Generation and Characterization of Super-Hydrophobic Micro- and Nano-structured Surfaces

Here we describe the use of a backside exposure method for the creation of high aspect ratio tapered microstructures with nano-porous sidewalls. These sidewalls result from the exposure and curing conditions of the SU8 matrix. The structures show ultra-hydrophobic behavior with water contact angles of more than 160°, without an additional coating of the SU8 polymer. By choosing appropriate exposure conditions, needlelike structures can be created with a high level of porosity, covering their entire surface. The contact angle hysteresis values of such structures lie in the range of 20°. After an additional deposition of smooth and thin metallic gold film and coating it with an alkyl thiol selfassembled monolayer (SAM), we were able to decrease this hysteresis to values of around 10°. By using thin and rough metallic films like wet chemically oxidized titanium oxide and a fluoralkylsilane SAM, the hysteresis values could be reduced to only 4°.