Single-step fabrication of superhydrophobic micro/nano dual-scale PDMS film replicated from ultra-low-surface-energy mold

This paper reports a single-step process to fabricate superhydrophobic micro/nano dual-scale (MNDS) poly(dimethylsiloxane) (PDMS) membrane replicated directly from ultra-low-surface-energy MNDS silicon substrate at high temperature without surfactant coating. MNDS silicon surface with ultra-low surface energy was simply fabricated by an improved deep reactive ion etching (DRIE) process. The huge reduction of surface energy and the formation of high-density nanostructures (i.e. nanotips) on well-designed microstructures (i.e. inverted pyramids and V-shape grooves) were realized simultaneously due to the enhancement of passivation step of DRIE process. Therefore, the high-temperature thermal cross-linking process, even higher than 180°C, can be directly utilized on the pattern replication of PDMS without surfactant coating to strengthen the precision. After studying of heating temperature and time, the MNDS PDMS membrane with the static contact angle (CA) of ~151° was realized at the optimized temperature of 85°C after 1-hour heating. The plasma treatment of the same improved DRIE process was utilized to enhance the hydrophobicity. The CA achieved up to more than 160°, while the CA hysteresis was reduced to below 10°.