Salvinia-Effect-Inspired “Sticky” Superhydrophobic Surfaces by Meniscus-Confined Electrodeposition

Inspired
by the Salvinia effect, we report the fabrication and
characterization of a novel “sticky” superhydrophobic
surface sustaining a Cassie–Baxter wetting state for water
droplets with high contact angles but strong solid–liquid retention.
Unlike superhydrophobic surfaces mimicking the lotus or petal effect,
whose hydrophobicity and droplet retention are typically regulated
by hierarchical micro- and nanostructures made of a homogeneous material
with the same surface energy, our superhydrophobic surface merely
requires singular microstructures covered with a hydrophobic coating
but creatively coupled with hydrophilic tips with different surface
energy. Hydrophilic tips are selectively formed by meniscus-confined
electrodeposition of a metal (e.g., nickel) layer on top of hydrophobic
microstructures. During the electrodeposition process, the superhydrophobic
surface retains its plastron so that the electrolyte cannot penetrate
into the cavity of hydrophobic microstructures, consequently making
the electrochemical reaction between solid and electrolyte occur only
on the tip. In contrast to typical superhydrophobic surfaces where
droplets are highly mobile, the “sticky” superhydrophobic
surface allows a water droplet to have strong local pinning and solid–liquid
retention on the hydrophilic tips, which is of great significance
in many droplet behaviors such as evaporation.