Delayed yield in reversible colloidal gels: a micro-mechanical perspective

We study via dynamic simulation the nonlinear response of a reversible colloidal gel undergoing deformation under applied stress, with a view toward elucidating mechanisms of macroscopic yield at the level of particle dynamics.~Under shear, such gels may flow then regain solidlike behavior upon removal of the stress. The transition from solidlike to liquidlike behavior is a yielding process that is not instantaneous but rather occurs after a finite delay. The delay length decreases as stress increases, but the underlying microstructural origin is not clear.~Recent experiments reveal two regimes, suggesting multiple yield mechanisms.~ Theories advanced to link gel structure to rheology aim to predict the ultimate state of a gel under an applied load.~While these hypothesize a competition between bond breakage and reconnection rates, no such particle-scale dynamics have been directly observed, and it is not clear these theories reconcile with ongoing structural evolution.~To study these behaviors, we conduct large-scale dynamic simulation to model structural evolution and particle transport in colloidal gels subjected to a step stress. A range of volume fraction, attraction strength, and stress is studied, with detailed connection between macroscopic response, microstructure, and particle dynamics.