Nematic and Smectic Ordering of 4-<i>n</i>-Octyl-4′-cyanobiphenyl Studied by Carbon- 13 NMR

Fung, B. M.; Poon, Chi‐Duen; Gangoda, Mahinda; Enwall, E.; Diep, Tuan A. D.; Bui, Chuong V.

doi:10.1080/00268948608079614

Cited by 35 publications

(12 citation statements)

References 17 publications

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“…The values of the order parameters were found in the range of 0.22 to 0.35 depending on the temperature and anion type. These values are significantly lower when compared to typical S > 0.5 in conventional smectic A phases of non-ionic LCs [24,25]. Similarly low S values in smectic phase were found in an analogous ILC with longer alkyl chain imidazolium-based cation and NO 3 anion, C 14 mimNO 3 [13].…”

Section: Molecular Order Smentioning

confidence: 68%

NMR Spectroscopic Study of Orientational Order in Imidazolium-Based Ionic Liquid Crystals

et al. 2019

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We report on molecular and local orientational order of a series of imidazolium-based ionic liquid crystals exhibiting layered smectic A mesophase. Materials constituting of 1-dodecyl-3-methylimidazolium cation, and different counter-ions, were investigated. We apply two-dimensional 13C-1H dipolar NMR spectroscopy to quantify orientational order of C-H bonds of the organic cation. The experimental data supported the structural model of the interdigitated chains aligned with the smectic layer normal. Molecular order parameter S was found to increase in the anion sequence BF4− < I− < Br− < Cl−. This trend correlates well with ionic radius, negative charge delocalization, and hydrogen-bonding properties of the anions.

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Section: Molecular Order Smentioning

confidence: 68%

NMR Spectroscopic Study of Orientational Order in Imidazolium-Based Ionic Liquid Crystals

et al. 2019

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“…Temperature dependence S(T) is displayed in Figure 4b, while temperature dependencies of the local bond order parameters for the imidazolium core and for the selected carbons in the chain are shown in Figure 4a. We conclude that the ionic smectic A phase is formed (counter-intuitively) with significantly lower value of the molecular order parameter S when comparing to non-ionic smectic mesogens [20][21][22]. Theoretical and computational studies suggest that, in contrast to neutral mesogens, the orientational ordering is less important for the stabilization of the smectic layers in ILC where dominant stabilizing effect is due to a "charge-ordered" nanoscale segregation induced by ionic interactions [1,19,23,24].…”

Section: Order Parametersmentioning

confidence: 78%

Molecular and Segmental Orientational Order in a Smectic Mesophase of a Thermotropic Ionic Liquid Crystal

2018

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We investigate conformational dynamics in the smectic A phase formed by the mesogenic ionic liquid 1-tetradecyl-3-methylimidazolium nitrate. Solid-state high-resolution 13C nuclear magnetic resonance (NMR) spectra are recorded in the sample with the mesophase director aligned in the magnetic field of the NMR spectrometer. The applied NMR method, proton encoded local field spectroscopy, delivers heteronuclear dipolar couplings of each 13C spin to its 1H neighbours. From the analysis of the dipolar couplings, orientational order parameters of the C–H bonds along the hydrocarbon chain were determined. The estimated value of the molecular order parameter S is significantly lower compared to that in smectic phases of conventional non-ionic liquid crystals.

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“…Fittings of the experimental data to the anisotropic, isotropic, and purely dipolar models described in the text. 25 where a different experimental technique was applied.…”

Section: Resultsmentioning

confidence: 99%

Many-spin quantum dynamics during cross polarization in 8CB

Chattah

Álvarez

Levstein

et al. 2003

The Journal of Chemical Physics

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We analyze theoretically and experimentally the quantum dynamics of a three-spin-1/2 system during cross polarization (CP). Our analysis takes into account a Hamiltonian behavior for a carbon C13 coupled to two protons H1 while the coupling to a spin bath is treated in the fast fluctuation approximation. This model is applied to the methylene and biphenyl groups of the smectic and nematic phases of the liquid crystal 4-n-octyl-4′-cyanobiphenyl (8CB). Experimental data from standard CP, combined with our theoretical results, allow us to separate the homonuclear H1-H1 and heteronuclear H1-C13 residual dipolar couplings. These values are in good agreement with those obtained by using a combination of CP under Lee–Goldburg conditions and standard CP data. A well differentiated relaxation behavior among the two phases seems to indicate that while the extreme narrowing approximation is appropriate for the nematic phase, the description of the smectic phase requires consideration of the slow-motion limit.

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Nematic and Smectic Ordering of 4-n-Octyl-4′-cyanobiphenyl Studied by Carbon- 13 NMR

Cited by 35 publications

References 17 publications

NMR Spectroscopic Study of Orientational Order in Imidazolium-Based Ionic Liquid Crystals

NMR Spectroscopic Study of Orientational Order in Imidazolium-Based Ionic Liquid Crystals

Molecular and Segmental Orientational Order in a Smectic Mesophase of a Thermotropic Ionic Liquid Crystal

Many-spin quantum dynamics during cross polarization in 8CB

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