Thermodynamic characterization of ternary solutions of uncharged polymers

The thermodynamic interactions in aqueous solutions of uncharged polymers were studied. Using a gel-deswelling method, the water activities (chemical potentials) in binary and ternary (two polymers in one solvent) solutions of methylcellulose (MC), polyvinyl alcohol (PVA) and polyvinyl pirrolidone (PVP), respectively were determined at various polymer volume fractions (1.0 × 10−2 < v2 < 1.0 × 10−1). On the theoretical basis of the Flory–Huggins approximations, the relevant solvent–segment (χ12 or χ13) and segment–segment pair interaction parameters (χ23) have been calculated. lvent activity curves (ln a1 versus polymer volume fraction) can be well described by a polynomial of third-degree in both the binary and the ternary solutions of the polymers. The solvent–segment interaction parameters exhibit a slight dependence on the polymer concentration. For each binary solution, the χ12−v2 function can be fitted by a straight line wich has a small positive slope. In the mixtures of two polymers, the values of the segment–segment (χ23) interaction parameters were close to zero or sligthly negative (χ23 ∼0 ± 0.03), indicating that under the studied conditions, the polymers in the ternary solutions are compatible.