Diffusion-Aggregation Controls Thixotropic Kinetics in Colloidal Gels

Thixotropic yield-stress fluids (TYSFs) possess properties that distinguish them from other yield-stress fluids, with their behavior influenced by both shear rate and shear history. Accurately predicting the structural evolution of TYSFs and the fundamental physics controlling this evolution remains challenging due to the strong interdependence between the structure, dynamics, and rheology. Here, we manipulate the interactions of the dispersed phase to control the kinetics of structural evolution and gain insights into the correlation between yield stress and microstructure. Specifically, we vary the ionic strength of a cellulose nanocrystal (CNC) suspension to create a model TYSF with tunable moduli and thixotropic recoveries. To investigate the yielding and aging behavior of the CNC network, we develop a novel rheological technique called serial creep divergence (SCD). SCD applies a series of creep measurements where a constant shear rate is applied to induce yielding, followed by resting periods and subsequent constant stress to measure yield time. Our research thus provides a deeper understanding of the mechanisms driving thixotropic recovery in colloidal gels, as well as the ability to control the properties of materials by modulating the interactions of the dispersed phase.