Structure and Dynamics Studies Using Nuclear Magnetic Resonance: From Simple Liquids to Extreme Networks Public Deposited

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Last Modified
  • March 20, 2019
Creator
  • Heist, Leah
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Nuclear magnetic resonance is a powerful analytical tool utilized by chemists and biochemists to extract structural information. However, NMR has utility beyond structure determination: it is also a powerful technique for interrogating dynamics at the microscopic level. In this thesis, I have used NMR to study a diverse range of fluid systems: • liquid state structure in molecular liquids using very high field NMR • orientational order in nonlinear liquid crystal dimers • molecular dynamics and structure in highly grafted “bottle-brush polymers” • high performance liquid crystal thermosetting polymers. NMR detects small changes in the magnetic energy of nuclei in different environments. With the advent of very-high field NMR spectrometers (i.e. 800, 950, and even 1000 MHz in recent years), extremely subtle interactions between nuclei and the magnetic field can be detected—interactions that are largely averaged out due to isotropic motion in lower field spectrometers. In Chapter 2, very high field NMR is exploited to measure field-induced nuclear quadrupolar interactions for prototypical molecular liquids. By measuring the field-induced biasing of molecular motion, it is possible to experimentally determine the leading tensor component of the pair correlation function in liquids, which provides a critical test of molecular dynamics simulation force fields. The incompletely averaged, anisotropic NMR interactions described in Chapter 2 for simple isotropic liquids are significant for anisotropic molecules (liquid crystals). One type of liquid crystal, the nematic phase, is characterized by molecules that tend to align their long axis on average parallel to one another in the fluid, but have no spatial correlations—no positional order. In Chapter 3, I attempt to describe the nature of a new nematic phase found in nonlinear liquid crystal dimers, introduced in 1991 by Hiro Toriumi, professor of chemistry at Tokyo University, by supplementing recent simulation data from Photinos and coworkers at the University of Patras with extensive 2H and 13C NMR studies. In Chapters 4 and 5, NMR studies on two very diverse soft matter networks are outlined: very soft, room temperature bottle-brush polymer networks and very tough high temperature (>300°C) liquid crystal thermosets.
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Rights statement
  • In Copyright
Advisor
  • Sheiko, Sergei
  • Madsen, Louis
  • Wightman, R. Mark
  • Samulski, Edward T.
  • Jorgenson, James
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2016
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