Tailoring the Superhydrophobicity of the Nano-Silica-Coated PUA Film Through a Facile Fabrication Method of its Re-entrant Morphology

The self-cleaning property of superhydrophobic surfaces is very useful for outdoor devices where dust accumulation is problematic. One of the novel methods to make a surface superhydrophobic is to engineer the surface with T-shaped or overhang structures, however, up-to-date preparation methods of such structures such as chemical etching or direct laser writing are usually costly, complicated and unscalable. Herein, we report a facile and scalable spraying method utilizing nano-silica to engineer overhang structure-based superhydrophobic coatings on UV curable polyurethane acrylate (PUA) micro-posts. By optimizing the spraying conditions, the overhang structures can be tunable so that an optimized T-shaped micro-post structure can be prepared in one step to achieve the desired superhydrophobicity and the transparency of the as-prepared film. The micropatterned PUA films were coated with nano-silica 1, 2, 3, and 4 times, with the 3-time coating yielding the best superhydrophobicity and transparency. This film shows a static contact angle (CA) of 150.7° ± 3.5° and a roll-off angle (RA) of 9° ± 1.8°. The as-fabricated film maintains its consistent superhydrophobicity after 60 days of outdoor exposure to sunlight. Moreover, its excellent mechanical properties are also proved by the water impacting and sandpaper abrasion tests. The fabrication technique is uncomplicated and scalable thereby showing the great potential of the film in applications of solar cells and other outdoor electronic devices protection.