Showing papers in "Colloid Journal in 2021"

Rearrangements in the Conformational Structure of Polypeptides on the Surface of a Metal Nanowire in Rotating Electric Field: Molecular Dynamics Simulation

Abstract: Molecular dynamics has been employed to study conformational rearrangements of polyampholytic and uniformly charged polypeptides adsorbed on the surface of a transversely polarized nanowire, in particular, upon rotation of the polarizing electric field vector. On the surface of the transversely polarized nanowire, a fringe consisting of polyampholitic polypeptide macromolecules is protruded in the direction of polarization, while uniformly charged polypeptide is shifted to the polarized regions of the cross section that are charged oppositely to the charge of macrochain units. The larger the distance between oppositely charged units in the polyampholytic polypeptide, the higher the ratio between the fringe thicknesses in the direction of polarization and in the orthogonal direction in the cross section plane. In an electric field rotating around the axis of the metal nanowire, uniformly charged polypeptides adsorbed on its surface rotate around the wire in the same direction. The same phenomenon has been observed for polyampholytic polypeptides, in which the distances between negatively and positively charged units in macrochains are longer than the half-circumference of the nanowire.

Molecular Dynamics Simulation of Uniformly Charged Polypeptides on the Surface of a Charged Metal Nanoparticle in an Alternating Electric Field

Abstract: Molecular dynamics simulation has been employed to study conformational rearrangements induced by an external field in uniformly charged polypeptides adsorbed on the surface of an oppositely charged gold nanoparticle, whose polarization direction varies with a frequency corresponding to the microwave electric field. The averaged angular and radial distributions of atom densities have been calculated for the polyelectrolytes adsorbed on the nanoparticle surface. The simulation has shown the formation of a ring-shaped fringe of polyelectrolyte units encircling the gold nanoparticle in its equatorial region. The density of the fringe of an adsorbed polyelectrolyte macromolecule on the nanoparticle surface depends on both the total charge of the nanoparticle and the fraction of charged units in the macromolecule.

On the Thermodynamics of Solubilization

Abstract: The thermodynamic theory of solubilization has been formulated with introducing the notion of standard solubilization affinity. An important component of this notion is the Laplace capillary pressure represented in the phase interpretation of the hydrocarbon core of a normal micelle. The partition coefficient of a solubilisate is also interpreted both in terms of a mole fraction within the formalism of chemical thermodynamics and in terms of concentration within the formalism of statistical mechanics. In contrast to the widespread approach using fictitious micellar “pseudophase,” this interpretation is based on the real physical picture of solubilisate partition between micelles and an ambient solution. Moreover, an exact solution has been presented for the problem of the effect of solubilization on the value of the critical micelle concentration (CMC). The consideration is based on the mass action law and new methods of defining the CMC via the constant of this law, aggregation number, and solubilisate concentration. The cases of solubilization from saturated (when studying solubility) and unsaturated (with an arbitrary concentration) solutions have been analyzed. However, the same result has been obtained in all variants, namely, solubilization decreases the CMC.

Molecular Dynamics Simulation of Conformational Rearrangements in Polyelectrolyte Macromolecules on the Surface of a Charged or Polarized Prolate Spheroidal Metal Nanoparticle

Abstract: Molecular dynamics simulation has been employed to study rearrangements in the conformational structure of polyelectrolytic polypeptides adsorbed on the surface of a charged prolate spheroidal gold nanoparticle, as well as such nanoparticle polarized along its major axis. An analytical model has been proposed for the structure of a Gaussian macrochain adsorbed on the spheroidal nanoparticle. The model reflects the features of the structure formation of the adsorbed macrochain in relation to the geometry of the uncharged and unpolarized prolate spheroidal nanoparticle. When necessary, it takes into account the surface charge or polarization of the particle by means of introducing the Boltzmann factor for equilibrium configurations of the macrochain in a potential field. Polyampholitic polypeptides adsorbed on the surface of the polarized prolate metal nanospheroid are swollen in the polar regions, while the units of uniformly charged polypeptides are shifted to the polar regions charged oppositely to the charge of the units. Being adsorbed on the surface of a charged prolate spheroidal gold nanoparticle, a polyelectrolyte macromolecule envelopes the entire nanoparticle and swells with an increase in the total charge of the nanospheroid.

