Equilibrium Properties of Reversibly Flocculated Dispersions
Dispersions are considered in which the floe structure changes nearly reversibly upon shearing. The general rheological characteristics of such systems are studied, using non-aqueous suspensions of fumed,silica. The water content of the particles is altered to investigate the effect of floe strength. For stronger floes the equilibrium viscosities are shown to drop over nine orders of magnitude in a narrow stress region. Yield stress and equilibrium storage modulus are measured as a function of concentration. The dependence is best described by a power law relation, the power law being identical for modulus and yield stress. Its value depends on floe strength. The results agree qualitatively with some percolation models. However, yielding is often dominated by kinetic phenomena, contrary to the assumptions of the models. The discrepancy shows up clearly in the erronous predictions of the critical strain.
KeywordsFumed Silica Percolation Model Kinetic Phenomenon Apparent Yield Stress Particulate Network
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