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Investigation of water -based silica and organically modified silicate sol -gel systems
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Investigation of water -based silica and organically modified silicate sol -gel systems
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Dissertation
Investigation of water -based silica and organically modified silicate sol -gel systems
1999
Overview
Scope and method of study. The purpose of this study was to address chemical issues associated with developing a water-based sol-gel system. The studies were conducted to provide a foundation for identifying chemical and structural formations in low and high water-content synthetic processes. Both silicate and organically modified silicate (ormosil) systems were investigated with respect to water content, precursor use, curing temperature, and organic content. In each system, gels and films were characterized using 13C and 29Si Nuclear Magnetic Resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and picnometry density measurements. Results of each study were used to identify fundamental chemical species evolution, and to help elucidate structural developments that take place in sol-gel materials derived from water-based processes. Findings and conclusions. Results from the pure silicate and organically modified silicate sol-gel systems indicated the use of variable water concentrations had profound effects on the resulting gel microstructure and chemical content. Results from the pure silica systems revealed a progressive development from linear chain to aggregate particle formation. The low water content gels were identified to have developed through the entanglement of linear chains to form dense microporous silica networks, while an increase in the water content led to increased cyclization of the polymeric siloxane chains and a progressive evolution in microstructure from branch-like to colloidal type particles. The effects of using a water-based process for the epoxide ormosil gels were identified with the stability of the epoxide functional group. Hydrolysis of the epoxide group and esterification of the diol-end group formation resulted in the development of two different types of networks. At low water concentrations, the diol group was esterified with silanol end groups resulting in the development of a carbosiloxane bond formation and a homogenous type hybrid network. At elevated water concentrations, the carbosiloxane formation was hydrolyzed resulting in non-terminated diol end groups with preferential orientation toward surface sites. Conclusions from the dissertation research have shown that the water content truly effects the final gel microstructure and chemical content.
Publisher
ProQuest Dissertations & Theses
Subject
ISBN
0599678062, 9780599678064
