The Preparation Study Of Colloidal Silica Particles And The Assemblies

As a kind of new functional materials brought forward in the 1980s, photonic crystals with a regular periodicity of dielectric structures have peculiar properties in inhibiting, modulating and enhancing photonic propagation. Thus photonic crystals have wide applications or application potential in functional device, optical fibers, infrared/radar cloaking device and other fields, and have become a research "hot spot" and a frontier field of functional materials. In recent years, the research about photonic crystals has made a great development.The key to develop photonic crystals is the fabrication of photonic crystals. The colloidal chemistry approach is an important method to prepare photonic crystal with artificial opals structure. The monodispersd colloidal particles is an essential building block to assembly two-or three-dimensional photon crystals with artificial anti opal structures. Therefore, after the plenty of the present literatures, and the consideration of the limitation of the properties and application scope of opal structured photonic crystals consisting of single colloidal particles and the feature of our laboratory, we studied on the preparation of silica spheres of monodispersed size and bimodal distribution and their based self-assembled colloidal crystals in this thesis. The main research contents and results were included in the following:The first priority is to prepare the monodispersed silica particles. SiO2 colloidal spheres were synthesized by the hydrolysis of tetraethylorthosilicate (TEOS) under the catalytic assistance of ammonia in ethanol. The as-synthesized SiO2 colloidal particles were characterized and analyzed by XRD, FT-IR, SEM and laser scattering particle analyzer. Highly uniform silica spheres with diameters from 300 nm to 1.8μm were obtained for colloidal crystals by adjusting different reaction conditions including the concentration of TEOS, ethanol, ammonia and the reaction temperature etc.Then, the opal photonic crystals were assembled in the ethanol solution of SiO2 colloidal spheres by a vertical deposition method. The structures of the as-obtained opal photonic crystals including the morphologies and defects were investigated by SEM. The as-obtained SiO2 colloidal crystals show an fee structure with cracks, dot defects and line defects. We discussed some basic factors that affect the quality of the colloidal crystals. The anti-opals structure photonic crystal was preliminarily prepared by filling the as-obtained SiO2 colloidal crystals with a gel polymer and etching the SiO2 colloidal crystals, sequentially.Finally, silica colloidal spheres with bimodal size distribution have been prepared by the hydrolysis of TEOS in ethanol solution when the ammonia concentration and feed ratio of TEOS are adjusted to be low enough for purpose. Based on the influence of reaction time, ammonia concentration and feed ratio of TEOS on the size and size distribution of the as-synthesized silica colloid particles, the formation mechanism of the silica colloid particles with bimodal size distribution has been also proposed in terms of the nuclear and growth of silica colloid particles. The special structure photonic crystals based on the silica particles with bimodal size distribution were prepared using a gravity deposition method.