Influence of Relative Air Humidity on Evaporation of Water–Ethanol Solution Droplets

Abstract: Evaporation of droplets of water–ethanol solutions with different concentrations has been experimentally studied at different relative humidities of ambient air. High-speed micrography has been employed to monitor the dynamics of variations in the sizes of the evaporating droplets. It has been found that relative humidity of the ambient air significantly affects variations in the diameters of water–ethanol solution droplets. Infrared thermography has been used to study variations in the temperature of the evaporating droplets. It has been shown that the temperature of the evaporating droplets decreases with an increase in ethanol concentration at all studied relative air humidities. The minimum values of evaporating droplet surface temperature and evaporation time increase with relative air humidity. The performed generalization of the obtained experimental data may be used when calculating the heat and mass transfer of evaporating droplets of water–ethanol solutions.

Photoinduced Hydrophilicity of Surfaces of Thin Films

Abstract: The published communications devoted to studying the phenomenon of photoinduced hydrophilicity of the surfaces of thin metal oxide films have been reviewed. This phenomenon underlies the capability of photoactive materials for self-cleaning. The novelty of the work consists in the generalization and the critical analysis of the vast information obtained on the problem under consideration beginning from the discovery of the photoinduced superhydrophilicity of titanium dioxide in 1997 up to the present. The essence of the phenomenon and the mechanisms proposed for it have been described, and the examples of the influence of different factors on the kinetics and thermodynamics of this photoinduced process have been presented. A mechanism of the process has been suggested. It is based on the photoactivation and photodeactivation of surface active sites responsible for subsequent restructuring of adsorbed water molecules in a hydroxyl-hydrated multilayer on an oxide film surface, with the restructuring leading to a change in the surface free energy and, hence, the surface hydrophilicity. In conclusion, possible methods have been considered for controlling the wettability of the surfaces of photoactive materials with the use of light, with the method of creating heterostructured coatings being especially singled out among them.

Influence of a Surfactant on Evaporation Intensity of Suspended Water Droplets

Abstract: Experimental data have been presented on the evaporation rate of suspended droplets of both pure water and water containing ≈1.5 wt % surfactant, sodium dodecyl sulfate. Evaporation occurs in a convective flow of dry air, with its velocity and temperature being varied within ranges of U0 = 1–5 m/s and T0 = 20–80°C, respectively. The density of the mass flux from the surface of the surfactant-containing droplets is 2–3 times lower than that in the case of pure water. For droplets in a dry air flow, the change in their diameter can be described by a set of similarity criteria, and a generalized linear empirical dependence of the evaporation rate on thermodynamic parameters may be constructed for these droplets.

Thermodynamic Study of Solubilization of Crown-Substituted Magnesium Phthalocyaninate in Aqueous Solutions of Sodium Dodecyl Sulfate

Abstract: A spectrophotometric study of the solubilization of crown-substituted magnesium phthalocyaninate (I) has been carried out in an aqueous solution of sodium dodecyl sulfate (II). The experiments have been performed with saturated solutions of I at a thermodynamic equilibrium of a solution with a precipitate of I. The known transition from dimers of I to monomers upon solubilization has been studied in detail. It has been found that monomerization of I begins at concentrations much lower than the critical micelle concentration (CMC) of II, while specific micelles of II are formed with involvement of I dimers at still lower surfactant concentrations. The presence of dimers is also observed when I is dissolved in pure water; the solubility of I has appeared to be 7.38 μM (chemists usually suppose I to be insoluble in water). Extinction coefficients of monomers and dimers of I have been determined in the methodological part of the work. The following thermodynamic characteristics of solubilization have been found on the basis of experimental data: solubilization capacity of micelles, coefficient of solubilizate partition between micelles and an ambient solution, and the standard solubilization affinity of I. The found value of the solubilization capacity as calculated per one molecule of I in a micelle leads to an abnormally large aggregation number (309). One explanation of this fact is the possible development of a bimodal distribution of micelles, at which solubilisate-containing micelles coexist with “empty” micelles; as a result, the average number of solubilizate molecules in a micelle can appear to be smaller than unity.

Percolation Threshold in Polymer Nanocomposites

Abstract: Two approaches to the calculation of the percolation threshold in polymer nanocomposites have been analyzed, namely, the excluded-volume theory and the model proposed by Li and Kim. It has been shown that the former approach yields a rough estimate of the threshold, while the latter one leads to simple relations that can be used, however, with essential corrections. It is necessary, first, to take into account the result of solving the problem of lattice sites, and, second, to average more exactly the orientation of anisodiametric nanoparticles. The role of interfacial layers has been analyzed.

