NMR methods applied to anisotropic diffusion

Furó, István; Dvinskikh, Sergey V.

doi:10.1002/mrc.1123

Cited by 72 publications

(43 citation statements)

References 191 publications

(137 reference statements)

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“…[26][27][28] By contrast, the interpretation of diffusive behavior measured by pulsed-gradient spin-echo (PGSE) NMR is more subtle. In locally anisotropic environments, the standard Stejskal-Tanner expression 29 must be modified to allow for the limited dimensionality of local diffusion, and the macroscopic distribution of the orientations of local domains.…”

Section: Introductionmentioning

confidence: 92%

Evolution of a Lamellar Domain Structure for an Equilibrating Lyotropic Liquid Crystal

2006

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Aerosol OT/water exhibits a lamellar phase over a wide range of concentrations. We show, by magnetic resonance (NMR) and scanning electron microscopy (SEM), that the morphology of the lamellar phase varies significantly across that range and that the rate of equilibration depends strongly on concentration (25, 33, and 50 wt %) with, paradoxically, the faster equilibration at higher surfactant concentrations. We find that the 25 wt % sample exhibits a defect-rich local structure, characteristic of a superposed L(3) character. Further into the lamellar region, at 33 wt %, this defect-rich structure persists heterogeneously, while, at 50 wt %, the lamellar phase domains are highly ordered. The NMR methods used here included (2)H spectroscopy and the two-dimensional NMR method, diffusion-diffusion exchange spectroscopy (DEXSY). The latter was used to obtain quantitative information on the domain sizes and defects within the polydomain lamellar mesophase. Comparison of the NMR with the SEM results suggests that, at 25 wt % AOT, bilayer defects play an important role in influencing the (2)H NMR and DEXSY NMR results.

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Section: Introductionmentioning

confidence: 92%

Evolution of a Lamellar Domain Structure for an Equilibrating Lyotropic Liquid Crystal

2006

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“…1 In particular, novel NMR experiments have been carried out to measure anisotropic diffusion in nematic and smectic thermotropic liquid crystals. 1 In particular, novel NMR experiments have been carried out to measure anisotropic diffusion in nematic and smectic thermotropic liquid crystals.…”

Section: Introductionmentioning

confidence: 99%

Smectic order parameters from diffusion data

Cifelli

Cinacchi

Gaetani

2006

The Journal of Chemical Physics

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Microcanonical molecular dynamics simulations have been performed in the smectic A phase of an elementary liquid-crystal model. Smectic order parameters and diffusion coefficients along directions parallel and perpendicular to the director have been calculated during the same trajectory for a number of state points. This has permitted the satisfactory testing of a procedure, adopted in the analysis of experimental self-diffusion coefficients, leading to an estimate of the temperature dependence of the smectic order parameters. This methodology has been then confidently applied to two smectogenic thermotropic liquid crystals belonging to the 4,4(')-di-n-alkyl-azoxybenzene series. The derived smectic order parameters are larger for the homologue compound with the longest alkyl chains. This is consistent with the well-established increased tendency, for members of a homologue series, to form a smectic phase as their alkyl chains become longer.

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“…Molecular transport in these smectic systems has been under intensive experimental and theoretical investigation. Recently, it has been possible to label rodlike viruses in fluorescence experiments [14,15] or perform NMR in spatially varying magnetic fields [16], which then reveals information about transport mechanisms and dynamics. Experiments performed in smectic phases of viruses (long, rigid, μm sized particles with very large aspect ratio, L/D ∼ 100, where L and D are the length and the diameter of the virus, respectively) [14,15] reveal a hopping type mechanism by which they move from one smectic layer to the next in quasiquantized steps of one layer thickness without any significant reorientation.…”

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Dual translocation pathways in smectic liquid crystals facilitated by molecular flexibility

2013

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We investigate translocation mechanisms in smectic A liquid crystals (LCs) by a realistic, coarse-grained model of a LC compound comprising a stiff azobenzene core with flexible tails. We observe that the molecules can permeate from one smectic layer to the next via two different mechanisms, with and without significant reorientation, the former being facilitated through transverse interlayer intermediates. This is possible due to the intrinsic flexibility of the molecules. The two processes lead to characteristic signatures in the Van Hove self-correlation function, which can also be observed experimentally.

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NMR methods applied to anisotropic diffusion

Cited by 72 publications

References 191 publications

Evolution of a Lamellar Domain Structure for an Equilibrating Lyotropic Liquid Crystal

Evolution of a Lamellar Domain Structure for an Equilibrating Lyotropic Liquid Crystal

Smectic order parameters from diffusion data

Dual translocation pathways in smectic liquid crystals facilitated by molecular flexibility

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