Controllable Porous Microspheres And Monoliths Fabricated From Pickering Emulsion Template

Porous polymer materials (such as multihollow polymer microspheres and porousmonoliths) have attracted more and more attention because of their special physical andchemical properties and applications endowed by their unique structure. This thesis describedthe development of new strategies for the preparation of different structure of porous ormulticore polymer microspheres and the porous polymer monoliths based on the Pickeringemulsion templates. The paper mainly includes the following six parts. The first chapter is theintroduction, summarizes the Pickering emulsion and the research progress of porous polymermaterials. The second chapter focuses on the fabrication of controllable multihollowmicrospheres based on the two-step multiple Pickering emulsion templates. The third chapterexplores one step method to prepare multiple emulsions and the fabrication of porous PLGAmicrospheres. The fourth chapter tries to use single emulsion template to manufacturepolymer microspheres with complex multicore structure. The fifth investigates usingcostabilizer of particles and surfactant to synergistically stabilize high internal phase emulsion.The last studies the costabilizer of particles and surfactant stablilized high internal phaseemulsion and the application of the emulsion-templated porous materials.The main research contents and results of this thesis are as follows:1. Fabrication of controllable multihollow polystyrene microspheres by simply adjustingthe volume ratios of inner water phase to oil phase. Hydrophobic and hydrophilic particleswere employed as emulsifiers for the primary W1/O and outer O/W2emulsion, respectively.Stable water-in-oil-in-water (W/O/W) multiple emulsions were prepared by two-step method.Multihollow polystyrene microspheres were obtained by polymering the styrene monomer inoil phase based on the multiple Pickering emulsion templates. The internal structure of themicrospheres and the location of the nanoparticles have been characterized by scanningelectron microscopy (SEM) and X-ray energy dispersive spectrum (EDS). The results showedthat the nanoparticles mainly located on the inner void wall and the outer surface of themicrospheres. By simple adjustment of volume ratios of internal water phase to oil phase, thenumber of voids in porous microspheres can be controlled. Moreover, high ratio of W1:O canalso make the internal pores change from the closed structure to interconnected pore structure.2. One step preparation of multiple emulsion and porous PLGA microspheres. We usesynthetic hydrophilic SiO2nanoparticles as stabilizer of oil-in-water emulsions, and PLGAsolution of methylene chloride as oil phase. W/O/W Pickering emulsion was one stepprepared by hand shaking the water and oil phase. We systematically investigated the influences of molecular structure of the PLGA, PLGA content in the oil phase, SiO2nanoparticles concentration in water phase and volume ratio of water to oil on the doubleemulsion formation and consequently on the structure of the PLGA microspheres. Opticalmicroscope and scanning electron microscope (SEM) were adopted to survey themicrospheres prepared under different conditions. The results showed that the multipleemulsions can only be obtained under proper conditions. Moreover, the emulsion templatesdirectly affect the morphology of the volatile products. Porous microspheres can be attainedonly after the volatilization of multiple emulsion templates.3. Fabrication of multi-core microspheres based on single Pickering emulsionpolymerization combining phase separation and nanoparticle nucleation. In this study,rattle-like polymer microspheres with multicores encapsulated in hollow spheres are facilelyfabricated via oil-in-water Pickering emulsion polymerization for the first time. Pickeringemulsions were stabilized by hydrophilic lignin nanoparticles. The oil phase containshydrophobic nanoparticles dispersed in polymerizable monomer, styrene and unpolymerizablesolvent, hexadecane. The multicore rattle-like microspheres are directly produced after thepolymerization of monomers in the oil droplets. The key point of this one-pot method for therattle-like microspheres lies in the nucleation of hydrophobic nanoparticles and the phaseseparation between the resulting polystyrene and hexadecane. We have systematicallyinvestigated the influences of the contents of hydrophobic nanoparticles, hexadecane,cross-linker and lignin particles on the structure and morphology of rattle-like microspheres.It is proven that the number and size of core, the shell thickness, size of rattle-likemicrosphere can be easily controlled by adjusting the various parameters. Moreover, specialfunctionalization of the rattle-like microspheres can be developed easily by adding differenthydrophobic nanoparticles in the oil phase. This work opens up a new route to fabricatemulti-level capsules or spheres.4. Fabrication of Pickering high internal phase emulsions (HIPEs) with ultrahigh internalphase fraction by using hydrophobic silica nanoparticles (H30) and nonionic surfactant ofSpan85as a dual emulsifier system. Water-in-hexane (W/O) HIPEs stabilized by a mixture ofH30and Span85were investigated. Increasing Span85concentration in mixture would resultin the appearance of smaller droplets of several to tens of micrometers in the HIPEs while apopulation of large droplets of hundreds of micrometers would appear with increasing H30concentration. Furthermore, the influences of Span85and H30on the formation of HIPEswere investigated from the polymerized HIPEs (polyHIPEs) synthesized through these HIPEstemplates using styrene as the oil phase. The synergism between particles and surfactant exists and plays a crucial role in the stability of HIPEs. This research opens up a new insight into thefabrication of Pickering HIPEs with an ultrahigh internal phase fraction. Moreover, porousmonoliths with different pore structure can be obtained from the co-emulsifier stabilizedHIPEs.5. One-pot prepared Artemisia argyi oil (AAO)-loaded macroporous antibacterialhydrogels through polymerizing oil-in-water Pickering high internal phase emulsions (HIPEs).The HIPEs were stabilized by hydrophilic silica nanoparticles (N20) with adding surfactantTween80. The void interconnectivity and pore size of the hydrogels could be tailored readilyby varying the N20nanoparticle and Tween80concentrations. The mechanical property ofthe porous hydrogels was related to the pore structure of the materials. The in vitro release ofthe AAO-loaded hydrogels with different inner morphologies was evaluated and showedcontrolled release activity. The antibacterial activity of the AAO-loaded hydrogel wasevaluated and exhibited excellent and long-term antibacterial activity.