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Morphology-tuned Synthesis of Inorganic/Polymer Nanocomposites or Inorganic Nanostructures

Author: WangDaiLong
Tutor: GuHongChen
School: Shanghai Jiaotong University
Course: Applied Chemistry
Keywords: inorganic/polymer nanocomposites emulsion polymerization miniemulsion polymerization surface modification local surface modification morphology-controlled synthesis dissymmetric morphology raspberry-like morphology mushroom-like morphology surface functionalization highly branched nanostructure
CLC: TB332
Type: PhD thesis
Year: 2009
Downloads: 452
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Abstract

In the past decades, morphology-controlled synthesis of nanoparticles was always one of the focuses of research on colloidal science. Among them, the inorganic/polymer composites and inorganic metallic nanocrystals have been attracting intensive interests. A lot of efforts have been made to design and tune the morphology and structure of inorganic/polymer nanocomposites by various synthetic methods and processes, which posed the situation of interdiscipline and rapid development of Materials Science, Chemistry, Physics and Biology. Recently, tailor-made preparation of inorganic/polymer nanocomposites with dissymmetric or symmetric complex morphologies and microstructures have been more important and attractive for both scientific community and industrial circle, while most of effort have been put in the research on synthesis of nanocomposites with symmetry and core-shell structure before. In this thesis, we are focusing on synthesis of inorganic/polymer composite nanoparticles with complex or dissymmetric morphologies. We did three main contributions to this research field based on combination of surface modification of inorganic particles and heterophase polymerization process: (1) synthesize the old morphology (raspberry-like) by novel miniemulsion polymerization method, and improve the preparation techniques, (2) obtain the inorganic/polymer composites with half raspberry-like and surface characters by conventional emulsion polymerization method, (3) develop novel inorganic/polymer composite nanoparticles with asymmetric morphology and surface property via miniemulsion polymerization, and realize the synthesis of composites with anisotropic surface functionalities. Furthermore, the formation and preparation of highly branched silver nanostructures or silver oxide octahedral particles via solution-base process were studied. The possible mechanisms of formation of those nsnostructures were explored by changing the reaction conditions correspondingly. The discribtion of main rdesults in each experimental chapter is lised as follows:In Chapter two, the raspberry-like Silica/PS composites were prepared via miniemulsion polymerization of monomer in the presence of methacryloxy(propyl)trimethoxysilane (MPS)-grafted silica particles. It is found that due to the different nucleation mechanism, the morphology of composites varied from raspberry-like in miniemulsion polymerization to core-shell structure in emulsion polymerization based on same modified silica particles. The synthetic route could be applied in synthesis of high surface to volume ratio Fe3O4@Silica/PS nanocomposites with similar morphology too. Furthermore, the Silica/PS composite nanoparticles with daisy-like morphology were prepared based on different size of silica particles modified by MPS with varied grafted density via emulsion polymerization of styrene monomer. The effect of grafted density of MPS on the morphology of composites nanoparticles was studied.In chapter three, a novel synthetic route characterized by combination of local surface modification of inorganic particles with n-octadecyltrimethoxysilane (ODMS) to miniemulsion polymerization was developed to prepare dissymmetric silica/polystyrene composite nanoparticles with mushroom-like shape. We also studied different parameters that influenced the morphology of composites. Furthermore, half-raspberry-like shape silica/PS composite nanoparticles were prepared via emulsion polymerization of St monomer based on MPS locally modified silica particles. And the effect of grafted density of MPS molecules on the morphology of composite was investigated. It is proved that the combination of local surface modification of inorganic particles and heterophase polymerization of monomer has provided us with bigger possibility to design and tune the asymmetric shape and structure of inorganic/polymer composite nanoparticles.In chapter four, we describe the further preparation of anisotropically dual-functionalized silica/polystyrene composite nanoparticles with asymmetric snowman-like morphology via two-step chemical method. In first step, snowman-like silica/carboxylated polystyrene composite nanoparticles were prepared via miniemulsion polymerization of St monomer initiated by ACPA in the presence of locally surface modified silica particles. And then, the amino groups were introduced into the surface of silica component of the composite by graft of APS molecules. Two kinds of fluorescence were selectively labeled onto the chemical groups on the composites to prepare the two fluorescent color composites, indicating that the anisotropic surface groups have biological reactivity.In chapter five, we report that the synthesis of highly branched silver nanostructure by aqueous solution method. Different parameters were studied to see their influence on the extent of branching due to the most simpleness of the reaction. The possible mechanism and needed condition for formation of such highly branched nanostructure was proposed according to the TEM observation of the aliquots taken from one reaction at different reaction time. SERS property of the silver branched nanostructures was examined and hollow Ag/Au alloy branched nanostructures were prepared through galvanic replacement reaction based on silver template. Furthermore, the octahedral silver oxide particles were obtained when we tried to adjust the kinetic condition by bubbling saturated O2 into the reduction of AgNO3 precursor stabilized by PAM in a polyol process. The mixed composition of the final products was analyzed by XPS measurement. We investigated the oxidative etching happened to the twinned seeds through electronic microscopy technique and UV-Vis spectra analysis. The effects of coupling agent and atmosphere on the shape of final product were studied as well.In summary, we have developed the methods for preparing the inorganic/polymer composite nanoparticles with different complex or asymmetric morphologies, and extended one of the methods to synthesis of magnetic inorganic/polymer composites with complex morphology. Meanwhile, the composites with anisotropic dual-functionality and two fluorescences were prepared based on the new method. Further more, highly branched silver nanostructures and octahedral silver oxide particles were synthesized respectively when the different reaction condition were controlled.

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