Role of anisotropic pinning and liquid properties during partial rebound of droplets on unidirectionally structured hydrophobic surfaces

Abstract

Droplet impact dynamics on super-hydrophobic micro-structured surfaces is vital in a multitude of processes such as spray coating, cooling, and inkjet printing etc. Majority of the research has been focused on the rebound phenomena while partial rebound is relatively underreported. Recent studies indicate that partial rebound is encountered where transition of wetting state may take place on super-hydrophobic surfaces. Herein, we report that satellite drops are formed during partial rebound of droplets even on hydrophobic surfaces with unidirectional topography created using a mask-less and stamp-less fabrication process. The simultaneous capillary driven retraction along the wrinkles and the strong contact line pinning across these anisotropic substrates leads to formation of satellite drops on hydrophobic surfaces. Excess rebound energy has been evaluated as functions of contact angle, contact angle hysteresis and the maximum spreading diameter to explain partial rebound on such surfaces with potential applications in the design of novel, functional surfaces.