am507584j_si_002.pdf (2.07 MB)
Robust Superhydrophobic Silicon without a Low Surface-Energy Hydrophobic Coating
journal contribution
posted on 2015-01-14, 00:00 authored by Sasha Hoshian, Ville Jokinen, Villeseveri Somerkivi, Arcot
R. Lokanathan, Sami FranssilaSuperhydrophobic
surfaces without low surface-energy (hydrophobic)
modification such as silanization or (fluoro)polymer coatings are
crucial for water-repellent applications that need to survive under
harsh UV or IR exposures and mechanical abrasion. In this work, robust
low-hysteresis superhydrophobic surfaces are demonstrated using a
novel hierarchical silicon structure without a low surface-energy
coating. The proposed geometry produces superhydrophobicity out of
silicon that is naturally hydrophilic. The structure is composed of
collapsed silicon nanowires on top and bottom of T-shaped micropillars.
Collapsed silicon nanowires cause superhydrophobicity due to nanoscale
air pockets trapped below them. T-shaped micropillars significantly
decrease the water contact angle hysteresis because microscale air
pockets are trapped between them and can not easily escape. Robustness
is studied under mechanical polishing, high-energy photoexposure,
high temperature, high-pressure water shower, and different acidic
and solvent environments. Mechanical abrasion damages the nanowires
on top of micropillars, but those at the bottom survive. Small increase
of hysteresis is seen, but the surface is still superhydrophobic after
abrasion.