Scaling analysis of mechanical and swelling properties of random polystyrene networks

The equilibrium swelling and shear moduli at swelling equilibrium of randomly cross-linked polystyrene gels have been determined in the excluded-volume limit (good solvent conditions), at the e temperature, and in intermediate regimes (below and above the 8 temperature). The results have been compared with data obtained by small-angle neutron scattering and quasi-elastic light-scattering measurements on the same gels and discussed by using current analogies between gels and semidilute solutions. An attempt has been made to correlate both macroscopic and molecular behavior in terms of a fundamental thermodynamic correlation length t,, the range of the monomer-monomer pair correlation function. Power law behavior for moduli and diffusion coefficients similar to that which has been reported for semidilute solutions was found in some cases, but departures from simple scaling behavior were also evident. Some of these discrepancies have tentatively been attributed to an increasingly loose structure in the gels as the cross-linking density decreases.