Preparations, Properties And Applicatons Of Polymer/SiO₂Composite Microspheres With Special Structure Fabricated Through Pickering Emulsion Template Method

The purpose of our investigation is to prepare supracolloidal structure polymer compositemicrosphere by means of Pickering emulsion template and also carry out a research on itsapplication. Different core materials and different types of Pickering emulsion template have beenchosen to fabricate organic-inorganic composite microsphere with different structures and properties.The main contents and the results of the dissertation are as follows:1) SiO2nanoparticles were prepared via sol-gel reaction and modified byEthacryloxypropyltrimethoxysilane (MPTMS). It was confirmed by FTIR and XPS that MPTMSwas successfully grafted to the surface of SiO2nanoparticles. The surface grafting degree of thefunctionalized SiO2nanoparticles was determined by TGA and the surface wettablity wasinvestigated through measuring the surface contact angle. The results showed that when the massratio of MPTMS to SiO2increased, the contact angle and the surface zeta potential increased, too.The surface wettablity could be tuned by controlling the grafting extent of MPTMS.Further, Pickering emulsions (styrene/water) stabilized by SiO2nanoparticles were investigated.It was shown that the particle wettability and the priority wettability had significant effect on thetype and stability of the emulsion prepared. Stable Pickering emulsion could not be obtained withparticles which were too hydrophilic or hydrophobic. The particles of moderate hydrophilieity couldstabilize O/W emulsions. For particles of moderate hydrophilieity/hydrophilieity, the prior wettibilitydecided the type of emulsion.2) Polystyrene/SiO2microspheres were fabricated via Pickering emulsion polymerizationstabilized by modified SiO2nanoparticles. The effect of particle wettability, particle concentrationand initiator sorts on the morphology of products was studied. It was found that at low particleconcentration, when hydrophilic initiator KPS was used, microspheres with SiO2nanoparticlesscattered on surface was obtained. Otherwise the product was aggregation when hydrophobicinitiator AIBN was used. At high particle concentration, when AIBN was applied as the initiator,dispersive microsphere with “densely packed” particle shell was prepared and when KPS was used,the products were hollow microspheres. The results showed that there were two nucleationmechanisms in the polymerizing process. The SiO2concentrations and initiator sorts wouldsynergistically impact the morphology of products corresponding to distinct formation mechanisms.3) W/O/W (water/styrene/water) Pickering emulsion stabilized by modified SiO2nanoparticles was prepared. Then polystyrene microspheres with aqueous cores were fabricated withthe multiple Pickering emulsion as template. The final structure and constituents of the microsphereswas investigated through SEM, XPS and TGA. It was found that multi-core structure exiting in the microsphere and most of SiO2nanoparticles were adsorbed at the inner wall of the core; when thevolume fraction of inner water was0.2, the inner structure of the microspheres obtained was porousand each pore was not interconnected; when the volume fraction of inner water increased to0.7,hollow microspheres were obtained. The results showed that the size and amount of aqueous cores inthe microspheres could be tuned by the original structure of the multiple Pickering emulsions.4) Using polyving akohol (PVA) solution as aqueous phase and Hexane as oil phase, W/OPickering emulsion stabilized modified SiO2nanoparticles was prepared. Subsequently, by applyingthe prepared Pickering emulsion as template, PVA/SiO2composite microsphere with PVA gel coresand shells of SiO2nanoparticles was fabricated through freezing-thawing method. The finalstructure and constituents of the microspheres were investigated by means of SEM, FTIR and TGA.The effect of PVA concentractoin, SiO2nanoparticles concentration and freezing-thawing cycletimes on the morphology of products was studied.The PVA/SiO2composite microspheres were applied as a drug carrier to study their controlledrelease behaviors and methylene blue was used as a model drug. It was found that PVAconcentractoin, SiO2nanoparticles concentration and freezing-thawing cycle times had effect on therelease behaviors. All release curves were respectively fitted by Monoexponential equation, Higuchiequation, the Weibull equation and Hixson-Crowell equation. Weibull equation was found to fit thebest to the release process. The fitted results proved that the drug release from the PVA/SiO2composite microsphere followed the Fick diffusion.