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 degrees to 171 degrees. Contact angle hysteresis was less than 2 degrees with needles (tip diameter <30 nm) and less than 11 degrees for rods (diameter <250 nm). Relatively thick (diameter similar to 600 nm) structures were still characterized by advancing contact angles exceeding 165 degrees and hysteresis <30 degrees. Formation of manometer-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 degrees and hysteresis <7 degrees.