Highly reproducible and scalable transparent PDMS thin film with super-hydrypobic surface

This paper describes a simple method of making an optically transparent super-hydrophobic PDMS thin film by using a reusable photo-curable polymer mold. A photoresist mold is prepared using underexposed and under-baked positive photoresist (PR), which create unique hierarchical micro/nano structures. The reverse image of the PR mold is replicated to a PDMS substrate on its surface. The patterns of replicated mold is transferred again to the photo-curable polymer using a home-made UV exposure system. The photo-curable polymer mold is very suitable for the use in a roll-to-roll system for mass production of the film. Nano-silica powder with hydrophobicity is additionally sprayed on the micro/nano structured PDMS surface for further improvement of the hydrophobicity, which slightly decrease the transparency of the film. The fabricated PDMS thin films with hierarchical micro-/nano-scale surface texturing show water contact angle of 150° or greater. Optical transmittance within the range of visible light of wavelengths between 400 and 800 nanometers is experimentally confirmed using a spectrophotometer. High optical transparency of the super-hydrophobic PDMS film is also confirmed on solar panels.