Preparation of hydrophobic surface on steel by patterning using laser ablation process

Currently there is an increasing demand for the application of hydrophobic surface in industrial and biological processes. It has been found that the contact angle with liquid, closely related to hydrophobicity of a solid surface, is largely determined by micro-geometrical structure and chemistry of the said surface. In this investigation, the hydrophobicity of steel surface was achieved by implementing micro-patterns on substrate using laser ablation process, and depositing amorphous carbon (a-C) thin film using magnetron sputtering technique. For the patterning, a short pulse excimer laser with a wavelength of 248 nm was used to etch the substrate surface to form different controlled patterns. Based on the models built by Wenzel and Cassie-Baxter, the depth of etched grooves, d, the clearance between two grooves, a, and the width of grooves, b, were optimized to obtain the largest contact angle. It was found that when a pattern was set at a = 25 μm, b = 50 μm and d = 8 μm, the contact angle of the surface could be increased to about 130°, compared to the 68.5° found from a plain smooth steel surface (R_a ≤ 0.01 µm). As a preliminary investigation, an amorphous carbon (a-C) coating was deposited on the patterned surface. It shows that the contact angle was increased further by about 10°-20° on a patterned surface.