Syntheis And Properties Of Nano-SiO₂ Composite Microspheres By Surface Photografting

The researchs on visible-light-mediated control/"active" free radical polymerization and the preparation of organic-inorganic nanocomposite materials have always received extensive attention,showing a good application prospects in many fields.In addition,with the rapid development of Pickering emulsions and adsorbent materials,there is a higher demand for particle surface graft modification methods.In this paper,the photo-initiated RAFT polymerization method was used to synthesize the surface grafted polymers on the thioester or vinyl modified silica nanoparticles.The surface modification of silica nanoparticles was carried out by introducing the thioester group of the RAFT polymer chain transfer agent or polymerizable vinyl group.The photo-RAFT polymerization method is used to control the graft structure on the surface of silica nanoparticles.The performance of polymer grafted silica as Pickering emulsifier and bisphenol A adsorbent were systematically studied,which provided a feasible and simple synthesis method for the design and performance optimization of Pickering emulsifier adsorption materials.The main research contents of this paper are as follows:1.The surface modification of silica nanoparticles(SNP)was carried out through the hydrolysis reaction of the coupling agent group,and the thioester-modified silica(SNP-g-CTA)and vinyl-modified silica(m-SNP)were successfully prepared.Grafting did not change the original structure and dispersion characteristics of silica.The grafted silica was still spherical,and the particle size was little enlargement.The results of TGA showed that the surface polymer mass fractions of m-SNP and SNP-g-CTA were 5%and 23%,and the thermal stability of m-SNP was better.Surface grafting has a greater impact on the wettability of the silica surface:the contact angle of the grafted silica increased,and the hydrophilicity decreased.Among them,the contact angle of SNP-g-CTA was larger,and hydrophilicity was worse.2.Through the strategy of "grafting through",m-SNP,which were used as the core nanoparticle were grafted with different kinds of homo－polymer brushes as poly(acrylic acid)(PAA),poly(N,Ndimethylacrylamide)(PDMA),poly(N-isopropylacrylamide)(PNIPAM)and poly(diacetone acrylamide)(PDAAM)after the 12 h exposure under the visible light provided by a daily used CFL source at room temperature.The grafted nanoparticles exhibited a highly variable interfacial activities in respect to the different structures of polymer brushes,which were illustrated by the interfacial tensions and the stabilization configurations in the corresponding Pickering emulsions.The sizes and distributions of emulsion droplet were dominated by the polymer/oil types with the water phase fixed.Moreover,the emulsion stabilized by SNP-g-PAA,SNP-gPNIPAM showed pH and temperature triggered emulsificationdemulsification behaviors,respectively,convincing again the contribution of the visible-light-mediated surface grafted polymer brushes in the interfacial modulating in Pickering emulsion.3.With m-SNP and SNP-g-CTA as the core nanoparticles,polymer nanospheres SNP-g-XPMAA,SNP-g-CTA-g-XPMAA,and SNP-g-CTAg-XPAM were successfully prepared by light-mediated controlled living radical polymerization(CLRP).The successful preparation of polymer microspheres on the silica surface was proved by results of TGA and EDS,and the mass fraction of the polymer can reach more than 70%.Therefore,the particle size of the polymer microspheres increased significantly after grafting,and they were irregularly spherical in the range of 300-500 nm.In addition,due to the presence of the hydrophilic polymer layer on the surface,the surface wettability of the polymer microspheres had changed significantly.The static adsorption method was used to explore the influence of the amount and initial concentration of polymer microspheres on the saturated adsorption capacity,and the adsorption kinetics were also investigated.The adsorption properties of polymer microspheres prepared by different grafting methods and different monomers were significantly different.