Mapping out the force network in shear thickening colloidal suspensions

When dense colloidal suspensions are sheared, the viscosity can increase by over an order of magnitude as illustrated by the many videos of people running on cornstarch-water mixtures. While there are many studies on both the macroscopic changes in the viscosity and the microscopic suspension properties that cause these bulk changes, little is known about the mesoscale – how the forces in these systems are transmitted and the force network that is set up in these suspensions. Here, we present a novel shear protocol that allows us to gain insight into the three dimensional force network in these shear thickening suspensions. We find a highly anisotropic stress distribution that depends on the applied shear rate, and the volume fraction. We compare the results of these experiments to those from a recently proposed tensorial model for shear thickening. These results are key to further understanding and tuning the behavior of shear thickening suspensions. Moreover, this protocol can be generalized to probe the different stress components in a variety of other systems.