| Colloidal crystals have attracted a great deal of attention due to their important applications in photonic crystals and electronic devices, etc. Nano-SiO2 microspheres with good monodispersity and high stability are the main material to obtain the colloidal crystals with high quality. Traditional self-assembly methods, such as horizontal deposition and gravity sedimentation, etc, have some inevitable defects. Therefore, it is important to find a simple and high efficiency method to prepare high quality colloidal crystals. Based on a plenty of literature investigation, we focused on the preparation of monodisperse silica microspheres and the self-assembly of colloidal crystals, and then carried out the following works:(1) Monodisperse SiO2 particles with different sizes were prepared, the effect factors such as the concentration of reactants and the reaction temperature on particle size and monodispersity were discussed. Then, the particle size and zeta potential with the different aging time were studied, and concluded the best aging time of colloidal suspension. Moreover, the relationship of pH and zeta potential of different particle sizes were discussed, and the isoelectric point (IEP) of all particles was obtained.(2) The SiO2 colloidal crystals were prepared by electrophoretic deposition in two modes, constant voltage and pulse voltage, and water as dispersing agent in each experiment. For the average particle size was 378nm, the optimum experimental conditions of constant voltage electrophoretic deposition were:pH= 11.22, ζ=-72.26 mV, deposition voltage was 4V or 5V, and deposition time for 5min. Pulse voltage electrophoretic deposition can greatly improve the quality of SiO2 colloidal crystal. For the average particle size was 207nm, the optimum experimental conditions of pulse voltage electrophoretic deposition were:pulse width was 0.2s, pulse voltage was 4V, and deposition time for 4min.(3) Hydrophilic SiO2 microspheres were modified with CTAB by physical adsorption, the monolayers with closed and ordered structure were obtained by gas-liquid interface device which was made by ourselves. The optimum CTAB concentration was 0.01 mM (corresponding Zeta potential was -36.67mV), and methanol as the best dispersant; When we used the device to get the monolayer silica colloidal crystal film, the UV-vis transmission peaks were great consistent with the theoretical values which were calculated by Bragg equation, and the AFM figures showed that the colloidal crystals with close packing structure, and the orderly structure covered the whole membrane surface. For the multilayers, there were two transmission peaks in each spectra, which were the first and the second diffraction, respectively, and this was the characteristics of the photonic crystals; With the increase of particle size, the position of the transmission peak appeared red shift, the particle size can be calculated from the wavelength location of transmission peak by Bragg equation, and the results showed that the particle size can be matched well with measured values by Nanosight.(4) We tried to build binary colloidal crystals with ordered structures by the gas-liquid interface method in two forms. Alternate structure of lager and small microspheres showed that the small particles can improve the integrity of colloidal crystal, and the lager particles destroyed the ordered structure to some extent. When we mixed two kinds of particle sizes to get binary colloidal crystal by the same method, the results showed that the large particles were arranged in good order and the small particles filled in their spaces. The ordering of colloid crystals was declining with the NS/L increase.In this paper, monodisperse silica microspheres of different particle sizes were synthesized at first. Then, a couple of quick and easy ways were released to obtain orderly structures of colloidal crystals. The way to build binary colloidal crystals with different structures was studied in the last part of this paper. These works were significant-innovative for the self-assembly of colloidal crystals. |
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