Superhydrophobic TiO2 coatings formed through a non-fluorinated wet chemistry route

We present a facile and low cost non-fluorinated wet chemistry route yielding rough and highly hydrophobic surfaces. This procedure is based on a nanosphere lithography (NSL) method using polystyrene (PS) spheres. Multilayer PS coatings were impregnated with a sol-gel TiO2 polymeric sol and then heat-treated at 500 °C. Derived NSL-structured TiO2 coatings were then grafted with hexadecyl trimethoxysilane (C16). The morphology of structured coatings was analyzed by optical, scanning electron, and atomic force microscopy, and the water wettability of TiO2 coating grafted with the C16 precursor was studied with respect to NSL features. It is shown that the synergy between the hydrophobicity imparted by the C16 precursor and roughness effects arising from NSL structuration leads to superhydrophobic coatings. In optimized conditions, the static contact angle of 11.6 μL water droplets deposited on the surface is around 160° with a corresponding tilt angle as low as 1°.