Making a splash with water repellency

Abstract

A splash is usually heard when a solid body enters water at large velocity. This phenomenon originates from the formation of an air cavity during the impact. The classical view of impacts on free surfaces relies solely on fluid inertia; therefore, surface properties and viscous effects should be negligible at sufficiently large velocities. In strong contrast to this large-scale hydrodynamic viewpoint, we demonstrate here that the wettability of the impacting body is a key factor in determining the degree of splashing. This unforeseen fact is further embodied in the dependence of the threshold velocity for air entrainment on the contact angle of the impacting body, as well as on the ratio between surface tension and fluid viscosity, thereby defining a critical capillary velocity. As a paradigm, superhydrophobic impactors make a big splash for any impact velocity. ©2007 Nature Publishing Group.