Rapid fabrication of organic/organic photonic bandgap films with robust mechanical properties using blended polymer spheres

Abstract

Photonic crystals were fabricated using self-assembled polystyrene (PS) submicrospheres with different content of nanospheres with different glass transition temperatures ( Tg: 100 to −54°C) and their opalescent and mechanical properties were investigated. PS spheres (185.4 nm) and nanospheres were prepared by soap-free emulsion polymerization. Nanospheres were prepared using one or two types of monomers, styrene, n-butyl methacrylate, and butyl acrylate with sodium p-styrenesulfonate. Surface morphology, particle size ( Dn), and wavelength ( λ) of photonic crystals were determined from scanning electron microscopy (SEM), effective refractive index equation, and modified Bragg’s law, respectively. The reflection wavelength ( λmax) was measured from ultraviolet-visible spectroscopy. SEM results showed that hard nanospheres were distributed around PS spheres in their photonic crystals. On the other hand, soft nanospheres were coated onto PS spheres in their photonic crystals. With increasing weight fraction of hard or soft nanospheres in the photonic crystals, Dn and λ were increased. The value of λmax corresponded to that of λ. The mechanical property of the photonic crystals was measured by the pencil hardness (PH) test. The result showed that by decreasing the Tg and increasing the weight fraction of nanospheres, PH was increased. The opal film prepared from PS spheres with 20% N-54 nanospheres had the highest PH (H).