Hydrophobic Hydration and Anomalous Excess Partial Molar Volume of tert-Butyl Alcohol–Water Mixture Studied by Quasielastic Neutron Scattering

Abstract

Quasielastic neutron scattering has been used to investigate the hydration of alcohol clusters in tert-butyl alcohol–water mixture. The measurements were made in a range of alcohol concentration, x_TBA, from 0.0 to 0.17 in mole fraction at 25 °C. Fraction, α, of water molecules hydrated to fractal-surface of alcohol clusters in tert-butyl alcohol–water mixture was obtained as a function of alcohol concentration. Average hydration number N_ws of tert-butyl alcohol molecule was derived from the value of α as a function of alcohol concentration. The value of N_ws for an isolated alcohol molecule in water was 19–21. The anomalous excess partial molar volume of tert-butyl alcohol–water mixture was interpreted successfully by applying the same model with the same values of volume parameter as used for 1-propanol–water mixture, δ₁ (=−0.36 cm³·mol⁻¹) and δ₂ (=0.60 cm³·mol⁻¹).