Effect of the hydrophobic alcohol chain length on the hydrogen-bond network of water.

The microscopic structure of the hydrogen-bond network of water-alcohol mixtures was studied using X-ray Raman scattering (XRS). To systematically examine how the hydrogen-bond network of water is affected by an increasing size of the hydrophobic group, small linear alcohols (methanol, ethanol, and propanol) in constant mole fractions were studied. The oxygen K-edge spectra were not altered upon hydration of the alcohols beyond a simple superposition of signals from alcohol and water. The experiment thus indicates that alcohols do not have a substantial effect on the structure of the hydrogen-bond network of water. In particular, no apparent breaking or forming of the hydrogen bonds is observed to take place in the overall structure. In addition, there is no indication of changes in the tetrahedrality of the hydrogen-bond network of water in the vicinity of alcohol molecules.