Self-Cleaning Diffractive Macroporous Films by Doctor Blade Coating

Here we report a scalable bottom-up technology for creating three-dimensionally highly ordered macroporous polymer films with excellent water-repelling and optical diffractive properties. A simple doctor blade coating process is first utilized to create silica colloidal crystal-polymer nanocomposites. The close-packed silica spheres are selectively removed to fabricate flexible macroporous polymer films with crystalline arrays of voids which are interconnected through small nanopores. The size of the voids can be easily controlled by tuning the duration of an oxygen reactive-ion etching process prior to the removal of the templating silica spheres. After surface functionalization with fluorosilane, superhydrophobic surface with large apparent water contact angle and small sliding angle can be obtained. The water-repelling property can be quantitatively explained by adapting the Cassie's dewetting model. We further demonstrate that self-cleaning functionality can be achieved on superhydrophobic macroporous coatings by preventing bacterial contamination. The high crystalline quality of the macroporous polymers also enables strong optical diffraction from the periodic lattice. The optical properties are evaluated by normal-incidence reflectance measurements and theoretical calculation using a scalar-wave approximation model. A good agreement between theory and experiment has been obtained. The simultaneous achievement of controlled dewetting and strong optical diffraction by templated porous films could open new applications in self-cleaning diffractive optics.