Quadri-directionally anisotropic droplets sliding surfaces fabricated by selective laser texturing of aluminum alloy plates

摘要

A periodic array patterned superhydrophobic surface consisted of asymmetric multi-directional stairway units was prepared by selective laser texturing of aluminum alloy plate, which was endowed for the first time with the quadri-directionally anisotropic droplets sliding characteristic. Through the layer-by-layer subtractive laser ablation procedure, the unique unequal tread depths of the micron-sized stairway-structure in four directions were ingeniously constructed. The achieved surface with an arbitrary desired sliding angle in any of the four directions constructed a transitional superhydrophobic state between Wenzel's and Cassie's states of the supported water droplets. The comprehensive mechanism of the supernatural quadri-directional anisotropy was verified to be mainly summarized into the synergy and balance between the droplet's resistance effect of gravity force and the pinning-effect controlled adhesion force. The two obstructive effects were verified to be in exact accordance with each other on the movement of water droplets. The quadri-directionally anisotropic sliding droplets characteristic induced by the simple but powerful selective laser texturing method can provide a fresh cognition of anisotropic wettability and enormous potential applications in microfluidic systems for biochemical separation.