Viscoelasticity of coagulated alumina suspensions

The solid-to-liquid transition of a model coagulated alumina suspension at concentrations above the gel point was investigated to explore the critical parameter for describing network failure under shear forces. Static (creep and creep-recovery) and dynamic (small and large amplitude oscillatory) shear experiments were combined to examine shear softening in these systems and time-based dependence in the yielding dynamics. The particulate network structure exhibits failure and viscous dissipation under creep and oscillatory shear tests at stress values well below the conventionally defined yield stress. Results from strain recovery tests highlight a time-dependence for failure, where only partial recovery of strain energy was possible once a specific duration of creep was surpassed. The system was observed to fail at a common strain value across all methods of rheology testing. These results are self-consistent, showing a clear transition from the linear to non-linear viscoelastic region for a coagulated material under shear stress. It provides the starting point to incorporate mechanical viscoelastic models to extract time constants for yielding behaviour. This work also presents one of the first reported LAOS and creep results for particulate suspensions using a vane geometry.