posted on 2019-01-10, 00:00authored byXiaolong Yang, Won Tae Choi, Jiyu Liu, Xin Liu
Superhydrophobic
copper surfaces patterned with non-round hydrophobic
areas were fabricated by a combination of through-mask chemical oxidation
and fluorocarbon film deposition techniques. The anisotropic sliding
resistance of droplets on typical non-round hydrophobic patterns such
as semicircle, V-shape, and line segment hydrophobic patterns was
observed. The dependence of sliding anisotropy on the pattern shape
and dimensions was investigated. Results showed that the experimental
sliding resistance was in good agreement with the calculated data
using a classical drag–resistance model (Furmidge equation).
By taking advantage of the anisotropic sliding resistance, these patterned
surfaces can be used as droplet mechanical hands to capture, transfer,
mix, and release in situ micro droplets by simply moving the surfaces
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 a large-sliding-resistance direction after
touching it, while the captured droplet can be released in situ with
nearly no mass loss by horizontally moving the surface in the low-sliding-resistance
direction. The lossless droplet manipulations using hydrophobic/superhydrophobic
patterned surfaces have advantages of being low in cost and easy to
operate and may have great promising applications to high throughput
drug screening, molecular detection, and other lab-on-chip devices.