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NMR Spectroscopy in Liquid Crystalline and Ordered Phases

Nuclear Magnetic Resonance and Electron Spin Resonance Spectroscopy

  1. Ronald Y. Dong

Published Online: 17 DEC 2012

DOI: 10.1002/9780470027318.a9297

Encyclopedia of Analytical Chemistry

Encyclopedia of Analytical Chemistry

How to Cite

Dong, R. Y. 2012. NMR Spectroscopy in Liquid Crystalline and Ordered Phases. Encyclopedia of Analytical Chemistry. .

Author Information

  1. University of British Columbia, Vancouver, B.C., Canada

Publication History

  1. Published Online: 17 DEC 2012

Abstract

Applications of nuclear magnetic resonance (NMR) spectroscopy as an analytical tool in liquid crystals (LCs) are surveyed. Proton, deuteron, carbon-13, and nitrogen-14 are commonly used as probes in solid-state NMR of condensed phases. Their usages in LCs are discussed in some details. Complex mathematical expressions needed to interpret NMR observables (both equilibrium and dynamic properties) are kept to a minimum, and the reader can refer to original articles and books for details. As it is impossible to provide an exhaustive coverage of the literature, selective examples are chosen to highlight areas of recent interests in the study of liquid-crystal materials, particularly thermotropics, in terms of their physics and chemistry. Orientational/positional order parameters are readily obtained in ordered liquid-crystal phases by means of NMR. They can serve as characteristic signatures of the studied mesophases. Liquid-crystal ordering depends on intermolecular potentials among neighboring molecules. Solutes dissolved in LC solvents are good candidates to reveal different ordering mechanisms. Nonzero spin interactions are used to determine molecular structure of large and small molecules, and/or their conformation statistics. Nuclear spin relaxation times are readily measured by means of different NMR pulse techniques and can be powerful for revealing dynamic properties of mesogens with increasing structural complexity.