RHEOLOGY OF THIXOTROPIC DISPERSIONS. TRANSIENT PHENOMENA WITH INCREASING SHEAR RATE

A structural rheological model is used to describe the thixotropic dispersed system of silicon dioxide in oil. The model includes a kinetic equation of the processes of formation and destruction of particle aggregates and a rheological equation containing a structural parameter (the number of aggregated particles in a unit volume). The case of an equilibrium plastic flow, which corresponds to experimental flow curves, is considered. The coefficients of the rheological equation are calculated. For a stepwise increase in the shear rate from γ1 to γ2 , the transient process is considered as a transition from one equilibrium state of the flow to another equilibrium state through a certain nonequilibrium state of the flow. The coefficient of deviation from equilibrium is introduced, and its dependence ζ(t) is calculated using exponential functions; the limiting value ζ0 is determined. The transient dependences τ1/2(t) are approximated.