Molecular motions in thermotropic liquid crystals studied by NMR spin-lattice relaxation

Nuclear magnetic resonance relaxation experiments with field cycling techniques proved to be a valuable tool for studying molecular motions in liquid crystals, allowing a very broad Larmor frequency variation, sufficient to separate the cooperative motions from the liquidlike molecular diffusion. In...

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Bibliographic Details
Published inBrazilian journal of physics Vol. 28; no. 4; pp. 314 - 328
Main Authors Zamar, R.C., González, C.E., Mensio, O.
Format Journal Article
LanguageEnglish
Portuguese
Published Sociedade Brasileira de Física 01.12.1998
Subjects
PHYSICS, MULTIDISCIPLINARY
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Summary:Nuclear magnetic resonance relaxation experiments with field cycling techniques proved to be a valuable tool for studying molecular motions in liquid crystals, allowing a very broad Larmor frequency variation, sufficient to separate the cooperative motions from the liquidlike molecular diffusion. In new experiments combining NMR field cycling with the Jeener Broekaert order-transfer pulse sequence, it is possible to measure the dipolar order relaxation time (T1D), in addition to the conventional Zeeman relaxation time (T1Z) in a frequency range of several decades. When applying this technique to nematic thermotropic liquid crystals, T1D showed to depend almost exclusively on the order fluctuation of the director mechanism in the whole frequency range. This unique characteristic of T1D makes dipolar order relaxation experiments specially useful for studying the frequency and temperature dependence of the spectral properties of the collective motions.
ISSN:0103-9733
1678-4448
DOI:10.1590/S0103-97331998000400007