Pairwise frictional profile between particles determines discontinuous shear thickening transition in non-colloidal suspensions

The process by which sheared suspensions go through a dramatic change in viscosity is

known as discontinuous shear thickening. Although well-characterized on the macroscale,

the microscopic mechanisms at play in this transition are still poorly understood. Here,

by developing new experimental procedures based on quartz-tuning fork atomic force

microscopy, we measure the pairwise frictional profile between approaching pairs of polyvinyl

chloride and cornstarch particles in solvent. We report a clear transition from a low-friction

regime, where pairs of particles support a finite normal load, while interacting purely

hydrodynamically, to a high-friction regime characterized by hard repulsive contact between

the particles and sliding friction. Critically, we show that the normal stress needed to enter

the frictional regime at nanoscale matches the critical stress at which shear thickening occurs

for macroscopic suspensions. Our experiments bridge nano and macroscales and provide

long needed demonstration of the role of frictional forces in discontinuous shear thickening.

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