Jammin' out and Relaxin': Impact and Relaxation Dynamics in Shear-thickening Fluids.

Drop impact and relaxation dynamics of shear-thickening fluids across variable shear rates remains an understudied problem despite many applications for these materials, such as in coatings, dampers, and impact-mitigation systems and technologies. Our work is focused on studying drop impact dynamics near the discontinuous shear-thickening transition in high volume fraction suspensions. Using experiments of both corn starch and silica sphere suspensions, we examine impact and relaxation time dynamics, and quantify how variations in shear rate modify both immediate post-impact (on the order of microseconds) and long-term relaxation (on the order of minutes) behaviors using a dual high speed camera drop impact apparatus. In these experiments, we expand upon our hypothesis that differences in stability, early time shear-thickening and jamming behavior, and relaxation are critically dependent on the size, geometry, and interactions of the suspension particles in shear-thickening fluids. These experiments advance our understanding of how suspension material properties give rise to rich dynamical differences in the rheological response of complex fluids.