Preparation And Characterization Of Organic/Inorganic Core-Shell Materials

In recent years, there has been increasing interest in core-shell materials due to its potential in developing novel materials with unique functions. The exterior coating structure is very useful in many applications in order to enhance the stability of dispersions, to protect the particles from interaction with surrounding medium, and to endow the core optical, conductive, magnetic, adsorptive, and surface reactive properties. Polymer organic-inorganic core-shell particles attract scientists'attention because it realizes the molecular scale fabrication. Combining the properties of organic and inorganic components, this kind of materials has excellent and special capability as compared to its components. The inorganic shell can improve the internal domain thermal stability, mechanical strength and scratch resistance. The latex core exhibits elasticity and film formation ability. The latex coated with inorganic matter imparts the core-shell particles with improved chemical and physical properties, creating synergistic effects.Many studies for coating process have been proceeded comprised of in situ deposition as well as layer-by-layer (LbL) technique. In situ deposition is to prepare the core-shell particles by controlled precipitation of inorganic precursors onto the core domain. The second approach, LbL technique is versatile method to synthesize core-shell materials. It's based on electrostatic interaction between particles, the species having opposite charge with core and absorbing on the surface of the core. The coated particles subsequently centrifuged and washed could be deposited in order to obtain the desirable coating thickness. Disadvantages of this technique are not only the time-consuming sequential polyelectrolyte deposition cycles and purification steps, but also the incorporation of redundant polyelectrolyte into shell. Chemical coprecipitation is first to immerge the polymer colloid with inorganic salts, next, by using in situ reaction, the organic core were coated with inorganic shell.Silica has many advantages:â…°) It is chemical inert and optical transparent;â…±) The silanol groups on the shell are available for further surface modification;â…²) Silica can be easily doped with fluorophores and dyes. These specific properties are utilized for technological application from medicine, paints, inks, to fillers. Titania is also a good kind of inorganic material, and it can be used as catalysts, white pigments etc. Here, we mainly study polymer-inorganic core-shell materials, specifically the silica coating.Here, PS/SiO₂ and OMC/SiO₂ core/shell nanoparticles were synthesized by two different methods. In the second chapter, monodisperse polystyrene latexes were prepared by emulsion polymerization. Then tetraethoxysilane (TEOS) was added to this system in acid condition using sol-gel method, and the obtained polystyrene latexes were employed as the template. The electrostatic interaction at the surfactant/inorganic interfaces governed the assembly process. As a result, there was a layer of about 17 nm silica at the surface of polystyrene latex. The polystyrene-silica particles were analyzed by TEM,SEM,DLS,FT-IR and DSC. In addition, effect of the amount of surfactant on diameter and conversion of polystyrene latexes was investigated in detail.In the third chapter, OMC/SiO₂ core/shell nanoparticles were prepared with a novel method. First, SiO₂ shell precursor was prepared with a sol-gel method. It contained a large amount of OH groups, which offers versatile possibilities for condensation polymerization under alkaline condition. Then an O/W emulsion was produced under the stirring of a homogenizer. After the outer surfaces of the emulsion droplets are solidified by the condensation reactions between the surface silanols, they may serve as self-templates. Subsequently, the un-reacted precursor within the emulsion droplets becomes solidified onto the templates as shell, while the core compounds stay inside as core, producing core-shell nanoparticles. In the last, the mechanism of this method for forming core-shell nanoparticles was discussed. The obtained core/shell particles were analyzed by TEM,SEM,DLS,FT-IR and UV.