Highly transparent fluorine-free superhydrophobic silica nanotube coatings

Transparent coatings with self-cleaning properties are required for protection of outdoor optical devices. Highly transparent, fluorine-free superhydrophobic coatings of silica nanotubes (SNT) on glass substrates are fabricated by using poly(dimethylsiloxane) (PDMS) as the silica source and multi-walled carbon nanotubes (MWCNTs) as the sacrificial template, following by hydrophobization through chemical vapor deposition (CVD) of cured PDMS. The influence of surface topography from SNT on the transparency and superhydrophobicity of the coatings is investigated. High transparency and excellent superhydrophobicity of the surface can be achieved by changing the concentration of PDMS (CPDMS) for SNT coatings as well as the amount of the cured PDMS (APDMS) for hydrophobization. The optimum coating has an average transmittance higher than 83% in the visible-light range (400–780 nm), a water contact angle (CA) of 165° and a slide angle (SA) lower than 3°. When applied as protective cover, the glass substrate with superhydrophobic coating has little effect on the power generation efficiency of solar cells and has outstanding self-cleaning properties.