NMR studies of the chemical additives effect on the sol-gel process
Chan, Jar-Bee
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Permalink
https://hdl.handle.net/2142/21434
Description
Title
NMR studies of the chemical additives effect on the sol-gel process
Author(s)
Chan, Jar-Bee
Issue Date
1990
Doctoral Committee Chair(s)
Jonas, Jiri
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
Due to its unique advantages, the sol-gel process has attracted considerable attention from both technical and scientific points of view during the past decade. Compared with the conventional method, the sol-gel process can make very pure and homogeneous ceramic materials at much lower temperatures. More importantly, it not only opens up the possibilities of preparing new multicomponent materials with specific properties but also provides a great deal of convenience in some chemical processings such as coating, thin film and fiber fabrication.
Chemical additives have been known to drastically influence the gelation process and the physical properties of the sol-gel derived materials, although the mechanism is still not elucidated. It is the aim of this thesis to study the chemical additives effect and gain a better molecular level understanding of the sol-gel process.
It is demonstrated that the gelation process is dramatically accelerated and the polymerization process proceeds through the formation of higher branched species from very early stage in the fluoride catalyzed sol-gel system. In addition, the fluoride catalyzed xerogel is shown to have larger average pore radius and narrower pore size distribution, as a result of the decrease of the amount of micropores in the silica network.
We have also studied the additive effect of various amides on the sol-gel process. All the amides studied, except N,N-dimethylformamide and N,N-dimethylacetamide, show some acceleration effect on the gelation and increase the pore size. Both hydroxyl and formamide are demonstrated to drastically increase the initial hydrolysis reaction rate whereas N,N-dimethylformamide shows only minor influence. Dynamic information about the solvent molecules in the catalyzed sol-gel systems is also investigated by measuring the spin-lattice relaxation time and the linewidth of NMR spectrum. It is shown that the rotational motion of water molecule is more restricted by the hydrogen bonding in the hydroxyl and formamide catalyzed sol-gel systems.
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