Wetting characteristics of bare micro-patterned cyclic olefin copolymer surfaces fabricated by ultra-precision raster milling

The sliding performance of hydrophobic micro-patterned surfaces is one of the major factors determining wettability. However, it is difficult for existing manufacturing methods such as lithography, laser etching, and chemical reaction to fabricate one-step bare hydrophobic micro-patterned surfaces with good sliding performance for mass production. In the present research, one-step fabrication of bare hydrophobic micro-grooved and micro-pillar cyclic olefin copolymer surfaces with high precision in geometries has been achieved by ultra-precision raster milling (UPRM). According to the comparison of the static contact angle with theoretical models, droplet anisotropy, droplet contact line, contact angle hysteresis, and sliding angle measurement from the experiment, it is found that the droplet under the Cassie and Baxter regime gives a good sliding performance on bare micro-directional grooved cyclic olefin copolymer surfaces due to the shape edges induced by the numerically-controlled tool path of the material removal process in mechanical machining. It is believed that the micro-directional grooved surface has great potential for mass production by plastic injection molding in microfluidic applications such as artificial self-cleaning surfaces.