Colloidal particles with various glass transition temperatures: Preparation, assembly, and the properties of stop bands under heat treatment

Monodisperse P(St-co-nBA-co-AA) colloidal microspheres with various glass transition temperatures (T_gs), whose average particle sizes were about 300 nm, were prepared using soap-free emulsion polymerization by adjusting the ratio of styrene and n-butyl acrylate. Colloidal photonic crystals were assembled with these microspheres by vertical deposition method. Stop bands of colloidal crystals under different temperatures have been characterized. The relationship between the stop band and temperature was indicated. The microstructure and reflectance spectra of photonic crystals were characterized by SEM and fiber spectrometer, respectively. Results showed that as the temperature increased, only a little red shift of stop band appeared in the vicinity of T_g and the intensity of the maximum reflection peak decreased until the stop bands disappeared. Furthermore, enough heating time at the T_g ±2°C could also lead to the disappearance of stop bands. What's more, colloidal crystal films with certain connection strength were obtained by simple heating.