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

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. © 2012 The Author(s).