Study on volume phase transition of gels induced by helix-coil transition

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We investigated time-evolution of shear moduli in the physical gelation process of 1,3:2,4-bis-0-(p-metylbenzylidene)-D-sorbitol (PDTS) in polystyrene melt system containing 2.5 wt% of PDTS. At the gel point, storage and loss shear moduli, G' and G'', were described by the power law of frequency ω, G'〜G''-ω^n, with the critical exponent n equal to 2/3, in agreement with the value predicted by the percolation theory. The exponent n and the gel strength S at the gel point measured as a function of quench depth ΔT indicated that the fractal network structure of PDTS does not change with ΔT but that the mechanical strength of the network increases with ΔT. Before reaching the gel point, G'(ω) and G''(ω) obtained at various times can be well superposed onto the master curves, indicating that the mechanical as well as structural self-similarity hold in this gelating process.