Superhydrophobic and anti-reflective coating films fabricated by using very cheap micro/nano-patterned alumina imprinting molds

It is well-known that superhydrophobic (SHP) surfaces like lotus leaf consisted of both microstructure and nanostructure reveal superhydrophobic. It was discovered that anti-reflective (AR) optical films with array of nano-pillars in the surfaces like mosquito’s eyes result in a continuous decrease of reflection index throughout the layer and suppress the reflection in the interface. So tremendous efforts to artificially mimic such micro- and nano-structures have been devoted to utilize such noble properties. It has been known that anodizing is a very simple and cheap method to make patterns of nanostructures 10 to 500 nm in size. Also UV-lithography technique has been known a cheap method to make patterns of microstructures in a micron size. We have developed micro-, nano- and micro/nano-porous anodic aluminum oxide (AAO) molds by using both techniques, and incorporated them to replicate their morphology by using various imprinting techniques on various polymeric films. As results, micro-, nano- and micro/nano-pillared PMMA, PC and PS replica films where the micro- and nano-pillars are uniformly well-arranged in a hexagonal array, were successfully fabricated. AR replica films of PMMA and PC only with an array of nano-pillars showed light transmittance of 94.3 and 93.9%, respectively. Also an AR and SHP PS replica film only with an array of nano-pillars of aspect ratio 4 revealing a transmittance of 90.3% and a water contact angle (WCA) of 153° could be fabricated. However, the mechanical property of such replica films is poor so that it needs much improved. By modifying the process to fabricating micro/nano-porous structure, high WCAs of 153~154° were obtained the PMMA and PC films with pillars of low aspect ratio. Studies to develop superhydrophobic/anti-fingerprint/ anti-scratch multi-functional coating films are on the way.

Keywords

Superhydrophobic, anti-reflection, nano imprint lithography, anodizing, UV-lithography