A facile synthetic approach to fabricate monodisperse silica composite particles

Abstract

The chemistry of hybrid silica materials remains an actively investigated topic despite vigorous research for over a many years because of its relevance to various fields such as biology, health science, and to many technical applications including adsorbents, optical devices, and catalysis. These hybrid materials also provide enormous opportunities for the development of materials with new structures as well as functionalities. In chapter 1, the overview is introduced to understand the basic sol-gel reaction with two reaction systems including emulsions and alcohol-water mixture media. The emulsion system is useful for controlling the porosity of the particles and the alcohol-water system has an advantage to prepare the monodisperse spheres. However, particle size cannot be controlled in emulsion reaction medium and effective hybrid materials have not been prepared using an alcohol-water mixture system. So, we try to solve these problems. In chapter 2, the successful one-step preparation method to synthesize monodisperse hybrid silica particles is studied using organosilane chemicals in aqueous solution. In general, almost all of the hybrid silica materials are made by employing a complex method where organic materials are coated on the surface of silica substrate via chemical reaction. However, the essence of our novel method is to prepare colloidal hybrid particles without using substrate material. This method has three advantages: (i) this simple method gives rise to the opportunity to incorporate hybrid particles with monodispersity through the self-hydrolysis reaction of various organosilane monomers in aqueous solution, (ii) this efficient method can be applied to load lots of organic functional groups onto the surface of silica particles through a one-step preparation method, and (iii) this effective method can be used to control of particle size of the product by changing the experimental conditions such as the concentration of the precursor, catalyst, or the reaction temperature. In chapter 3, taking advantage of the simple one-step co-condensation process mentioned in chapter 2, we synthesize nano or microsized silica spheres functionalized organic groups from mixtures of surfactant, organosilane, water, and ammonium hydroxide solution. Silica particles have a narrow size distribution and their size can be controlled from nanometer to micrometer by adjusting and changing the surfactants and reaction temperature. In chapter 4, two types of thermo-sensitive poly(N-isopropylacrylamide) (PNIPAm)-silica organic/inorganic hybrid particles are successfully synthesized in aqueous solution with a facile synthetic process. Silane coupler of vinyl organic groups connects with the PNIPAm polymer and silica sources. First, hybrid spheres are prepared by grafting to PNIPAm polymer hybrid particles using a VTMS (vinyl trimethoxysilane) silica spheres as a substrate. The thickness of polymer shell on the silica surfaces can be easily controlled by varying the concentration of NIPAm monomer. Second, other type of hybrid particles is fabricated by encapsulating with a PNIPAm polymer. Using the NIPAm-VTMS monomer enables complete encapsulation of PNIPAm by silica spheres. In chapter 5, the MPTMS (3-mercaptopropyl trimethoxysilane) @M (M=Ag, Au, Pd, Pt) particles are prepared by accumulating the noble metal nanoparticles on the surfaces of thiol-functionalized MPTMS silica, which is accomplished by the chemisorption between noble metal nanoparticles and thiol groups. In conventional method, the fabrication methods, in which silica spheres are coated by metals using LBL (Layer-By-Layer) or core-shell synthesis is not efficient due to the complexity of synthetic method, the low surface coverage of functional group on the particles, and the low loading capacity of noble metal particles. The synthetic method developed in this study can overcome these limitations and allow us to prepare the MPTMS@M (M=Ag, Au, Pd, Pt) and Pt metal-hollow particles with substantial metallic layer via the self-assembly behavior induced by chemisorption between noble metal nanoparticles and thiol groups.