ABSTRACT
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. Deuteriumwith 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
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.
