PDMS nano-coating for glass substrates

Polydimethylsiloxane (PDMS) nano-structured layers were investigated as possible candidates for inexpensive and hydrophobic coatings to be used on glass substrates. A mature manufacturing process, developed for moulding a single layer of micro-hemispheres on a PDMS film, was used to create a single layer of nano-hemispheres that can act like a nano-structured coating. The nano-hemispheres on the PDMS film were created by using a self-assembly process [1]. The index of refraction of the PDMS is very similar to the one of glass so it can be conveniently used for coating glass surfaces. In principle it could also be used for coating other SiO2 surfaces such as those deposited on PV cells or LEDs, thus improving the performances of those devices. The nano-hemispheres on the PDMS film have a size of about 300nm. The nano-structured coating was characterized by comparing the transmission of a glass substrate with and without the nano-coating. The transmission measurements were performed at different angles of incidence and over a wide range of wavelengths, ranging from about 400nm to about 900nm. The results show an improvement in the transmission of the glass. The best improvement was obtained at normal incidence, with an increase of more than 1% in the transmission of a single surface. Such value has to be compared with the typical loss of about 4% introduced by a single uncoated glass surface. Future research will focus on reducing the size and changing the shape of the nano-structure in order to improve the coating performances, and testing the coating on different substrates.