Frequency Dependence of Proton Spin Relaxation in Liquid Crystalline PAA

1975 ◽  
Vol 30 (4) ◽  
pp. 437-441 ◽  
Author(s):  
W. Wölfel ◽  
F. Noack ◽  
M. Stohrer
Keyword(s):  
Relaxation Time ◽  
Transition Temperature ◽  
Frequency Dependence ◽  
Spin Relaxation ◽  
Correlation Time ◽  
Liquid Crystalline ◽  
Larmor Frequency ◽  
Proton Spin ◽  
Isotropic Phase ◽  
Frequency Range

Abstract We report on measurements of the Larmor frequency dependence of the proton spin relaxation time T1 in the nematic and isotropic phase of p-azoxyanisole (frequency range: 3.8 kHz ≦ ωL/2 π≦75 MHz) . In both cases our results clearly support the Pincus-Cahane mechanism of spin relaxation by order fluctuations ("ωL−½-law") and exclude the alternative translational dif­fusion model (“ωL+½-law”). For the isotropic phase it was possible to evaluate the correlation time τ of the liquid crystalline order fluctuations from the observed T1 dispersion. As a function of the deviation ⊿ν=ν-νc from the critical nematic-isotropic transition temperature, νc= (136± 0.5)°C, we found τ=2.71·10-7-⊿ν-0.25s .

scholarly journals Nitrogen Nuclear Quadrupole Resonance Dips in the Proton Spin Relaxation Dispersion of Nematic and Smectic Thermotropic Liquid Crystals

1992 ◽  
Vol 47 (11) ◽  
pp. 1105-1114 ◽  
Author(s):  
D. J. Pusiol ◽  
R. Humpfer ◽  
F. Noack
Keyword(s):  
Spin Relaxation ◽  
Liquid Crystalline ◽  
Larmor Frequency ◽  
Quadrupole Coupling Constant ◽  
Proton Spin ◽  
Relaxation Dispersion ◽  
Coupling Constants ◽  
Smectic Phases ◽  
Nematic State ◽  
Quadrupole Coupling

Abstract The Larmor frequency dependence of the proton spin relaxation time, obtained by means of the fast field-cycling NMR technique, has been used to study the 14N quadrupole coupling constant K and its asymmetry parameter η in the nematic and smectic phases of some liquid crystalline azoxybenzenes (PAA, BAB, HAB, HpAB), cyanobiphenyls (8CB, 9CB, 11CB) and oxycyanobiphenyls (9 OCB). Due to fast molecular reorientations, the effective quadrupole coupling constants are relatively small, whereas surprisingly the asymmetry parameters are rather large. The temperature dependence of both K and η within the mesophases, as well as their discontinuities at the different mesophase transitions, can be interpreted by the anisotropy of molecular rotations. It is found that temperature effects are significantly more pronounced for the (biaxial) smectic-C phase of the heptyloxyazoxybenzene (HpAB) than for the (uniaxial) smectic-A phase of the various investigated cyano- and oxycyanobiphenyls. As a rule, η turned out smaller in the smectic than in the nematic state, whereas K has similar values in both phases

Proton spin relaxation in hydrogen–nitrogen mixtures: a test of the single relaxation time approximation

1977 ◽  
Vol 55 (12) ◽  
pp. 1083-1091 ◽  
Author(s):  
Wallace Kalechstein ◽  
Robin L. Armstrong
Keyword(s):  
Relaxation Time ◽  
Concentration Dependence ◽  
Spin Relaxation ◽  
Correlation Time ◽  
Proton Spin ◽  
Time Approximation ◽  
Single Relaxation Time ◽  
Definitive Evidence ◽  
Relaxation Time Approximation ◽  
Limit Approximation

Accurate measurements of the concentration dependence of the longitudinal proton spin relaxation time in hydrogen–nitrogen mixtures at 300 K are presented. The data are taken at 39 MHz and at densities for which the short correlation time limit approximation is valid. The measurements provide definitive evidence of deviations from the single relaxation time approximation. The Bloom–Oppenheim two-level theory is used to explain the detailed concentration dependence of the data.

Proton spin-spin relaxation time of peel and flesh of navel orange varieties exposed to freezing temperature

2005 ◽  
Vol 85 (14) ◽  
pp. 2482-2486 ◽  
Author(s):  
Prem N Gambhir ◽  
Young J Choi ◽  
David C Slaughter ◽  
James F Thompson ◽  
Michael J McCarthy
Keyword(s):  
Relaxation Time ◽  
Spin Relaxation ◽  
Freezing Temperature ◽  
Proton Spin ◽  
Spin Relaxation Time ◽  
Navel Orange

scholarly journals Perylene-like Dyes in Liquid Crystalline Media

1996 ◽  
Vol 51 (7) ◽  
pp. 843-850 ◽  
Author(s):  
Ewa Mykowska ◽  
Danuta Bauman
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Order Parameter ◽  
Liquid Crystalline ◽  
Fluorescent Dyes ◽  
Liquid Crystal Display ◽  
Isotropic Phase ◽  
Display Devices ◽  
Electrooptical Properties ◽  
Derivatives Of

Abstract The spectral and electrooptical properties of some dichroic fluorescent dyes (derivatives of 3.4,9,10-perylenetetracorboxylic acid and of 3,4,9-perylenetricarboxylic acid) in isotropic solvents and nematic liquid crystals have been studied. The order parameter of the dyes in the anisotropic matrices has been determined by means of optical spectroscopy methods. Moreover, the influence of the dye addition on the nematic-isotropic phase transition temperature of the pure host has been investigated. It was found that some of the dyes studied can be utilized in guest-host liquid crystal display devices.

