Artificial latex-based opals prepared by spin casting of monodispersed nano particles

Artificial opals are a division of photonic crystals composed of monodispersed nano particles. In this work, a polymeric dispersion with a core-shell structure was prepared by semi-continuous emulsion polymerization. The dispersion consisted of polystyrene-based hard core coated with a poly methyl methacrylate-co-butyl acrylate shell. Particle size distribution was measured using a dynamic light scattering method. The synthesized latex was cast by a spin-casting machine. Due to centrifugal forces, this machine arranges the dispersed spheres into hexagonal structures. Formation of such arrangements was confirmed by scanning electron microscopy. The optical properties of the latex-based opal were investigated by spectrophotometric and goniospectrophotometric techniques. A color-shift from green to blue was found due to near hexagonal arrangements of spheres upon spin casting compared to random arrangements of such spheres obtained without spin casting. Furthermore, the colorimetric data showed more uniform variations in the hue angle (h°) with respect to the aspecular angles for the sample prepared by the spin-casting machine.