A mixture of two self- and mutually-associating liquids. I. Phase behavior, second virial coefficients, and entropy-enthalpy compensation in the free energy of mixing

Published

August 14, 2017

Author(s)

Jack F. Douglas, Jacek Dudowicz, Karl Freed

Abstract

The theoretical description of the phase behavior of polymers dissolved in binary mixtures of water and other miscible solvents is greatly complicated by the self- and mutual-association of the solvent molecules. As a first step in treating these complex and widely encoun- tered solutions, we have developed an extension of Flory-Huggins (FH) theory to describe mixtures of two self- and mutually-associating fluids comprised of small molecules. Ana- lytic expressions are derived for basic thermodynamic properties of fluid mixtures, including the spinodal phase boundaries, the second osmotic virial coefficients, and the enthalpy and entropy of mixing of associating solvents. Many of these mixtures are found to characteris- tically exhibit closed loop phase boundaries and entropy-enthalpy compensation in the free energy parameters governing the thermodynamics of fluid mixing in the low temperature regime where the liquid components are found to be miscible. As discussed by Widom et al.,1 these basic trends in the thermodynamic properties serve to define the “hydrophobic effect”, and are quite distinct from trends observed in non-associating solvents. To better understand the phase behavior of binary mixtures of associating solvents, we calculate the second osmotic virial coefficients since these properties serve to quantify the solubility of simple non-associating fluids and some associating mixtures studied by us previously. We discuss why no correlation exists between the phase behavior and the second osmotic virial coefficients of a mixture of two self- and mutually-associating liquids. 2

Citation

Journal of Chemical Physics

Pub Type

Journals

Keywords

mixture of associating fluids, hydrophobic effect, entropy-enthalpy compensation, aqueous solutions

Citation

Douglas, J. , Dudowicz, J. and Freed, K. (2017), A mixture of two self- and mutually-associating liquids. I. Phase behavior, second virial coefficients, and entropy-enthalpy compensation in the free energy of mixing, Journal of Chemical Physics (Accessed May 19, 2024)