Molecular motion in solid odd-numbered paraffin C19H40: Proton spin relaxation spectroscopy from 5.8 kHz to 86 MHz

Stohrer, M.; Noack, F.

doi:10.1063/1.435313

Cited by 61 publications

(12 citation statements)

References 67 publications

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“…Next, interpretations of these coincidencies consisting in identifications of the underlying physical processes from relevant literature dynamic and own thermodynamic studies are presented. .02 Â 10 À 13 exp (2.6 kcal/mol/RT) from NMR [33,34] shows acceptable agreement strongly supporting the afore-mentioned local dynamic hypothesis. Similar observation at low temperatures in the glassy state of small molecular glass-former with small mobile side groups, diethyl phthalate (DEP), seems to support this interpretation [35].…”

Section: Discussionsupporting

confidence: 72%

Spin probe dynamics in relation to free volume in crystalline organics from ESR and PALS: N-tridecane

Lukešová

Zgardzińska

Švajdlenková

et al. 2015

Physica B: Condensed Matter

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Section: Discussionsupporting

confidence: 72%

Spin probe dynamics in relation to free volume in crystalline organics from ESR and PALS: N-tridecane

Lukešová

Zgardzińska

Švajdlenková

et al. 2015

Physica B: Condensed Matter

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“…In those times, T, experiments were crucial to understand the relaxation process when both the multispin nature of the system at low fields and conduction electron spin-nuclear spin interaction were present. Extension to low fields was also used for the study of slow motions in crystals [40,41].…”

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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“…Above 10 MHz we used a conventional frequency variable spectrometer [15], whereas the low-frequency data were obtained by means of a home-built field-cycling apparatus [10]. With both instruments the random error of the individual Tj points is less than 10% after appropriate signal averaging, and the sample temperature can be controlled with an accuracy of at least 0.5 °C.…”

Section: Sample Preparation and Experimental Techniquesmentioning

confidence: 99%

Proton Spin Relaxation of a Liquid Crystal with a Glassy Cholesteric State

Pusiol

Noack

Aguilera

1990

Zeitschrift Für Naturforschung A

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Field-cycling and standard pulsed NMR techniques have been used to study the frequency dependence of the longitudinal proton spin relaxation time T x in the crystalline estradiol compound ( + )3,l,7-/?-bis-(4n-butoxybenzoyloxy)-estra-l,3,5-(10)-trien or BET, which is a mesogenic material with a chiral molecular structure. From the measured Larmor frequency and temperature dependences we conclude that, at low NMR frequencies in the cholesteric phase, T, reflects in addition to the relaxation process familiar from nematic liquid crystals (director fluctuation modes) another slow mechanism theoretically predicted for cholesteric systems, namely diffusion induced rotational molecular reorientation. These relaxation processes are not or much less effective in the crystalline and glassy state, where they are frozen. Also the high NMR frequency relaxation dispersion strongly differs between the cholesteric mesophase and the not liquid crystalline samples. This is interpreted by a change from essentially translational self-diffusion to rotational diffusion controlled proton relaxation. Aim of this WorkMolecular motions in cholesteric liquid crystals are more intricate than in untwisted mesogens because of the long-range helical ordering of the average orientation of the molecules. This circumstance complicates most spectroscopic approaches to analyse and separate the various kinds of motional processes, like translational self-diffusion along different axes and individual or collective rotational reorientations of whole molecules or special segments. In the following, we briefly describe a Larmor frequency dependent study of the longitudinal proton relaxation time T t for the cholesteric liquid crystalline estradiol compound (+) 3,1,7-/?-bis-(4 n-butoxybenzoyloxy)-estra-l ,3,5-( 10)-trien, henceforth denoted by BET. Up to now, only very few spin relaxation measurements of cholesteric mesophases have been described in the literature [1 -4], In particular, there exist no frequency dependent measurements over a range sufficient to allow a satisfac-* Permanent address: Facultad de Matemätica, Astronomia y Fisica, Universidad Nacional de Cordoba, 5000 Cordoba, Argentina. ** Permanent address: Departamento de Quimica, Facultad de Ciencias, Concepciön, Chile.Reprint requests to Prof. Dr. F Noack, Physikalisches Institut der Universität Stuttgart, 7000 Stuttgart-80, PfafTenwaldring 57, BRD. tory Separation of the underlying intensity spectra of different molecular reorientation mechanisms.Available experimental data on the longitudinal proton relaxation of cholesteric liquid crystals essentially show two complications in comparison with results for untwisted nematic systems, namely: On the one hand, the longitudinal magnetization decay is often non-exponential [1], i.e. not fully explicable by a single time constant T t . On the other hand, it has been pointed out that the self-diffusion of molecules along the helix axis should induce a special rotational relaxation contribution typical for cholesteric systems [4][5][6] (dif...

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Molecular motion in solid odd-numbered paraffin C19H40: Proton spin relaxation spectroscopy from 5.8 kHz to 86 MHz

Cited by 61 publications

References 67 publications

Spin probe dynamics in relation to free volume in crystalline organics from ESR and PALS: N-tridecane

Spin probe dynamics in relation to free volume in crystalline organics from ESR and PALS: N-tridecane

Fast-field-cycling NMR: Applications and instrumentation

Proton Spin Relaxation of a Liquid Crystal with a Glassy Cholesteric State

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