Insights Gained from Refined Force-Field for Pure and Aqueous Ethylene Glycol through Molecular Dynamics Simulations.

Abstract

Recent experimental and first-principles simulation studies have shown that in liquid phase of ethylene glycol (EG), an equilibrium between both more prevalent gauche conformers and less probable trans conformers of EG molecule exists. Gleaning into the complexities faced during classical molecular dynamics (MD) simulations of condensed phase EG due to its conformational richness and considering the aforesaid observations, here we propose a refined force-field for EG molecule for atomistic MD studies. By employing the refined parameters, we have thoroughly investigated the structure and dynamics of pure EG liquid and its aqueous mixtures and compared the results with the available experimental data. The proposed force-field justifies the important role played by intra- and intermolecular hydrogen bonding rendered by EG molecules. The simulated X-ray scattering structure function for pure EG liquid at 298 K is found to be in excellent agreement with experimental X-ray scattering structure function which precisely confirms the ability of the proposed force-field to mimic the structure of liquid phase EG. Additionally, the accuracy of the refined force-field for the microscopic dynamics and self-diffusion coefficient of pure as well as aqueous EG were also assessed here. Temperature dependence of hydrogen bonding interactions and their dynamics reveals that with increasing temperature the intermolecular hydrogen bonds in pure ethylene glycol becomes weaker and consequently render faster dynamics. In aqueous mixture, intermolecular hydrogen bonding interaction between EG molecules tends to decrease with decrease in ethylene glycol mole fraction due to invasion of water.