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

研究了1，3：2，4-双-O-（对甲基苯亚甲基）-D-山梨醇（PDTS）在含2.5wt% PDTS的聚苯乙烯熔体中的物理凝胶化过程中剪切模量随时间的变化。在凝胶点，储存和损耗剪切模量G'和G“由频率ω的幂律G'<$G”-ω^n描述，临界指数n = 2/3，与逾渗理论预测的值一致。指数n和凝胶点处的凝胶强度S随淬火深度ΔT的变化表明，PDTS的分形网络结构不随淬火深度ΔT的变化而变化，但网络的机械强度随淬火深度ΔT的增加而增加。在达到凝胶点之前，在不同时间获得的G '（ω）和G“（ω）可以很好地叠加在主曲线上，表明在该凝胶化过程中具有力学和结构自相似性。

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.