Ordered-to-Disordered Transformation of Enhanced Water Structure on Hydrophobic Surfaces in Concentrated Alcohol-Water Solutions.

The effects of hydrophobic solutes on the structure of the surrounding water have been a topic of debate for almost 70 years. However, a consistent description of the physical insight into the causes of the anomalous thermodynamic properties of alcohol-water mixtures is lacking. Here we report experimental results that combined temperature-dependent linear and femtosecond infrared spectroscopy measurements to explore the water structural transformation in concentrated alcohol-water solutions. Experiments show that the enhancement of water structure arises around microhydrophobic interfaces at room temperature in the solutions. As temperature increases, this ordered water structure disappears and a surface topography-dependent new disordered water structure arises at concentrated solutions of large alcohols. The water structural transformation is dependent on not only the length of the alkyl chain but also the clustering of the alcohols. A more-ordered-than-water structure can transform into a less-ordered-than-water structure.