EFFECTS OF SALT CONCENTRATION AND DEGREE OF IONIZATION ON THE HYDROPHOBIC COUNTERION BINDING TO IONIC GEL AND THE CONTRACTION OF THE GEL VOLUME

Effects of the salt concentration and the degree of ionization on the behavior of dodecylpyridinium ion binding to polyacrylic acid gel and the volume contraction due to the binding were examined. It was found that the binding was highly cooperative and that the salt concentratio n dependence of the binding behavior was very similar to that of the p olyelectrolyte in solutions. The volume contraction was proportional t o the degree of binding and the proportionality constants increased li nearly with the volume in the binding-free state. The result suggests that the gel is composed of two distinct regions; one consisting of th e expanding chains and the other consisting of the collapsed chains. T he gel contracts as the fraction of the latter region is increased.