Study Of The Application Of Silica Particals

Nano-silica as good raw material for rubber, plastic and other industries, is an important inorganic chemical products, meanwhile, colloidal crystal assembed by monodisperse nano-silica has attracted an inereasing interest due to its various applications in the fields of Photonic band-gap crystals and Photoelectron devices etc. Because nano-silica has high energy surface, it is easily to gather into groups and hardly to fully mixed with organic solvent. To resolve the problems of dispersion and compatibility with organic component, the surface of silica particles must be modified. After assembly of colloidal crystals during drying is its ability to achieve key nanoscale structures, compared with the normal drying in the supercritical fluid conditions, drying of the colloidal crystal can effectively avoid the gel during the drying process of contraction, maximize their gel network structure.Four silane coupling agents with different group were used to modify nano-silica in this experiment. DTS test results show that the particles of modified nano-SiO2 were increased, and PDI values were first declined, then increased with the increasments of coupling agent contents. It was indicated that organic molecular chains were bonded in the surface of modified nano-SiO2 particle dispersion can be improved with suitable coupling agent contents, because the particles hydrophobic ability was enhanced and the agglomeration between nano-particles was reduced in this condition. The experimental results show that infrared intensity of Si-OH bonds on the surface is decreased by using FT-IR, which indicates Si-OH bonds on the surface of silica has reacted with silicon coupling reagent by chemical bonds. All these show that the modification reaction was completed.Hybrid nanoparticles are prepared by direct polymerization of three monomers of styrene, methyl-methacrylate (MMA), and vinyl acetate (VAC) onto the hydrophilic surface of SiO2 particles in a semi-continuous process of emulsifier-free emulsion polymerization. The monomer of styrene, MMA or VAC is constantly fed at 0.01, 0.02, 0.04 mL/min with a pump. The semi-continuous processes are sampled each hour for five hours. The growth of the core-shell nanoparticles are measured by a laser particle size analyzer and SEM, and the surfaces of the nanoparticles by FT-IR. DTS and SEM test results revealed that it can be polymerized onto the hydrophilic surface of silica particles by the means of emulsifier-free emulsion polymerization, however, the particle growth differs in the size distribution depending on the hydrophobic characteristics of the three polymers. DTS test results also show that with MMA and VAC as monomer, both PMMA and PVAC shells grew constantly on the hydrophilic surface of silica particles. When we use the St as monomer, however SiO2/PSt nanoparticles grew much faster compared with SiO2/PMMA and SiO2/PVAC, sub-micron SiO2 as core, SEM showed that the seed SiO2 particles can only adsorb a limit thin PSt layer, which consisted of small PSt particles around 10~30nm. Once the PSt shell reached a limit of ~ 20nm, the PSt layer shattered. Therefore the hydrophilic characteristics of a polymer played an important role in the formation of SiO2/polymer hybrid particles in the semi-continuous soup-free polymerization.In the supercritical drying experiment, Steps for supercritical drying process were discussed. Supercritical conditions and operation methods in the existing experimental conditions was explored to reduce drying colloidal crystals breaking or crack appearing by examining the factors as the degree of drying the wet gel, supercritical temperature, inert gas pre-pressure etc. on experimental results.