Phase equilibria in ternary systems involving a polymer and two polar solvents

Abstract

AbstractA recent treatment of phase equilibria in nonpolar ternary systems is modified to permit application to the interesting case of a polymer and two polar liquids which may associate. The deviations from ideality exhibited by associated liquids are incorporated with the pair interaction free energy in the X parameter for the liquid pair. Hence, the expressions for the chemical potentials remain unaltered, but the X parameters for the polar liquid pair are concentration dependent; furthermore, the relation X12 = (V1/V2)X21, no longer applies. The equation deduced allows theoretical description of the phase equilibria in polar ternary systems provided sufficient information is available to characterize the binary polar liquid mixture. The predictions arising from the modified theory are tested using data obtained from phase composition analysis of the two ternary systems: nitrocellulose‐ethanol‐water and nitrocellulose‐diethylene glycol‐water. The isotherms obtained for the former system provide excellent confirmation of the theoretical predictions. Although for the second system studied the polymer‐solvent interaction parameters appear to be concentration dependent; nevertheless, application of theory yields values for the difference (lX − X) over the concentration range of interest. The (lX − X) differences deduced from the data for both ternary systems yield values for the nitrocellulose‐water interaction parameter which stand in good agreement with the value directly deduced from the sorption isotherm for that binary system, thus providing further confirmation of the theoretical treatment.