Influence of Surface Morphology on the Wettability of Microstructured ZnO-Based Surfaces

The effect of sample microstructure on water dynamic wetting behavior was examined for superhydrophobic ZnO films. Surface morphology ranging from needle arrays to overlapping platelets was controlled through judicious choice of hydrothermal reaction conditions. Structure modification with alkyl and perfluoroalkyl chains yielded films characterized by advancing contact angles that ranged from 159° to 171°. Contact angle hysteresis was less than 2° with needles (tip diameter <30 nm) and less than 11° for rods (diameter <250 nm). Relatively thick (diameter ∼600 nm) structures were still characterized by advancing contact angles exceeding 165° and hysteresis <30°. Formation of nanometer-scale roughness on top of the microstructure via silica deposition significantly enhanced the surface superhydrophobicity. Similarly, following perfluoroalkane treatment, all examined microstructures exhibited advancing contact angles >169° and hysteresis <7°.