MICRORHEOLOGY OF LOW-CONCENTRATION COLLOIDAL GELS - STRATIFICATION INOSCILLATING SHEAR

The previous [1, 2] hypothesis concerning the coexistence of ''solid-l ike'' and ''fluid-like'' layers in flowing colloidal gels which arise due to the condition of the minimum rate of energy dissipation was con firmed by the data on the viscoelastic response of low-concentration g els. The theoretical model proposed in this article based on this hypo thesis explained the strong dependence of the storage modulus G' and l oss modulus G'' of the gels on the oscillating shear amplitude in a ce rtain amplitude region, observed in a number of studies [3-8]. In addi tion, the model predicted a version with an uneven decrease in modulus G' and a maximum in the time sweep of modulus G'' at the beginning of the region of the strong dependence of both moduli on the amplitude. The predicted version was detected experimentally in 2.5% quartz gels. This version is relatively weighty, evidence in support of the above hypothesis. The version corresponds to the abrupt appearance of the fi nal fraction of fluid-like layers in the gel sample and carries inform ation on the mechanism and kinetics of stratification. The predictions of the theoretical model and the experimental data were quantitativel y compared.