Characteristics of electrical properties of wide temperature range TGB phases in liquid crystal dimers

2009 ◽  
Vol 17 (2) ◽  
Author(s):  
R. Dhar ◽  
M. Pandey ◽  
V. Pandey ◽  
A. Pandey ◽  
I. Das ◽  
...  
Keyword(s):  
Soft Mode ◽  
Electrical Parameter ◽  
Optically Active ◽  
Dielectric Anisotropy ◽  
Relaxation Processes ◽  
Goldstone Mode ◽  
Dielectric Studies ◽  
Frequency Range ◽  
Temperature Ranges ◽  
Dimeric Compound

Abstract4-n-decyloxy-4′-(cholesteryloxycarbonyl-1-butyloxy) chalcone and its two successive homologous are optically active dimeric compound derived from cholesterol. They possess wide temperature ranges of two twist grain boundary (TGB) phases namely TGBA and TGBC*. Comprehensive dielectric studies have been carried out for these compounds in the frequency range of 1 Hz to 10 MHz for different conditions of molecular anchoring. Various electrical parameter viz. dielectric permittivity, dielectric anisotropy, dc conductivity, and activation energy have been determined for these two TGB phases. Weak relaxation processes have been detected under planar anchoring of molecules in the TGBA and TGBC* phases presumably due to amplitude (soft mode) and phase (Goldstone mode) fluctuations.

Dielectric studies of Goldstone mode and soft mode in the vicinity of the A-C* transition

1991 ◽  
Vol 1 (2) ◽  
pp. 171-180 ◽  
Author(s):  
S. M. Khened ◽  
S. Krishna Prasad ◽  
B. Shivkumar ◽  
B. K. Sadashiva
Keyword(s):  
Soft Mode ◽  
Goldstone Mode ◽  
Dielectric Studies

Dielectric Studies of a Substance with Negative Dielectric Anisotropy

1998 ◽  
Vol 53 (3-4) ◽  
pp. 134-140 ◽  
Author(s):  
S. Urban ◽  
B. Gestblom ◽  
R. Dąbrowski ◽  
H. Kresse
Keyword(s):  
Relaxation Times ◽  
Mean Field ◽  
Dielectric Anisotropy ◽  
Relaxation Processes ◽  
Network Analyzer ◽  
Dielectric Studies ◽  
Molecular Reorientation ◽  
Transverse Relaxation ◽  
Activation Barriers ◽  
The Mean

Abstract The results of dielectric studies of 6BAP(F) (1-[4-(hexylbicyclo[2,2,2]octyl]-2-(3-fluoro-4-methoxy-phenyl)ethane) in the nematic and isotropic phases are presented. The substance has a negative dielectric anisotropy. By applying two experimental techniques, using a network analyzer and time domain spectrometer (TDS), the two main relaxation processes, connected with the molecular reorientation around the short and long axes, respectively, were resolved in the phases studied. The activation barriers hindering the motions were obtained. By extrapolation of the longitudinal and transverse relaxation times from the isotropic to the nematic phase the retardation factors, g∥ and g⊥, and the nematic potential versus temperature could be calculated. These are discussed together with the order parameter S obtained from the refractive index, and are compared with the predictions of the mean-field theories.

Dielectric Studies of Inter-and Intramolecular Motions in the Nematic and Isotropic Phases of 7CP5BOC

1999 ◽  
Vol 54 (8-9) ◽  
pp. 545-548 ◽  
Author(s):  
Stanisław Urban ◽  
Bo Gestblom ◽  
Roman Dąbrowski
Keyword(s):  
Relaxation Time ◽  
Dielectric Permittivity ◽  
Time Domain ◽  
Nematic Phase ◽  
Activation Enthalpy ◽  
Dielectric Anisotropy ◽  
Dielectric Studies ◽  
Frequency Range ◽  
Impedance Analyzer ◽  
Intramolecular Motions

The dielectric relaxation of 7CP5BOC (2-chloro-4-heptylphenly 4-pentylbicyclo-[2,2,2]octan-l-car-boxylate) in its isotropic and nematic phase has been studied. The substance has a negative dielectric anisotropy. The complex dielectric permittivity was measured in the frequency range 10 kHz -3 GHz with the aid of an impedance analyzer and a time domain spectroscopy (TDS) method. The relaxation time, activation enthalpy and dielectric increments, characterizing the rotation of the molecules about the principal inertia axes, were obtained. It was found that the relaxation process connected with rota-tions about the long axis can be split into two independent motions of molecular moieties around the

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