Dielectric studies of different phases of a thin-layered ferroelectric liquid crystal with a small pitch and high spontaneous polarization

Abstract

Dielectric spectroscopy of a ferroelectric liquid crystal with planar texture in the frequency range 100 Hz to 1 MHz has been carried out as a function of temperature from 25°C to 60°C at different DC fields varying from 0 to 12 kVcm-'. From the measured dielectric strengths and relaxation frequencies, it is observed that the material has a SY-SX transition at 56.1"C and a SX-I transition at 58°C. The data of the SE phase have been assigned to the Goldstone mode. The rotational viscosity and elastic constant have been calculated from the observed data. The capacitance shows an abrupt drop at the critical DC field where unwinding of the helix occurs. The measured value of the critical field decreases with temperature and agrees to literature data from electrooptical experiments. On applying a DC field greater than 6.5 kVcm-' at room temperature, the liquid crystal shows the unwound S z and S; phases. IntroductionThe complex dielectric permittivity of a ferroelectric liquid crystal can be directly measured by dielectric spectroscopic techniques. With the emergence of enhanced accuracies of computer controlled bridges, it is possible to acquire dielectric permittivity and dielectric loss data rather quickly over a wide frequency range at very small frequency steps. The dielectric spectroscopy of a large number of ferroelectric liquid crystals have been recently reported and possible information about the molecular orientation and the relaxation processes have been discussed [ 1-10]. The planar oriented ferroelectric liquid crystal exhibits the chiral smectic C S,* phase over a wide temperature range; the dielectric behaviour of this phase is described to two relaxation processes [l, 91. The dominant Goldstone mode appears because of the fluctuations of the phase in the azimuthal orientation of the director, whereas the soft mode appears due to the fluctuations in the amplitude of the tilt angle 0. The dielectric relaxation frequencies of the Goldstone mode are weakly dependent on the tempera-

Dielectric Relaxations in a Short Pitch Ferroelectric Liquid Crystal

“…Their values are found to be 0.59Hz, 0.134, 427.77 respectively at 45°C. These values were in good agreement with theory [20]. fi varies slowly with increasing temperature in the SmC' phase due to the "GM" contribution while the dielectric strength decreases suddenly.…”

Dielectric Relaxation of FLC Showing Anomalous Behavior

“…It is clear from the figure that relaxation frequency is almost temperature independent in the SmC Ã phase but increases sharply near SmC Ã -SmA phase transition temperature. This type of behavior for the relaxation frequency of the Goldstone mode has also been reported by other researchers (20)(21)(22)(23). This nature of relaxation frequency curve can also be explained with the help of the following equation (24) …”

Investigation of relaxation processes in anticlinic smectic C* (Sm) phase of Liquid Crystals by dielectric spectroscopy

“…However, in ferroelectric SmC Ã phase e 0 ? has, another collective mode due to phase fluctuations (Goldstone mode) [9][10][11] phase contains two characteristic relaxation modes observed in kHz and MHz regions, respectively [12][13][14][15][16][17][18][19][20]. Here it would be worthwhile to mention that, although the temperature-dependent dielectric behaviour in the antiferroelectric phase have been investigated in different types of antiferroelectric liquid crystal (AFLC) materials, yet a unique interpretation or assignment of different relaxation modes has not been possible [12][13][14][15][16][17].…”

“…Dielectric relaxation spectroscopy has proven to be a powerful technique to study the dipolar ordering and molecular dynamics of collective and non-collective molecular processes in chiral smectic liquid crystals possessing paraelectric, ferroelectric and antiferroelectric phases [8][9][10][11]. In paraelectric SmA Ã phase, the dielectric permittivity (e 0 ? )…”