Phase properties and wetting transitions of simple gases on graphite─characteristic temperatures of monolayer adsorbate

• Main Authors: Loi, Quang K., Tan, Johnathan Shiliang, Do, D. D., Nicholson, D.
• Other Authors: School of Chemical and Biomedical Engineering
• Format: Article
• Language: English
• Published: 2022
• Subjects: Engineering::Chemical engineering; Kinetic Monte-Carlo; Vapor-Liquid-Equilibria
• Online Access: https://hdl.handle.net/10356/163925
• Institution: Nanyang Technological University

Computer simulations were performed to study the characteristic transition temperatures of the adsorbate monolayer transitions on graphite and to determine the layering temperatures for higher layers at temperatures less than the bulk triple point temperature. Two models for graphite were studied to examine the effects of finite size of the graphene layer on the evolution of the characteristics of the monolayer, its boundary with the gas phase, and the resulting isotherm and isosteric heat versus loading. Both models give good agreement with experiment for the 2D-critical point and the 2D-triple point, but the finite model is more successful in representing the experimental isotherm and isosteric heat. Radial density distribution for the monolayer supports this, and it illustrates the manner in which the monolayer is compressed with loading, by mass transfer of molecules from the gas phase through the 1D-boundary of the 2D monolayer adsorbate. As the adsorbed phase grows beyond the monolayer, the structure of the thick adsorbed film was shown to lie between the crystalline structure and the dense supercooled liquid, as reflected in partial wetting, defined as finite loading of the adsorbed film at the bulk sublimation pressure.