CONCENTRATION POLYDISPERSITY IN POLYMER GELS

For swollen polymer networks there is no generally accepted relation b etween the macroscopic osmotic properties and the scattering behaviour . Detailed information on the relationship between these properties ca n, however, be deduced from complementary measurements of osmotic and elastic behaviour, small angle neutron and X-ray scattering (SANS and SAXS) and quasi-elastic light scattering. We describe such an investig ation in two types of networks, differing in the mechanism of cross-li nking. The SANS spectra yield information on the structure, which is g enerated both by the dynamics of the system and by long range static c onstraints. The former, arising from thermodynamic concentration fluct uations, governs the macroscopic osmotic and elastic moduli of the swo llen network. The static superstructure in the gel reflects local vari ations in the cross-link density. The resulting concentration polydisp ersity, <delta phi(2)>/phi(2), is determined by the details of the cro ss-linking procedure. Its concentration dependence as a function of ge l swelling can be expressed in terms of the same macroscopic osmotic a nd elastic variables as those that govern the thermodynamic properties of the gel.