Direct observation of dynamic shear jamming in dense suspensions

Abstract

Liquid-like at rest, dense suspensions of hard particles can undergo striking transformations in behaviour when agitated or sheared1. These phenomena include solidification during rapid impact2,3, as well as strong shear thickening characterized by discontinuous, orders of magnitude increases in suspension viscosity4-8. Much of this highly non-Newtonian behaviour has recently been interpreted within the framework of a jamming transition. However, while jamming indeed induces solid-like rigidity9-11, even a strongly shear-thickened state still flows and thus cannot be fully jammed12,13. Furthermore, while suspensions are incompressible, the onset of rigidity in the standard jamming scenario requires an increase in particle density9,10,14. Finally, while shear thickening occurs in the steady state, impact-induced solidification is transient15-17. As a result, it has remained unsettled how these dense suspension phenomena are related and how they are connected to jamming. Here we resolve this by systematically exploring both the steady-state and transient regimes with the same experimental system. We demonstrate that a fully jammed, solid-like state can be reached without compression and instead purely by shear, as recently proposed for dry granular systems18,19. In contrast to dry granular materials, however, this state is created by transient shear-jamming fronts, which we track for the first time directly. We also show that shear stress, rather than shear rate, is the key control parameter. From these findings we map out a state diagram with particle density and shear stress as variables. Discontinuous shear thickening is newly identified with a marginally jammed regime just below the onset of full, solid-like jamming20. This state diagram provides a new, unifying framework, compatible with prior experimental and simulation results on dense suspensions, that connects steady-state and transient behaviour in terms of a dynamic shear-jamming process.

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ORCID for I. Peters: orcid.org/0000-0002-3549-3322

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