EXPERIMENTAL STUDIES OF ELASTOMERIC AND OPTICAL-PROPERTIES, AND STRAIN-INDUCED LIQUID-CRYSTALLINE PHASE-TRANSITIONS, IN DEFORMED (HYDROXYPROPYL)CELLULOSE NETWORKS IN THE SWOLLEN STATE

Experimentally-determined stress-strain and strain-birefringence isotherms were used to characterize orientation, optical birefringence, and strain-induced liquid-crystalline phase transitions in (hydroxypropyl)cellulose networks. These networks were prepared by cross-linking the polymer in the isotropic state in dimethyl sulfoxide, with the network structure preserving the liquid-crystalline order exhibited by these semirigid chains. Measurements were carried out on the swollen networks, in both the anisotropic and the isotropic states. Discontinuities in the stress-strain and strain-birefringence isotherms were observed, suggesting a strain-induced isotropic-to-nematic phase transformation. The experimental results are in at least qulitative agreement with recent theoretical results based on a lattice model.