Rheology in Longitudinal (Ultrasound) Mode. Review

Abstract: This review is dedicated to the topic of longitudinal rheology, a branch of rheology that is complementary to traditional shear rheology, and yet not as widely explored. Longitudinal rheology differs from typical shear rheology by the type of stress applied. Longitudinal stress is a wave, which causes liquid expansion and compression that occurs when ultrasound propagates through such liquid. The penetration depth of a longitudinal stress is much longer than for a shear stress, which allows this method to be used for studying liquid bulk properties at the MHz range. The concept of longitudinal rheology has been known for centuries, but only became available in commercial instruments as recently as the 1990s. We describe here the main principles of this technique, as well as present an overview of existing published applications, which include: —Bulk viscosity —Microviscosity —Hookean coefficient of inter-particle bonds —Newtonian liquid test at MHz range —Compressibility —Sol-gel transition —Micellar systems —Dissolution of polymers —Liquid mixtures

Structural and Electrokinetic Characteristics of High-Silica Porous Glasses in Nickel Chloride Solutions

Abstract: The structural (structural resistance coefficient, volume porosity, tortuosity coefficient, filtration coefficient, and specific surface area) and electrokinetic (specific electrical conductivity, streaming potential, and electrophoretic mobility of particles) characteristics of micro- and macroporous glasses prepared from sodium borosilicate two-phase glass have been studied in nickel chloride solutions with ionic strengths of 10–4–0.3 M. Obtained experimental data have been used to calculate the average pore radius, efficiency coefficient, and electrokinetic potential of the glasses. The dependences of the structural and electrokinetic characteristics of the porous glasses on counterion charge have been analyzed for a series Na+, Ni2+, and La3+.

Protomicelles of Sodium Dodecyl Sulfate in a Strongly Diluted Aqueous Solution of Crown-Substituted Magnesium Phthalocyaninate

Abstract: Protomicelles represent a new concept of colloid science relevant to micelle-like aggregates of surfactants in solutions. In contrast to ordinary micelles, their formation requires no critical micelle concentration (CMC) and proceeds gradually through the adsorption of surfactant molecules or ions on a solubilization core at concentrations much lower than the CMC. A completely formed protomicelle looks like an ordinary solubilisate-containing micelle. Protomicelles can be formed on phthalocyanine monomers and dimers. In this work, the role of protomicelles in monomerization of crown-substituted magnesium phthalocyaninate (I) in aqueous sodium dodecyl sulfate (II) solutions has been studied spectrophotometrically at compound I concentrations of 0.38 and 1.2 μМ. Empirical methods have been developed for determining a new parameter, monomerization concentration (concentration of II required to initiate the monomerization of I), and it has been shown that the monomerization concentration decreases with an increase in the concentration of I. Another new parameter defined as the concentration of II corresponding to nearly complete monomerization of I has been studied in comparison with the CMC of II. For this purpose, the CMC has, for the first time, being measured (by conductometry) in the presence of protomicelles. The latter circumstance has been shown to decrease the CMC. At the same time, it has been revealed that the concentration corresponding to the completion of monomerization in the studied system nearly coincides with the CMC.

Protomicelles of Tetradecyltriphenylphosphonium Bromide in an Aqueous Solution of Crown-Substituted Magnesium Phthalocyaninate

Abstract: Protomicelle is a new term in colloid science that refers to micelle-like surfactant aggregates in solutions. Unlike conventional micelles, protomicelles have no critical micelle concentration (CMC) and are formed gradually via adsorption of surfactant molecules or ions on solubilization cores at concentrations significantly lower than the CMC. A completely formed protomicelle looks like an ordinary solubilisate-containing micelle. In this work, the process of monomerization of a given amount of crown-substituted magnesium phthalocyaninate (I) in a premicellar aqueous solution of tetradecyltriphenylphosphonium bromide (II) has been studied by spectrophotometry. It has been shown that compound I monomers are absent in a solution in pure water, while the content of dimers increases as surfactant II is added to the solution. This phenomenon strictly proves the existence of higher-order molecular aggregates of I in aqueous solutions. A new physicochemical parameter of phthalocyanine monomerization has been defined, namely, the monomerization concentration, i.e., compound II concentration that corresponds to the beginning of this process. It has been shown that phthalocyanine monomerization, which has begun long before the CMC of II, continues above the CMC, although at a lower rate. At this stage, monomerization of I proceeds exclusively at the expense of dimers.

