Pressure effects on the dynamics of ions and solvent molecules in liquid methanol under ambient and cold conditions: Importance of solvent's H-bonding network

Abstract

The effects of pressure on the dynamics of ions in liquid methanol at 258 and 298K are investigated by classical molecular dynamics simulations. It is found that the self-diffusion coefficient of ions in methanol decreases with pressure at both temperatures. The similar fashion of the translational and rotational dynamics of solvent molecules is also observed with application of pressure. Unlike aqueous solution, no such pressure dependence anomaly is observed when an ion (Na+/Cl−) is dissolved in methanol. To explore the observed behavior, we have calculated the hydrogen bond properties of liquid methanol, and it is found that methanol is more like chain-structure with a maximum number of two hydrogen bonds. The hydrogen-bond lifetime and structural–relaxation time of methanol are increasing monotonically with application of pressure and the results are more prominent at low temperatures, whereas in case of water, an opposite trend of the hydrogen bond dynamics is observed under similar conditions.