Superhydrophobic NiTi shape memory alloy arrays with switchable controlled anisotropic droplet sliding

Abstract

Smart microstructured surfaces have attracted extensive attention in recent years, because the surface microstructure morphology can be tuned using an external field to change the wettability. Inspired by the surface microstructures of butterfly wings, a tilted array microstructure was fabricated on the surface of NiTi shape memory alloy (NiTi-SMA) using wire electrical discharge machining (WEDM). The modified surface with fluorosilane showed superhydrophobicity and anisotropic droplet sliding. As the shape of the tilted microarray structure could be repeatedly switched between the original shape and deformation under the action of force and heat, the contact angle of the surface was repeatedly switched between 155.9° ± 0.2° and 150.3° ± 0.3°, and the anisotropic sliding angle of the surface was repeatedly switched between 7.9° ± 1.6° and 22.9° ± 1.3°, and 19.6° ± 0.6° and 53.4° ± 2.9°. The range of switchable anisotropic sliding could be adjusted by changing the microstructure spacing L. In addition, the surface of the tilted microarray structure showed a directional water transport ability under the action of vibrations, and the directional transmission of water droplets could be selectively controlled by changing the morphology of the surface microstructure. Therefore, a smart surface with switchable wettability was realized on the NiTi-SMA surface, providing a new method to realize the smart control of droplets on smart microstructured surfaces.