Fabrication Of Polymethyl Methacrylate (PMMA) Nanosphere And Its Ag Shell-coating Technique

In recent years, fabrication of core-shell nanoparticles (CSNs) has developed intoan increasingly important research area in material science and engineering, due totheir potential applications in new sensor, photon crystal, drug delivery, catalyzer andso on. People have shown strong interest in CSNs with silver shell in particular,because CSNs with silver shell have unique properties of surface plasmon resonance(SPR) and catalyzing. Up to now, several routes, including surface chemical reduction,lay-by-lay self-assembly, and ultrasonic chemistry etc, have been explored forfabrication of such CSNs with silver shell. Although some fabrications of CSNs bycoating of insulator cores with silver shells have been reported recently, thefabrication techniques reported, however, are far from being established and still havemany shortcomings. For example, they either required cores of large size (even up tomicrometer regime) to ensure a uniform coating shell with a good dispersion orresulted in a non uniform coating with a poor dispersion of the products if the coresize was not larger enough. On the basis of the former works, in the present thesis, animproved multiple step technique was developed for fabrication of PMMA/Ag CSNs .Firstly, the monodisperse PMMA nanospheres were fabricated by emulsifier-freeemulsion polymerization. Then, the surface of PMMA nanospheres was modifiedfirstly with (3-methacryloxypropyl) trimethoxysilane (MATS) and then with(3-mercaptopropyl) trimethoxysilane (MPTMS), resulting in a uniform, sulfhydryl(SH) group-modified outlayer. Finally Ag nanoparticles further grew on the modifiedsurface of PMMA nanospheres with vigorous interaction between sulfhydryl (SH)groups and Ag ions and Ag ions was subsequently reduced. In doing so, PMMA/AgCSNs were successfully synthesized. The process for such fabrication of thePMMA/Ag CSNs was extensively investigated. The three major steps involved in theprocess can be summarized as follow:(1) For the preparation of PMMA nanoparticles: The monodisperse PMMA nanospheres were successfully synthesized by emulsifier-free emulsion polymerization. Effect of MMA monomer concentration, initiator concentration and reaction temperature responding to particle diameter were discussed. The mean diameter of PMMA nanospheres prepared by this method could be varied from 90nm to 240nm. The further growth of PMMA nanospheres was attained via a method called seeded-emulsion polymerization.(2) For the surface modification of PMMA nanospheres: With the desired surface modification, the MATS-Modified PMMA nanospheres and the MPTMS-MATS-Modified PMMA nanospheres were still monodisperse.(3) For the fabrication of PMMA/Ag CSNs: Using the above MPTMS-MATS-modified PMMA nanospheres as cores, PMMA/Ag CSNs with a quite uniform Ag shell was successfully synthesized via liquid phase chemical deposition technique. The research demonstrated that several parameters during the process such as concentration of Ammonia, quantity of PMMA powder, and reaction temperature etc could effectively regulate the coating process, among which the concentration of Ammonia was particularly crucial to controll the morphology of Ag shell.