A simple and scalable approach towards the preparation of superhydrophobic surfaces - importance of the surface roughness skewness

A simple and easily up-scalable approach towards the preparation of fluorine-free superhydrophobic surfaces is proposed. Surfaces with water contact angle (WCA) as high as 170 degrees and contact angle hysteresis (CAH) down to 5 degrees are obtained on industrial metallic foils (cold-rolled aluminium foils and electrodeposited copper foils) coated thanks to an atmospheric pressure plasma-enhanced chemical vapour deposition method. Nano- and micro-scale roughness characterisation of the surface, performed by atomic force microscopy (AFM) and confocal microscopy, provided evidence for the substrate surface skewness as the major parameter influencing the WCA for identical nano-rough plasma-polymerised PDMS coatings. A symmetric height distribution, Rsk(m) = 0, is shown to be more desirable to achieve superhydrophobic surfaces.