(396a) Multi-Component Diffusion in Polymer-Solvent Systems

Four independent diffusion coefficients are required to describe diffusion in a ternary system. In the conventional extension of the Fickian constitutive equation to ternary systems, the diffusive flux of a species depends not only on the concentration gradient of itself but also the concentration gradient of a second component. However, conventional wisdom is that for most systems the cross or coupling diffusion coefficient is negligible compared to the main term. Consequently, diffusion in most ternary systems is approximated by the use of effective binary diffusion coefficients.

This study will show that for some ternary systems involving a polymer and two solvents, the cross terms in the diffusive flux relationship can play a dominant role. It will be shown that in order to theoretically predict the experimental observation of bubble formation during the drying of polymer solutions that the coupling terms must be included in the analysis. Consequently, the ternary systems involving two solvents and a polymer may be unique in that the cross terms are not only important but can play a dominant role.