Fluctuation theory of microheterogeneous systems in the molecular-field approximation

Principles of the fluctuation theory of microheterogeneous systems are considered based on the example of adsorption on a heterogeneous surface of microcrystals and spherical liquid droplets in the vapor phase. Equations that describe the equilibrium distributions of molecules are derived within the lattice gas model with allowance for lateral interactions in the mean-field approximation. This approximation does not take into account the correlation effects of interacting particles. We discuss the structure of entropy and energy contributions in the derived equations and the relationship between the molecular chemical potential and the expansion pressure, which is analogous to the equation of the state, as well as the molecular interpretation of the concept of pressure in an ensemble of small particles and its relation to the mechanical interpretation of the surface tension.