ADSORPTION OF CYCLOALKANES ON SURFACES WITH DIFFERENT SYMMETRY AND COMPOSITION

Adsorption of gas molecules on solid surfaces plays a major role in many physical and chemical processes involved in catalysis, surface wetting, lubrication, gas storage and separation. The homologous series of cycloalkane is an important group of compounds in petrochemical and synthetic industries. These molecules offer conformational varieties that change dramatically with the change in ring size. In this study the effect of surface and molecular symmetry on the physical adsorption properties of thin films of cycloalkanes on three different substrates were investigated. The changes in molecular configuration and dynamics within these films were studied using thermodynamic and molecular modeling methods. High-resolution volumetric adsorption isotherms of cycloalkane (C5- to C8-) on magnesium oxide (MgO) (100), graphite and hexagonal boron nitride (hBN) basal planes were recorded over a broad range of temperature (195K-263K). These isotherms were analyzed to determine the thermodynamics of adsorption (i.e. heats of adsorption, isosteric heats, differential enthalpy and entropy) and to identify regions of possible phase transitions. Molecular dynamics simulations of mono- and multilayers of cycloalkanes (C5- to C8-) on these surfaces were used to obtain binding energies, molecular trajectories, pair-correlation functions and molecular distribution perpendicular to the surface plane of the adsorbent substrate. These experimental and modeling results can serve as the prelude to elastic and inelastic neutron scattering experiments.