Computer simulation of chain molecule-inorganic interphases: Chromatographic stationary phases and rigid rod self-assembled monolayers

Molecular dynamics simulations of alkane chains chemically tethered to silica surfaces are presented. The system was modeled after the stationary phases of chromatographic columns. The interphase properties were computed as functions of chain length, surface bonding density, and temperature. At densities appropriate for chromatography, the chains undergo a gradual transition with increasing temperature from a glassy state to a liquid-like state. The simulations are consistent with extensive experimental data including neutron scattering, NMR, IR, and EPR methods. The implications for chromatographic retention are discussed. In a second series of studies, we explored driving forces for observed ordering on the solid surface in terms of the various components of the chain-chain and chain-surface forces. Interfacial z profiles are sensitive functions of each of the forces. Finally, we present preliminary Monte Carlo results on origins of tilt behavior in self assembled monolayers of rigid chain species on metal surfaces.