SOLUBILITY PARAMETERS ARE USED in the coatings industry to select solvents. Liquids with similar solubility parameters will be miscible, and polymers will dissolve in solvents whose solubility parameters are not too different from their own. The basic principle is like dissolves like. Solubility parameters help put numbers into this simple qualitative idea.

Solubility parameter correlations based on breakthrough times are presented. Solubility parameters have been used previously to estimate whether or not a given permeant will swell or dissolve in a given membrane. Increased solubility is predicted when the solubility parameters for the polymer and penetrant approach each other. Some experimental work is required to characterize either the permeant or the membrane if no data are already available. Since the diffusion coefficients for organic permeants in organic membranes increase exponentially with permeant concentration, there is a very strong dependence of permeation on solubility and therefore on solubility parameters. All other things being equal, penetrants with bulky structures and side groups will permeate more slowly than those with more linear and less voluminous structures. For this reason elimination of permeants with either very small or very large molecular size significantly improves most of the correlations presented, but limits their range of usefulness.

Simple molecular parameters, describing affinity and size, are shown to model permeation of Challenge 5100R and Challenge 5200R materials (fiber-reinforced fluoropolymers). Solubility parameter eodels based on permeation test data are described, and shown to be very similar for the two materials. Figures combining both solubility parameter affinities and size parameters are presented as potential predictive models for the barrier effectiveness of the materials. The size parameter and the presence of double bonds are shown to have a profound influence on permeation. The results from this model are described, and evaluated using data obtained before and after model development. The model is compared with a different empirical model developed by Arthur D. Little, Inc. (ADL). The ADL model uses a rule system to predict permeation through the fluoropolymer materials based on the structure and size of the challenge chemical. Both approaches correctly describe the permeation behavior in about 90% of the cases in the present data set.