Microfabrication of Re-entrant Surface with Hydrophobicity

Abstract

Re-entrant texturing may potentially improve the hydrophobicity of a solid surface. In this study, 17 types of re-entrant textures are fabricated in order to discuss the water hydrophobicity by comparing the calculated and measured values. Samples with a spherical curvature are created from an ultra-violet-cure resin and poly (tetrafluoroethylene) microbeads with diameters between 2.3 to 1350 microns by spin coating on a glass substrate. A side view of samples showing the spherical curvature reveals that a re-entrant texture indeed forms. For appropriate microbead diameters, the apparent contact angle peaks at 144.6 degrees and the minimum sliding angle is 5 degrees. The relationship between the microbead diameters and the apparent contact angles are calculated using the theoretical equation based on the Cassie-Baxter model. Under these conditions, the calculated values agree well with the measured values. This microfabrication method for re-entrant surfaces could prove useful for generating hydrophobic surfaces.