Large-angle X-ray scattering investigation of the structure of 2-propanol-water mixtures

Abstract

The structure of 2-propanol and its aqueous mixtures has been investigated at 25 °C, using a large-angle X-ray scattering (LAXS) technique. The total radial distribution function of neat 2-propanol has shown that hydrogen-bonded chains of 2-propanol molecules are formed. In the 2-propanol-water mixtures, 2-propanol chains predominate at mole fractions x2pr > > ∼0.1. When x2pr decreases from x2pr = 1, the number of hydrogen bonds reaches a plateau of 3.4 ± 0.1 at x2pr ≤ ≤ ∼0.1, suggesting that the tetrahedral-like structure of water is mainly formed. On the basis of the present findings, together with previous results on methanol-water and ethanol-water mixtures, effects of hydrophobic groups on the structure of the alcohol-water mixtures are discussed. The heat of mixing at 25 °C as a function of x2pr has been interpreted in terms of the structural transition of solvent clusters.