Colloidal drops under extreme stress

We investigate the non-Newtonian behavior of dense colloidal suspensions by impacting a millimetric size droplet onto a solid surface. This method provides a unique platform to gain insight into suspension flow at high stresses and velocity gradients, a regime that is non-trivial to access using conventional rheometric techniques. Here, we present a comprehensive study of colloidal drop impact. We measure the maximal spread of the impacting colloidal drop while varying impact velocity and particle volume fraction. We find that the extent of spreading decreases with increasing volume fraction or decreasing impact velocity. Moreover, there exists a critical volume fraction below which the colloidal drop spreads radially into a flattened disc as commonly observed for Newtonian fluids. Above this critical volume fraction, no inertial spreading is observed, suggesting the onset of a jamming transition inside the colloidal drop. Furthermore, we observe a variety of elastic behaviors which manifest above the critical volume fraction and are controlled by impact velocity.