SWELLING AND CROSS-LINKING DENSITY EFFECTS ON THE STRUCTURE OF PARTIALLY-IONIZED GELS

We report on small angle neutron scattering experiments performed on w eakly ionized gels at various cross-link densities or swelling ratios and on the corresponding solutions. The excess of scattering intensity observed in the gels compared to the equivalent solutions is attribut ed to frozen fluctuations of concentration associated with more densel y cross-linked regions. The variation of the excess scattering intensi ty with cross-linking degree or swelling ratio supports the picture of a rather compact structure for these regions in contrast with the lar ge branched overlapping structure suggested for other gels. The presen ce of electrostatic interactions during the gelation reaction reduces noticeably the extent and the amplitude of the frozen fluctuations.