DYNAMIC VISCOELASTICITY DURING A SOL-GEL REACTION

The dynamic storage and loss shear moduli, G() and G(), have been measured with the multiple lumped resonator instrument for a tetraethylorthosilicate reaction as it proceeds through the macroscopic gel point. For five frequencies from 104 to 6200 Hz, lnG() vs time shows a sharp increase during the sol portion of the reaction prior to formation of a gel. The loss tangent shows a frequency-dependent maximum prior to gelation and then falls to 1. The power-law dependence on frequency for G and G varies from 0.9 to 0.7 and 1.5 to 0.7, respectively, during the reaction. © 1990 The American Physical Society.