measuring water contact angle and surface free energy values. It has been shown that doping with niobium ions affects the wettability of titanium dioxide, while its hydrophilic state remains unchanged upon doping with scandium and aluminum ions. It has been found that the incorporation of niobium ions into anatase drastically increases the hydrophilicity of the surface with a simultaneous change in its acidity and work function. At the same time, as Nb content increases, the electronic factor prevails. The kinetic dependences obtained for the photoinduced water contact angles have shown an increase in the surface hydrophilicity of all investigated coatings irrespective of a dopant type within the studied dopant concentration range, thereby indicating their self-cleaning ability. At the same time, the final UV-induced hydrophilic state depends on a dopant type. The maximum surface hydrophilicity is achieved upon UV irradiation of TiO₂ doped with Nb regardless of its content. UV-irradiated Al-doped TiO₂ coatings exhibit small contact angles, while the photoinduced surface hydrophilicity of Sc-doped titanium dioxide films decreases with increasing scandium concentration.

In the last two decades, a great interest has been focused on the creation and study of superhydrophobic nanomaterials based on the “lotus effect.” This effect is caused by the heterogeneous wetting of rough surfaces, when the grooves of a rough surface are filled with air (vapor) and water contacts only with the tops of the protrusions. A drop forms a sphere on the surface and rolls down picking up dirt particles when the surface is slightly tilted. Diverse methods have been developed for producing such materials, and the potential of the ion-track technology (ITT) is being investigated. The goal of this work is to study the wettability of surface microtextures by the examples of two materials with different initial degrees of hydrophobicity. The ITT has been employed to obtain samples with maximum water contact angles of 140 ± 5° and 151 ± 5° by modifying the surfaces of polycarbonate and polypropylene films, respectively. It has been shown that such angles are characteristic of microtextures, for which surface fraction f that is in contact with a droplet is decreased to a range of 0 < f < 0.3. Materials with tilted microtextures have been obtained in order to increase the probability of droplet rolling down a material surface in a certain direction. In this case, the wettability becomes anisotropic. A droplet loses its spherical shape and is deformed in the direction of the tilt of needle-like surface elements. It has been found that the anisotropy of wettability is higher at a tilt angle of the texture elements of 45° than that at 30° (relative to the flat surface).

A method has been developed for the formation of hybrid membranes consisting of a hydrophilic microporous substrate and a hydrophobic nanofibrous polymer layer deposited by electrospinning. A track-etched poly(ethylene terephthalate) membrane has been used as the hydrophilic microporous substrate, onto the surface of which a thin layer of titanium is deposited by magnetron sputtering to provide the nanofibrous layer with adhesion. Simultaneously, this layer has been used as an electrode of a deposition collector for the electrospinning formation the nanofibrous coating. It has been shown that the application of this method for the preparation of polymer coatings using poly(vinylidene fluoride) as a starting material for the formation of nanofibers makes it possible to obtain a highly hydrophobic layer, the surface of which has an average water contact angle of 143.3 ± 1.3° depending on the deposition density. The morphological study of the nanofibrous coating has shown that its microstructure is typical of nonwoven materials. The nanofibers that form the porous system of this layer have a wide scatter of sizes. FTIR spectroscopic and X-ray diffraction investigations of the molecular structure of the nanofibrous layer have shown that the β-phase prevails in its structure, with this phase being characterized by the maximum dipole moment. It has been shown that the elaborated hybrid membranes ensure high separation selectivity of desalinating an aqueous 26.5 g/L sodium chloride solution by the membrane distillation method. In the studied regime of the membrane distillation, the salt rejection coefficient for membranes with nanofibrous layer densities of 20.7 ± 0.2–27.6 ± 0.2 g/m² is 99.97−99.98%. It has been found that the use of a highly hydrophobic nanofibrous layer with a developed porous structure in combination with a hydrophilic microporous substrate makes it possible to increase the productivity of the membrane distillation process. The value of the maximum condensate flow through the membranes is, on average, 7.0 kg m²/h, and its value depends on the density of the deposited nanofibrous layer.

New composite materials (ionogels) have been obtained based on imidazolium ionic liquids immobilized in highly porous polymers, i.e., polyamide 6,6 (nylon 6,6) and low-density polyethylene. A method has been proposed for determining the rate of ionic liquid removal from an ionogel upon contact with water, with this method being based on continuous measuring the conductivity of an aqueous phase. The results of the conductometric measurements have been confirmed by high-performance liquid chromatography data. It has been shown that the stability of ionogels upon contact with water is determined by both the hydrophobicity of a polymer matrix and the solubility of an ionic liquid in water. The highest degree of ionic liquid removal (more than 80%) has been observed for composites based on porous polyamide 6,6 (hydrophilic matrix) and dicyanimide 1-butyl-3-methylimidazolium (completely miscible with water). Ionogels based on low-density polyethylene (hydrophobic matrix) and bis(trifluoromethylsulfonyl)imide 1-butyl-3-methylimidazolium (poorly soluble , <1 wt %, in water) have shown the highest stability (washout degree of no more than 53% over 24 h). The method proposed for analyzing the rate of ionic liquid dissolution in water has been used to discuss the mechanism of this process.

The green synthesis of gold nanoparticles (AuNPs-E) by bioreduction of chloroauric acid (HAuCl₄), using the aqueous extracts (E) of blackberry (Rubus spp.) leaves, was presented in this work. The E were obtained by maceration at room T and reflux extraction at boiling T, while the AuNPs-E were synthesized at room T and T = 80°C. The synthesized AuNPs-E were structurally and physicochemically characterized by UV-Vis and FTIR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, dynamic light scattering (DLS) and zeta potential measuring. The changes in the FTIR spectra suggested that biocompounds containing C=O, C–O–C, and OH functional groups play the main role as capping and stabilizing agents providing the stability of AuNPs-E confirmed by UV-Vis spectroscopy. The crystal structure was proved by XRD analysis confirming the (111) reflection plane at 2θ = 38.2° as dominant in the AuNPs-E face-centered cubic lattice. Negative zeta potential of AuNPs-E in the range of –11.67 ± 0.45 and –17.70 ± 0.27 mV suggests moderate stability of AuNPs-E with the average size in the range of 61.6 ± 11.5 to 93.9 ± 1.4 nm determined by DLS. The qualitative and quantitative presence of Au in the formed AuNPs-E, together with the elements from the extracts’ biomolecules, was proven by the EDX spectroscopy. Finally, the antioxidant and antibacterial activities of AuNPs-E were tested by DPPH test and disc diffusion method, respectively, suggesting that AuNPs-E synthesized by described method should be certainly taken into consideration, alone or in combination with the silver nanoparticles, in dermal and cosmetic preparations design.