V. I. Roldughin

Kinetic Phenomena in the Diffusion of Gases in Capillaries and Porous Bodies

The flow of gases and gaseous mixtures in capillaries and porous bodies were considered. Phenomenological transfer equations were derived using methods of non-equilibrium thermodynamics. Integral and local equations of non-equilibrium thermodynamics were constructed and phenomenological relations of two types were obtained. Different approaches to the calculation of kinetic coefficients were indicated. Methods of kinetic theory based on Boltzmanns equation and the dusty gas model were analyzed separately. Results of the calculations of kinetic coefficients for small and large Knudsen numbers were reported with allowance for incomplete accommodation of molecules on the surface of channel walls. A number of kinetic effects exhibiting during the flow of gases and gaseous mixtures through the capillaries and porous bodies was discussed.

Formation of Silver Nanoparticles in Aqueous Carboxymethyl Cellulose Solutions and the Evolution of their Sizes

Size dependences of silver nanoparticles synthesized in aqueous carboxymethyl cellulose solutions and dependences of their ζ-potentials on solution pH are studied by the dynamic light scattering method. Variations in nanoparticle size distributions and ζ-potential of particles with time are monitored. It is revealed that the size of silver nanoparticles decreases linearly with an increase in solution pH. The size of particles noticeably decreases in the aging process of the colloidal solution. The ζ-potential tends to one and the same value with time for all studied hydrosol samples.

Effect of Surface Forces on the Gas Flow in Nanosized Capillaries

The flow of temperature-inhomogeneous gas in ultrathin capillary is considered with allowance for the action of surface forces. It is shown that the presence of surface forces considerably increases the effect of thermal transpiration compared to the classical value determined in a free molecular regime of gas flow. The coefficient responsible for the mechanocaloric effect for the case of the gas flow under the pressure gradient was also determined using Onsager relations for the kinetic coefficients calculated with account of the effect of surface forces.

The effect of ozone on plasmon absorption of gold hydrosols. Quasi-metal and metal nanoparticles

The character of the interaction between ultrasmall gold nanoparticles and ozone is shown to be mainly governed by the particle structure. For borohydride sols of gold nanoparticles with sizes of ≈3 nm, which are characterized by metallic properties, this interaction is reduced to reversible adsorption of ozone on their surface. At the same time, ozone adsorption on “nonplasmon” Au particles that have a diameter of 2 nm and a very defective structure results in their irreversible structural rearrangement and transition to a metallic state, which is accompanied by the appearance of a surface plasmon resonance. The set of the results obtained shows that nanoparticles of borohydride gold sols are more efficient as possible hemosensors of ozone than are larger particles synthesized by the citrate method.

Surface faceting of gold nanoparticles and adsorption of organic macromolecules

Dispersions of nanosized gold particles are synthesized in methyl hydroxyethyl-, carboxymethyl-, and hydroxy propylmethyl cellulose solutions by chemical reduction. Sizes of nanoparticles are determined using dynamic light scattering method. Ultrathin particle layers are prepared on the surfaces of polycrystalline gold films by self-organization technique. Characteristics of these layers and constituting particles are determined by scanning tunnel microscopy. It is shown that steps with heights of 0.7–4 nm and terraces are formed on nanoparticles. It is revealed that the height of a step depends to a greater extent on the chemical nature of employed reducer (tannin or formaldehyde) than on the nature of stabilizer (cellulose derivatives). Components of dispersion medium are selectively adsorbed on these steps.

Diffusion deposition of finite size particles on fibrous filters at intermediate Knudsen numbers

Diffusion deposition of aerosol particles from the flow on model filter made of ultrathin fibers with allowance for the “intrinsic size” of particles was considered in the range of Knudsen numbers Kn = 0.1–10. The problem was solved in the approximation of diffuse boundary layer. It was shown that the value of capture coefficient at small Kn seems to be larger and, at larger Kn, lower than the sum of individual capture coefficients due to the diffusion and interception. The calculated value of the radius of the most penetrable particles at Kn ≈ 1 agrees with experimental data.

Aggregation stability of gold citrate hydrosol: Effect of ozone

Optical spectroscopy, dynamic light scattering, electrophoresis, and transmission electron microscopy are used to study the action of ozone on the stability of a gold hydrosol produced by the citrate method. It is shown that gold nanoparticles are not oxidized, even upon long-term ozonation. At short times of ozonation, changes that occur in the state of the sol are reversible. Nevertheless, even at this stage, organic ligands, which stabilize the hydrosol, are oxidized, while adsorbed ozone molecules can play the role of a stabilizer. At long ozonation times, when the oxidation of organic substances present in the system is actually completed, the colloidal solution loses its aggregation stability.

Simulation of ESR spectra of metal nanoparticle aggregates

Aggregates of polydisperse particles characterized by the preset values of the fractal dimensions and prefactor are built with the use of a special algorithm. ESR spectra of such aggregates are calculated in the self-consistent field approximation. It is shown that, even in sufficiently large aggregates with fractal structure, spectra greatly depend on the character of packing of large and small particles in the aggregate.

Absorption of electromagnetic radiation by a nanoparticle in a nanocomposite: Going beyond the Maxwell-Garnett approximation

A model has been proposed for calculating the polarizability of a metal nanoparticle in a composite consisting of a dielectric matrix and monodisperse nanoparticles with more exact allowance for the influence of neighboring particles going beyond the Maxwell-Garnett approximation. The main attention has been focused on the imaginary component of the polarizability, which determines electromagnetic radiation absorption by a nanoparticle in the dipole approximation. It has been shown that the absorption may be noticeably enhanced or diminished depending on the incident radiation frequency.

Kinetic coefficients of the adsorption of polysaccharides from aqueous solutions by Sibunit

The kinetics of adsorption of T-40, T-70, and T-500 dextrans from aqueous solutions by a Sibunit carbon sorbent at 298 K is studied. Kinetic coefficients of polysaccharide adsorption are calculated. The dependence of the kinetic coefficient on a molecular mass and a size of macromolecular coil upon the adsorption of polysaccharide from aqueous solutions by Sibunit is discussed.