Drop impact of anisotropic colloidal suspensions*

Fluid drop impact has been an active field of study for more than a century, but the impact of complex fluid drops is a relatively young field. The impact of colloidal drops at high impact velocities allows us to probe suspension flow behavior at shear rates larger than existing rheometers can access. Recently, suspension drops of spherical particles have been observed to exhibit jamming at high impact velocities. In order to explore the effect of anisotropy on impact dynamics, we experimentally study the drop impact of rod-shaped colloidal suspensions. We prepare and use micron-sized silica rods of multiple aspect ratios, thus treating aspect ratio as another parameter in the state diagram of suspension behavior, in addition to impact velocity and suspension volume fraction. Our observations suggest that impacting drops of rod-shaped suspensions show thickening and jamming at lower volume fractions as compared to sphere suspensions, which is in agreement with recent rheological studies of rod-shaped particle suspensions. Furthermore, the extent of jamming and elastic behavior is more pronounced for higher impact velocities and aspect ratios.