Structure and Charge Distribution in Poly(styrenesulfonate) Ion Exchange Resins

Poly(styrenesulfonate) ion exchange resins were investigated with small angle neutron scattering. The polymer, polymer counterion, and counterion partial structure functions and charge structure function were obtained with contrast matching in water. In the reciprocal space interval q < 1 nm -1, all partial structure functions display an upturn. This is attributed to different swelling of regions with differences in cross-link concentration, resulting in similar long range static heterogeneity in polymer and small ion density. The charge structure function was found to satisfy the sum rules and demonstrates the strong suppression of large scale temporal fluctuations. At larger wave vectors, the structure functions reflect the distribution of counterions with respect to the polymer charges. An effective charge screening length is obtained, and its value agrees with a strong association of the ionic species.