Droplet jump-off force on a superhydrophobic surface

Droplet impact onto solid substrates is not only an interesting natural phenomenon, but also has applications in various fields. Recent studies in the literature reported that following the first peak of the force exerted on a superhydrophobic substrate by the droplet at the moment of impact, the droplet retraction and jump-off led to the emergence of a second peak of this force, which scales with the inertia-dominated impact force. In this paper, we have found this result to fail in the case of droplets with a broadly varying viscosity. New scaling models based on the observation of flow focusing are proposed to express the relevant timescale and the magnitude of the second force peak.