Photopatternable Superhydrophobic Nanocomposites for Microfabrication

In this paper, we first report on direct-photolithography-based microfabrication of transparent super-hydrophobic micropatterns using novel photodefinable nanocomposites, combining the nanomorphology and hydrophobicity of polytetrafluoroethylene (PTFE) nanoparticles and the photopatternability and transparency of an SU-8 photoresist using both direct-mixing and coating-immobilization methods. The direct mixture of PTFE-SU-8 nanocomposite can be reliably spin-coated and photopatterned onto transparent substrates (e.g., glass or polymers) with a minimal feature resolution of 50 ¿m. The resulting nanocomposite film possesses a contact angle of water at 150°, although its optical transparency is less than 30%. Furthermore, a modified coating-immobilization approach, employing spray coating and thermal immobilization of PTFE nanoparticles onto an SU-8 polymer matrix, significantly enhances superhydrophobicity, lithography resolution, as well as optical transparency. The highest optical transparency of 80% and a minimal feature resolution of 10 ¿m have been achieved using the standard photolithography approach, while the contact angle of water above 165° enables extraordinary superhydrophobicity with low hysteresis. The novel PTFE-SU-8 nanocomposites provide a unique combination of superhydrophobicity, optical transparency, and photopatternability, along with excellent adaptability and simple processability, which offer great extension to rapidly evolving micro-nanoengineering applications.