The Suprastructure Organic-inorganic Hybrid Microspheres Fabricated Through Pickering Emulsion Droplet Template Method

The organic/inorganic hybrid core-shell microspheres fabricated by the Pickering emulsion droplet template method have enjoyed great popularity. The microspheres obtained by this method have supracolloidal structures, which gives the microspheres special function. Colloid particles adsorb on the surface of the emulsion droplets and self-assemble into an ordering spherical solid shell. The colloid particles are fixed to prepare the core-shell microcapsules. The microcapsules with the shell of colloid particles are also called the colloidosomes. In this dissertation, we used the Pickering emulsion droplet template method to prepare the organic-inorganic hybrid core-shell microspheres. The different original materials for the core and the different method for fixing the colloid particles absorb onto the droplet have been chosen to obtain colloidosomes with different structures and property. Further, the application of the colloidosome for controlled release of drug and the biomimetic reactors can also be researched. Different kinds of nanoparticles were used to prepare the multiple Pickering emulsions. The prepare method and the effect on the stability of the emulsions were investigated. We also prepared dual nanocomposite multihollow polymer microspheres by multiple Pickering emulsion polymerization. The main contents and the results of the research are as following:1. Based on intermediate hydrophobic SiO₂ nanoparticles stabilized water-in-Hexane emulsion, colloidosome microcapsules Alg/SiO₂ with alginate gel cores and shells of SiO₂ nanoparticles were prepared by chelation with calcium cations from in situ release. Insulin microcrystals as water-nonsoluble drug were encapsulated into Alg/SiO₂ colloidosome microcapsules by dispersing them in the alginate sodium aqueous solution before emulsification. The sustained release of Insulin microcrystals could be obtained in model release medium due to the advantage of two levels of encapsulation of alginate gel cores and shells of SiO₂ nanoparticles. Meanwhile the whole release curves were respectivelly fitted by Monoexponential equation, Higuchi equation, the Weibull equation and Hixson-Crowell equation. The release mechanism could be explained by the Weibull equation. The fitted results of the Weibull equation proved that the drug release from the colloidosomes followed Fick diffusion.2. The colloidosome used as a biomimetic reactor was demonstrated at the first time. The colloidosome microcapsules with SiO₂ nanoparticle shells and gellan gel cores were facilely and efficiently prepared by self-assembly of colloidal particles at the liquid-liquid interfaces and subsequently in-situ gelation of gellan gum by reducing the temperature. The urease-loaded colloidosomes were used as an enzymatic reactor to produce calcium carbonate precipitates by urease-catalyzed urea hydrolysis in the presence of calcium cation. The CaCO₃/SiO₂ shells were formed around the gellan gel cores at the end of the reaction.3. SiO₂ nanoparticles could self-assembly at liquid-liquid interfaces to form stable water-in-oil inverse Pickering emulsion. Monomers dissolving in suspended aqueous droplets were subsequently polymerized at different temperatures. The hollow microcapsules with SiO₂/PNIPAm nanocomposite shells were obtained when the reaction temperature was above the lower critical solution temperature (LCST) of PNIPAm. While the core-shell microcapsules with SiO₂ nanoparticles shells and PNIPAm gel cores were produced when the polymerization was conducted at the temperature lower than LCST using UV light radiation. The interesting properties of both microcapsules were their ability of reversibly swelling during drying/wetting cycles and responsive to temperature stimulus. Such functional microcapsules may find applications in double control release system due to the presence of the supracolloidal structures and thermo-sensitivity.4. A series of w/o/w or o/w/o emulsion stabilized only by two different types of solid particles were prepared by a two-step method. We explored the option of particular emulsifiers for the Pickering multiple emulsions and a variety of nanoparticles (silica, iron oxide and clay particles) only differing in their wettability was used. The primary w/o emulsion was obtained by the hydrophobic particles, and then the hydrophilic particles were used as in the secondary emulsification to prepare the w/o/w emulsions. In a similar way, the primary o/w emulsion of the o/w/o emulsions were stabilized by the hydrophilic particles, while the secondary emulsification to prepare the o/w/o emulsions were effected with the hydrophobic silica. The resultant multiple emulsions are stable to coalescence for more than 3 months, except the w/o/w emulsions of which the secondary emulsion stabilized by clay particles become a simple o/w emulsion in a day after preparation. Moreover, the introduction of the temperature and pH sensitive poly(N-isopropylacrylamide) (PNIPAm) microgels could obtain the stimulus-responsive multiple emulsions. Such microgels stabilized multiple emulsions could realize the efficient controlled release on demand in a multiple-emulsion delivery system. 5. The nanocomposite multiple-core polymer microspheres with supracolloidal structures were obtained by the multiple Pickering emulsion polymerization at the first time. The oil soluble monomer (styrene) and the water soluble monomer (acrylamide or N-isopropylacrylamide) were respectively added into the solid stablized the w/o/w and o/w/o emulsion,and then polymerized to prepared the l multihollow polystyrene microspheres and multihollow gel microspheres. In the nanocomposite multiple-core polymer microspheres, the first nanoparticles mainly located on the surface of inner pores and the second nanoparticles mainly located onto the shell of the whole microsphere; this composite structure were confirmed by the CLSM, SEM, TG and FITR. The oil soluble monomer (styrene) and the water soluble monomer (acrylamide) were added in the oil phase and the inner water phase of he multiple Pickering emulsion (w/o/w), and then simultaneously polymerized to obtain the composite multiple-core PS-PAm microspheres. The inner structure of nanocomposite PS/PAm microspheres is porous and each pore is not interconnected. The independent pores inside the microspheres also suggests that the high stabilization of the multiple emulsion in the polymerization process. It was found that after drying, the surfaces of the inner pore were covered with a nodular structure by the PAm gel.