Rheological study on thermal-induced gelation behavior of polyacrylonitrile solution

Thermal-induced gelation process of different polyacrylonitrile (PAN) solutions was investigated through dynamic rheological measurements. The rheological material parameters characterizing the gelation behavior of the PAN solutions were measured and the effects of such factors as water content, solvent type and concentration on the gelation process were analyzed. It is found that the gel point T _gel of PAN/DMSO (dimethyl sulfoxide)–water solution increases with increased water content in the solution. Also, T _gel becomes higher when the solvent has a lower solvency for PAN. A linear relationship between logG′ and logω, logG″ and logω indicates the beginning of gelation. The PAN concentration of the solution affects T _gel in a way similar to that of the water content. The relaxation exponent n is found to relate to the fractal dimension of the polymer gel. For PAN/DMSO–water solution, this exponent n remains almost constant when the water content differs. The solvent type and concentration respectively influences n value in their own way. The PAN/DMSO–water solution systems in our work exhibit similar characteristics of gel structure, concluded from the n and d _f values of these systems. A logarithmic plot between G′ and G″ can be used to evaluate the structural evolution of the solution, and a comparatively steep slope of the curve is an indication of gelation.