High Pressure NMR Studies of Supercooled Viscous Fluids
Welsh, Michael John
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Permalink
https://hdl.handle.net/2142/70397
Description
Title
High Pressure NMR Studies of Supercooled Viscous Fluids
Author(s)
Welsh, Michael John
Issue Date
1987
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
Abstract
The spin-lattice relaxation times, viscosities, and densities of several supercooled viscous fluids have been previously measured as a function of temperature and pressure in order to investigate the adequacy of the modified Debye equation over a large range of viscosities. In this study, a more detailed look was taken at the rotational-translational coupling characterized by the coupling parameter $\kappa$ of isopropylbenzene and toluene. It was shown that the nature of the density dependence of $\kappa$ for isopropylbenzene-d$\sb1$ is the same as the density dependence of $\kappa$ for isopropylbenzene-d$\sb5$. However, toluene represents a transition between molecules with no axis of unhindered reorientation like isopropylbenzene, to more symmetric molecules which may have one or more than one axis of unhindered reorientation. The second half of this study deals with an investigation of the effect of a permanent dipole moment on the rotational-translational coupling parameter. It was shown for the cyclic carbonate system, 4-methyl-1,3-dioxolan-2-one, 4-chloro-1,3-dioxolan-2-one, and 4,5-dichloro-1,3-dioxolan-2-one, that the permanent dipole plays a important role in determining the rotational-translational coupling. Using constant reduced isochoric plots of $\tau\sb{\theta}$ versus $\eta$/T, the modified Debye equation was applied to investigate the nature and the degree of rotational-translational coupling with increasing density as a function of the molecular shape, and as a function of the size of the permanent dipole of the model molecules.
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