Scalable fabrication of superhydrophobic hierarchical colloidal arrays

Here we report a scalable bottom-up technology for assembling hierarchical colloidal arrays with superhydrophobic surface. Non-close-packed (NCP) colloidal multilayers, which facilitate the formation of more hydrophobic surface than close-packed arrays due to a higher fraction of entrapped air in between colloidal particles, are first fabricated by a simple spin-coating technology. Uniform silica nanoparticles are then assembled on the NCP microsphere arrays by a second spin-coating process. After surface functionalization of silica particles with fluorosilane, the resulting hierarchical colloidal arrays exhibit superhydrophobic surface with high apparent water contact angle (159°) and low contact angle hysteresis (4.7°). The experimental results on both the wettability and contact angle hysteresis can be qualitatively explained by adapting the Cassie's model. This spin-coating-based colloidal self-assembly technology is compatible with standard microfabrication and enables large-scale production of superhydrophobic coatings that could find important technological applications ranging from self-cleaning diffractive optics to microfluidic devices.