Hydrogen bond induced solvent ordering in aqueous poly (sodium p-styrenesulfonate)

Abstract

Molecular dynamics simulations were used to investigate the structure and dynamics of the diffuse interphase in aqueous poly (sodium p-styrenesulfonate) (NaPSS). The effect of temperature and the distance between Sδ+Oδ– and Oδ–Hδ+ dipoles on the ordering of explicit solvent molecules were extensively studied. With an increase in temperature, the atomic radial distribution function indicated a reduced density of water in the immediate vicinity of SO3− groups and a slight increase in density afterward. Using the dipole radial distribution function, water molecules were classified into multiple layers on the basis of the distance between Sδ+Oδ– (PSS) and Oδ–Hδ+ (H2O) dipoles. Orientation of Oδ–Hδ+ around Sδ+Oδ–, influenced by coulombic interactions, resulted in a greater number of hydrogen bonds (H-bonds) and improved H-bond correlation function between adjacent layers. The altered H-bond dynamics were found to severely restrict the solvent mobility in the layer close to SO3− groups. While the number of inter-layer H-bonds was found to be a result of water orientation, the H-bond correlation function was dependent on the mobility of water molecules. Mean square displacement and autocorrelation of dipole radial distances were calculated to distinguish between inter- and intra-layer solvent mobility. Our results provide molecular-level insights into the structure and dynamics of solvent water molecules in the diffuse interphase with a polyelectrolyte.