A rheological signature of frictional interactions in shear thickening suspensions
John R. Royer, Daniel L. Blair, Steven D Hudson
Understanding shear thickening presents a significant challenge in colloidal physics. As the applied shear pushes particles into close contact, the macroscopic rheology is increasingly controlled by the microscopic details of short ranged particle interactions. We elucidate the relative contributions from hydrodynamic lubrication and frictional contact forces to colloidal shear thickening by measuring both the viscosity $\eta$ and first normal stress difference $N_1$ in suspensions of silica spheres over a wide range of volume fractions. The first normal stress difference reveals a transition not apparent in the viscosity alone, from $N_1 0$ at larger values of $\phi$. While the $N_1 0$ behavior (dilation) is instead a characteristic of frictional `granular' suspensions. Fitting our viscosity profiles $\eta(\sigma, \phi)$ to a model for friction-driven shear thickening, we capture the shear thickening for $\phi \geq 0.52$ but must adjust the adjust the maximum fraction of frictional contacts to fit at lower volume fractions. Our results bring together two contrasting theories for shear thickening; they show that friction drives shear thickening in concentrated colloidal suspensions, but also highlight the need to include hydrodynamic effects to fully describe the rheology at moderate concentrations.
, Blair, D.
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A rheological signature of frictional interactions in shear thickening suspensions, Physical Review Letters, [online], https://doi.org/10.1103/PhysRevLett.116.188301
(Accessed July 3, 2022)