Synthesis of photonic crystal film by self-assembly of core/shell poly(styrene)/poly(styrene-co-butyl methacrylate) submicrospheres

Abstract

Monodisperse core–shell poly(styrene) (poly(St))/poly(styrene- co-butyl methacrylate) spheres were fabricated from styrene (St) and butyl methacrylate (BMA) monomers by a two-step, soap-free emulsion polymerization process at the boiling point. The two-step process involves initial polymerization for a fixed period of time, followed by the addition of BMA monomer to generate the core–shell structure microsphere. Formation of the shell portion increased as the initial polymerization time period was decreased. Differential scanning calorimetric analysis showed that the core–shell microsphere exhibited glass transition temperatures ( Tgs), when the monomer conversion during the initial St polymerization step was higher than 40%. The Tgs of the core and shell occurred at 107°C and 41.9–56.7°C, respectively. These core–shell structure spheres were used to fabricate a colloidal crystal film, the photonic band gap of which could be shifted from 455–631 nm by employing core–shell spheres of various sizes. These films having photonic band gaps in the visible region were obtained by self-assembly of the core–shell spheres at 30, 50, and 80°C. The pencil hardness of the films prepared using the core–shell spheres could be increased from 5B to HB by increasing the preparation temperature, whereas the hardness of the film prepared using simple poly(St) spheres was lower than 6B.