Difference in aqueous solution structure at 293.2 and 473.2 K between ethanol and ethylene glycol via molecular dynamics

Abstract

Our recent experimental study found that ethylene glycol–water mixture at 473.2 K and 10 MPa has a positive excess molar volume in water-rich region in contrast to the negative one at 293.2 K and 0.1 MPa and that in ethanol–water mixture [1]. The present study performed molecular dynamics simulation to clarify the difference in the solution structure between the two aqueous mixtures at the two temperatures. Radial distribution functions, coordination (hydration) numbers, numbers of hydrogen bonding and spatial distribution functions were calculated around the hydroxyl groups of alcohol and water molecules. In both mixtures, hydrogen bonds between alcohol and water molecules and between water molecules were shown to remain even at 473.2 K although the number of hydrogen bond decreased upon the temperature increase. In addition, at the high temperatures, it was indicated that tetrahedral-like hydrogen bonding network among water molecules was lost in ethylene glycol–water mixture whereas it remained in ethanol–water one.