Structure and Dynamics of Acetonitrile Confined in a Silica Nanopore

Acetonitrile confined in silica nanopores with surfaces of varying functionality is studied by means of molecular dynamics simulation. The hydrogen-bonding interaction between the surface and the liquid is parametrized by means of first-principles molecular dynamics simulations. It is found that acetonitrile orders into bilayer like structures near the surface, in agreement with prior simulations and experiments. A newly developed method is applied to calculate relevant time correlation functions for molecules in different layers of the pore. This method takes into account the short lifetimes of the molecules in the layers. We compare this method with prior techniques that do not take this lifetime into account and discuss their pitfalls. We show that in agreement with experiment, the dynamics of the system may be described by a two population model that accounts for bulk-like relaxation in the center and frustrated dynamics near the surface of the pore. Specific hydrogen-bonding interactions are found to play a large role in engendering this behavior.