Direct-micro-fabrication of Hydrophobic Surface with Re-entrant Texture on Metal Produced by Femtosecond-pulsed Laser

Abstract

AbstractRe-entrant textures are promising geometries for hydrophobic surfaces, however a direct processing method of microscale re-entrant textures applicable for general industrial materials such as metals has yet to be established. The purpose of this study was to demonstrate a possibility of direct processing method of microscale re-entrant textures by using a femtosecond-pulsed laser. We designed a novel and simple optical unit including a pair of step mirrors and a newly designed aspherical condenser lens that enable processing of reverse-tapered uniaxial grooves. A maximum reverse-taper angle of 20° was achieved on stainless steel using a femtosecond-pulsed laser that could be controlled linearly with the step mirror angles. Four types of test-pieces with re-entrant texture composed of reverse-tapered grooves were fabricated with reverse-tapered angles of 5 – 20°. It was demonstrated that the apparent contact angle exhibited an increase in the processed angle of the re-entrant texture. The re-entrant structures on stainless steel achieved a hydrophobicity over 140° of apparent contact angle with good stability, and allowing water droplets to slide off.