The Prepartion And Structure Of Photonic Crystal Fabricated By Polymer/Silica Nanocomposite Latex

Photonic crystals have been the focus in material science and technology because of its manipulations of photon propagation and promising application in communication, sensor and detector, coating and displays. Self assembly strategy of colloidal spheres into photonic crystals had been one of the most widely used methods since this strategy is relatively simple, cost-efficient. Usually, self-assembly of colloidal spheres is based on the so called "hard" spheres such as colloidal silica, polystyrene, poly(methyl methacrylate), as a result, the obtained colloidal crystal (CC) films have neither mechanical property nor the desirable large-area. To solve these problems, the dispersions of soft polymer and silica particles were studied to fabrications of the tough photonic crystals. Though self assembly of colloidal spheres into photonic crystals are simple, mass producible and least expensive, it is inevitable to introduce random defects, such as missing particles, uncontrolled orientation, mixture of phases and dislocations during the self assembly processes. These defects decrease the reflectivity of stop band, and scatter the wavelength light outside the stop band. Thus, the light we usually observe not only contains the wavelength corresponding to the expected color, but also these unwanted wavelengths. As a result, the color from the colloidal crystal with defects is not as vivid as natural opals or appeared in low saturation. In order to improve the color of the colloidal crystal film, carbon black was added to the dispersion and the colloidal crystal films with vivid color had been fabricated successfully.(1) This paper presents a novel and facile approach to fabricate robust crystal balls directly through the self-assembly of soft colloidal polymer spheres by the aid of nano silica using electrospraying technique. In this approach, soft colloidal polymer spheres are synthesized by emulsion polymerization and then blended with colloidal silica to obtain nanocomposite dispersion. When this dispersion is loaded into injector and forced to flow through the nozzle under direct electric field, the detached droplets are collected by an oil solvent. As water and solvent evaporate, the colloidal polymer spheres and silica beads can directly self-assemble into robust crystal balls driven by static repulsive force, capillary force and interfacial tension.. Neither soft matrix nor post-treatment is needed. The obtained crystal balls have not only excellent mechanical properties to withstand external The shape and morphology could be controlled by electric field strength, solvent properties, substrate and Zeta potential of the polymer spheres, which provided a paradigm for the fabrication of tough photonic crystal balls.(2) Self-assembly of colloidal spheres is the most frequently used for the synthesis of structural colors, but the artificial structural colors are usually not as vivid as those of nature. This paper presents a facile and large-scale fabrication method of the vivid structural colors by doping carbon black into the self-assembly of colloidal polymer spheres and nanosilica particles. The lightness of the structure color decreased with the increasing carbon black content and increased with the increasing silica content. The chroma factor could be improved greatly under the optimal carbon black content and silica content. This approach can not only generate very gorgeous structural colors which can be observed under natural lighting condition, moreover, the chroma of structural colors can be controlled by the contents of carbon black and silica. Thus, the brilliant and tunable structural colors, robust mechanical properties plus large-scales can guarantee the obtained polymer films to find more practical applications, which opened up a new way to fabricate the tough photonic crystals with vivid color controllable in lightness and chroma factor.(3) In order to get the tough colloidal crystal film with vivid color and least defects, the effects of fabrication factors on the films quality were carried out by the controlled evaporation methods. The result showed that the temperature, relative humidity and silica content had effect not only on the evaporation rate of the dispersion but also on the reflection spectra and micrographs of the films. The peak position blue shifted with the increasing evaporation temperature and relative humidity while red shifted with the increasing silica content. The structure color with vivid color and least defects could be obtained under suitable conditions.