Protonenspinrelaxation und Wasserbeweglichkeit in Muskelgewebe / Proton Spin Relaxation and Mobility of Water in Muscle Tissue

1973 ◽  
Vol 28 (1-2) ◽  
pp. 59-62 ◽  
Author(s):  
G. Held ◽  
F. Noack ◽  
V. Pollak ◽  
B. Melton
Keyword(s):  
Spin Relaxation ◽  
Muscle Tissue ◽  
Continuous Distribution ◽  
Larmor Frequency ◽  
Close Relation ◽  
Rana Esculenta ◽  
Proton Spin ◽  
Protein Solutions ◽  
Two Phase ◽  
Muscle Water

The frequency dependence of the proton spin relaxation in muscle tissue shows that the mobility of the muscle water must be described by a continuous distribution of jumping times instead of the usually assumed two-phase model. Measurements on frog muscles (rana esculenta and rana pipiens, gastrocnemius) in the Larmor frequency range 3 kHz to 75 MHz can be understood quantitatively by a log-gaussian distribution, which supports a close relation to protein solutions.

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

1990 ◽  
Vol 45 (9-10) ◽  
pp. 1077-1084 ◽  
Author(s):  
D. Pusiol ◽  
F. Noack ◽  
C. Aguilera
Keyword(s):  
Spin Relaxation ◽  
Rotational Diffusion ◽  
Glassy State ◽  
Larmor Frequency ◽  
Proton Spin ◽  
Relaxation Dispersion ◽  
Proton Relaxation ◽  
Relaxation Processes ◽  
Molecular Reorientation ◽  
Cholesteric Phase

Abstract 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 (+)3,1,7-ß-bis-(4n-butoxybenzoyloxy)-estra-1,3,5-(10)-trien or BET, which is a mesogenic material with a chiral molecular structure. From the measured Larmor frequency and temperature depen-dences we conclude that, at low NMR frequencies in the cholesteric phase, T1 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.

1093 SENSITIVITY OF MAGNETIC RESONANCE PROTON SPIN-SPIN RELAXATION TIME AS AN INDEX OF MUSCLE ACTIVATION

1994 ◽  
Vol 26 (Supplement) ◽  
pp. S194
Author(s):  
G. Yue ◽  
A. L. Alexander ◽  
D. H. Laidlaw ◽  
A. F. Gmitro ◽  
E. C. Unger ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Magnetic Resonance ◽  
Spin Relaxation ◽  
Muscle Activation ◽  
Proton Spin ◽  
Spin Relaxation Time

Preparation and Characterization of Chiral Cyclosiloxane-Based Liquid-Crystalline Elastomers Bearing Menthyl Groups

2012 ◽  
Vol 466-467 ◽  
pp. 445-448
Author(s):  
Qian Yue Li ◽  
Jun Xu ◽  
Wen Zheng Zhang ◽  
Peng Li
Keyword(s):  
Transition Temperature ◽  
Liquid Crystalline ◽  
Helical Structure ◽  
Visual Observation ◽  
Side Chain ◽  
Isotropic Phase ◽  
Long Wavelength ◽  
Chemical Structures ◽  
One Step

Chiral side-chain liquid-crystalline elastomers (LCEs) IP~IVP containig menthyl groups were synthesized by a one-step hydrosilylation reaction. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques. The effect of crosslinking mesogens on mesomorphic properties of the chiral LCEs was studied by swelling experiments. All the samples IP~IVP showed cholesteric mesophase when they were heated and cooled, proved by visual observation and X-ray measurements. The glass transition temperature (Tg) of elastomers increased slightly with increase of crosslinking mesogens in the polymer systems, but mesophase-isotropic phase transition temperature (Ti) decreased slightly, suggesting that the temperature range of mesophase became narrow with increase of crosslinking mesogens for all the elastomers. The maximum reflection bands shift slightly to long wavelength and become broad at the same temperature, indicating that the helical structure is partially disrupted because of both the constraint of chemical crosslinking agents and the different mesogenic units.

Dielectric Studies of a Series of Liquid Crystalline Pyridine Derivates

1996 ◽  
Vol 51 (9) ◽  
pp. 1019-1026 ◽  
Author(s):  
S. Heinemann ◽  
H. Kresse ◽  
S. Saito ◽  
D. Demus
Keyword(s):  
Frequency Dependence ◽  
Crystalline State ◽  
Liquid Crystalline ◽  
Structural Changes ◽  
Alkoxy Group ◽  
Dielectric Constants ◽  
Dielectric Studies ◽  
Frequency Range ◽  
Liquid Crystalline Phases ◽  
Static Dielectric Constants

Abstract Measurements of the temperature and frequency dependence of dielectric constants have been performed for five homologues in the range 100 Hz -10 MHz. These substances exhibit a negative anisotropy of the dielectric constants and two relaxation regions (rotation of the molecules around the short resp. long axis) in the investigated frequency range. Even in the crystalline state dipolar reorientations are possible which have been interpreted as rotations of the alkoxy group. Changes of the static dielectric constants, relaxation frequencies and transition entropies are discussed as a measure of structural changes passing the several liquid crystalline phases.

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