Bio-Inspired Design of Bi/Tridirectionally Anisotropic Sliding Superhydrophobic Titanium Alloy Surfaces.

Zuobin Wang,Jinkai Xu,Zhongxu Lian,Zhanjiang Yu,Huadong Yu,Yonggang Hou

doi:10.3390/nano10112140

Abstract

Many biological surfaces with the multi-scale microstructure show obvious anisotropic wetting characteristics, which have many potential applications in microfluidic systems, biomedicine, and biological excitation systems. However, it is still a challenge to accurately prepare a metal microstructured surface with multidirectional anisotropy using a simple but effective method. In this paper, inspired by the microstructures of rice leaves and butterfly wings, wire electrical discharge machining was used to build dual-level (submillimeter/micrometer) periodic groove structures on the surface of titanium alloy, and then a nanometer structure was obtained after alkali-hydrothermal reaction, forming a three-level (submillimeter/micrometer/nanometer) structure. The surface shows the obvious difference of bidirectional superhydrophobic and tridirectional anisotropic sliding after modification, and the special wettability is easily adjusted by changing the spacing and angle of the inclined groove. In addition, the results indicate that the ability of water droplets to spread along parallel and perpendicular directions on the submillimeter groove structure and the different resistances generated by the inclined groove surface are the main reasons for the multi-anisotropic wettability. The research gives insights into the potential applications of metal materials with multidirectional anisotropic wetting properties.

Highlights

Many biological surfaces in nature exhibit directional wettability, which comes from the fact that nature provides a variety of submillimeter/micron/nanocomposite multi-scale microstructural surfaces, and the different arrangements and combinations of multi-scale structures directly affect the motion direction of water droplets [1,2,3,4,5]
For example, show bidirectional anisotropic sliding characteristics on rice leaves because the large-scale wavy structure and the surface with micro/nanostructure on the rice leaves forms a periodic one-dimensional arrangement, and the water droplets first slide longitudinally along with the rice leaf rather than perpendicularly. This anisotropic sliding ability makes the water droplets move along the vein and reach the root, providing more opportunities for rice to survive in arid environments [6,7,8]; the wings of a butterfly are covered with a micro-scale structure on which the single ridge nanostripes are evenly distributed
Beetles living in the desert use the combination of protrusions and depressions of the hydrophobic and hydrophilic areas on the back to capture water they need from the humid air [1,11]; this anisotropic wettability can be found on the surfaces of some other organisms, such as the spider silk [2], legs of water strider [5], pitcher plants [4], cactus spine, and other organisms [3]

Summary

Introduction

Many biological surfaces in nature exhibit directional wettability, which comes from the fact that nature provides a variety of submillimeter/micron/nanocomposite multi-scale microstructural surfaces, and the different arrangements and combinations of multi-scale structures directly affect the motion direction of water droplets [1,2,3,4,5]. This anisotropic sliding ability makes the water droplets move along the vein and reach the root, providing more opportunities for rice to survive in arid environments [6,7,8]; the wings of a butterfly are covered with a micro-scale structure on which the single ridge nanostripes are evenly distributed On these nanostripes, multi-layer lamella with different lengthens are stacked stepwise, and the nanotips extend top of the nanostripes, which are tilted slightly upward. Beetles living in the desert use the combination of protrusions and depressions of the hydrophobic and hydrophilic areas on the back to capture water they need from the humid air [1,11]; this anisotropic wettability can be found on the surfaces of some other organisms, such as the spider silk [2], legs of water strider [5], pitcher plants [4], cactus spine, and other organisms [3]

Methods

Results

Conclusion