Vol 86, No 6 (2024)

The possibility of implementing an original methodology for studying the kinetics of aggregation of colloidal solutions based on the joint application of dynamic and static light scattering methods is discussed. The theoretical justification of the proposed methodology is based on the concept of fractal dimension and scaling. Its experimental implementation is carried out using the example of the aggregation process of a colloidal gold solution initiated by a change in the ionic strength of the solution. The fractal dimension of Au clusters is determined by the angular and kinetic dependences of static light scattering (SLS). The hydrodynamic radii of clusters are determined by the dynamic light scattering (DLS) method. Based on the experimental results and the formed model dependence of the light scattering intensity on the size of clusters, the kinetic dependence of the concentration of Au clusters is constructed and the rate of their aggregation is estimated. The proposed method can be applied to study the kinetics of aggregation of fractal clusters in various colloidal systems.

In this work, electro–optical and electrophoretic studies of hydrosols containing tungsten (VI) oxide nanoparticles were carried out. The influence of multivalent ions (tetravalent thorium cation and trivalent lanthanum cation) on the zeta potential and polarizability of tungsten (VI) oxide particles was 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 particles on the concentration of thorium and lanthanum cations in the sol were observed. The polarizability of particles was low and weakly depended on the frequency of the field which polarizes the particles. This is not typical for colloidal particles, the thickness of the dense part of the electrical double layer of which is comparable with the size of the molecules, and the polarization of the electrical double layer is determined by its diffuse part. The results obtained allowed us to conclude that for tungsten (VI) oxide particles in the studied concentration range, the predominant fraction of multiply charged counterions is located in the dense part of the electrical double layer, which is associated with their high adsorption potentials.

In order to develop innovative methods of plant protection, the key properties of Tween 80 aqueous micellar solutions as means of delivery of biologically active substances inhibiting the reproduction of various pathogens have been studied. The absence of negative effects of these solutions upon contact with potato leaves has been shown. The wetting isotherms for Tween 80 aqueous solutions confirmed the hydrophilization of the potato leaf and the hydrophobic polymer film modeling its surface. By combining the methods of tensiometry and wetting, the maximum adsorption of Tween 80 on the surface of the polymer was determined, which made it possible to predict the structure of the adsorption layer of this surfactant on the surface of the potato leaf. For micellar solutions of Tween 80, characterized by maximum wetting ability, a significant increase in the rate of penetration into the leaf was recorded.

SERS tags are of great interest as bioanalysis platforms due to their combination of strong optical signal, photostability, and narrow spectral lines. Despite significant progress in the synthesis of new types of SERS tags based on gold nanoparticles, obtaining microparticles with a Raman scattering intensity sufficient for detection of a single tag using a conventional Raman microscope is not a trivial task. In this paper, hybrid colloidal nanocomposites based on silica microparticles and gold nanostars (AuNSTs) with the composition SiO₂/AuNSTs/SiO₂ were synthesized and characterized. Two types of gold nanostars, one with a plasmon resonance at 700 nm and the other with two maxima at 650 and 900 nm, were pre-synthesized and adsorbed on the surface of monodisperse colloidal silica particles with a diameter of 1.5 μm. Three types of thiolated aromatic molecules were used as Raman reporters: 4-nitrothiophenol, naphthalenethiol, and 1,4-benzenedithiol. The possibility of measuring the SERS signal from a single microparticle with an intensity variation of no more than 20% has been demonstrated, as well as the possibility of multiplex determination of various microparticles in one Raman image. A comprehensive assessment of the stability, including photostability, of the measured SERS signal over time was carried out when the physicochemical parameters of the microenvironment changed.

An iterative approach to analyzing the interaction between the processes of intensive evaporation and bulk condensation near the evaporation surface is proposed. This approach employs the results of the numerical solution of the Boltzmann kinetic equation for intensive evaporation from the interfacial surface to calculate the kinetics of the bulk condensation process near the evaporation surface. It is demonstrated that during the period of supersaturation predicted on the basis of the solution that does not consider condensation, the condensation aerosol has sufficient time to form. The results indicate that the formation of droplets near the evaporation surface and the thermal effect of condensation on the vapor parameters should be incorporated into the analysis of intense evaporation from the interfacial surface.

Mechanisms of self-organization of graphene oxide in aqueous dispersions during interaction with detonation nanodiamonds having different surface potential signs were studied using small-angle neutron scattering technique. Negatively charged graphene oxide, mixed with a hydrosol of positively charged diamonds, created a stable colloid due to the formation of planar heterostructures in the form of a pair of sheets, tightly connected through diamonds (weight fraction 25%) when the sheets were joined. Diamonds with a negative potential under similar conditions were localized between graphene sheets, forming at an increased fraction (44 wt. %) less dense assemblies with a gap between the sheets around a diamond particle radius. The binding of graphene oxide to diamonds was confirmed by transmission electron microscopy data.

The influence of small additions of Fe³⁺ ions on the processes of hydrolysis of tetraethoxysilane and subsequent polycondensation of products was studied using viscosimetry and dynamic light scattering methods. Experiments were carried out at 50^оC, hydrolysis pH was 1.5; 2.5; 5.0 or 7.0, the amount of doping cation varied from 1.5 to 3.8 at. %. In the absence of a doping cation, the gelation time grows with increasing pH from 1.5 to 5.0, and at pH 7.0, polycondensation occurs without gelation. At pH 1.5, the introduction of a dopant increases the gelation time, at pH 2.5 and 5.0 it decreases. With increasing dopant content, the gelation time increases at all three pH values. The size of the particles formed during the polycondensation process depends on the pH and the amount of dopant. The smallest particles with a median diameter of about 10 nm are formed at pH 2.5. It has been suggested that the cause of all the observed effects is the incorporation of iron cations into the siloxane matrix. The degree of incorporation depends on the degree of hydrolysis of iron cations. This assumption is confirmed by the values of the electrokinetic potential of the systems under study and the dynamics of changes in the zeta potential with varying pH and dopant content.

The paper presents the results of computer modeling of structure formation in nanodispersed magnetic fluids and the influence of this process on the kinetics of their magnetization reversal. A system of identical spherical single-domain ferromagnetic particles suspended in a Newtonian fluid with magnetic moments “frozen” into their bodies is considered. The particles are involved in intense Brownian motion. The magnetic interaction of all particles with all, as well as with an external magnetic field, is considered.

The results show that the evolution of internal structures with a change in the external field can greatly, by several orders of magnitude, change the characteristic time of magnetization reversal of a ferrofluid. The results obtained can be useful for the development of both the general theory of these systems and many methods of their high-tech application.