Structural investigation of aqueous ethylene glycol solutions at various concentrations by total neutron scattering

The concentration dependent structure of ethylene glycol/water mixtures at room temperature was investigated. Mixtures with concentrations X_EG = 1, 0.9, 0.46, 0.11 were examined by total neutron scattering. The neutron scattering data was then used to constrain molecular simulations of the studied systems to allow for in depth analysis of the systems' structures. It was found that at low ethylene glycol concentrations (X_EG = 0.11) water structure was preserved, and ethylene glycol molecules were well hydrated. At the intermediate concentrations (X_EG = 0.46) the tetrahedral ordering of water was lost and water molecules existed as interconnected string-like structures. At high concentrations (X_EG = 0.9), water molecules were completely isolated mostly existing as single molecules or dimers. This behaviour is in contrast to aqueous mixtures of mono-alcohols such as methanol, isopropanol, tert -butanol where water structure can be found to persist even at high alcohol concentrations. Evidence for intra -molecular hydrogen bonding in ethylene glycol was found at all concentrations but became much more significant in the more diluted mixtures. These structural features of the ethylene glycol/water mixtures may explain their cryoprotectant or antifreeze properties as well as other concentration dependent properties.