Synthesis of artificial opals with core-shell morphology via emulsion polymerization technique

Abstract

Colloidal crystals with a refractive index varying periodically on the scale of the light wavelengths have been prepared by various methods. These photonic crystals reflect light and exhibit, at sufficiently strong contrast, even a complete band-gap in which light cannot propagate in any direction. In this study we first synthesize the latex spheres with a hard, crosslinked core and a grafted-on elastomeric shell that flows at elevated temperatures under uniaxial compression much like other polymer melts. However, the spheres start crystallizing at the plates of the press, whereupon the crystalline order grows, layer by layer, into the flowing melt. The process is fast and yields large area films, thin or thick, in which the latex spheres are crystallized. The refractive index contrast of these purely polymeric films is too small for a complete band-gap photonic crystal, but the films are attractive color materials showing wavelength and angle dependent reflection colors.