SMALL-ANGLE NEUTRON-SCATTERING STUDY OF END-LINKED GELS

Monomer concentration fluctuations in end-linked gels are investigated as a function of the swelling ratio with the help of small angle neutron scattering. The signals scattered by the gels are compared to those of semidilute solutions of linear chains of the same concentration. It is shown that the gels scatter a signal at small angles much stronger than the equivalent solutions. Such a scattering excess is attributed to the presence of two types of heterogeneities in the gel. Two different types of behavior are observed: at intermediate values of the scattering vector, q, the spectra exhibit a ''shoulder'' suggesting that ''starlike'' objects are present in the gel while at very small angles, the scattering intensity, I(q), increases very strongly with q. In a log representation, the scattering intensity is roughly described by approximately phiq-3. This scattering law at small values of q is interpreted in terms of a distribution of starlike objects in space.