The rotational and vibrational behavior of cycloalkanes, e.g. pseudorotation in cyclopentane and the interconversion of the two chair conformations of cyclohexane, have been topics of fundamental interest for several decades. Investigation of the effect of surface symmetry on the physical adsorption properties of thin films of these cyclic molecules is the focus of this study. Understanding how the molecular structure/configuration and dynamics within these films and the effect on the wetting properties has been studied using thermodynamic and molecular modeling methods. High-resolution volumetric adsorption isotherms of cyclopentane and cyclohexane on MgO (100), graphite and hBN basal planes have been recorded over a broad range of temperature (195K-263K). These isotherms were used to determine the adsorption thermodynamic properties (i.e. heats of adsorption, isosteric heats, differential enthalpy and entropy) and to identify regions where phase transitions might occur. Molecular dynamics simulations of mono- and multilayers of cycloalkanes (C3- to C6-) on these surfaces have been used to obtain binding energies, molecular trajectories, pair-correlation functions and Z-distribution of molecules perpendicular to the adsorbing surface plane. These experimental results serve as the prelude to elastic and inelastic neutron scattering experiments. Preliminary investigation of the microscopic film dynamics using neutron spin echo experiments has been performed on sub-monolayer of cyclohexane adsorbed on MgO and graphite. Future neutron diffraction and inelastic neutron scattering studies will be used to investigate the microscopic structure and molecular vibrations in the adsorbed layers. Comparison of the scattering results with the thermodynamic and modeling studies will be presented.

Adsorption of cycloalkanes on MgO (100), graphite and hexagonal boron nitride: A thermodynamic, modeling and neutron scattering study

256th National Meeting (2018)

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