Carbon-13 NMR Relaxation Study of Motional Dynamics in Complex Liquids
Kim, Yoo Joong
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Permalink
https://hdl.handle.net/2142/84360
Description
Title
Carbon-13 NMR Relaxation Study of Motional Dynamics in Complex Liquids
Author(s)
Kim, Yoo Joong
Issue Date
1997
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)
Physics, Molecular
Language
eng
Abstract
The motional behavior of complex liquids of various phthalates and structurally related compounds has been investigated using $\sp{13}$C NMR relaxation measurements. Natural abundance $\sp{13}$C NMR spin-lattice relaxation times (T$\sb1),$ spin-spin relaxation times (T$\sb2),$ and nuclear Overhauser effects of individual carbon nuclei in the complex phthalate liquids were measured as a function of temperature and pressure. In addition, an unambiguous $\sp{13}$C peak assignments were carried out using both 2D hydrogen-carbon chemical shift correlation and specific relaxation of individual carbons in the molecule. The choice of model for the spectral density function was critical for proper analysis of the NMR relaxation data in terms of the molecular motion of these molecules, which have flexible side chains attached to a relatively rigid framework composed of phenyl ring and conjugated ester groups. The temperature and pressure dependencies of the relaxation behavior were successfully interpreted in terms of a theoretical model assuming a Cole-Davidson distribution of correlation times, which in turn provided information on the overall and internal motions. Based on these results, the effects of structural variation, both in a relatively rigid framework and in the flexible alkyl side chains of phthalates, on the change in motional behavior and bulk flow properties have been investigated. The $\sp{13}$C NMR relaxation data of individual nuclei for these molecules analyzed in terms of the Cole-Davidson distribution model have provided detailed information about the effect of structural change on their motional characteristics. The motional behavior of these compounds was significantly affected by both the structural shape of the framework and the branching of the side chain, which could be represented by the parameter $\beta$ in the Cole-Davidson distribution model. It was found that the mobility gradient along the alkyl side chains was independent of the relatively rigid framework composed of a ring and carboxyl group. The motional characteristics influenced by the molecular structure for the phthalates could be related to the macroscopic physical property of viscosity and its temperature dependence.
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