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COMPARISON OF SHORT-RANGE INTERACTIONS IN NEMATIC LIQUID-CRYSTALS - A H-2-NMR STUDY OF 5CB-D(19) AS A SOLUTE

TitleCOMPARISON OF SHORT-RANGE INTERACTIONS IN NEMATIC LIQUID-CRYSTALS - A H-2-NMR STUDY OF 5CB-D(19) AS A SOLUTE
Publication TypeJournal Article
Year of Publication1994
AuthorsChandrakumar, T, Zimmerman, DS, Bates, GS, Burnell, EE
JournalLiquid Crystals
Volume17
Pagination457-485
Date PublishedOct
Type of ArticleArticle
ISBN Number0267-8292
KeywordsBINARY-MIXTURES, EQUILIBRIUM, FLEXIBILITY, MAGNETIC-RESONANCE, MOLECULAR-STRUCTURE, MULTIPLE-QUANTUM NMR, NORMAL-BUTANE, orientational order, RAMAN-SPECTRA, SPECTROSCOPY
Abstract

Previous studies using dideuterium as a solute have demonstrated the importance for orientation of the interaction between the solute molecular quadrupole moment and the average electric field gradient present in liquid crystals. With the aim of learning about additional orientational mechanisms, we have studied the temperature dependence of the H-2-NMR spectra of the liquid crystal 5CB-d(19) as the solute in three liquid crystal mixtures: 55 wt % 1132/EBBA, 56.5 wt % 1132/EBBA and 70 wt % 5CB/EBBA. In these mixtures, the contribution from the environment to the average electric field gradient at the H-2 nucleus of dideuterium is zero. The spectra of 5CB-d(19) in the mixtures 55 wt % 1132/EBBA and 56.5 wt % 1132/EBBA are equivalent, but are different from those in 70 wt % 5CB/EBBA. The spectra of 5CB in 55 wt % 1132/EBBA and 70 wt % 5CB/EBBA are analysed using two different models for the short range potential, and parameters of the models are used to compare the potentials in the different mixtures. For a given spectral splitting of the chain C-1 deuteron, the reduced short range potential is the same in all three mixtures studied. The spectral differences observed are a consequence of different nematic-isotropic phase transition temperatures combined with the effect of trans/gauche-isomerization in the hydrocarbon chain.

URL<Go to ISI>://A1994PH47000001