Gelation behavior of polyacrylonitrile solution in relation to aging process and gel concentration

Polyacrylonitrile (PAN) was dissolved in dimethyl sulfoxide (DMSO) to prepare PAN solutions with various concentrations, and physical gel can form in PAN solution either after a long period of aging or at a low temperature, via physical cross-linking of PAN molecules. Through rheological measurements, we investigated the viscoelastic properties of the PAN solutions both at aging process and frequency scanning (given concentration and temperature). First based on the Winter and Chambon theory, we measured the critical gel time and the corresponding loss tangent tan δ for the PAN solutions during the aging processes. Then the critical gel concentration at different temperatures was examined by tracing the dynamic rheological parameters in frequency scanning tests. Difference was found to exist between the critical n values obtained in aging processes (0.74-0.76) and frequency scanning tests (0.64-0.65). Our results also showed that the power law relationships, i.e., η0∝ɛ−γ and Ge∝ɛz, are valid within experimental error for the PAN solutions before and beyond the gel point.