MICRORHEOLOGY OF LOW-CONCENTRATION COLLOIDAL GELS - FRACTAL MODELS

Low-concentration colloidal gels (LCG) formed as a result of aggregati on of colloidal particles have a fractal structure in a certain range of scales. The concepts concerning the fractal structure of LCG were r eviewed for using them in describing the mechanical and rheological pr operties of these gels. The viscosity and moduli of 2.5% gels of collo idal quartz particles were measured in conditions of continuous and os cillating shear. An uneven change in the viscosity by nine orders of m agnitude when the threshold stress was passed was observed in conditio ns of continuous shear. Mechanisms of flow were proposed based on the concepts concerning the fractal structure of gels and theoretical esti mations of the viscosity and stress relaxation time in states of flow before and after the threshold were made.