NMR Spectroscopy of Anisotropic Fluid Systems: Theory and Experiment

Introduction

In the study of anisotropic fluids using high-field nuclear magnetic resonance (NMR) spectroscopy several nuclei carrying a spin can be used as probes. The most used probes in anisotropic fluids are the nuclei of hydrogen, deuterium, carbon 13, nitrogen, and fluorine. Hydrogen with a nucleus of spin 1/2 has the advantage of giving high signal-to-noise ratios because of its high gyromagnetic ratio and also because it is present in high numbers in the system's molecules. It has the disadvantage that the information obtained is nonselective because many different hydrogens in a molecule contribute to the response of the system. Also the high number of hydrogen nuclei interacting through dipolar coupling significantly hampers a detailed simulation of the data. Deuterium with a nucleus of spin 1 is not present naturally in anisotropic fluid molecules, and its use requires the replacement of hydrogen atoms in the molecule by deuterium atoms, a process called deuteration. The small number

NMR ofLiquid Crystal Dendrimers

Carlos R. Cruz, Joao L. Figueirinhas, and PedroJ. Sebastiao Copyright © 2017 Pan Stanford Publishing Pte. Ltd.

ISBN 978-981-4745-72-7 (Hardcover), 978-981-4745-73-4 (eBook) www.panstanford.com of interacting particles necessary to consider when deuterium is the probe nucleus enables a full and unique interpretation of the spectroscopic data. Nitrogen and fluorine are less used; they are present in much smaller quantities in anisotropic fluid molecules or not present at all. For some of these nuclei short spin-lattice relaxation times present in these probes broaden the spectral lines, making the interpretation of the data difficult.

 
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