Triggering flow asymmetry by lamella deflection during drop impact on superhydrophobic surfaces

TL;DR

This study demonstrates that lamella deflection during drop impact on bathtub-like superhydrophobic surfaces induces flow asymmetry, significantly reducing contact time without the need for surface curvature or elliptical impact footprint.

Contribution

It reveals a new mechanism for flow asymmetry in drop impacts, showing lamella deflection alone can break symmetry and reduce contact time on flat superhydrophobic surfaces.

Findings

Lamella deflection causes flow asymmetry during impact.

Flow asymmetry reduces contact time significantly.

Reduction occurs even without surface curvature or elliptical impact.

Abstract

Water drop impacting a superhydrophobic surface (SHS) rebounds completely with remarkable elasticity. For such an impact, the balance between the inertial and capillary forces ascertain the contact time. This is found to be fairly constant for any macroscopically flat SHS and for a given drop volume. Recently, various studies have shown that breaking the radial symmetry during the drop impact can significantly reduce the contact time below that of a flat SHS. One such study has been performed on a cylindrical SHS with a curvature comparable to the drop. The reduction in contact time has been attributed to the radially anisotropic flow imparted by the tangential component of momentum and the elliptical footprint of the drop during the crash. Here, we perform drop impact experiments on bathtub-like SHS and show that the radial anisotropy can be triggered even in the absence of both the criteria mentioned above. This is shown to be a consequence of the lamella deflection during the spreading of the drop. The reduction in contact time is quite clearly evident in this experimental regime.