On the Theory of Phthalocyanine Monomerization in Aqueous Surfactant Solutions

Abstract: A thermodynamic theory has been formulated to substantiate a number of new phenomena experimentally revealed in the colloid science of surfactants. A description has been given for the formation of particular micelles via surfactant adsorption on their cores, the role of which is played by monomers and dimers of phthalocyanines. This gives rise to the formation of surfactant micelles and protomicelles containing solubilized monomers and dimers. The gradual formation of the (proto)micelles (coverage of the core surface with surfactant molecules or ions) upon the addition of a surfactant to a system is completed before the critical micelle concentration of the surfactant is reached. In terms of the chemical potentials and concentrations, equations have been derived to describe the influence of surfactants on the state of the monomers and dimers of phthalocyanines in aqueous solutions. It has been found that the concentrations of both particles grow with surfactant concentration. Alterations in the distribution of dimers over their structural forms with variations in surfactant concentration have been analyzed. It has been shown that, as surfactant content in a solution increases, the distribution of dimers shifts toward labile structures with the inevitable disintegration of phthalocyanine dimers into monomers. An equation has been derived to determine a new physical parameter, monomerization concentration, which corresponds to the passage from the dimeric state (inherent in phthalocyanines in pure water or dilute surfactant solutions) to the monomeric state in surfactant solutions. Equations have been presented for the chemical potentials of micelles (containing solubilized phthalocyanine monomers) and protomicelles (containing solubilized dimers). The latter actually disappear when the surfactant concentration rises approaching the critical micelle concentration.

Enhanced Photoelectrocatalytic Degradation Activity of Titanium Dioxide Photoelectrode: Effect of Film Thickness

Abstract: The present work reports synthesis of titanium dioxide (TiO2) thin films deposited from ethanolic titanium diisopropoxide bis-acetyl acetonate precursor solution by using spray pyrolysis technique. The deposition of films were carried out on both amorphous and fluorine doped tin oxide (F:SnO2) glasses. The effect of film thickness on photoelectrochemical, structural, morphological and optical properties of TiO2 thin films was studied. The photoelectrochemical performance showed highest short circuit current and open circuit voltage at the optimized thickness of the film of 0.921 μm. X-ray diffraction study revealed that the films are polycrystalline, and exhibit anatase phase having tetragonal crystal structure. The TiO2 electrodes deposited on fluorine-doped substrates were further used in the photoelectrochemical degradation of pollutants such as Methylene blue dye and benzoic acid. The degradation efficiencies were found to be 76 and 55% for the dye and benzoic acid, respectively.

Structural Characteristics and Ionic Composition of a Colloidal Solution of Silver Nanoparticles Obtained by Electrical-Spark Discharge in Water

Abstract: This work is devoted to studying the structural and morphological properties of a silver colloidal solution obtained by the method of electrical-spark discharge in distilled water. Silver nanoparticles are formed as a result of metal sputtering from the surfaces of silver electrodes, between which a high-voltage electric discharge is generated. The solution is stabilized by forming a layer of anions around the nanoparticles. The structural characteristics of the colloidal solution are studied by small-angle X-ray scattering and transmission electron microscopy. The ionic composition is determined qualitatively using electrospray ionization mass spectrometry, while silver concentration is measured by inductively coupled plasma atomic emission spectrometry.

Thermodynamic Study of the Solubilization of Crown-Substituted Magnesium Phthalocyaninate in Aqueous Solutions of Cationic Surfactants

Abstract: Solubilization of crown-substituted magnesium phthalocyaninate(I) has been studied by spectrophotometry in aqueous solutions of tetradecyltrimethylammonium(II), hexadecyltrimethylammonium(III), and hexadecyltriphenylphosphonium bromides. The experiments have been carried out with saturated solutions of I occurring at the thermodynamic equilibrium with its precipitate. The experimental data have been used to determine the following thermodynamic characteristics of the solubilization: the solubilization capacity of micelles, the coefficient of solubilisate partition between micelles and an ambient solution, and the standard solubilization affinity of I. It has been shown that, in spite of different structures of the surfactants, the standard works of a I molecule transfer to micelles of all three surfactants are almost equal. The found values of the solubilization capacity, as calculated per one molecule of I, in micelles of II and III lead to abnormally large aggregation numbers. This fact may be explained by possible development of a bimodal distribution of micelles, at which solubilisate-containing micelles coexist with “empty” micelles; as a result, the average number of solubilisate molecules in a micelle may appear to be smaller than unity.

