Preparation And Characterization Of Colloidal Photonic Crystals

In recent years, Photonic crystals or Photonic bandgap materials has attracted considerable attention because of its potentially powerful applications in optical communication functional materials. This kind of materials is periodically arrayed in three-dimentional spaces by mesoscopic particles which diameter in the range of a few nanometers to tens of mierometers. Due to the dielectric constant of these materials suffers a spatially periodic variation, a band gap will occur when a certain wavelength electromagnetism propagates through its ordered lattice, and some newly photoelectronic properties will be presented, such as restraining spontaneous radiation of atoms and moleculars. It will exhibit greatly potential in basic research and practical application.One important way to produce photonic cryrsatls is using monodisperse polystyrene self assembled. In this research, the preparations of monodisperse particles and the applications of them in bioassay, free-standing film were studied as follows.(1) PMMA is a kind of colloidal photonic crystals which was studied most by far, PMMA particles were prepared by soap-free emulsion polymerization in boiling water, The influences factors such as the concentration of monomer MMA, MAA and the initiator on the diameter of PMMA microspheres were studied. And explain the chromogenic mechanism of nanoparticle self-assembly films;(2) In order to improve the bending strength of PMMA, improve its deficiency in practical application, Add BA in PMMA system, then P (MMA-BA) particles were prepared via soap-free emulsion polymerization at boiling status. The influence of BA/MMA ratio on the polymer P (MMA-BA) morphology was studied by field emission scanning electron microscopy. The result showed that the drying films were transparent, and after dipping in the water the films showed bright colors. During the deformation the reflection spectrum of the film appeared blue-shift and the color slowly turned into purple, which were caused by the deformation of particles occurred in the layers that the round particles changed into the elliptical ones under the external force. And this phenomenon confirmed that the films were flexible and tensile.(3) P(St-MMA-BA) particles were prepared by soap-free emulsion polymerization at boiling status.The influences factors such as the concentration of monomer MMA, St, MAA and the BA/MMA ratio on the diameter of P(St-MMA-BA) microspheres were studied. And the effect of heating on reflection wavelength of colloidal crystal films was also researched. Finally, P(St-MMA-BA) particles assemble into colloidal crystal microspheres for bioassay.