Making Superhydrophobic Surfaces with Microstripe Array Structure by Diffusion Bonding and Their Applications in Magnetic Control Microdroplet Release Systems

Hundreds of copper foils and iron foils with different thicknesses are alternatingly stacked and diffusion bonded, respectively. Cross-sections of the diffusion bonded bulks are investigated via scanning electron microscopy (SEM) and energy dispersive spectroscopy. Hierarchical microstripe array structures with different groove depths and widths are successfully manufactured via selective corrosion followed by oxidation of the cross-sections of the diffusion bonded bulks. The products are characterized via X-ray diffraction, SEM, and transmission electron microscopy. In addition, the as-obtained surfaces are modified with 1-dodecanethiol to afford anisotropic superhydrophobicity. The chemical composition of the as-obtained surfaces before and after modification is investigated by X-ray photoelectron spectroscopy. The contact angles (CAs) and sliding angles (SAs) are measured parallel and perpendicular to the grooves. The surface with a groove depth-to-width ratio of 0.75 and a groove-width-to-bulge-width ratio of five shows the best superhydrophobicity, on which the CAs and SAs are 162.5° and 2.0° in the direction perpendicular to the grooves and 161.1° and 0.9° in the direction parallel to the grooves, respectively. A magnetic control microdroplet release system is built using the reversible transformation of the contact states of the superparamagnetic microdroplet on the as-prepared superhydrophobic microstripe array surface.