| Molecular Dynamics (MD) simulation methods were used to perform simulations of the adsorption of multilayer films of three fluoromethane compounds --- nonpolar CF4 and its polar relatives, CF3Cl and CF 3Br --- onto two chemically and structurally different substrates: graphite and hydroxylated alpha-quartz (a form of silica). The purpose of the simulations was to determine how differences in polarity and substrate type affect the structure of film layers at the adsorption surface, as well as to compare how these factors affect the mobility of molecules near the surface as they move along or away from the surface, to see how each of these factors affects the substrate affinity for the adsorbed compound. Simulations were performed for pure fluoromethane films as well as films created from binary mixtures of the above fluoromethanes adsorbed on each substrate over a range of temperatures from 80 K to 280 K. Analysis suggests a strong influence of substrate characteristics on both the structure and mobility of molecules in adsorbed layers, an effect that is partially temperature dependent but only weakly suggestive of effects due to the differences in polarity of the adsorbed molecules. |
