Role of liquid viscosity and of air entrapped on the splashing of drops impacting over superhydrophobic substrates

Abstract

We analyze the splash transition of millimetric drops of liquids of varying viscosities impacting normally over different types of superhydrophobic substrates in which the amplitude of random surface asperities is varied from hundreds of nanometers to tens of microns. Our experiments indicate that the amount of air entrapped between the substrate and the drop increases when the value of the relative roughness is increased, thus reducing friction. We are able to predict the spreading-splashing transition using a previous model once the effect of the surface asperities is taken into account in the expression of the shear stress at the wall.