Determination of correlation lengths in swollen polymer networks by small-angle neutron-scattering

The analogy between semidilute polymer solutions and swollen polymer networks is reviewed and some implications of current theories are considered. Small-angle neutron scattering has been used to measure a characteristic correlation length in randomly cross-linked polystyrene gels at swelling equilibrium in cyclohexane over the range 308-333 K and in toluene at ambient temperature. The equilibrium polymer volume fraction ranged from ca. 0.01 to 0.3, depending on the cross-link density and the solvent used. These results, together with those from earlier quasi-elastic light scattering measurements, were compared with reported scaling laws for polymer solutions. Although similar behavior was noted, the presence of permanent cross-links restricts the region wherein strong excluded volume effects are evident.