Robust Omniphobic Surfaces
Tuteja, A., Choi, W., Mabry, J.M., Cohen, R.E. and McKinley, G.H.

Superhydrophobic surfaces display water contact angles greater than 150° in conjunction
with low contact angle hysteresis. Microscopic pockets of air trapped beneath the water
droplets placed on these surfaces lead to a composite solid-liquid-air interface in
thermodynamic equilibrium. Previous experimental and theoretical studies suggest that it
may not be possible to form similar fully-equilibrated, composite interfaces with drops of
liquids such as alkanes or alcohols that possess significantly lower surface tension than
water (\gamma_{lv} = 72.1 mN/m). In this work we develop surfaces possessing re-entrant texture
that can support strongly metastable composite solid-liquid-air interfaces even with
extremely low surface tension liquids such as pentane (
\gamma_{lv} = 15.7 mN/m). Furthermore,
we propose four design parameters that predict the measured contact angles for a liquid
droplet on a textured surface, as well as the robustness of the composite interface, based
on the properties of the solid surface and the contacting liquid. These design parameters
allow us to produce two different families of re-entrant surfaces – randomly-deposited
electrospun fiber mats and precisely fabricated micro-hoodoo surfaces – that can each
support a robust composite interface with essentially any liquid. These omniphobic
surfaces display contact angles greater than 150° and low contact angle hysteresis with
both polar and non-polar liquids possessing a wide range of surface tensions.