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Title: Synthesis, characterization and application of smart magnetic core-shell polymeric particles
Authors: Ho, Kin-man Edmond
Degree: Ph.D.
Issue Date: 2007
Abstract: There has been increasing interest in the design and fabrication of magnetic core-shell (MCS) polymeric particles, due to their magnetic-responsive properties. Such core-shell particles have been successfully synthesized through various approaches, such as suspension-crosslinking, layer-by-layer (LBL), and other polymerization techniques. Nevertheless, there are still some drawbacks including, leaching and dissolution problem of magnetic nanoparticles under an acidic environment, ill-defined core-shell nanostructure, incomplete encapsulation of magnetic nanoparticles, tedious synthetic procedures, and the use of large amounts of emulsifiers and surfactants. In addition, the particles produced through these approaches have limited amount of functional groups on their particle surface. The work presented in this thesis aims to develop a simple, convenient, inexpensive, and surfactant/emulsifier-free approach to prepare MCS particles, and the use of MCS particles for electromagnetic interference (EMI) shielding application has also been explored. The MCS particles containing v-Fe2O3 nanoparticles inside the polymer cores were prepared via a two-step synthesis: 1) preparation of vinyl-coated magnetic nanoparticles (MPS-Fe2O3); 2) synthesis of magnetic core-shell (MCS) particles via hydroperoxide-induced graft copolymerization of methyl methacrylate (MMA) from chitosan in the presence of MPS-Fe2O3 nanoparticles. Part I - Synthesis of vinyl-coated magnetic nanoparticles MPS-Fe2O3 nanoparticles ere prepared via co-precipitation of aqueous solutions of Fe2+ and Fe3+ salts in a NH4OH solution, followed by coating them with trisodium citrate to generate citrate-coated iron oxide (C-Fe2O3) nanoparticles (~10 nm). These nanoparticles were then modified via hydrolysis and condensation of tetraethyl orthosilicate (TEOS) and 3-(trimethoxysilyl)propyl methacrylate (MPS) to generate MPS-Fe2O3 nanoparticles (Chapter 4). Properties of these nanoparticles including particle size, surface charge density, composition and magnetic responsiveness were characterized with dynamic light scattering, zeta-potential, FT-IR spectroscopy, thermogravimetry analysis (TGA) and vibrating sample magnetometer (VSM), respectively. Part II - Synthesis of magnetic core-shell (MCS) particles MCS particles were synthesized via hydroperoxide-induced graft copolymerization of methyl methacrylate (MMA) from chitosan in the presence of the MPS-Fe2O3 nanoparticles (Chapter 5). The MCS particles were produced in high yield. Transmission electron microscopy (TEM) images of the MCS particles clearly revealed a well-defined core-shell nanostructure, where the poly(methyl methacrylate) cores containing v-Fe2O3 nanoparticles were coated with chitosan shells. The presence of chitosan shell was confirmed with a xi-potential measurement. Particle size measurement determined that the MCS particles had sizes around 200 nm with narrow size distribution. Magnetization measurement of the particles using vibrating sample magnetometer (VSM) showed that the core-shell particles possessed a good magnetic responsiveness with superparamagnetic property. Part III -Multi-functional core-shell nanocomposites as a water-based coating for electromagnetic interference (EMI) shielding applications Electromagnetic interference (EMI) is a well-known problem in electronic circuits. Electromagnetic radiation particularly at high frequencies not only interferes with electronics, but may also have potential hazard to human being. Thus, there is a critical need in developing versatile and effective EMI shielding materials. In the last part of this thesis, a novel magnetic and conducting nanocomposite as a water-based multi-functional coating for EMI shielding applications is described (Chapter 6). Formation of these nanocomposites was achieved by simply mixing the MCS particles with purified single-walled carbon nanotubes (SWNTs). TEM images of the nanocomposites showed that the SWNTs formed a bridge between MCS particles. Furthermore, the presence of MCS particles can significantly avoid the formation of large SWNTs buddles, which is a major challenge in using the SWNTs. Atomic force microscopy (AFM) images of the nanocomposites showed that these nanocomposites formed a continuous film on a glass substrate, indicating that they possessed a good film forming ability. Exploration of the MCS particles-SWNTs nanocomposites for electromagnetic interference (EMI) shielding will be attempted. Thus, this novel material could have great potential for EMI shielding applications.
Subjects: Hong Kong Polytechnic University -- Dissertations.
Magnetic cores.
Nanoparticles -- Magnetic properties.
Pages: xxii, 304 p. : ill. ; 30 cm.
Appears in Collections:Thesis

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