Super Hydrophobic Parylene-C Produced by Consecutive and Plasma Treatment

The wetting behavior of polymeric biomaterials is of great importance for biomedical research and pharmaceutical applications. Tailoring of polymer surface wettability is particularly effective to address biomedical issues such as biofouling control and biocompatibility improvement. In this paper, we conducted comprehensive experiments and analytical modeling to understand the effects of a consecutive-O₂-SF₆ plasma treatment on the super hydrophobicity of parylene-C. Experimentally, super hydrophobic parylene-C surfaces with a maximum water contact angle of ~169° have been successfully achieved. Atomic force microscopy and X-ray photoelectron spectroscopy results strongly suggest that the modification of surface wettability can be attributed to the variation in surface roughness and the plasma-induced surface chemistry. Analytically, a transition of droplet status from the Wenzel state to the Cassie state on hydrophobic parylene-C surfaces has been demonstrated after sufficient roughening by O₂ plasma pre-treatment. The surface morphology of plasma-treated parylene-C films has also been analyzed and the hexagonal-close-packed model of downward crowns shows the best agreement with experimental results. Our simple and time-efficient treatment eliminates the need for creating well-defined patterns, is completely compatible with conventional microfabrication techniques, and can also be applied to curved parylene surfaces.