Structures of thin ionomer films in solvent mixtures

We have used neutron reflectivity to measure the concentration profiles of polystyrenesulfonated acid (PSSA(x)) films with three different degrees of sulfonation (x = 3.4%, 12.8%, and 27.0%) in water, CCl4, and a mixture of t he two solvents. The data show that; except for the x = 3.4% films where CC l4 is a good solvent, the largest degree of swelling occurred in the mixed solvent. Contrast matching the water to the polymer layer enabled us to pro file the CCl4. concentration. The results showed that CCl4 and water were m ixed within the polymer film in a ratio of 1:2 and 1:4 for 12.8 mol % and 2 7.0 mol % PSSA, respectively. Self-consistent-field calculations indicated that the number of adsorbed sulfonated blocks scales linearly with the degr ee of sulfonation. Using the interaction parameters between the PS and SA b locks obtained by fitting to the data in pure solvents, excellent agreement is obtained for the profiles of the polymer and the solvent mixtures for a ll values of x.