Impact of Structural Heterogeneity and Pre-shearing on the Yielding of "Pristine" Colloidal Gels*

Recent studies have introduced a number of kinetic and thermal processing strategies for manipulating the formation of colloidal gels to produce heterogeneous structures. Understanding the impact of controlled structure on gel rheology, including viscoelasticity and yielding, would impact a number of applications in food science, structural materials, and additive manufacturing. However, measuring gel rheology for many systems is made difficult by the necessity for various “pre-shear” and “shear rejuvenation” protocols employed to produce a repeatable initial state of the material for conventional rheometry measurements. This prohibits characterization of gels in their “pristine”, as-formed state, and therefore has been a roadblock in understanding the influence of controlled heterogeneity on gel. To overcome this limitation, we combine a thermoresponsive colloidal system that can be gelled in situ with advanced rheo-microscopy measurements in order to simultaneously measure gel rheology and restructuring in flow, allowing us to assess how large-scale structural heterogeneities, as well as pre-shear, influence the viscoelasticity and yielding of colloidal gels.