Fabrication of hierarchically structured surfaces with "rose petal" effect by a modified breath figure method

Biomimetic surfaces with the hierarchical structure consisting of multilayered pore microstructures and TiO2 hollow nanostructures were fabricated by combining a modified breath figure method and a dip-coating technique. For creating the hierarchical structure, acetylacetone-chelated and non-chelated tetrabutyltitanates in the coating solution were used as the titanium sources to produce the titanium-based gel film and hollowly nanostructured TiO2, respectively. Meanwhile, the smaller and larger water droplets condensed in sequence during the breath figure process were used as the templates to generate the hollow structures and pore structures, respectively. The parameters of the hierarchical structures, including the pore diameter, pore density and the output of TiO2 hollow nanostructures, were conveniently tailored by varying the volume ratio of tetrabutyltitanate to acetylacetone in the coating solution. The as-prepared titanium-based gel films on glass substrates can be transformed into the corresponding anatase TiO2 films by a subsequent annealing process. The synthesized films were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction pattern, thermogravimetry and Fourier transform infrared spectroscopy. The designed hierarchical structure effectively endows the films with the rose-like superhydrophobic behavior, and the introduction of TiO2 hollow nanostructures within multilayered pores plays an important role in the superhydrophobic property and the strong adhesion to a water droplet.