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|Title:||Experimental study of physical-chemical factors in the sol-gel process|
|Doctoral Committee Chair(s):||Jonas, Jiri|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||A variety of experimental techniques (multinuclear NMR, Raman, small angle neutron scattering, fluorescence polarization, viscosity, turbidity, static and dynamic light scattering experiments) have been employed to investigate the nature of the sol-gel process of tetramethyl orthosilicate; Si(OCH$\sb3$)$\sb4$; TMOS. These experiments probe changes in structural and dynamical properties at the macroscopic and microscopic level in the course of the sol-gel process and the transition state. The experimental results are compared with recent theories for the gelation process.
Another important factor that influence the gel formation is the catalyst, usually a base or acid, or the so called drying control chemical additives (DCCA) which not only can greatly reduce the gelation time but can avoid cracking during the sintering process. Small angle neutron scattering measurement has been used to investigate the particle size, structural evolution and growth process of the fluorine catalyzed sols. The effect on pore structure of the resulting gels and its evolution during heat treatment have been studied by the nitrogen ad(de)sorption isotherm (BET) measurements. The applicability of catalyst fluoride on the sol-gel systems and the comparison with the plain gel are studied.
Pressure is also a parameter that affects the sol-gel process, especially the kinetics. Since the existing functional reactivity theory for the sol-gel kinetics has only been applied on the acidic catalyzed system, the application of this theory to the plain (neutral) system seemed necessary. In addition the pressure effects on the kinetics can provide information about the origin of the mechanisms of the process. The experiment shows that both the hydrolysis and condensation reactions are accelerated by the pressure, the latter being affected to a larger extent. The experimental data obtained allow us to use the functionality theory for the beginning stage of the sol-gel process. (Abstract shortened with permission of author.)
|Rights Information:||Copyright 1991 Hua, Duen-Wu|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9124426|