Non-wetting drop dynamics

Abstract

The impact of droplets on solids or weakly-deformable surfaces can lead to non-wetting outcomes, depending on the control parameters. Here, we perform experiments and develop a simple model to understand the impact dynamics by varying three important drop parameters: the Ohnesorge number $\mathcal{O}h$, the Bond number $\mathcal{B}o$ and the Weber number $\mathcal{W}e$. The model suggests that the droplet dynamics is captured by only two non-dimensional groups, namely $\ \mathcal{O}h$ and $\xi = \mathcal{B}o/\sqrt{\mathcal{W}e}$. For $\xi \ll 1$, the droplet dynamics is fully dominated by $\mathcal{O}h$, but for $\xi \gg 1$, the dynamics depends both on $\mathcal{O}h$ and $\xi$. While the model results show some discrepancies for small $\mathcal{O}h$, they are in very good agreement with the experiments for moderately large $\mathcal{O}h$. The work thereby offers an elaborate description of the droplet impact dynamics in a non-wetting scenario.