Rheological manifestation of microstructural change of colloidal gel under oscillatory shear flow

The rheological manifestation of intra-cycle microstructural change of a model colloidal gel under oscillatory shearing is studied with Brownian dynamics simulation and a fully quantitative sequence of physical process (SPP) technique. The microstructural change of the model colloidal gels is identified with the rigidity concept and correlated with the rheological behavior quantified via the SPP metrics. The model colloidal gel exhibits complex nonlinear stress response in the large amplitude oscillatory shearing (LAOS), which is divided into four physical processes: viscoplastic flow, recovery network structure, early stage yielding with rupture of a few bonds, and late stage yielding accompanying catastrophic structure failure. For each process, the SPP metrics that represent rheological transitions are successfully paired to microstructural changes that are discussed in terms of rigid to soft chain structure change or vice versa. Based on our findings, we further discuss the intra-cycle rheological transition at various oscillatory shearing conditions. We show that larger deformations do not necessarily lead to a broader range of intra-cycle rheological transitions and also that the rigid chain structure affects elasticity differently in floppy and stiff networks. Our study shows that the SPP analysis is a promising tool for microstructure-rheology consistent interpretations of nonlinear rheological behavior.