Superhydrophobic polyimide films with high thermal endurance via UV photo-oxidation

Abstract

UV photo-oxidation was first applied to fabricate superhydrophobic polyimide (PI) films in combination with fluoroalkylsilane (FAS) modification. During prolonged UV irradiation, commercial flat PI films evolved to form unique micro/nanostructures. Meanwhile, the root mean square (RMS) surface roughness increased from 1.74 to 53.70 nm, leading to a gradual increase of WCA from 105.1 to 159.2° after FAS treatment. After 72 h of UV radiation exposure, the micro/nano-structured and FAS-modified PI films exhibited superhydrophobicity with water contact angle (WCA) larger than 150° and sliding angle (SA) less than 5°. The superhydrophobicity remained even after annealing at 350°C, which enabled stable utilization under elevated temperature. Stable micro/nanostructures and chemical bonding of FAS were found to contribute to the high thermal endurance. Moreover, the formation mechanism of the superhydrophobic PI films was investigated. The proposed UV photo-oxidation method provides a new route for the industrial fabrication of thermally stable superhydrophobic PI films.

Keywords

• Nanomaterials
• Superhydrophobic polyimide
• UV photo-oxidation
• Thermal properties