| Photonic crystals are the ordered structure of the material in periodical arrangement of diaelectric constand or refractive index. Under certain conditions, the freguency is in the band gap of the electromagnetic, propagation of which is prohibited. The common semiconductor crystals have the energy gap and the electronic energy. Photonic crystals have characteristics similar to semiconductor crystals. They also havev photonic energy band and energy gap. When the photon’s frequency is in the photonic band gap, the photon can not transit in the photonic crystals.Because photonic crystals have special optical properties, they have broad application prospects in many fields. So more and more scientists focuse on the photonic crystals’study. The concept of photonic crystals was taken by E.Yablonoviteh and S.John independently in1975. A variety of bands of one-dimensional and two-dimensional photonic crystals were continuously produced. But from the prospect of the applicatons, they can be prepared visible band of three-dimensional photonic crystals that people are really interested in.Monodisperse nanoparticles could be assemblied into close-paked structure of three-dimensional colloidal crystals that have a long-range order. In this research, we prepared silica, cross-linked PMMA and P(MMA-EA) by soap-free emulsion. What is more, we made use of these three kinds of nano-microspheres to prepare different kinds of colloidal crystal thin films. A series of experiments in the colloidal crystals are generalized on the following aspects:(1) Monodispersed silicon dioxide spherical particles were obtained with teraethoxy silane(TEOS) as silicon source, ammonia as catalyst and ethanol as solvent. With the premise that well-monodispersed silica spheres between200nm and300nm have been synthesed we discuss the influence of factors on silica nanoparticles diameter, such as the temperature of reaction, the concentration of initiator and monomer and the type of solution. Then, we discuss the influence of factors on the preparation of colloidal silica crystal film, such as temperature, particle size of silicon dioxide microspheres, the volume fraction of silica microspheres and the evaporation rate of solvent respectively.(2) Crosslinked PMMA nano-microspheres have been prepared by soap-free emulsion polymerization in boiling water. We discussed the influence of factors on diameter of PMMA nano-microspheres, such as the concentration of initiator and the concentration of initiator and monomer and assisted stabilizer. Furthermore, we even discussed influence of the concentration of crosslinking agent on degree of crosslinking PMMA microspheres. The results showed that crosslinking extent of PMMA microspheres increased with increasing concentration of crosslinking agent. Finally, we used czochralski method to prepare crosslinking PMMA colloidal thin films and discussed the influence of czochralski rate, methods of drying thin films, kinds of solvent on colloidal crystal thin films.(3) In this paper, we took advantage of soap free emulsion polymerization P(MMA-EA) nano-mirospheres and made a series of experiments by changing the ratio of VEA/VMMA and the concentration of MMA. The results confirmed the best value of prepared P(MMA-EA) elastic colloidal films. The films were transparent in dry states. In the process of films soaked in the water for some time, the wavelength of photonic gap increased with time increment. If we change the tatal concentration of monomers, colloidal crytal films with different colors can be prepared. We chose thin flim with bright colour to do the tensil experiment, then the change of colour and reflection spectrμm of the thin flim can be observed and detected in the process of tensiling. The particular optical and mechanical properties of the elastic colloidal crystal films provide the basis of the application in tension sensors. |
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