Surfactant Effects on the Dynamics of Capillary Rise and Finger Formation in Square Capillaries.

We investigate the influence of surfactants on capillary rise and corner flow in angular pores. We therefore study capillary rise for simple fluids and surfactant solutions, comparing square to cylindrical capillaries. We show that fingers start to form in the corners of the square capillaries when the capillary rise slows down before reaching the equilibrium height.

High-velocity impact of solid objects on Non-Newtonian Fluids.

We investigate which property of non-Newtonian fluids determines the deceleration of a high-speed impacting object. Using high-speed camera footage, we measure the velocity decrease of a high-speed spherical object impacting a typical Newtonian fluid (water) as a reference and compare it with a shear thickening fluid (cornstarch) and a shear thinning viscoelastic fluid (a weakly cross-linked polymer gel). Three models describing the kinetic energy loss of the object are considered: fluid inertia, shear thickening and viscoelasticity.