Tuning the contact time of an impacting droplet by superhydrophobic particles.

The interaction between a droplet and superhydrophobic particles has a duration that significantly deviates from the inertia-capillary timescale. Both the rapid and delayed rebounds of the droplet are observed on the superhydrophobic particles with various particle sizes and impact velocities. Typically, the former occurs with little attachment of the particles to the rebounding droplet, while the latter emerges with the signature of a liquid marble formation. We propose a simplified model to predict the contact time of the droplet on the superhydrophobic particles by considering the additional surface deformation underneath the droplet and the possible formation of a liquid marble induced by the particles. This proposed model not only supplies the upper and lower bounds of the contact time that covers all the experimentally measured data, but also provides a way to estimate the effective viscosity in the liquid-particle mixture, which collapses the maximum spreading factor of all tested impact cases to one curve.