Sorption and diffusion measurements in ternary polymer–solvent–solvent systems by means of a magnetic suspension balance—Experimental methods and correlations with a modified Flory–Huggins and free-volume theory

Diffusion and sorption data of methanol and toluene in the ternary system methanol–toluene–poly(vinylacetate) (pvac) were measured by means of a magnetic suspension balance (MSB). Ternary diffusion coefficients were determined from sorption kinetics with a method of Crank [1975. The Mathematics of Diffusion, second ed. Claredon Press, Oxford] classically used for binary polymer solvent systems. Assumptions and limitations for this method are discussed. Sorption data of methanol and toluene in the ternary system were correlated with a modified Flory–Huggins theory taking four instead of three interaction parameters into account and compared with predictions of UNIFAC-FV. All four binary Flory–Huggins interaction parameters were correlated as a function of concentration, determined from binary polymer–solvent sorption measurements and from solvent–solvent equilibrium data. The modified Flory–Huggins approach for ternary systems predicts the two limiting cases for the binary polymer–solvent as well the two solvent–solvent equilibria. Diffusion coefficients determined from sorption kinetics measurements were correlated with free-volume theory predictions of Vrentas et al. [1984. Self diffusion in polymer–solvent–solvent systems. Journal of Polymer Science, Polymer Physics Edition, 22, 459–469] and compared with a few available literature data from Surana et al. [1998. Diffusion and equilibrium measurements in ternary polymer–solvent–solvent systems using inverse gas chromatography. Industrial and Engineering Chemistry Research, 37, 3203–3207]. Cross diffusion terms are not taken into account. Diffusion and sorption data, determined with this gravimetric method, were used in model simulations with modified Flory–Huggins and free-volume theory to predict drying curves of ternary methanol–toluene–pvac solutions. The results were compared with previously published experimental results performed by means of Inverse-Micro-Raman-Spectroscopy (IMRS) from Schabel [2004. Trocknung von Polymerfilmen - Messung von Konzentrationsprofilen mit der Inversen-Mikro-Raman-Spektroskopie. Ph.D. Thesis, Universität Karlsruhe (TH), Germany].