The Preparation Of Mono-dispersed Spherical SiO₂ Particles And The Ordered Self-assembly

According to the research of the scientists during recent years,the study of silicon dioxide as a kind of functional materials can be used widely in the field of photonic crystals,catalysis,adsorption,biology,the application of membrane reactor,etc.The colloidal crystals synthesized by self-assembly method with mono-dispersed silica microspheres have become a research hotspot due to their excellent properties in light,electricity and magnetic fields.Therefore,the study of mono-dispersed silica microspheres has important significance and high value of application.Based on the analysis of the present situation of colloidal crystals,this paper studies the preparation and the self-assembly of silica microspheres.There are several specific aspects.?1?The mono-dispersed spherical SiO₂ particles were obtained with the improved St?ber method under the effects of the TEOS concentration,ultrapure water concentration,ammonia concentration and reaction temperature.The size and mono-dispersity of the spherical SiO₂ colloidal particle were explored during the preparation process.The results show that,with the increase of TEOS concentration and ammonia concentration,the particle size of single dispersed spherical SiO₂ also tends to increase.As the concentration of super pure water increases gradually,the particle size of spherical SiO₂ particles increases first and then decreases.Along with the reaction temperature change from 30?to 60?,the size of spherical SiO₂mono-disperse colloidal particle decreases.In addition,the Zeta potential of mono-dispersed SiO₂ particles were measured by using the micro electrophoresis apparatus,and it can be used to characterize interfacial electric properties of SiO₂particles.The effect of pH value and concentration of electrolyte solution on the interfacial properties of particle was discussed,and it is concluded that the isoelectric point of spherical mono-dispersed SiO₂ particles is about pH=2.5-3.5.Through the analysis of the assembly process,it is concluded that the pH=7.0-10.0 and the electrolyte concentration of less than 0.1 mol/L are suited to the assembly.?2?A method called wedge-shaped vertical deposition between two substrates was designed.Inserting the wedge-shaped double substrates vertically into the suspension of SiO₂ particles'with a certain concentration,under the action of capillary force and the convection of the evaporation,eventually the silica colloidal crystals with bright color were self-assemblied between the wedge-shaped substrates.The colloidal crystals show wedge-shaped,and it becomes thick to thin from the top to the bottom,because the layer of the silicon dioxide colloidal crystals is gradually to be less from the top to the bottom.Finally the high quality colloidal crystal was got with stability and good mechanical strength.In additional,the experimental conditions were investigated to get an optimal assembly conditions.The result shows that the crystals assemblied using ethanol as solvent have a greater ordered array,and the suitable concentration of the silica particles is from 3%to 7%.?3?In the method of natural sedimentation,the SiO₂ particle suspension had a slow assembly under a certain temperature and dry environment with the effect of gravity,and the process of assembly isolated from other environmental factors at the beginning of the experiment to explore the influence of experimental conditions,such as temperature,solvent properties and the pH in this assembly method.The results show that the suited temperature is between the room temperature to 50?in ethanol,and the high pH value tends to get colloidal crystals with high quality.The particles with different size can assembly to the colloidal crystals with different colors.The relationship between the angle of observation and the color of the colloidal crystal were discussed based on the Bragg's diffraction equation.?4?The ordered silica colloidal crystal obtained by above methods can be used as a template.The template can be put into the polymer monomer solution after modification by the silane coupling agent to form a silica and polymer composites.When the template can be removed by etching with hydrofluoric acid,the three-dimensional porous PS material was synthesized eventually.