Gelation of polyacrylonitrile in a mixed solvent: scaling and fractal analysis

Abstract

The gelation and fractal characteristics of polyacrylonitrile (PAN) in a mixed solvent of DMSO and water were investigated using rheological approaches. The results of steady-shear rheology showed that the gelation behavior of PAN solution was very sensitive to the water content in the solution. Furthermore the formed PAN gel structure recovered immediately after being disrupted, revealing that the dipole–dipole attraction may play the major role of cross-linking in the gel. Also the critical strain γ₀ was found to increase with decreasing PAN concentration, indicating that such cross-links in the PAN gels were relatively strong. Next the possible range of the fractal dimension d_f for the PAN gels, containing 2 wt% and 4 wt% water respectively, was determined through frequency scanning, using the solutions aged for different time periods according to Winter's theory. Over this determined range, Wu and Morbidelli's theory was then employed to obtain the specific d_f values, i.e., d_f = 2.185 and 2.143 for the PAN solutions with 2 wt% and 4 wt% water, respectively. These d_f values were found so close with the results obtained independently by AFM image analysis that it might suggest certain self-similarities at different hierarchical scales in the PAN gel.