Comparative SANS and SAXS studies on a mesoscopically heterogeneous structure in the dehydrated NIPA/SA gel

Mesoscopic structures of a dehydrated N-isopropylacrylamide/sodium acrylate (NIPA/SA) gel and the re-moistened one are investigated with complementary use of the small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) methods. The SAXS profile of the dehydrated NIPA/SA gel shows a clear peak at q = 0.026 Å^-1 but that of the re-moistened one does not. On the other hand, only the SANS profile of the re-moistened NIPA/SA gel shows a peak at q = 0.022 Å^-1. Taking into account that SAXS is sensitive to the fluctuation of the distribution of the SA bases and SANS is sensitive to that of the water in the NIPA/SA gel, these results indicate that inhomogeneous evaporation of water in the NIPA/SA gel occurs on the dehydration and that the SA clusters are finally generated.