Droplet Mechanical Hand Based on Anisotropic Water Adhesion of Hydrophobic-Superhydrophobic Patterned surfaces.

Superhydrophobic copper surfaces patterned with non-round hydrophobic areas were fabricated by combining through-mask chemical oxidation and fluorocarbon film deposition technique. Anisotropic sliding resistance of droplets on typical non-round hydrophobic patterns such as semicircle, V-shaped and line segment hydrophobic patterns was observed. The dependence of sliding anisotropy on the pattern shape and dimensions was investigated. Results showed that experimental sliding resistance was in good agreement with the calculated data using classical drag-resistance model (Furmidge equation). By taking advantage of the anisotropic sliding resistance, these patterned surfaces can be used as droplet mechanical hand to capture, transfer, mix and in-situ release micro droplets by simply moving the surface in different directions. A droplet pinned on a non-round hydrophobic pattern can be captured by lifting a surface with another non-round hydrophobic pattern in large-sliding-resistance direction after touching it while the captured droplet can be in-situ released with nearly no mass loss by horizontally moving the surface in low-sliding-resistance direction. The lossless droplet manipulations using the hydrophobic/superhydrophobic patterned surfaces have advantages of low-cost and easy-to-operate, and may have great promising applications to high throughput drug screening, molecular detection and other lab-on-chip devices.