Effects of rugged nanoprotrusions on the surface hydrophobicity and water adhesion of anisotropic micropatterns.

A facile laser-etching method was used for the one-step creation of various controllable dimensions of anisotropic micropatterns consisting of an alternating arrangement of microgrooves and microstripes with rugged nanoprotrusions, which after modified with fluoroalkylsilane reagent, showed perfect isotropic superhydrophobicity without apparent CA hystereses, water adhesion, and drag resistance, other than the conventional view of anisotropic surface microstructures with anisotropic surface dewetting. The detailed experiments and analyses have indicated that the introduction of the rugged nanoprotrusions on the surface of microstripes provided ideal 3D roughness, which could not only enhance the apparent contact angles close to 180 degrees by the "point" contact fashion to maximally reduce the liquid-solid contact area but, most importantly, make droplets easily roll off the surface without apparent CA hysteresis by regulating the triple-phase contact line (TCL) to become extremely discrete. These findings would be helpful in understanding the role of complex micro- and nanostructures on natural superhydrophobic biosurfaces and guiding the design of perfect artificial superhydrophobic materials for technological innovations such as the raindrop easy-cleaning, aquatic super-floating, and drag-reducing coatings.