Colloid Journal最新文献

In the present paper, we report data on the influence of choice of dispersion medium-precipitating agent pair on sol–gel process for lead zirconate-titanate ceramic precursor manufacturing. Acetic acid and 2-methoxyethanol were studied as dispersion media, whereas ethylene glycol and water as respective precipitating agents. Changes in optical, rheological properties and particle size distributions during the sol–gel transition were studied at different concentrations of precipitating agents. It was shown that the nature and relative concentration of dispersion medium and precipitating agent provide wide-range control of lead zirconate-titanate sol and gel properties as well as the rate of sol–gel process, mechanism of formation and structure of the gels.

Hydrosols containing tungsten(VI) oxide nanoparticles have been studied by the electrooptical and electrophoretic methods. The influence of multivalent ions (tetravalent thorium and trivalent lanthanum cations) on the zeta-potential and polarizability of tungsten(VI) oxide particles has been determined. The dispersion dependences of the polarizability of tungsten(VI) oxide particles have been studied. A strong dependence of the electrokinetic potential and a weak dependence of the polarizability of the particles on the concentrations of thorium and lanthanum cations in the sols have been found. The polarizability of the particles is low and weakly depends on the frequency of the field polarizing the particles. This is atypical for colloidal particles, for which the thickness of the dense part of the electrical double layer is comparable with the size of molecules, while the polarization of the electrical double layer is determined by its diffuse part. The obtained results have led to a conclusion that, for tungsten(VI) oxide particles in the studied concentration range, the majority of multivalent counterions are located in the dense part of the electrical double layer due to their high adsorption potential.

The influence of small additives of Fe³⁺ ions on tetraethoxysilane hydrolysis and subsequent polycondensation of products has been studied by the viscometry and dynamic light scattering methods. Experiments have been carried out at 50°C. Hydrolysis has been carried out at pH 1.5, 2.5, 5.0, or 7.0. The amount of the dopant cations has been varied from 1.5 to 3.8 at %. In the absence of the dopant cations, the gelation time grows with increasing pH from 1.5 to 5.0, while polycondensation occurs without gelation at pH 7.0. If the dopant is added at pH 1.5, the gelation time increases, but, at pH 2.5 and 5.0, it decreases. The gelation time increases with the dopant content at all three pH values. The size of the particles formed during the polycondensation process depends on the pH and the amount of the dopant. The smallest particles with a median diameter of about 10 nm are formed at pH 2.5. It is assumed that the cause of all observed effects is the incorporation of iron cations into the siloxane matrix. The degree of the incorporation depends on the degree of iron cation hydrolysis. This assumption is confirmed by the values of the electrokinetic potential of the studied systems and the dynamics of variations in the zeta-potential with varying pH and dopant content.

A culture of human bone marrow mesenchymal stromal cells (MSCs) has been investigated. The cell culture has been grown as a monolayer in a nutrient medium containing a stabilized aqueous suspension of magnetic maghemite (γ-Fe₂O₃) nanoparticles (MNPs). The MNPs have been synthesized by the electrophysical method of laser target evaporation. A method has been proposed for stabilizing the suspension in the nutrient medium with a high ionic strength. The possibility of MNP internalization (either by fixing on the cell membrane or by incorporating into the cell space) with human MSCs has been evaluated using optical microscopy, scanning (SEM) and transmission (TEM) electron microscopy, and SQUID magnetometry. Comparative analysis of the structure and magnetic properties has been performed, and assumptions have been put forward about the features of MNP internalization with the cells in this system. It has been revealed that the limiting amount of MNPs that can be reliably analyzed in a biological sample of the studied type is about 0.005 mg. It has been found that, in the considered range of initial concentrations of magnetic nanoparticles in biological samples based on human MSCs, the level of accumulation of magnetic nanoparticles in cell cultures depends on their concentration.

