Measurement of Self-Diffusion in Liquid Crystals by a Multiple-Pulse NMR Method

Blinc, R.; Pirš, J.; Zupančić, I.

doi:10.1103/physrevlett.30.546

Cited by 72 publications

(23 citation statements)

References 3 publications

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“…The same strategy, applied also in MRI of solids, 106 can be explored for anisotropic diffusion experiments. The problem, as pointed out 107 in connection with the first such attempts, 108,109 is that dipolar decoupling sequences perform badly in the case of a large frequency offset. Hence, initially one applied only very short gradient pulses in between the r.f.…”

Section: Efficiency Of Gradient Encoding: Refocusing and Decoupling Tmentioning

confidence: 97%

NMR methods applied to anisotropic diffusion

Furó

Dvinskikh

2002

Magnetic Reson in Chemistry

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The methodology of NMR experiments intended to measure anisotropic diffusion is reviewed. Experiments of this kind preferably require oriented samples and/or orientation-dependent spin coupling and/or magnetic field gradients in different directions. One strategy of diffusion experiments in anisotropic systems with broad NMR lines employs line narrowing techniques, thereby allowing for efficient gradient encoding/decoding. Depending on the nuclei, spin couplings and samples, the preferred methods vary from decoupling through echo techniques to magic angle sample orientation and spinning. Another avenue to efficient gradient encoding/decoding is through very strong magnetic field gradients. Either way, anisotropic diffusion reveals new structural features as illustrated by a few selected examples in liquid crystals and in biological tissues.

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Section: Efficiency Of Gradient Encoding: Refocusing and Decoupling Tmentioning

confidence: 97%

NMR methods applied to anisotropic diffusion

Furó

Dvinskikh

2002

Magnetic Reson in Chemistry

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“…PFGNMR has been used to investigate diffusion in nematic liquid crystals (Hayter et al 1974;Zupancic et al 1974). In a study of the water diffusion in nematic perfiuorooctanoate/water mesophases, the low diffusion anisotropy has been related to the shape of nematic aggregates (Boden et al 1984). have obtained the angular dependence of TBBA self-diffusion, shown in Fig.…”

Section: Anisotropic Diffusionmentioning

confidence: 99%

“…pulse sequences. In a sophisticated experiment, Blinc et al (1973) have superposed a rapid multiple 90° r.f. sequence (Ostroff and Waugh 1966), a pulsed magnetic field gradient sequence and a slow Carr-Purcell train of r.f.…”

Section: Tensor Interactionsmentioning

confidence: 99%

Pulsed Field Gradient Nuclear Magnetic Resonance as a Probe of Liquid State Molecular Organization

Callaghan¹

1984

Aust. J. Phys.

234

131

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The imposition of magnetic field gradients on a nuclear magnetic resonance experiment imparts a spatial tag to the molecules via the Larmor frequencies of the nuclei (commonly protons) within. A sensitive measure of changes in the frequency distribution is afforded by detecting the loss of phase coherence in a spin-echo experiment performed in the presence of gradient pulses. Here the molecular displacements may be measured over the duration given by the pulse separation. Pulsed field gradient nuclear magnetic resonance (PFGNMR) employs timesca1es of tens of milliseconds and has a displacement sensitivity of the order 100 nm.For molecules undergoing Brownian motion, PFGNMR can determine molecular self-diffusion coefficients in liquid and mesomorphic phases down to a lower limit of 10-14 m 2 S-1. These coefficients directly probe dynamical processes. For example, in polymer systems such measurements are sensitive to molecular conformation and chain relaxation processes such as reptation. 10 disperse phases PFGNMR can be used to probe diffusive barriers and reveal molecular organization. The timescale dependence of displacement is especially useful in this regard. Examples of studies on poly-and mono-domain lyotropic liquid crystals are presented.Recent use of nuclei with spin >t offers interesting prospects for PFGNMR. The deuterium quadrupole interaction can be used as a signature for order in anisotropic molecular environments. The preparation in the NMR experi~ent of tensor polarization, such as states of two quantum coherence, increases precessional dephasing and may yield a considerable increase in displacement sensitivity.

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“…2 . [2] coil end effect to within 1%, L must be longer than 20 times Generally, when crystals or liquid crystals are placed in this field, the principal axes of the D tensor are represented by 1, 2, and 3, and none of them is parallel to z or x. The observed diffusion coefficient (D obs ) in this case is obtained by rotational transformation to the FG principal-axes frame, i.e.,…”

Section: Self-diffusion By Using a Rotatablementioning

confidence: 99%