Mechanism and Dynamics of Molecular Exchange at the Silica/Binary Solvent Mixtures Interface

Nonequilibrium molecular dynamics simulations of acetonitrile/methanol mixtures in contact with a hydroxylated silica surface are used to elucidate the mechanism of molecular exchange at a hydrophilic liquid/solid interface. The different hydrogen-bonding ability of the two solvents provides a driving force for the adsorption/desorption process, which is followed by examining several structural and energetic properties of the system. Two different reaction coordinates for the hydrogen bonding exchange are defined and are used to identify transition states in which the methanol attains a well-defined orientation. The reaction coordinates are used to examine the mechanism and dynamics of the exchange. We find that the exchange process involves multiple recrossing of the transition state and can progress via two different mechanisms, depending whether the methanol first acts as a hydrogen bond donor or acceptor at the silica surface.