Universal yielding framework for soft particulate systems: insights from Soft Earth suspension rheology

A fundamental understanding of shear-induced yielding in soft particulate systems is crucial across various applications, from additive manufacturing of consumer products to developing hazard prediction models for environmental flows. Previous research in this field has primarily focused on connecting microstructural signatures with the macroscopic flow associated with the transition from rate-independent to rate-dependent plastic flow. Recent work from our lab (PNAS 2022, Nat Comms 2024) revealed that natural soil-based suspension systems exhibit two distinct transitions across the entire range of applied non-inertial shear rates: (a) from elastic (shear-independent) to plastic (shear-dependent) and (b) from plastic to viscous. Here, we extend this framework to encompass other soft particulate systems, including colloidal suspensions, athermal suspensions, athermal gels, emulsions, and granular matter. We demonstrate the existence of a universal yielding description for non-inertial yielding in soft particulate systems. This description establishes that: (i) particulate systems can be categorized as either frictional or non-frictional; (ii) every non-frictional particulate system possesses two critical points that are dependent on average interparticle interactions; and (iii) the rate-dependent yielding envelope is a function of the distance between these two critical points. Our findings are supported by models for the yielding of idealized amorphous solids and existing granular rheology frameworks, suggesting that the paradigm developed for understanding complex behaviors in Soft Earth suspensions can generalize the solid-fluid transition for a broad range of soft particulate systems.