Molecular dynamics simulation of structural, mobility effects between dilute aqueous CH3CN solution and crosslinked PAA Part 2. Dynamics

Abstract

Using molecular simulations we have investigated the diversity of the mobility of water molecules in a three-component system of crosslinked PAA/water/acetonitrile affected by local structural inhomogeneities. We examine quantitative analysis concepts for the extraction of local structure and dynamics properties in anisotropic fluids from molecular dynamics simulations. By calculation of local translational and reorientational correlation functions on trajectories of individual molecules in equivalent local environments, it is possible to extract local reorientational and translational diffusion quantities. In our simulated liquid mixtures, we classify the environments of different centres like crosslinkers, side chains, pores and water regions in the complex structure. We get insight into the local molecular dynamics of water molecules from the calculation of local reorientational relaxation times and diffusion coefficients from the slope of the mean square displacements of the water molecules in the specific local environments. In addition, we calculate a distance dependent curve for the reorientational mobility of the water molecules on the PAA/water interface. Finally, we extract dynamical information by linking the ensemble-averaged diffusion data from the simulations to stimulated spin-echo experiments with pulsed magnetic field gradients to study time dependent local self-diffusion processes of the water solution in swollen crosslinked polyacrylamide gels.