Transverse deuteron spin relaxation in thermotropic liquid crystal polymers: determination of viscoelastic properties

Heaton, N.; Reimer, D.; Kothe, G.

doi:10.1016/0009-2614(92)85632-k

Cited by 27 publications

(15 citation statements)

References 22 publications

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“…This correlation time is typically associated with local effects on the molecular distance scale such as diffusion of ions about polymer segments and internal polymer dynamics. 1,15 The longer correlation time on the order of microseconds is usually connected with, e.g., collective fluctuations in liquid crystals 24 or long-range diffusion of ions through a microheterogeneous polymer gel. 6 In our spinlock frequency range, both the fast and intermediate processes are in the extreme narrowing limit, ω 1 τ F , 1 and ω 1 τ M , 1, respectively.…”

Section: Resultsmentioning

confidence: 99%

Extremely Slow Counterion Dynamics in Xanthan Liquid Crystal through ²³Na and ¹⁴N NMR

2002

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To describe the structure and dynamics in a lyotropic xanthan liquid crystal, we have done 23 Na and 14 N NMR experiments. The spectra are consistent with a powder average over randomly oriented liquid-crystalline domains. From 14 N quadrupolar echo experiments it was concluded that the exchange among the several micron sized domains is slow with residence times in the millisecond range. Conventional spin-lock experiments ( 14 N and 23 Na) as well as spin-lock experiments filtered through the quadrupolar spin polarization order ( 23 Na only) revealed the existence of an extremely low frequency, submegahertz dispersion in the spectral densities pertaining to both sodium and ammonium counterions. The corresponding correlation times are on the order of tens of microseconds and agree with a structural correlation length on the order of 500 nm. The latter correlation times reflect the rearrangement of counterions among polymer segments over the same spatial extent as the polymer persistence length.

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Section: Resultsmentioning

confidence: 99%

Extremely Slow Counterion Dynamics in Xanthan Liquid Crystal through ²³Na and ¹⁴N NMR

2002

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“…In particular, NMR field cycling 20,21 and frequency dependent transverse spin relaxation studies 22,23 indicate that low frequency modes are consistent with small amplitude director fluctuations. [24][25][26][27]23,28 and dielectric relaxation [29][30][31] investigations suggest that LCPs also undergo large amplitude reorientation that may be reasonably described by anisotropic rotational diffusion models.…”

Section: Introductionmentioning

confidence: 94%

“…In contrast, slow collective modes could certainly contribute to transverse spin relaxation and may be identified by their characteristic orientation dependence. 22,23 Figure 2 shows the location of the axis systems and transformations which define the ''individual molecule'' and intramolecular dynamics in the main chain/side chain LCP. Note that the term ''individual molecule'' here refers to an effective segment of the chain, which may be taken to be the monomer unit.…”

Section: B Separation Of Motionsmentioning

confidence: 99%

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Phenyl ring dynamics and chain reorientation in liquid crystal polymers: A deuteron spin relaxation study

Heaton

Kothe

1998

The Journal of Chemical Physics

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Reorientation dynamics in a nematic liquid crystal studied by fast field cycling nuclear magnetic resonance A detailed description of phenyl ring dynamics and spin relaxation in a highly ordered main chain/side chain liquid crystal polymer is presented. Models for the different motional processes are discussed with reference to experimental measurements of the deuteron spectral densities, J M (M 0 ), measured in the smectic A and nematic phases between 330 K and 500 K, and measured as a function of orientation at 410 K, close to the minima in the relaxation times for Zeeman and quadrupolar order, T 1Z and T 1Q . Intramolecular motion of phenyl rings about the para-axis is regarded as a diffusive process in a two-fold symmetric potential. Theoretical analysis of this model provides the rate constants and amplitudes for passage across the potential barriers and libration within the minima. These are governed entirely by the height of the potential barrier, the potential shape, and the diffusion constant. It is demonstrated that other models for the intramolecular ring dynamics cannot simultaneously account for the magnitudes of the observed J M (M 0 ) in the vicinity of the T 1Z and T 1Q minima. Large amplitude reorientation of the polymer chain is regarded as rotational diffusion in an orienting potential. In order to reproduce both the temperature and orientation dependences of the J M (M 0 ), an additional low amplitude motion of the polymer about the main chain axis, with correlation times in the 10 Ϫ9 s regime at Tϳ400 K, must be included. This is modeled as a one-dimensional diffusion process modulated by a harmonic potential, representing torsional motion of the extented polymer chains. Analysis of the experimental deuteron spin relaxation data yields values for the correlation times and amplitudes for each of the individual processes, providing estimates for the parameters describing each of the potentials which modulate the intramolecular and whole molecule motion, as well as the temperature dependences of the various diffusion constants.

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“…In this sequence, quadrupolar order is prepared the frequency regime over which a motional process contrieither by the traditional JB excitation sequence, butes to transverse relaxation. In several oriented liquid crys-90Њ x -t JB -45Њ y , or by a broadband version such as tal and membrane systems we have observed that there exists 90Њ x -2t JB -67.5Њ 0y -2t JB -45Њ y -t JB -45Њ y (20, 21), a prominent dispersion regime in which T CP 2 increases as t where t JB is a delay set to 1/(2»Dn Q …) and »Dn Q … denotes is decreased (13,14). Because of this pulse frequency dethe average splitting.…”

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confidence: 95%

Application of the Quadrupolar Carr–Purcell–Meiboom–Gill Pulse Train for Sensitivity Enhancement in Deuteron NMR of Liquid Crystals

Prosser

Heaton

Kothe

1996

Journal of Magnetic Resonance, Series B

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Transverse deuteron spin relaxation in thermotropic liquid crystal polymers: determination of viscoelastic properties

Cited by 27 publications

References 22 publications

Extremely Slow Counterion Dynamics in Xanthan Liquid Crystal through ²³Na and ¹⁴N NMR

Extremely Slow Counterion Dynamics in Xanthan Liquid Crystal through ²³Na and ¹⁴N NMR

Phenyl ring dynamics and chain reorientation in liquid crystal polymers: A deuteron spin relaxation study

Application of the Quadrupolar Carr–Purcell–Meiboom–Gill Pulse Train for Sensitivity Enhancement in Deuteron NMR of Liquid Crystals

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Transverse deuteron spin relaxation in thermotropic liquid crystal polymers: determination of viscoelastic properties

Cited by 27 publications

References 22 publications

Extremely Slow Counterion Dynamics in Xanthan Liquid Crystal through 23Na and 14N NMR

Extremely Slow Counterion Dynamics in Xanthan Liquid Crystal through 23Na and 14N NMR

Phenyl ring dynamics and chain reorientation in liquid crystal polymers: A deuteron spin relaxation study

Application of the Quadrupolar Carr–Purcell–Meiboom–Gill Pulse Train for Sensitivity Enhancement in Deuteron NMR of Liquid Crystals

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Extremely Slow Counterion Dynamics in Xanthan Liquid Crystal through ²³Na and ¹⁴N NMR

Extremely Slow Counterion Dynamics in Xanthan Liquid Crystal through ²³Na and ¹⁴N NMR