Reducing the contact time using macro anisotropic superhydrophobic surfaces — effect of parallel wire spacing on the drop impact

Surfaces designed to reduce the contact time of impacting droplets are potentially of great importance for fundamental science and technological applications, for example, anti-icing, self-cleaning and heating transfer applications. Previous studies have shown that the contact time can be reduced via introducing one or several crossing macroscale wires on superhydrophobic surfaces (SHSs). However, the impacts that strike far from the wires (off-center impacts) have contact times that are equal to those obtained on SHSs. Here we demonstrate that this problem can be largely solved by using macro anisotropic SHSs (macro-aniso-SHSs)—in which the wires are parallel and macroscaled. The droplet contact time depends on the spacing between the macrostripes and is remarkably reduced by 40–50% when the spacing is comparable to the droplet size. Obvious differences in the contact time are not observed for impacts that are centered on the stripe and in the groove. The impacts centered in the groove produce new hydrodynamics that are characterized by extended spreading, easy break up and bouncing in a flying-eagle configuration. The study discusses the underlying mechanisms of the impact processes. Moreover, the effect of parallel wires on the contact time is discussed by comparing the droplet impact data for grooved rice leaves and non-grooved cabbage leaves. The enhanced drop mobility associated with the macro-aniso-SHSs should be very useful in many industrial applications.