Large-Range, Reversible Directional Spreading of Droplet on a Double-Gradient Wrinkled Surface Adjusted Under Mechanical Strain

Abstract

Dynamical regulation to unidirectional wetting has received considerable attention in recent years due to its important role in flexible electronics, microfluidics, drug transportation, and so forth. It is of great significance to prepare a surface which allows the droplet to spread directionally on it with the length of droplet reversibly fluctuated within a broad range under external stimulation. In this paper, a double-gradient wrinkled structure is prepared by constructing the structure-gradient pillar arrays on a mechanics-adjusted wrinkled surface and subsequently making chemical gradient by oxygen plasma treatment. Under the synergistic effect of the structural gradient, chemical gradient, and wrinkled structure, the droplet can undergo unidirectional spreading and realize dynamic regulation of the spreading length on the flexible structure. This will provide a propagable method for the regulation of surface wetting.