title: Theory of competitive solvation of polymers by two solvents and entropy-enthalpy compensation in the solvation free energy upon dilution with the second solvent.
abstract: We develop a statistical mechanical lattice theory for polymer solvation by a pair of relatively low molar mass solvents that compete for binding to the polymer backbone. A theory for the equilibrium mixture of solvated polymer clusters {AiBCj} and free unassociated molecules A, B, and C is formulated in the spirit of Flory-Huggins mean-field approximation. This theoretical framework enables us to derive expressions for the boundaries for phase stability (spinodals) and other basic properties of these polymer solutions: the internal energy U, entropy S, specific heat CV, extent of solvation Φsolv, average degree of solvation 〈Nsolv〉, and second osmotic virial coefficient B2 as functions of temperature and the composition of the mixture. Our theory predicts many new phenomena, but the current paper applies the theory to describe the entropy-enthalpy compensation in the free energy of polymer solvation, a phenomenon observed for many years without theoretical explanation and with significant relevance to liquid chromatography and other polymer separation methods.
authors.affiliation: The James Franck Institute and the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Jacek
authors.initials: J
authors.lastname: Dudowicz
authors.affiliation: The James Franck Institute and the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Karl F
authors.initials: KF
authors.lastname: Freed
authors.affiliation: Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
authors.forename: Jack F
authors.initials: JF
authors.lastname: Douglas