Nano Sio <sub> 2 </ Sub> Synthesis And Applications Of Composite Emulsion

Inorganic nanoparticle is a particle with the characteristic dimension smaller than 100 nm, it lies between macroscopic solid and sub-stable state of mater. It possesses small-dimension effect, quantum dimensional effect and surface effect. Polymer/ inorganic nano composite material is a very active domain at present, displaying good prospects of exploitation and application. Silica is used to be the filler of plastics, rubber, coating and adhesive, due to its good properties of heat-resistance, resistance to elements, and chemical stability. Therefore, the preparation of SiO₂ nanoparticles is very valuable for application. In addition, the preparations of SiO₂ nanoparticles/ polymers composite emulsion have atracted more and more atentions. They combine the advantages of polymers (such as elasticity, transparency, or dielectric properties) and SiO₂ nanoparticles (such as ultraviolet resistance, water resistance, and solvent resistance). However, it is very difficult for SiO₂ nanoparticles to disperse in the emulsion at the nano scales due to high surface energy and agglomerating during polymerizing.In this paper, nano SiO₂ / polyacrylic composite emulsion was synthesized by core-shell emulsion polymerization under the basic condition and by the straight entering method under the acidity and the neutral conditions.The following is the first method: Under the basic condition, the surfaces of nano-SiO₂ particles were changed from hydrophilic to hydrophobic and active organic functional groups were grafted to the particles' surfaces by being modified with different silane coupling agents. The modified nano-particles could stay stably and agglomeration was avoided. Nano-SiO₂/organosilicon modified acrylic composite emulsion was obtained by sol-gel method. The processing conditions and the factors of influencing on emulsion polymerization were determined by a lot of experimental researches. The composite had the best overall mechanical properties when the modified nano-silica content was 3%.The following is the second method: the composite emulsion has been prepared through commixing the emulsion and the nano-silica under the acidity and the neutral conditions. We find that the content of silica and the dosage of silane coupling agents have a great impact on the product emulsion.The data shows that the mechanic property of membrane formed increased, such as tensile strength, elongation at break. The water absorbency has reduced and the standing against solvent has been improved.