Systematic control of hydrophobic and superhydrophobic properties using double-rough structures based on mixtures of metal oxide nanoparticles.

Double-rough surfaces were prepared by using mixtures of metal oxide nanoparticles with diameters on two different length scales. The degree of double-roughness of these surfaces was controlled using defined ratios of larger (approximately 300 nm) and smaller (approximately 30 nm) particles. If the preparation method was chosen such that the smaller particles decorate the larger ones, a roughness on two length scales was induced and an increase of contact angles from 130 degrees to 160 degrees with increasing double-roughness was observed.