Rheological behavior during thermotropic gelation of polyacrylonitrile concentrated solutions

Dynamic viscoelastic properties of polyacrylonitrile(PAN)/DMSO/H2O solutions with different H2O contents were studied as a function of temperature. These PAN solutions gradually became gel with decreasing temperature. The sol-gel transition took place at a critical gel temperature, at which the scaling law of G′(ω)∼G″(ω)∝ωn held, allowing an accurate determination of the critical gel temperature by means of the frequency independence of the loss tangent. The gel point of PAN solutions increases with increasing H2O content. The scaling exponent n (=0.86) at the gel point is confirmed to be universal for PAN gels, which is independent of temperature, suggesting the similarity of the fractal structure in the critical PAN gels.