Recommendation for The Use of The Code Letters G And H for Smectic Phases

Demus, D.; Goodby, J. W.; Gray, G. W.; Sackmann, H.

doi:10.1080/01406568008070143

Cited by 90 publications

(64 citation statements)

References 2 publications

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“…The very small dipolar interactions between distant spins in solution and even in gases have been shown to generate macroscopic signals if the spatial symmetry of the sample is broken [39][40][41][42][43][44]. These long range couplings could be expected to be more pronounced in a LC due to the restricted molecular diffusion [45] and the instrinsic asymmetry on the sample inntroduced by the molecular alignment. Also, due to the high long-range molecular correlation of liquid crystals, intermolecular contributions should be expected to contribute to dipolar order relaxation and decoherence.…”

Section: Since the Tensor Form Of H Dmentioning

confidence: 99%

Quasiequilibrium states in thermotropic liquid crystals studied by multiple-quantum NMR

Buljubasich

Monti

Acosta

et al. 2009

The Journal of Chemical Physics

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Previous work showed that by means of the Jeener-Broekaert (JB) experiment, two quasiequilibrium states can be selectively prepared in the proton spin system of thermotropic nematic liquid crystals (LC) in a strong magnetic field. The similarity of the experimental results obtained in a variety of LC in a broad Larmor frequency range, with crystal hydrates, supports the assumption that also in LC the two spin reservoirs into which the Zeeman order is transferred, originate in the dipolar energy and that they are associated with a separation in energy scales: a constant of motion related to the stronger dipolar interactions (S), and a second one (W) corresponding to the secular part of the weaker dipolar interactions with regard to the Zeeman and the strong dipolar part. We study the nature of these quasiinvariants in nematic 5CB (4'-pentyl-4-biphenylcarbonitrile) and measure their relaxation times by encoding the multiple quantum coherences of the states following the JB pulse pair on two orthogonal bases, Z and X. The experiments were also performed in powder adamantane at 301 K which is used as a reference compound having only one dipolar quasiinvariant. We show that the evolution of the quantum states during the build up of the quasi-equilibrium state in 5CB prepared under the S condition is similar to the case of powder adamantane and that their quasi-equilibrium density operators have the same tensor structure.In contrast, the second constant of motion, whose explicit operator form is not known, involves a richer composition of multiple quantum coherences on the X basis of even order, in consistency with the truncation inherent in its definition. We exploited the exclusive presence coherences ±4, ±6, ±8, besides 0 and ±2 under the W condition to measure the spin-lattice relaxation time T W accurately, so avoiding experimental difficulties that usually impair dipolar order relaxation measurement such as Zeeman contamination at high fields, and also superposition of the different quasiinvariants. This procedure opens the possibility of measuring the spin-lattice relaxation of a quasiinvariant independent of the Zeeman and S reservoirs, so incorporating a new relaxation parameter useful for studying the complex molecular dynamics in mesophases. In fact, we report the first measurement of T W in a liquid crystal at high magnetic fields. The comparison of the obtained value with the one corresponding to a lower field (16 MHz) points out that the relaxation of the W-order strongly depends on the intensity of the external magnetic field, similarly to the case of the S reservoir, indicating that the relaxation of the W-quasiinvariant is also governed by the cooperative molecular motions.

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Section: Since the Tensor Form Of H Dmentioning

confidence: 99%

Quasiequilibrium states in thermotropic liquid crystals studied by multiple-quantum NMR

Buljubasich

Monti

Acosta

et al. 2009

The Journal of Chemical Physics

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“…LCs have been widely used in displays, sensors, drug delivery vehicles, photonic band gap structures, as well as in optical elements such as controllable lenses and lasers [31,32]. LC is anisotropic fluid, combining the flow property of ordinary liquid with the anisotropic physical parameters of crystals.…”

Section: Liquid Crystals (Lcs)mentioning

confidence: 99%

Lyotropic liquid crystal directed synthesis of nanostructured materials

Wang

Chen

Jiao

2009

Science and Technology of Advanced Materials

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This review introduces and summarizes lyotropic liquid crystal (LLC) directed syntheses of nanostructured materials consisting of porous nanostructures and zero-dimensional (0-D), one-dimensional (1-D) and two-dimensional (2-D) nanostructures. After a brief introduction to the liquid crystals, the LLCs used to prepare mesoporous materials are discussed; in particular, recent advances in controlling mesostructures are summarized. The LLC templates directing the syntheses of nanoparticles, nanorods, nanowires and nanoplates are also presented. Finally, future development in this field is discussed.

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“…The studies on phase transitions in thermotropic liquid crystal have seen considerable progress since 1980 [1]. With the availability of high resolution and sensitive experimental techniques, it could be made easy to record precisely the transformations that occur during mesophase changes.…”

Section: Introductionmentioning

confidence: 99%

Image Analysis Studies for Phase Transitions of Ferroelectric Liquid Crystals

Sastry

Rao

Mahalakshmi

et al. 2012

ISRN Condensed Matter Physics

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Phase transition temperatures of ferroelectric liquid crystals ((S)-(-)-2-methylbutyl 4 -(4 -n-alkanoyloxybenzoyloxy) biphenyl-4-carboxylates (where n = 16 and 18)) are studied through two techniques of image analysis. One is a statistical method, applied to compute the statistical parameters from the textures of each sample and the other, computation of Legendre moments being applied as image moment analysis, both of which are considered as a function of temperature. The textures of the samples are recorded with the polarizing optical microscope (POM) attached to the hot stage and high resolution camera. The phase transition temperatures of samples are inferred by the abrupt changes in the computed parameter values. The results obtained from the present methodology are in good agreement with those published in earlier literature done by the different techniques, like differential scanning calorimetry (DSC).

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Recommendation for The Use of The Code Letters G And H for Smectic Phases

Cited by 90 publications

References 2 publications

Quasiequilibrium states in thermotropic liquid crystals studied by multiple-quantum NMR

Quasiequilibrium states in thermotropic liquid crystals studied by multiple-quantum NMR

Lyotropic liquid crystal directed synthesis of nanostructured materials

Image Analysis Studies for Phase Transitions of Ferroelectric Liquid Crystals

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