Bioinspired, cysteamine-catalyzed co-silicification of (1 H, 1 H, 2 H, 2 H-perfluorooctyl)triethoxysilane and tetraethyl orthosilicate: Formation of superhydrophobic surfaces

Bioinspired silicification attracts a great deal of interest because of its physiologically relevant, mild conditions for hydrolysis and condensation of silica precursors, which makes the bioinspired approach superior to the conventional sol-gel process, particularly when dealing with biological entities. However, the morphological control of silica structures with incorporation of functional groups in the bioinspired silicilication has been unexplored. In this work, we co-silicificated (1 H, 1 H, 2 H, 2 H-perfluorooctyl)triethoxysilane and tetraethyl orthosilicate to investigate the morphological evolution of fluorinated silica structures in the cetyltrimethylammonium bromide-mediated, cysteamine-catalyzed silicification. The generated micrometer-long worm-like and spherical silica structures display superhydrophobicity after film formation. Interestingly, the measurement of dynamic water contact angles shows that the morphological difference leads to a different wetting state, either the self-cleaning or the pinning state of the superhydrophobic surface. Not a can of worms: The co-silicification of tetraethyl orthosilicate and (1 H, 1 H, 2 H, 2H-perfluorooctyl)triethoxysilane generated worm-like or particulate fluorinated silica structures, depending on the water-to-ethanol ratio and the ratio of the two silica precursors. The substrate coated with the fluorinated silica displayed superhydrophobicity, and its surface free energy was much lower than that of Teflon.