ENERGY DISSIPATION FOR BOUNCING DROP
When a drop impacts on a dry rigid solid substrate, it can
lead to deposition, splashing or bouncing. The fate of drop
spreading depends on several factors like wetting characteristics of the surface, droplet inertia, surface tension, viscosity of the drop and the surrounding gas and ambient pressure. In this study, we investigate small scale flows where surface force is comparable to inertia force. In such a limit, the drop upon impacting a super-hydrophobic substrate undergoes a complete rebound. This is due to the surface tension force which works like an elastic spring receding the drop spreading. The drop bouncing dynamics is similar to that of an elastic ball bouncing on a rigid substrate. Due to various losses, we find that the coefficient
of restitution is less than unity. Upon carefully inspection,
we identify two main sources of energy loss - contact line friction and viscous dissipation during ballistic motion of the drop. A detailed study characterising these dissipation mechanisms is presented. The current study would lead to a better understanding of how drops behave on complex surfaces including elastic surfaces.