Structural Transformations in Magnetic Emulsions upon Their Interaction with an Alternating Electric Field

Abstract: Specific features of the interaction between magnetic emulsions and an alternating magnetic field have been studied. The emulsions are represented by a system of microdroplets of hydrocarbon-based magnetic fluids suspended in an oil medium immiscible with them. It has been shown that an alternating magnetic field can be employed to form different structural lattices in such media. The type of the lattices can be altered by varying field frequency and temperature, as well as by imposing an additional constant magnetic field. The results obtained have been analyzed taking into account the motion of the liquid phases caused by free charges accumulated at interfaces.

Graphene-Based Aerogels Possessing Superhydrophilic and Superhydrophobic Properties and Their Application for Electroreduction of Molecular Oxygen

Abstract: A composite aerogel with superhydrophobic external surface has been synthesized from reduced graphene oxide and polytetrafluoroethylene taken in a weight ratio of 1 : 1. The porous structure of the aerogel has been studied by the standard contact porosimetry method (SCPM). The porosimetric curves measured with respect to octane and water intersect in the region of small pores, thereby leading to the fact that the specific surface area of the aerogel in water is much larger than that in octane, although octane is known to wet any material almost ideally. This phenomenon, which is referred to as “superhydrophilicity,” is explained by the fact that, in the region of mesopores, a sample swells in water due to the hydration of surface –CO and –COH groups, which have been identified with the help of IR and Raman spectroscopies. Thus, the outside surface of the aerogel granules is superhydrophobic, while their interior is superhydrophilic in the region of small pores. As follows from the SCPM data, the total porosity and specific surface area of the aerogel are substantially larger than those of Vulcan XC-72 carbon black, which is a standard carrier for Pt catalysts used in fuel cells based on proton-exchange membranes. Oxygen electroreduction at the aerogel, containing Pt deposited in an amount of 28 µg/cm2, has been studied by the method of rotating disk electrode (RDE) in an aqueous 0.5 M H2SO4 solution, and the results obtained have been compared with the data on standard commercial Pt (20%)/Vulcan XC-72 catalyst. It has been shown that the limiting diffusion RDE currents for Pt supported on the hydrophobic–hydrophilic aerogel are markedly higher than those for the standard catalyst because of the easier access of oxygen to the reaction zone as compared with hydrophilic Vulcan XC-72 carbon black carrier.

Encapsulation of Oil Phases with Different Compositions into a Shell Composed of Nanoparticles of Natural Hydrothermal Silica and Polyelectrolyte Layers

Abstract: Particles of natural hydrothermal nanosilica have been characterized, and the conditions of their self-organization have been chosen for the stabilization of oil-in-water emulsions with the use of a cationic surfactant. Microcapsules, which consist of shells composed of layer-by-layer deposited chitosan and calcium alginate and contain dodecane, soybean and sesame oils, a 30% α-tocopherol acetate solution in sunflower oil, and shea butter, have been prepared on the basis of Pickering emulsions. Conclusions on the mechanical stability of the Pickering emulsions and capsules based thereon have been inferred from changes occurring in the colloidal system as a result of centrifugation at 27 000g. The capsules with the vegetable oils have exhibited a higher stability than those containing dodecane. The three-layer polymer shell has been shown to prevent the nanocapsules from coalescence and breakage upon centrifugation.

Chemical Composition, Structure, and Electrokinetic Potential of Nickel- and Iron-Containing Vitreous Materials

Abstract: The chemical composition, structure, and electrokinetic characteristics have been studied for different vitreous materials, including basic silicate glasses and those modified with iron and nickel oxides in the course of melting. The position of the isoelectric point and the value of the electrokinetic potential of monolithic particles (two-phase glasses and quartz-like glasses) and microporous samples obtained by acidic leaching have been analyzed as depending on the chemical composition and surface structure of the materials in a solution of NaCl as an indifferent electrolyte. The influence of specifically sorbable nickel ions on the electrokinetic characteristics of silicate glasses and nickel-containing vitreous materials has been investigated.

