Proton Spin Relaxation Dispersion for Some Nematic Homologues of the Liquid Crystal PAA

1983 ◽  
Vol 23 (3) ◽  
pp. 380-387 ◽  
Author(s):  
G. Nagel ◽  
W. Wölfel ◽  
F. Noack
Keyword(s):  
Liquid Crystal ◽  
Spin Relaxation ◽  
Proton Spin ◽  
Relaxation Dispersion

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.

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

NMR Investigation of Order Fluctuations, Self-Diffusion and Rotational Motions in the Nematic Liquid Crystal MBBA by T1-Relaxation Spectroscopy

1977 ◽  
Vol 32 (1) ◽  
pp. 61-72 ◽  
Author(s):  
V. Graf ◽  
F. Noack ◽  
M. Stohrer
Keyword(s):  
Liquid Crystal ◽  
Optimization Procedure ◽  
Larmor Frequency ◽  
Proton Spin ◽  
Relaxation Dispersion ◽  
Self Diffusion ◽  
T1 Relaxation ◽  
Computer Optimization ◽  
Rotational Motions ◽  
Experimental Findings

Abstract We report on measurements of the proton spin T1 relaxation dispersion at various temperatures in the nematic phase of the liquid crystal MBBA in the Larmor frequency range from 2 kHz to 270 MHz, which exceeds previous studies by more than 3 orders of magnitude. The new results cannot be interpreted in terms of either order fluctuations or self-diffusion as recently proposed by Doane et al.1 and Blinc et al.2, respectively. Instead, the dispersion and its temperature dependence indicate the significance of at least three relaxation mechanisms, namely order fluctuations (OF), self-diffusion (SD) and rotation of the molecular ellipsoids about the short axis (R). The combined OF-SD-R model presented in this work allows a quantitative analysis of the experimental findings! The correlation times and activation energies of the three molecular reorientations evaluated from the T1 dispersion by means of a computer optimization procedure are in essential agreement with data provided by other spectroscopic methods [light scattering, tracer technique, dielectric relaxation], but differ from former NMR conclusions.

A Site-Specific Study of the Magnetic Field-Dependent Proton Spin Relaxation of an Iridium N-Heterocyclic Carbene Complex

2017 ◽  
Vol 231 (4) ◽  
Author(s):  
Andrey N. Pravdivtsev ◽  
Alexandra V. Yurkovskaya ◽  
Pavel A. Petrov ◽  
Konstantin L. Ivanov
Keyword(s):  
Spin Relaxation ◽  
Proton Spin ◽  
Relaxation Dispersion ◽  
Wide Field ◽  
Field Range ◽  
Carbene Complex ◽  
Relaxation Measurements ◽  
A Site ◽  
Nuclear Magnetic

AbstractWe report a study of proton spin relaxation of an Iridium N-heterocyclic carbene complex [Ir(COD)(IMes)Cl] complex (where COD=1,5-cyclooctadiene, Imes=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene). This compound is a pre-catalyst of the most efficient complex allowing the signal amplification by reversible exchange (SABRE) effect, relevant for enhancing weak signals in nuclear magnetic resonance (NMR). An important feature of the study is a combination of relaxation measurements over a wide field range with high-resolution NMR detection. As a result, we are able to measure nuclear magnetic relaxation dispersion (NMRD) curves in the field range 0.1 mT–16.4 T (corresponding to the frequency range 4 kHz–700 MHz) for individual protons in the complex under study. This attractive possibility enables determination of the motional correlation times,

Proton spin relaxation dispersion studies of phospholipid membranes

1988 ◽  
Vol 92 (10) ◽  
pp. 2981-2987 ◽  
Author(s):  
Eberhard Rommel ◽  
Friedrich Noack ◽  
Peter Meier ◽  
Gerd Kothe
Keyword(s):  
Spin Relaxation ◽  
Proton Spin ◽  
Relaxation Dispersion ◽  
Phospholipid Membranes

Proton Spin Relaxation in the Liquid Crystal PAA

1971 ◽  
Vol 55 (1) ◽  
pp. 145-151 ◽  
Author(s):  
Ronald Y. Dong ◽  
W. F. Forbes ◽  
M. M. Pintar
Keyword(s):  
Liquid Crystal ◽  
Spin Relaxation ◽  
Proton Spin
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