Mass-Transfer Coefficients in Dense Binary Mixtures

A modified elementary kinetic theory of gases is generalized to arbitrary densities of mixtures (from the gaseous to the solid state). Derived expressions for the mass-transfer coefficients are based on the lattice gas model, which is applicable to all the three aggregation states. For a rarefied gas, the expression for the mutual diffusion coefficient that is derived in terms of the modified theory is consistent with that obtained in terms of the rigorous kinetic theory of gases. The migration of particles is described in terms of transition state theory. The theory takes into account the role of thermal fluctuations in surmounting the activation barrier in dense phases. The label diffusion coefficient, pressure diffusion coefficient, thermal diffusion coefficient, and forced diffusion coefficient are discussed.     

The effect of system volume limitation on the surface tension of a vapor–liquid interface

The effect of the system volume limitation on the thermodynamic characteristics of a vapor–liquid interface, that is, the phase states of a substance and the surface tension, is considered. The molecular theory is used based on the lattice gas model, which describes the two-phase state of a vapor–liquid system. To simplify the calculations, the molecular characteristics of the spherical interface of a drop inside a spherical region of vapor having a single dimensional parameter, namely, the radius of the system, are assessed. It is found that, when the radius of the system decreases, the critical temperature decreases, while the internal pressure, the chemical potential, and the surface tension increase.     

Rheological Properties of Flows of a Dense Gas and Liquids in Narrow Slot‐Like Pores

The concentration dependences of the coefficients of shear viscosity of molecules in a wide range of pore fillings (from a rarefied gas to a liquid state) for different potentials of molecule–surface interactions have been theoretically investigated with the use of the latticegas model allowing for the volume occupied by atoms and the interaction between the atoms in the quasichemical approximation. This model allows one to find the selfconsistent equilibrium characteristics of a vaporliquid system and the coefficients of shear viscosity of molecules with the use of a single set of energy parameters. Molecular interpretation of the coefficient of sliding friction of the fluid near the pore walls is discussed.     

Dynamics of the flow of a dense fluid in narrow pores

A new approach was employed for the theoretical study of a dense fluid flow (gas and liquid) in narrow pores. Calculations were made on the basis of the Navier-Stokes equations. The transfer coefficients and the equations of state were derived within the framework of the simplest molecular model, namely, the lattice gas model. This model takes into account the volume of molecules and their interaction with one another. The transfer coefficients and the equations of state prove to be dependent on the local values of the fluid density and temperature. A study was performed into the dynamic modes of flow of a monoatomic gas (argon) in slitlike pores of various widths at a given pressure drop across the pore ends. It was shown that, at low densities, there is a high anisotropy of the flow owing to the attraction of argon atoms to the pore walls, which gives rise to a strong dependence of the local viscosity on the distance from the pore wall and to the film flow. An investigation was carried out into the dynamics of the interaction between the gas and liquid zones, which is accompanied by the breakdown of the interface.     

Nonuniform Surfaces and the Inflection Point in Polylayer Adsorption Isotherms

The position of the inflection point in polylayer adsorption isotherms, which has been traditionally used to determine the specific surface of many disperse systems, is analyzed. The inflection point positions versus the molecular parameters of the adsorption system and the degree of surface nonuniformity are considered. The surface heterogeneity is exemplified by the droplet roughness formed on rapid cooling. The vapor–liquid-droplet interface creates the thermal heterogeneity of the surface on which gas-phase molecules are adsorbed after cooling. Conditions for using the inflection point to estimate the specific surface of silica samples during argon and nitrogen adsorption are discussed, along with distinctions between the monolayer capacity found from the isotherm and complete filling of the monolayer itself determined by the degree of filling surface centers.     

Gas and Liquid Transfer in Narrow Pores

A microhydrodynamic approach is formulated to describe the molecular flows in micro- and mesoporous systems, including the region of capillary phenomena, where one needs a single set of equations characterizing the flows of both dense gases and liquids. The set of equations of the transfer of dense fluids in narrow pores is closed by using the simplest molecular model, specifically, the lattice gas model, which describes the behavior of fluids over wide ranges of concentrations (from the gas to the liquid state) and temperatures, including the critical region. This model takes into account the volume of molecules and the intermolecular interactions in a quasi-chemical approximation, which retains short-range order correlations. The model reflects the strong anisotropy of the molecular distributions along a normal to the pore wall (because of the adsorption forces) and along the pore axis if there is capillary condensation. The derived set of equations is a set of finite-difference equations in increments of coordinates (instead of derivatives). The dissipative coefficients have a nonlocal anisotropic character. The equations of the transfer in near-wall cells and the prospects of the microhydrodynamic approach are discussed.     

Effect of Adsorption on the State of Equilibrium Rough Surfaces at Interfaces

Protection of Metals and Physical Chemistry of Surfaces - The effect of adsorption on the characteristics of equilibrium rough surfaces of vapor–liquid and vapor–solid interfaces at a...     

Molecular theory of adsorption in meso- and macropores and Kelvin equation

The molecular theory of adsorption is used to estimate the upper bound of the validity of the Kelvin equation for calculating the saturated vapor pressure in meso- and macroporous adsorbents. The values of saturated vapor pressure are compared according to the theoretical adsorption isotherms obtained in terms of the lattice gas model and the Kelvin equation for atoms of argon and molecules of nitrogen and tetrachloride carbon. As the temperature increases, the agreement between the two methods improves. It is shown that the validity of the results obtained using the Kelvin equation for problems of absorption porometry is even limited for pores as small as 50 nm.