Molecular dynamic simulation of structural, mobility effects between dilute aqueous CH3CN solution and crosslinked PAA Part 1. Structure

The diversity of the water structure in a three-component system consisting of diluted acetonitrile (AN), water and crosslinked polyacrylamide (PAA) is caused by local structural inhomogeneities and has been investigated by molecular simulations. We extract local structure information of anisotropic fluids from molecular dynamic simulations. For comparison, reference simulations have been performed on binary mixtures of AN/water and PAA/water. In our simulated liquid mixtures, we characterize the local water structure in the vicinity of different functional groups such as the keto-, amino groups and side chains of the crosslinker and polyacrylamide as well as AN molecules in terms of the classical site–site pair correlation functions. By calculation of radial pair correlation functions on spherical spatial-sectors at the AN, it is possible to extract coordination numbers and detailed local information of anisotropic water distributions surrounding the AN molecules. By calculation of the distance angle resolved pair correlation function, we get insight into the structure of microheterogeneity of a diluted AN/water mixture and the changes in the presence of a PAA net. The calculated results for AN cluster arrangements of our diluted AN/water mixture are in line with experimental data for binary mixtures of higher AN concentration.