A Molecular Dynamics Simulation Study of the Hydrogen Bond Networks in Water-Glycerol Mixtures

Abstract

Molecular Dynamics simulations are performed over a wide range of water-glycerol concentrations to observe the intermolecular hydrogen bond (H-bond) populations at each concentration. The measured values from simulations are justified from both a probabilistic model of H-bonding and from observing the dynamic behavior of each type of H-bond. The populations of H-bonds that exist at a given concentration of glycerol are largely governed by the probability of one oxygen atom randomly associating with another oxygen atom. However, the H-bonds that glycerol oxygen can form are dependent on the H-bonds that are formed by the other intramolecular glycerol oxygen. Based on the dynamic analysis of each type of H-bond, there are deviations from randomly associating with another oxygen. Water oxygen have an increased likelihood to be donating a hydrogen to a glycerol oxygen than to another water oxygen. Glycerol oxygen have a near-equal likelihood for donating a hydrogen to either another glycerol oxygen or a water oxygen. This has an effect of increasing the number of H-bonds between water and glycerol molecules and decreasing H-bonds between two water molecules. A maximum contribution of H-bonds between water and glycerol occurs around 30 mol% glycerol which is a concentration where several of the mixture’s properties have an observed maxima or minima.