Erratum to: Modification of Multiliposomal Nanocontainers with Albumin as a Method for Increasing Their Resistance to Enzymatic Hydrolysis

Abstract: The influence of a pancreatic enzyme, lipase, on doxorubicin-loaded anionic liposomes, their complexes with spherical polycationic brushes, and ternary complexes with brushes and bovine serum albumin has been studied. The two-stage kinetics of the enzyme-induced disturbance of liposomal membrane integrity has been investigated using fluorescence spectroscopy. A 120-min induction period free of any serious damage to liposome membranes has been found for all enzyme-treated samples. This period is followed by rapid release of encapsulated doxorubicin. Enzymatic hydrolysis of the liposomes and their binary complexes with brushes has been found to proceed at the same rate, while a rather long resistance to the disturbance of liposome integrity has been observed for the ternary complexes. It has been assumed that albumin plays the role of a sterically screening agent, which hinders the enzymatic hydrolysis in multiliposomal complexes.

Preparation of Dispersed Magnetite–Bentonite Composites and Kazcaine Adsorption on Them

Abstract: Magnetite particles are prepared from a mixed aqueous solution of FeCl2 and FeCl3, and magnetite−bentonite composite particles are obtained from a mixed dispersion of magnetite and bentonite by precipitation with ammonia. The dispersions are examined by the X-ray diffraction, transmission electron microscopy, IR spectroscopy, dynamic light scattering, and electrophoresis methods. In the presence of magnetite, the basal reflection at 2θ = 6.06° in the X-ray diffraction pattern of bentonite shifts to 7.14° due to the replacement of K+, Na+, and Mg2+ ions by Fe3+ ions. Moreover, peaks corresponding to iron compounds arise in the diffraction pattern, while an absorption band at 1405 cm–1 assigned to Fe–O bonds appears in the IR spectrum of the composite particles, thereby probably indicating the formation of small magnetite particles between bentonite layers. Along with the indicated changes, the passage from original bentonite to the magnetite−bentonite composite is accompanied by an increase in the ζ-potential of the particles from –35.1 to –25.7 mV and a decrease in their sizes from 300 to 220 nm. The latter phenomenon is explained by ion exchange, water removal from the interlayer space, and the contribution of smaller particles of magnetite. To test the functional potential of the obtained composite particles, the adsorption of a drug, kazcaine, on them is studied, and the maximum kazcaine adsorption value is found to be as large as 74.65 mg/g. The analysis of kazcaine adsorption kinetics at different temperatures is carried out to determine the thermodynamic parameters of the process. The results obtained show that the process can be described by a pseudo-second-order kinetic equation. The Langmuir model appears to be most suitable for describing the adsorption mechanism.

A Unified Approach to Disjoining Pressure in Liquid and Vapor Interlayer within the Framework of the Density Functional Theory

Abstract: The classical density functional theory makes it possible to explicitly calculate the local density profiles, the components of the pressure tensor, and the thicknesses of thin interlayers between a lyophilic or lyophobic solid surface and, accordingly, gas or liquid phases at different values of the chemical potentials of the phases. Within the framework of a unified approach based on the gradient approximation of the classical density functional theory, it has been shown that, at certain values of parameters characterizing the wettability or nonwettability of a solid, equilibrium liquid films or vapor layers of a uniform thickness are formed around a spherical particle, if its surface is lyophilic or lyophobic, respectively. Mechanical and thermodynamic definitions have been given for the disjoining pressure in the spherical liquid or vapor interlayer around a solid particle, and the agreement between the definitions has been proven by calculations at different interlayer thicknesses and particle radii. It has been shown that the disjoining pressure in a vapor interlayer around a nanosized lyophobic particle decreases with an increase in particle radius, with this phenomenon being opposite to the situation with liquid films.

Self-Assembly of Metal-Organic Frameworks in Pickering Emulsions Stabilized with Graphene Oxide

Abstract: Metal-organic frameworks (MOFs) integrated with inorganic colloidal carriers compose a new class of functional hybrid materials possessing properties useful for a number of applications, in particular, selective sorption and (photo)catalysis. A new method has been developed for the synthesis of porous composites consisting of graphene oxide and MOF crystallites based on porphyrins. Graphene oxide serves simultaneously as a protective matrix for MOF and an emulsifier providing the assembly of immiscible components, which have different solubilities, in Pickering emulsions. Zinc acetate plays the role of a metal cluster, which immobilizes MOF crystallites on graphene oxide surface and participates in the MOF synthesis as a secondary structural block. This combination of the components makes it possible to avoid a chemical modification of graphene oxide during the assembly of the composite material. This strategy has been employed to obtain two series of model supramolecular composites based on zinc meso-tetra(4-pyridyl)porphyrinate and zinc meso-di(4-pyridyl)-di(4-carboxyphenyl)pophyrinate and study the relation between their structure, morphology, and properties. The developed colloid-chemical method makes it possible to simplify the synthesis of supramolecular composite materials and may be adapted to different combinations of inorganic matrices and MOFs.

