Effects of microstructure geometry and plasma modification on wetting properties of SU-8 surfaces

We describe the wetting properties of various geometric microstructures fabricated with SU-8 (negative photosensitive epoxy resin) and the effects of chemical modification by SF6 plasma irradiation. Contact angles of water droplets were measured on ten types of microstructures such as circular pillar, square pillar, cross pillar, and mesh pattern fabricated on SU-8 layers. Moreover, these patterned surfaces were chemically modified by fluorine radicals to change their wetting properties. Contours of the water droplets were also examined from not only the side view but also from the bottom view, through the reverse side of the glass substrate, to investigate the wetting properties. Results revealed that the contact angles on the SU-8 surfaces with microstructures increased after SF6 plasma irradiation because of C–F bond induction. Only in the mesh patterns, which have isolated cavities, the contact angles less increased as a result of the irradiation, in spite of the fact that the wetting state changed from the Wenzel mode to the Cassie-Baxter mode.