SYNTHESIS AND APPLICATION OF SiO2/PVAc INORAGNIC-ORGANIC COMPOSITE PARTICLES
SiO2/PVAc无机-有机复合微球的合成及其膜性能研究

This paper presented a method for the preparation of raspberry-like inorganic-organic composite particles with poly(vinyl acetate)(PVAc) as core and nanosilica particles as shell.A small amount of anionic reactive surfactant,3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt(HAPS) was used as co-stabilizer.Composite particles were obtained via the free radical copolymerization of VAc with HAPS in the presence of aqueous nano-silica dispersions.At the same time,nanosilica particles were deposited onto the surfaces of organic particles via the formation of hydrogen bonds between nanosilica particles and PVAc particles.It turned out that only acidic silica sol could stabilize the latex.Samples prepared using basic silica sol(modified with ammonia) showed large aggregates during the polymerization.At the same time,a very small amount of various surfactants,e.g.,nonionic surfactant(OP-10,OP-40),anionic surfactant(SDS,HAPS) and cationic surfactant(MTC,CTAB) were tried for the synthesis of SiO_2/PVAc latex in combination with nanosilica particles as stabilizer,it was found that only HAPS could act as the co-stabilizer to ensure the polymerization stability,which maybe due to the electrostatic interaction between nanosilica particles and the surfactant.TEM showed that the obtained composite particles have typical raspberrylike morphology,indicating the hydrogen bonds between nanosilica particles and PVAc were strong enough for the formation of long-stable composite spheres.It was found that the average particle size of SiO_2/PVAc composite particles ranged from 200 nm to 500 nm and tended to decrease with increasing silica content from 3 g to 21 g,which had the same behavior as traditional emulsifiers.At the same time,The latexes prepared by 3 g and 9 g of silica only exhibited slight shear-thinning behavior(very close to the Newtonian fluid).However,when 15 g or 21 g silica were employed,the latexes displayed a strong shear-thinning behavior.Based on the stabilization mechanism presented in our previous work,it was believed that some hydrogen bonds formed between hydroxyl groups of the silica particles and increased the viscosity of the latex.However,the hydrogen bonds were easily cleaved under mechanical stirring.