Structure study of water in alcohol-water binary system based on Raman spectroscopy

Abstract

The structure of water and the interaction between in the binary mixture of methanol-water and isopropanol-water at various mole fractions of alcohols were investigated by Raman spectroscopy. The results show that the tetrahedral hydrogen bonding network of water molecules is expanded at 0 < X methanol < 0.4, and the coordination number of water molecules becomes lower at 0.4 < Xmethanol < 0.5, which is due to the aggregation of methanol molecules under hydrophobic hydration as the molar fraction of methanol increases, resulting in a decrease in the total area of interaction between hydrophobic groups and water molecules in solution. In turn, the hydrophilic groups of methanol molecules break the hydrogen bonds between water molecules by forming hydrogen bonds with the free water molecules around them. When Xmethanol > 0.5, the hydrogen bonding network of water molecules becomes loose and eventually exists in solution as clusters of varying sizes. Due to the difference in chain length, the number of alkyl groups in isopropanol and methanol is different, so the hydrophobic group interacts with water more strongly and has a stronger effect on “breaking up” the water clusters.