Time evolution of dynamic shear moduli in a physical gelation process of 1,3:2,4-bis-O-(<i>p</i>-methylbenzylidene)-D-sorbitol in polystyrene melt: Critical exponent and gel strength

Abstract

We investigated time evolution of shear moduli in the physical gelation process of 1,3:2,4-bis-O-(p-methylbenzylidene)-D-sorbitol (PDTS) in the 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 omega, G' approximately G" approximately omega(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 DeltaT indicated that the fractal network structure of PDTS does not change with DeltaT but that the mechanical strength of the network increases with DeltaT. Before reaching the gel point, G'(omega) and G"(omega) 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 gelation process.