Fabrication of hierarchically structured superhydrophobic PDMS surfaces by CuO casting

Poly(dimethylsiloxane) (PDMS) is used to define channels for chemical and biological analysis due to its transparency and bio-compatibility. Rendering the channel surface superhydrophobic reduces the effective contact with the channel walls and lowers the needed pressure to push through fluids. This paper reports a novel method to fabricate superhydrophobic PDMS surfaces, with a hierarchical roughness using single-step casting of a patterned cupric oxide (CuO) mold. A structured copper surface with microscale non-communicating roughness is thermally oxidized to generate high aspect-ratio CuO whiskers. Casting PDMS films from the mold creates a micro/nanoscale hierarchical roughness, with the resulting surface exhibiting superhydrophobic characteristics (contact angle > 150° and hysteresis <;10°). With reusable large area molds fabricated in a single patterning step, this process is simpler and cheaper than alternatives based on deep reactive ion etching or laser roughening.