NMR relaxation and the orientational structure factor

“…The molecular dynamics under strong adsorption conditions can also be described in terms of bulkmediated surface diffusion (BMSD) [58] and Lévy walks [59]. Different systems have been studied with FC relaxometry and interpreted through this relaxation mechanism [60][61][62][63][64][65][66][67].…”

Section: Laboratory Frame Relaxometry (Ti )mentioning

confidence: 99%

Fast-field-cycling NMR: Applications and instrumentation

Anoardo¹,

Galli²,

Ferrante³

2001

Appl. Magn. Reson.

193

136

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Magnetic field cycling in nuclear magnetic resonance (NMR) experiments has been used since the early days of NMR. Originally such time-dependent magnetic field experiments were motivated to study cross relaxation, spin system thermodynamics and indirect detection of quadrupolar resonance. The first apparatus used mechanical or pneumatic systems to shoot the sample between two magnets, the typical "flying time" being a few hundreds of milliseconds. As a natural evolution of the experimental technique and the need to extend its application to samples with higher relaxation rates, faster magnetic field switching devices were developed during the last years. Special electric networks combined with sophisticated air core magnets allowed one to switch magnetic fields between zero and fields of the order of 0.5 T in a few milliseconds. Today we refer to this new generation of instruments as "fast-field-cycling" devices. The technique has been successfully used during the last years to obtain information on the molecular dynamics and order in different materials, ranging from organic solids, metals, polymers, liquid crystals, porous media to biological systems. At present it is also turning to be an important tool for the design of contrast agents for magnetic resonance imaging. Fast field cycling was mainly oriented to T, relaxometry as a unique technique offering a dynamic window of several decades, ranging from few kilohertz to several megahertz. However, there exist less conventional applications of the technique that can also provide relevant information concerning molecular dynamics, structure and molecular order. In this article we will briefly deal with basic aspects of the technique, its evolution, present-day relevant applications and the last improvements concerning specialized instrumentation.

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“…On the other hand, a process called "Reorientations Mediated by Translational Displacements" (RMTD) [13] influences the dynamics and relaxation dispersion of molecules in non-frozen surface layers. With water and tetradecane, two systems have been investigated where the exchange between the crystal and the nonfrozen layer is negligible and the liquid film could be selectively detected due to the crystal's short T 2.…”

Section: Cyclohexane Confined In Large Poresmentioning

confidence: 99%

“…While the different T 1 dispersions for liquids in the "weak" and "strong" adsorption cases could be interpreted by combining the formalisms of "Bulk-Mediated Surface Diffusion" (BMSD) [10][11][12] and "Reorientations Mediated by Translational Displacements" (RMTD) [13,14], this difference vanishes when the free liquid in the pore is frozen. In this situation, molecules in the non-frozen film are reoriented due to diffusion along the curved pore surface irrespective of their polarity.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of plastic and liquid cyclohexane in bulk and in porous glasses studied by NMR methods

1997

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Cyclohexane was investigated both in bulk and in porous glasses with pore diameters between 4 and 208 nm in the temperature range 136 K _< T_< 300 K. The methods involved were field-eycling NMR relaxometry, field-gradient NMR diffusometry, transverse-relaxation spectroseopy, and differential seanning calorimetry (DSC). The field-cycling data for the bulk material can best be described assuming translational modulation of interrnolecular dipole-dipole coupling. This interpretation is conf'mned by expefiments with different degrees of deuteration, and is in accordance with diffusion coefficients determined with the aid of field-gradient diffusometry. The confinement in pores produces substantial ehanges in the phase behaviour and in molecular dynamics. For pote diameters of 30 nm and above, a non-frozen two monolayers thick film on the surface retains a diffusivity about one order of magnitude lower than in the bulk liquid, but two orders of magnitude larger than in the bulk plastic phase. Experiments indieate an exchange mechanism between this layer and the crystallite inside the pore. In glass with a pote diameter of 4 nm, all applied methods eorroborate DSC results of the virtual absence of a phase transition and reveal a continuously decreasing translational mobility down to temperatures more than 100 K below the bulk liquid/cubic phase transition temperature.

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NMR relaxation and the orientational structure factor

Cited by 88 publications

References 22 publications

A New Formalism for the Evaluation of Order-Fluctuation Modes in Liquid Crystals from Field-Cycling NMR-Relaxometry Data

A New Formalism for the Evaluation of Order-Fluctuation Modes in Liquid Crystals from Field-Cycling NMR-Relaxometry Data

Fast-field-cycling NMR: Applications and instrumentation

Dynamics of plastic and liquid cyclohexane in bulk and in porous glasses studied by NMR methods

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