Estimation of Ion-Exchange Equilibrium Constant Using Membrane Conductivity Data

Abstract: The possibility of calculating the ionic composition of a membrane and the ion-exchange equilibrium constant on the basis of the concentration dependences of the specific conductivity of the membrane in individual and mixed solutions has been studied for an ion-exchange membrane–solution system, in which the solution contains two types of counterions and a common coion. The calculation has been carried out for MF-4SK and MK-40 membranes in a mixed solution of calcium and sodium chlorides, and a satisfactory agreement of the obtained values with those reported in the literature has been shown. This approach has been used to estimate the ion-exchange equilibrium constant for polyaniline-modified MF-4SK and MK-40 membranes, and a correlation has been shown between the results of the conductivity studies and the assessments of the counterion fluxes during the electrodialysis of the mixed solutions.

Formation of Silver Nanoparticles in Aqueous Oligochitosan Solutions

Abstract: Formation of stable silver dispersions with a unimodal particle size distribution has been studied in aqueous solutions of oligochitosans with different molecular masses. The character of the interaction of oligochitosans with silver ions and nanoparticles has been revealed. Spectral studies have shown that hydroxyl and amino groups of oligochitosans are involved in the formation and stabilization of the aqueous dispersions containing metal nanoparticles with sizes of 45–90 nm. Such dispersions are promising for biomedical applications.

Transport Numbers of Singly-, Doubly- and Triply-Charged Cations in Porous Glasses

Abstract: Transport numbers of sodium, nickel, and lanthanum counterions have been studied in microporous (average pore radius is r = 2–3.4 nm) and macroporous (r = 16–27 nm) magnetite-free glasses and those containing magnetite in their matrices. It has been found that, in the case of microporous glasses, the relation between the transport numbers of the studied cations is primarily governed by the structure of secondary silica in pore channels. For membranes prepared from macroporous glasses, the transport numbers of the cations in the pore space depend on the surface charge magnitude and the structure of the electrical double layer.

Kinetics of Air Bubble Growth on a Silicon Substrate in Alcohol and Water–Alcohol Media

Abstract: The spontaneous growth of sessile air bubbles with sizes of 1 mm and below on a solid surface has been experimentally studied in ethanol and its aqueous solutions under constant external conditions (atmospheric pressure and a temperature of 20°С). A noticeable growth of bubble volume has been observed for at least 2 h in ethanol solutions beginning from an alcohol concentration of 50%. The time dependences of bubble volume have different patterns in ethanol solutions and undiluted alcohol.

A Study of Cryostructuring of Polymer Systems. 54. Hybrid Organo-Inorganic Poly(vinyl alcohol) Cryogels Filled with In situ Formed Silica

Abstract: Macroporous viscoelastic poly(vinyl alcohol) (PVA) cryogels are formed via the cryogenic processing (freezing/incubation in the frozen state/defrosting) of concentrated solutions of the polymer. Such materials are of significant scientific and applied interest. This also concerns various complex and composite PVA cryogels containing soluble and insoluble (fillers) additives, respectively. Novel organo-inorganic hybrid PVA cryogels containing silica components have been obtained and studied in this work. These hybrid cryogels are formed via the interaction of sodium silicate with hydrochloric acid, which are introduced into an aqueous PVA solution immediately before its cryogenic processing. As a result, the transformation of the inorganic components occurs simultaneously with the cryotropic gelation of PVA. It has been found that the physicomechanical properties, heat endurance, and macroporous morphology of the obtained samples depend on the concentration of the inorganic additives and the temperature conditions of the cryogenic process. Moreover, it has been revealed that formed NaCl and additionally polarized hydrogen bonds between OH groups of PVA and silanol groups of in situ formed poly/oligo(silicic acids) have substantial effects on the characteristics of resulting hybrid cryogels.