Physical and Theoretical Chemistry

Biography

Biography: Eugene A Ustinov

Abstract

There is a significant progress in the part of physical chemistry dealing with thin films, adsorption, coating and other surface phenomena. Sophisticated methods have been developed for the design networks of organic molecules, visualization and description of the structure of molecular layers. However, not much is known on thermodynamics of two-dimensional crystalline phases. The aim of this study is to show how the chemical potential of the crystalline molecular layer can be determined. We developed a methodology based on a kinetic Monte Carlo simulation of the gas-solid system in the cell with a variable external potential imposed on the gas phase. At equilibrium the chemical potential is the same over the cell and, therefore, this technique guaranties its reliable determination in the solid phase as that in the gas phase is easily evaluated. This approach proved to be very efficient in studying thermodynamic properties of contact layers of argon, krypton, nitrogen and hydrogen on solid surfaces and confined in nanoporous materials at cryogenic temperatures, as well as the melting and orientational (N₂) long-to-short order transitions. The most challenging task is thermodynamic behavior of orientationally ordered layers formed by relatively large organic molecules. The reason is an extremely small primary molecular flux from the crystal and, therefore, its negligible contribution to the chemical potential compared to the secondary (reflected) flux. Nonetheless, the presence of the gas-solid interface allows us to circumvent the problem. Thus, we have successfully modeled the structures formed by trimesic acid and determined thermodynamic potentials and entropy of the chicken-wire structure and several flower-like polymorphs. From our viewpoint, the method has a significant potential for analysis of 2D crystals, their growth, thermodynamic stability, orientational and first order transitions.