Structure Regulation And Optical Properties Study Of Polystyrene Particle Assembled Colloidal Crystal

Photonic crystals are materials with a periodically modulated dielectric constant, with the characteristics in inhibiting, modulating, or enhancing photon propagation. Thus they have been successfully used in functional devices, optical waveguides, optical fiber and other fields. Photonic crystals display beautiful colors, usually based on the periodically ordered structure on reflection of the specific wavelength light, which followed the Bragg's law:λ=2ndsinθ. According to the above equation, the wavelength(λ) of reflected light is relevant to the interplanar spacing(d), the effective refractive index(n) and the incident angle(θ).Monodisperse polystyrene latex spheres, with the size range of88-244nm, have been successfully prepared by free-emulsion polymerization method through controlling the weight of MAA. Based on polystyrene particles, this thesis studied structure of colloidal crystals was regulated through centrifugal force field combined with freeze-drying method and refractive index of building blocks. Finally we studied optical properties of colloidal crystals. The main results are as follows:(1) Centrifugation method is one of the commonly used method for the preparation of photonic crystal. Forcing the colloidal particles assembled in the most stable way, and people often use low-speed long-term centrifugation to fabrication hexagonal close-packed colloidal crystals. In this paper, PS latex spheres of different diameters assemble rainbow colloidal crystals in ethanol solution and freeze-dry by high-speed short-term centrifugation combined with freeze-drying method. The as-gained PS colloidal crystals were characterized by SEM. The results showed that the structure of PS latex spheres were arranged by a random arrangement into the quartet of non-close slowly transition to the four closely-packed, and ultimately to hexagonal close-packed with the increase of centrifugal speed and the extension of centrifugal time. Multi-structure color of colloidal crystals can be achieved through high-speed short-term centrifugation combined with freeze-drying method. With increases of centrifugation force along axial of centrifugal tube, the thickness of colloidal crystals was gradually increase, and the arrangement of PS latex spheres were transition from the four closely-packed to hexagonal close-packed, producing multi-structure color. Surface properties of substrate had a significant effect on intensity of reflected light. With increase of absorption degree on transmission light, the reflected chance of stray light, it turned out that the purity of the reflected light became improved, making the strength of the peaks enhance.(2) PS core-shell particles, coated of different refractive index materials SiO2and TiO2, were prepared by ultrasonic-assisted chemical deposition method. The as-gained core-shell particles colloidal crystals were characterized and analyzed by SEM combined with fiber-optic spectrometer. The results showed that the photonic bandgap was significantly widened with the increase of the refractive index of shell material, and the introduction of the high refractive index made photonic bandgap widen and the reflection peak also enhance.