Fabrication of anisotropically oleophobic surface with inverse-tapered structure using micromolding in capillaries and microtransfer molding

Fabrication of inverse-tapered structure remains as a problem in the fabrication of oleophobic surface mostly due to the complications and the high cost of processes. In this paper, we propose a simple and low-cost fabrication method of inverse-tapered structured oleophobic surface using micromolding in capillaries (MIMIC) and microtransfer molding followed by MEMS processes. Silicon wafer molds for the formation of inverse-tapered structure were made using MEMS processes such as photolithography and anisotropic KOH etching of silicon wafer. The geometry of structure could be changed by controlling the etching depth of the silicon wafer mold. After covering the surface of the mold using flat UV tape, the formed space between mold and UV tape was filled with pre-cured PDMS by capillary force and then cured in oven. The tapered structure on UV tape was transferred and bonded to glass wafer by O₂ plasma treatment. The fabricated inverse-tapered structure was coated with a fluoroalkylsilane monolayer to reduce its surface energy. The wetting behaviors were investigated by the contact angle (CA) measurement of hexadecane droplets. This study demonstrates that an inverse-tapered structure can be fabricated on a substrate using micromolding in capillaries and microtransfer molding, whose surface shows the superoleophobicity.