Shear thickening in dense suspensions with "sticky" interactions

Advances in physical and chemical control for unconventional particle-particle interactions have enabled tunable shear thickening behaviors as the particles form different degrees of flow constraints under shear. However, such constraints disappear rapidly when the applied shear is removed. Using recently developed dynamic dense suspensions where particles form shear-induced constraints via dynamic covalent bonds^1,2, we demonstrate the shear thickening of suspensions with a finite bond lifetime between hydrogen bonds and permanent covalent bonds. The dynamic suspension is stabilized, in a quiescent state, by polymer brushes that can change their conformation to bridging when sheared at the onset stress for shear thickening; hence, rheology shows that the onset stress scales with particle diameter with an exponent -1.75, comparable to that of the theoretical polymer-grafted colloidal suspension. Moreover, the first normal stress difference describes the size-dependent flow constraints where the dilation occurs at a lower volume fraction for smaller particles. This size-dependence drastically influences the mechanics of shear-thickened state, thereby decreasing the jamming volume fraction for smaller particles.