Facile Synthesis and Application of Multifunctional Hybrid Silica (MHS) Particles

Abstract

Functionalized organic-inorganic hybrid materials have received great attention due to their potential for scientific and industrial applications. Among various methods used in the preparation of functionalized hybrid particles, the surface modification of silica particles has been used extensively because of its simplicity. However, the introduction of multi-functionality on silica particles has not been reported yet. Functional groups in silica particles could endow several interesting features such as selective chemical and physical properties as well as controlled assembly. For example, tri-functional hybrid particles can be used as biological labeling materials with targeting, anchoring, and separation ability depending on the functional groups. In this study, organic-inorganic hybrid silica particles were synthesized using a controlled sol-gel process with various silane monomers. Further surface modification of these multifunctional hybrid silica particles could extend the types of functional groups on the silica particles. Self-assembly to 3-dimentional structure demonstrated a potential ability of MHS particles for building block through acid-base reaction between two MHS particles. In chapter 2, Multi-functional hybrid silica (MHS) particles having di- and tri-functional groups were prepared by simple one pot synthesis. Monodispersed spherical particles ranging in size from 200 nm to 1 μm are produced in a co-condensation of trialkoxy silane monomers with various funtional groups without any external structure-directing material. The existence and population of multiple functional groups in MHS particles were revealed by selective chemical reaction of each functional groups with corresponding fluorescent dyes such as fluroescamine and rhodamine B isothiocyanate. The surface reaction of these MHS particles with various organic or inorganic materials not only endowed additional functionalities, but also produced metallic hybrid composite particles. In addition, multiplex tasking ability of multifunctional hybrid particles were demonstrated by 3-dimentional self-assembly between two MHS particles with different size and functionalities as well as by dye-tagging and selective binding to a patterned surface. In chapter 3, Phenyl-amine-mercapto based MHS monolayer film was prepared by self-assembly process at interfaces between hexane and water. The addition of methyl methacrylate monomer to hexane layer produced monolayer covered with rather thick film of PMMA after UV curing. And then, asymmetric chemical reaction of surface functional groups on MHS particles with organic and inorganic (or metallic) groups was performed in the water phase. Therefore different types of Janus particles such as organic-inorganic and organic-metallic biphasic colloidal particles are prepared by an asymmetric chemical modification of MHS particles at interfaces between hexane and water. In chapter 4, we demonstrated a potential ability of metal sensor device for environmental application. TMPyP (α,β,γ,δ– tetrakis(1-methylpyridinium-4-yl)porphine p– toluenesulfonate) sensor mulecules were successfully introduced on surface modified MHS particles by using strong ion-pair interaction between positive charge of TMPyP molecules and negative charge of MHS particles. As increasing metal ion (Cd2+, Zn2+, and Hg2+) concentration, the color of sensor particles changed from red brown to green. Furthermore, Un-vis adsorption spectrum of sensor particles exhibited a shift from 430 nm to 470 nm by complexation of metal ion with sensor tagged MHS particles. In chapter 5, Thermo-sensitive hybrid silica particles, octadecyltrimethoxysilane (OTS) particles and composite particles with vinyltrimethoxysilane (VTMS), were synthesized using modified sol-gel process without a surfactant. The DSC profile of OTS particle exhibited solid-liquid transition temperature above 58 degrees due to the alkyl chain interaction of layered structure. The transition temperature of OTS/VTMS composite particles was about 10 degrees lower than OTS particles because the alkyl chain interaction of layered structure was partially interrupted by vinyl group from VTMS. According to XRD pattern of OTS/VTMS composite particles, the intensity of the peak at 2θ = 21.5°, which corresponds chain to chain spacing, was significantly reduced as compared with OTS particles. In chapter 6, we report a colloidal self-assembly growth mechanism for the formation of POSS cubic crystals based on observation using electron microscopy. The self assembly processes can be summarized by following steps. First, the nano-sized spherical particles are formed through hydrolysis and condensation of precursors. Second, these zero dimensional particles condense to chain-shaped one dimensional spherical particle arrays. Third, the one dimensional particle arrays are converted to pseudo two dimensional flower-shaped cluster particles. Finally, the cubic three dimensional POSS crystals are formed by the self-assembly of two dimensional flower-shaped clusters.