The Preparation Of Polymer Composite Microspheres Based On Pickering Emulsions

The study on polymer based composite microspheres has got wide attention in the recent years,including both the preparation methods and the theoretical researches.Among the various preparation methods,heterogeneous polymerization through the building of Pickering emulsion has received more and more attention as the experimental material is diverse and the preparation process is relatively simple,etc.In the dissertation,we explored the use of organic aramid nanofibers(ANF)and inorganic Mg-Al layered doable hydroxide nanosheets(LDH)as solid particle emulsifiers to prepare polystyrene(PS)/ANF and PS/LDH composite microspheres by the design of Pickering suspension polymerization system.We systematically studied the influence of the special ID and 2D nano structure Pickering particles on the stable mechanism of the composite emulsion and the morphology control of the composite polymer microspheres.The main work of this dissertation is as follows.1.The preparation of PS/ANF composite microspheresWe used the PEG modified ANF with high aspect ratio from a bottom-up synthesis as the Pickering emulsifier for the first time and achieved the in-situ composite of ANF and PS by suspension polymerization condition.We prepared the composite microspheres with relatively uniform shapes and sizes and characterized them by scanning electron microscope(SEM)and thermal gravimetric analyzer(TGA).We have found that,the size of obtained microspheres is dependent on the synthesis parameters and the diameter varies in the range of 30-500?m.The surfaces of spheres are rough and coated by nanofiber networks.The microspheres also show improved thermal stability.By monitoring on the emulsion degradation,the microsphere size and polymerization kinetics,we systematically studied the influence of ANF as the Pickering emulsifier.We also discussed the effects of different polymerization methods,monomers,initiators,pH and electrolyte concentrations in detail.The results indicate that ANF is absorbed onto the surface of monomer droplets driven by the interfacial tension;the networks of self-associated ANF would serve as physical barriers to separate the droplets.The polymerization in the Pickering emulsion proceeds via suspension polymerization mechanism.2.Preparation of PS/LDH composite microspheresBy using LDH nanosheets as the Pickering emulsifier,we achieved the in-situ composite of LDH and PS by suspension polymerization under similar Pickering emulsion condition.We prepared composite microspheres with relatively uniform shapes and sizes.We used SEM and energy dispersive spectrum analysis(EDS)to characterize the composite microspheres,and found that the diameter of microspheres is in the range of 10-200?m,which is also in response to the polymerization conditions.The surface of microspheres is rough as a result of the incorporation of LDH.The LDH on the sphere surfaces is also convinced by the existence of inorganic elements like Mg and Al.We systematically studied the influence of LDH content,monomers,initiators,pH and electrolyte concentrations on the emulsion stabilities and sphere morphologies of the synthetic products.We also did researches on the polymerization kinetics.The results show that apart from the mechanical barrier effect,electrostatic screen of positively charged LDH layer on the droplets surface also plays an important role in the emulsion stabilization as well as the size of the PS/LDH spheres.Through the electrostatic adsorption effect of LDH and lauryl sodium sulfate(SDS),we successfully induced the phase inversion of the Pickering emulsion,high internal phase emulsion was obtained.And we also prepared porous material based on the high internal phase emulsion.