Compressibility of<i>tert</i>-Butyl Alcohol-Water Mixtures: The Rism Theory

Abstract

The isothermal compressibility χ T of binary mixtures of water and tert-butyl alcohol (TBA) is calculated using the reference interaction site model (RISM) integral equation theory. The calculations are performed over the whole concentration from x = 0 to 1 and a wide temperature from T = 283 to 313 K ranges employing the extended point charge model for water and optimized site–site potentials for TBA molecules. The results obtained are compared versus available experimental data. It is demonstrated that, despite an approximate character of the model potentials and closure relation applied, the theory is able to reproduce qualitatively all main features of the x- and T-dependencies of χ T inherent in real experiment. Such features include the decrease of compressibility with increasing T in the low TBA concentration limit x → 0 (pure water), and the increase of χ T with rising T in the opposite regime x → 1 (pure alcohol); the presence of a concentration region where the function χ T (x, T) does not depend much on T; as well as the existence of a minimum in χ T with respect to x at each given T. The question of how to achieve a quantitative agreement between the theoretical and experimental values by correcting the closure relation is also discussed.