Preparation temperature dependence and effects of hydrolysis on static inhomogeneities of poly(acrylamide) gels

The concentration fluctuations of poly(acrylamide) (PAAm) hydrogels prepared at different preparation temperatures, T-prep's, have been studied by dynamic light scattering (DLS). The ensemble average light scattered intensities obtained at the scattering angle of 90 degrees, [I](E), was decomposed into two contributions: one from the static inhomogeneities, [I-C](E), and the other from thermal fluctuations, I-F. Contrary to the case of poly(N-isopropylacrylamide) (PNIPAm) gel, [I](E) was a decreasing function of T-prep. This indicates that these gels have opposite T-prep dependence with respect to the static inhomogeneities. However, the liquidlike properties of these gels, such as I-F and the cooperative diffusion coefficient, D, were found to be independent of T-prep, as they should be. It was also found by DLS and swelling experiments that, unlike PNIPAm gels, PAAm gels prepared by redox polymerization were subject to hydrolysis and changed to partially charged gels.