Rheological behavior during thermotropic gelation of polyacrylonitrile concentrated solutions

Abstract

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.

Keywords

polyacrylonitrile / gel point / thermotropic gelation / rheological behavior

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