Viscoelastic behavior of polyacrylonitrile/dimethyl sulfoxide concentrated solution during thermal-induced gelation

Thermal-induced gelation of polyacrylonitrile (PAN)/dimethyl sulfoxide (DMSO) concentrated solution has been rheologically investigated in relation to temperature and aging. Phase behavior of PAN/DMSO solution was studied through examining the intrinsic viscosities [eta]. The gelation temperature T(g), gel time t(g), and the critical values of relaxation exponent n were obtained by measuring the viscoelastic functions (G', G'', tan delta, and eta*) based on the Winter and Chambon theory. The solution with higher PAN concentration was found to be more sensitive to the temperature, which makes it gel at a higher temperature. The n value, however, changes little with varied concentration. The gel strength S was found to depend on the concentration of the solution. Gelation of the 23 wt % PAN/DMSO solution occurs after being aged at 25 degrees C for a period of time, i.e., gel time t(g). The critical n value (S value) at t(g) was larger (smaller) than that at T(g) in the cooling process, attributed to the different critical feature of the PAN gels formed in different conditions. The power law relations eta(0) proportional, variant epsilon(-gamma) and G(e) proportional, variant epsilon(z) were found to be valid for PAN/DMSO solution before and beyond the gel time t(g), respectively.