The deposition of submicron aerosol particles in model filters consisting of micron-sized fibers containing radial nanowhiskers (needles) on their surfaces is considered. Numerical simulation has been performed for the transverse 3D Stokes flow field in a model filter—an isolated row of whisker-coated parallel fibers taking into account the gas slip effect on their surface. The fiber drag force and the fiber collection efficiency have been calculated as functions of the length and packing density of the whiskers and the distance between the fibers. The dependence of the fiber collection efficiency on the particle radius has been determined.

An iterative approach has been proposed for analyzing the relation between the processes of intensive evaporation and bulk condensation near an evaporation surface. This approach employs the results of the numerical solution of the Boltzmann kinetic equation for intensive evaporation from an interfacial surface to calculate the kinetics of the bulk condensation near the evaporation surface. It has been shown that, during the lifetime of the supersaturated state of the vapor predicted on the basis of the solution without condensation, the condensation aerosol has sufficient time to be formed. The results obtained indicate that the formation of droplets near the evaporation surface and the thermal effect of the condensation on the vapor parameters must be taken into account when analyzing the intensive evaporation from an interfacial surface.

The article is devoted to theoretical studying the dynamic response of ensembles of nanosized ferromagnetic particles immobilized in a nonmagnetic medium to an external field. The main attention of the work is paid to analyzing the effect of interparticle magnetic interactions on the complex magnetic susceptibility of a composite and the intensity of heat generation in it under the action of the alternating magnetic field. The analysis has shown that the dependence of the magnitude of the thermal effect on the parameter of the interparticle magnetodipole interaction is nonmonotonic and passes through a maximum. We hope that this result will help to understand the physical reason for the qualitative contradictions between the conclusions inferred in different studies devoted to the influence of the interparticle interactions on the components of the complex magnetic susceptibility of magnetic composites and the intensity of the heat generation under the action of alternating fields.

It has been shown that associates of cationic glycerolipid (CGL), rac-N-{4-[(2-ethoxy-3-octadecyloxyprop-1-yl)oxycarbonyl]butyl}-N'-methylimidazolium iodide, which has a pronounced antitumor effect, can be used for the solubilization of two hydrophobic biologically active compounds (curcumin and capsaicin) and as templates in the sol–gel synthesis of silica mesoporous container particles (MCPs). The thermodynamic characteristics of solubilization are determined, and it is shown that this process contributes to a significant increase in the solubility of both hydrophobic drugs in water. The hydrolytic condensation of tetraethoxysilane in the presence of CGL associates containing curcumin or capsaicin leads to the formation of MCPs characterized by a narrow size distribution and a high content of encapsulated drugs. This combination of the stages of the synthesis and loading of MCPs is of undoubted interest in relation to the nanoencapsulation of cationic glycerolipids (including in combination with other drugs).

The key properties of aqueous Tween 80 micellar solutions as means for the delivery of biologically active substances inhibiting the reproduction of various pathogens have been studied in order to develop innovative methods for plant protection. It has been shown that these solutions exhibit no negative effects upon the contact with potato leaves. The wetting isotherms plotted for aqueous Tween 80 solutions have confirmed the hydrophilization of a potato leaf and a hydrophobic polymer film simulating its surface. The maximum adsorption of Tween 80 on the polymer surface has been determined by combining the methods of tensiometry and wetting, thereby making it possible to predict the structure of the adsorption layer of this surfactant on the surface of the potato leaf. A significant increase in the velocity of penetration into the leaf has been recorded for Tween 80 micellar solutions characterized by the maximum wetting ability.

The paper presents the results of computer simulating the structure formation in nanodisperse magnetic fluids and the influence of this process on the kinetics of their magnetization reversal. The work considers a system of identical spherical single-domain ferromagnetic particles suspended in a Newtonian fluid with magnetic moments “frozen” into the particle bodies. The particles are involved in intense Brownian motion. The magnetic interactions of all particles with each other, as well as of the particles with an external magnetic field, are considered. The results have shown that the evolution of the internal structures upon a change in the external field can greatly, by several orders of magnitude, change the characteristic time of ferrofluid magnetization reversal. The results obtained may be useful for the development of both the general theory of these systems and many methods for their high-tech applications.