Proton Spin-Lattice Relaxation Study of Order Fluctuations Above The Smectic A-Isotropic Transition in a Liquid Crystal

1974 ◽  
Vol 52 (14) ◽  
pp. 1331-1335 ◽  
Author(s):  
Ronald Y. Dong ◽  
M. Wiszniewska ◽  
E. Tomchuk ◽  
E. Bock
Keyword(s):  
Relaxation Time ◽  
Liquid Crystal ◽  
Effective Viscosity ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Isotropic Phase ◽  
Spin Lattice ◽  
Smectic A

The proton spin-lattice relaxation time T1 in the isotropic phase of the smectic A liquid crystal diethylazoxybenzoate was measured at several Larmor frequencies in the range from 5 to 60 MHz. The frequency dependent T1 at 25 °C above the smectic A-isotropic phase transition (Tc) is attributed to molecular diffusion. The critical temperature dependent (T1)cf, the spin-lattice relaxation time due to critical order fluctuations, at 5 MHz can be understood by assuming that the effective viscosity has a critical temperature behavior just above Tc. It was deduced that the effective viscosity diverges as ξ2 in the mean field approximation, where ξ is a coherence length describing the short range order.

A proton FFT study of the aromatic and alkyl motions in the liquid crystal CBOOA: Orientational order fluctuations in the isotropic phase

1976 ◽  
Vol 54 (22) ◽  
pp. 2282-2286 ◽  
Author(s):  
J. J. Visintainer ◽  
E. Bock ◽  
Ronald Y. Dong ◽  
E. Tomchuk
Keyword(s):  
Liquid Crystal ◽  
Critical Temperature ◽  
Orientational Order ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Isotropic Phase ◽  
Spin Lattice ◽  
Temperature Dependences

Proton line shapes and spin–lattice relaxation were studied in the isotropic phase of the liquid crystal n-p-cyanobenzylidene-p-n-octyloxyaniline (CBOOA) using Fast Fourier Transform (FFT) spectroscopy. The proton spin–lattice relaxation time T1 above the nematic–isotropic phase transition was measured, at several Larmor frequencies, for the resolved peaks in the FFT spectra. The critical temperature dependences of (T1)cf, the T1, due to collective order fluctuations, are thus studied for the aromatic and the alkyl proton groups. The critical temperature behavior of CBOOA is compared with the predictions of the model based on short-range nematic orientational order fluctuations.

Proton NMR Study of Molecular Dynamics in Hydrazinium Perchlorate

1990 ◽  
Vol 45 (2) ◽  
pp. 102-106
Author(s):  
K. Ganesan ◽  
R. Damle ◽  
J. Ramakrishna
Keyword(s):  
Molecular Dynamics ◽  
Relaxation Time ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Temperature Minimum ◽  
Second Moment ◽  
Spin Lattice ◽  
Nmr Study

AbstractThe proton spin-lattice relaxation time T1 (at 5.4, 10 and 15 MHz) and second moment M2 (at 9.8 MHz) have been measured in hydrazinium Perchlorate (N2H5ClO4). The temperature dependence of T, shows two minima. The low temperature T, minimum has been explained in terms of NH3 reorientation about the N-N axis while the high temperature minimum is attributed to the exchange of protons within the NH2 group (180° flip about the H - N - H bisectrix). The activation energies for NH3 and NH: motions are found to be 20.5 kJ mol-1 and 39.8 kJ mol-1 , respectively. The second moment variation with temperature shows two transitions around 120 K and 210 K and has been discussed in terms of NH3/NH2 motions.

Sign in / Sign up

Export Citation Format

Share Document