Retraction dynamics of aqueous drops upon impact on non-wetting surfaces

We study the impact and subsequent retraction of liquid droplets upon high-speed impact on hydrophobic surfaces. Extensive experiments show that the drop retraction rate is a material constant and does not depend on the impact velocity. We show that on increasing the Ohnesorge number, $\Oh\,{=}\,\eta/\sqrt{\rho R_{\rm I} \gamma}$ , the retraction, i.e. dewetting, dynamics crosses from a capillary-inertial regime to a capillary-viscous regime. We rationalize the experimental observations by a simple but robust semi-quantitative model for the solid-liquid contact line dynamics inspired by the standard theories for thin-film dewetting.