Preparation And Application Of Anisotropic And Hollow Microspheres

Recently, microspheres with special functions or morphologies have gained increased attentions. In this thesis, we developed new approaches for the fabrication of anisotropic and hollow microspheres. Their properties and structures were tuned by adjusting the reaction conditions. Anisotropic microspheres were applied as solid surfactants to stabilize emulsions and then to construct hierarchical materials via radiation emulsion polymerization, while hollow microspheres were used as carriers in the field of drug delivery and catalysis. Detailed contents in this thesis were shown as follows:1. We described the synthesis of snowman-like magnetic/none-magnetic nanocomposite asymmetric particles (SMNAPs) via seeded emulsion polymerization initiated by y-ray radiation. In-situ formation of magnetite in the presence of the emulsified poly(styrene-divinylbenzene-acrylic acid)[P(St-DVB-AA)] microspheres affords raspberry-like magnetic nanocomposite particles (RMNPs), which are used as seeds for further seeded emulsion polymerization induced by y-ray radiation. We study the effect of the kind of surfactant, the kind and content of second monomer, and the content of swelling agent on the morphologies of the final nanocomposite particles. It is found that SMNAPs can be fabricated in high yield using12-acryloxy-9-octadecenoic acid (AOA) as the surfactant and styrene as the second monomer with the addition of2-butanone (a swelling agent). The as-synthesized SMNAPs may serve as magnetically-controllable solid surfactants to stabilize O/W immiscible mixtures, which preferentially orientated at the interface.2. Novel worm-like P(St-AA)@Fe3O4/SiO2Janus nanocomposite particles were successfully prepared. Fe3O4nanoparticles were formed at the surface of P(St-AA) microspheres by in situ chemical deposition, leading to the formation of raspberry-like superparamagnetic P(St-AA)@Fe3O4nanocomposite particles. Based on the CATB micelle template, worm-like silica body was formed at one side of the P(St-AA)@Fe3O4composite particle by a sol-gel process. The effects of different variables such as the amount of cetyltrimethyl ammonium bromide (CTAB), tetraethyl orthosilicate (TEOS) and ammonia, the composition of inorganic precursors and surfactants on the morphologies of final particles were studied. It is worth mentioning that although owing relative hydrophilic properties, the as-prepared worm-like particles can serve as solid surfactants to stabilize oil/water mixtures due to the amphiphilic difference between the two parts as well as their special morphologies, which is different from uniform spherical particles. That might provide a new category of functional solid surfactants in Pickering emulsions and the fabrication of hierarchical materials.3. Snowman-like P(St-DVB-AA)@SiO2/P(St-DVB) asymmetric composite particles could be obtained via y-ray initiated seeded emulsion polymerization after a hydrolytic condensation process on the surface of second monomer swollen P(St-DVB-AA) seeds. Effects of the amounts and kinds of second monomer and inorganic precursor, different radiation polymerization conditions including dose rates and absorbed doses on the morphology of the obtained particles were investigated. The obtained anisotropic particles can serve as ideal solid surfactants to stabilize the water-in-oil (W/O) emulsions, and soap-free hierarchical materials were obtained by polymerization of monomers in water or oil phase.4. By combining radiation seeded emulsion polymerization with hydrolytic condensation, P(St-DVB-AA)/poly[3-(methacryloxy)propyl trimethoxysilane-styrene][P(MPS-St)] hybrid particles could be facilely obtained. The morphologies of the particles could be tuned from raspberry-like to snowman-like by simply changing the feeding amount of second monomer or inorganic precursor. The fabricated raspberry-like ones could be modified to obtain hydrophobic surface with a contact angle up to146°. And the snowman-like ones could be used as solid surfactant to stabilize water/styrene (W/St) mixtures, thus hierarchical porous materials could be obtained after the polymerization of monomer phase. The preliminary application of such soap-free porous block materials in oil-polluted water treatment was also investigated.5. Superparamagnetic mesoporous hollow Fe3O4@m-SiO2particles were obtained by a simple method. Raspberry-like P(St-AA)@Fe3O4particles were used as seed particles, and P(St-AA) core could be dissolved simultaneously during the formation of mesoporous silica shell by sol-gel process, avoiding the damage to hollow shell or the troublesome post-treatments. The effects of variables as the feeding amount of CTAB, TEOS and ammonia, the composition of solvent and the sol-gel reaction time on the structure of the final particles were investigated. The preliminary application of hollow Fe3O4@m-SiO2particles as drug carrier was also studied.6. We demonstrated a facile emulsion-based interfacial reaction method for large-scale synthesis of hollow zeolitic imidazolate framework (ZIF-8) microspheres with controllable shell thickness. Noble metal nanoparticles (NMNPs, as Pd) could be encapsulated during the emulsification process thus worked as active centers for catalysis. The inherent crystalline nature of the MOF shell as well as the tunable integral structures make the Pd@ZIF-8spheres promising catalysts in selective hydrogenation of a, β-unsaturated aldehydes.