A Pulsed NMR Study of Transient and Persistent Molecular Order in Nematic Liquid Crystals
The proton absorption spectrum of a typical nematic liquid crystal shows one or more well separated pairs of lines arising from the large dipolar interaction of protons on the phenyl rings. Because these interactions have cylindrical symmetry with respect to the nematic director, observation of the splittings gives a direct measure of the orientation of the director with respect to the magnetic field. Experiments are reported in which pulsed NMR techniques were used to determine persistent molecular order and orientation in response to applied electric fields. From these experiments it was possible to determine the temperature dependence of the flow alignment angle for PAA. These data show the first evidence of flow alignment in the super-cooled nematic state. In addition studies of CBEOA yielded information about the time evolution of molecular order and orientation in response to the sudden application of an electric field.
KeywordsAnisotropy Torque Phenyl Aniline Cose
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- 3.D. P. McLemore, Ph.D. Thesis, Univ. of Maine, 1973 (unpublished).Google Scholar