Fabrication of Optically Transparent PDMS Artificial Lotus Leaf Film Using Underexposed and Underbaked Photoresist Mold

• Published in: Journal of microelectromechanical systems Vol. 22; no. 5; pp. 1073 - 1080
• Main Authors: Yoon, Youngsam, Lee, Dong-Weon, Lee, Jeong-Bong
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.10.2013; Institute of Electrical and Electronics Engineers
• Subjects: Adsorption and desorption kinetics; evaporation and condensation; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; PDMS; Physics; Solid-fluid interfaces; superhydrophobicity; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); underbaking; underexposure; Dimethylsiloxane polymer; Solvents; superhydrophobicity; Hydrophobicity; Nanostructures; underexposure; Thin films; Photoresists; Microstructure; Photolithography; Mold; underbaking; PDMS
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2013.2264729

We report an extremely simple method of making an optically transparent superhydrophobic polydimethyl-siloxane (PDMS) thin film using underexposed and underbaked positive photoresist (PR) mold. Significant under soft-bake condition makes PR retain good amount of solvents, which greatly increases the dissolution rate of the PR during developing. A combination of optimal underbaking and underexposure condition created a unique hierarchical micro-/nano- structure on the PR mold, and inverse image of the PR mold was replicated to create a hierarchical micro/nano structured broccoli-shaped PDMS thin film. A 100-nm-thick fluorocarbon film was optionally deposited on the broccoli-shaped PDMS film to further enhance superhydrophobicity. Advancing and receding angles of the film for 4- μL water droplet were found to be 161.33±0.763 ° and 133.33±0.29 ° , respectively, showing superhydrophobicity. It was also found that the optical transmittance at around 550 nm for this PDMS film was approximately 90%.