Dynamics of Nanoconfined Acetonitrile

Abstract

The results of dynamics simulations of confined acetonitrile are presented. Confinement is achieved by filling previously formed silica pores having hydroxyl-terminated head groups with liquid acetonitrile. These pores are of the same nominal radius--1.2 nm--and have approximately the same surface coverage of hydroxyl groups, forming a hydrophilic surface. The three-site acetonitrile molecule with parameters previously tested was used for classical molecular dynamics simulations. The main components of interest in the simulations are the diffusion coefficients and reorientational correlation times, two dynamical constants of a given system, and the causes of the magnitudes and variability of each is explored. The acetonitrile molecules are first tested in the bulk system and are shown to yield reasonable results and then are confined in order to extract more information regarding dynamical changes when confinement occurs. Drastic changes are seen when the solvent is confined. The mean squared displacement is used to find the diffusion coefficient both for the whole system and for molecules separated according to where they sit relative to the pore wall or the z-axis. Both of these analyses were performed for calculating the reorientation time by using the reorientational autocorrelation function and then fitting those curves to multi-exponential and stretched exponential functions.