Rheological properties of poly(dimethylsiloxane) filled with fumed silica: II. Stress relaxation and stress growth

The steady-state viscosity, stress relaxation, and stress growth function were measured for a 3.0% by weight dispersion of fumed silica in poly(dimethylsiloxane); using a two-step shear rate history. For short rest times the stress growth function η⁺ increased monotonically towards steady-state, while at long rest times η⁺ exhibited large overshoot followed by a monotonic decrease to steady-state. For intermediate rest times η⁺ exhibited more complicated transient behaviour. The effect of both shear rates in the two-step shear-rate history on η⁺ have been studied, and the resulting rheological behaviour is discussed in terms of phenomenological microstructural models.