Microstructure and swelling behavior of ion-exchange resin

The microstructure and swelling kinetics of ion-exchange resins having sulfonic acid groups were investigated by small-angle neutron scattering (SANS) and swelling experiments as functions of the crosslinking density (CD), pH, and the salt concentration (C-salt). The swelling kinetics was analyzed on the basis of the Tanaka-Fillmore swelling equation for the cooperative diffusion of polymer gels. The swelling behavior was very sensitive to CD, but not to pH and C-salt. The SANS intensity functions, I(q), were independent of CD and well described with a power law function, I(q) similar to q(-D), where q and D are the magnitude of the scattering vector and the mass-fractal dimension, respectively. D was estimated to be similar to 2, indicating that the resin consisted of a rather coarsely interconnected domains irrespective of CD at swelling equilibrium. It was found that CD is the most important parameter determining the swelling power of ion-exchange resin. However, no remarkable variations were found in the microstructure in the order of tens to hundreds of angstrom. (C) 1996 John Wiley & Sons, Inc.