Photonic Crystal Films Based on Polymer Particles with a Core/Shell Structure Responding to Ethanol.

Responsive photonic crystals assembled from colloidal particles have been increasingly utilized in detection and sensing devices owing to their attractive ability to change color in response to external conditions. Methods of semi-batch emulsifier-free emulsion and seed copolymerization are successfully applied for the synthesis of monodisperse submicron particles with a core/shell structure, a core being formed by polystyrene or poly(styrene-co-methyl methacrylate) and a shell being formed by poly(methyl methacrylate--butyl acrylate). The particle shape and diameter are analyzed by the dynamic light scattering method and scanning electron microscopy, and the composition is investigated by ATR-FTIR spectroscopy. As shown by scanning electron microscopy and optical spectroscopy, the thin-film 3D-ordered structures based on poly(styrene-co-methyl methacrylate)@poly(methyl methacrylate--butyl acrylate) particles exhibited the properties of photonic crystals with minimum number of defects. For polymeric photonic crystal structures based on core/shell particles, a pronounced solvatochromism with respect to ethanol vapor (less than 10 vol %) is observed. Moreover, the nature of the crosslinking agent has a significant effect on the solvatochromic properties of 3D-ordered films.