Diffusion in quaternary polymer solutions : Model development and validation

Abstract Multicomponent diffusion in polymer solutions is a complex and not yet completely understood phenomenon. Available studies are so far almost exclusively limited to ternary systems containing a polymer and two solvents. In this work measurement data in form of isothermal drying curves in quaternary systems, consisting of the polymer poly(vinyl acetate) (PVAC) and the solvents dichloromethane, methanol and toluene obtained by inverse micro-Raman spectroscopy (IMRS) is presented. The measurements show that the diffusive behaviour is a function of the overall composition of the mixture, as additional solvents accelerate diffusion. Since no numerical model for such systems has been validated in literature, a framework for the simulation of mass transfer processes in quaternary systems has been developed. The shrinking of the film due to evaporation is taken into account by a transformation of the frame of reference. The concentration-dependent diffusion coefficients are calculated by an expression only requiring binary data, previously only tested in ternary systems, enabling predictions in uncharacterized multicomponent systems. Cross-term diffusion is neglected. The numerical model, validated by the measurement data, is able to predict the experimental results reliably for varying initial conditions.