Selective-swelling-induced porous block copolymers and their robust TiO2 replicas viaatomic layer deposition for antireflective applications

Abstract

We prepared antireflective nanoporous membranes by an extremely simple method which only involves the immersion of the optical substrates coated with amphiphilic block copolymers in hot ethanol for hours and a subsequent air drying process. Nanometer-sized pores were formed throughout the copolymer films through the swelling-induced pore generation mechanism. The pore structure and size, and consequently the antireflective properties of the porous copolymer membranes, could be modulated by changing the concentrations of the copolymer solutions and also the swelling temperature and time. A transmittance higher than 99% of the copolymer-coated glass substrate could be obtained at optimized conditions. Furthermore, to obtain robust and easily cleanable antireflective layers, we deposited TiO₂ on the porous copolymer membranes by atomic layer deposition followed by calcination in air to burn off the polymer components, producing highly porous TiO₂ membranes composed of interconnected nanotubes with thin tube walls. The replicated TiO₂ membranes also displayed a good antireflective function because of their high porosity. Thanks to the conformal deposition of TiO₂ on the copolymer membranes, the TiO₂ replicas maintained structural integrity and mechanical robustness after high temperature calcination, and were tightly adhered to the glass substrate. Moreover, the calcined TiO₂ was transformed to anatase and exhibited a photocatalytic effect. We demonstrated that contaminated TiO₂ layers could recover their original high transmittance, either by directly rinsing with water or organic solvents, or by UV exposure to degrade organic contaminants.