Andika Fajar

Nonlinear Electrooptical Measurements in the Smectic-Cα* Phase

We performed electrooptical measurements in the smectic-Cα* (SmCα*) phase of the antiferroelectric liquid crystal, 4-(1-methyl-heptyloxycarbonyl)phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC), and showed that the frequency dispersion of the second-order electrooptic response strongly depends on the angle between the polarizer and the layer normal while that of the linear response does not. Usually in the SmCα* phase we can observe both the amplitude mode and the ferroelectric mode by second-order electrooptic spectroscopy. In a particular experimental condition, we succeeded in suppressing the ferroelectric mode contribution in the frequency dispersion spectrum and clearly observed only the amplitude mode. The results were discussed and analyzed on the basis of the phenomenological theory.

E-T Phase Diagrams of an Antiferroelectric Liquid Crystal with Re-Entrant Smectic C* Phase

We have investigated the phase transition behaviors of an antiferroelectric liquid crystal, which was reported to exhibit a re-entrant phase transition (SmC*-SmCA*-SmC*-SmA in the order of increasing temperature) by application of electric fields. By birefringence and dielectric measurements an electric-field-temperature (E-T) phase diagram was obtained. In the E-T phase diagram, it was observed that the SmC A* phase disappears under high electric fields and it is isolated. In addition, there is a boundary line between the high- and low-temperature SmC* phases.

OBSERVATION OF AMPLITUDE MODE UNDER DC ELECTRIC FIELD IN SMECTIC-C α * PHASE

Linear and nonlinear dielectric spectroscopy under DC electric fields has been performed in the high temperature region of smectic-Cα* phase of an antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl) phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC) to obtain a deeper insight of dynamic properties. It is observed a softening of amplitude mode and ferroelectric mode with increasing the DC field close to the smectic-Cα*-smectic-A(C) phase boundary line. It was seen that the relaxation frequency of the amplitude mode obeys the Curie-Weiss law with respect to the applied electric field. Keywords: Dielectric relaxation, Nonlinear dielectric,MHPOCBC, DC field.

NONLINEAR DIELECTRIC MEASUREMENTS IN THE SMECTIC-A-SMECTIC-Cα* PHASE TRANSITION

Abstract We have performed precise measurements of the third-order dielectric constant in an antifer-roelectric crystal MHPOCBC. In the vicinity of the SmA- SmCα* phase transition point an anomalous increase of it was observed. We have developed a Landau theory taking into account the pretransitional fluctuations and shown that the fluctuation can contribute to the third-order response. The anomalous behavior near the transition point was discussed on the basis of the theoretical results.

FLUCTUATION-INDUCED KERR EFFECT NEAR THE SMECTIC-A‒SMECTIC-Cα* PHASE TRANSITION

Abstract The anomalous increase of Kerr effect due to pretransitional fluctuations has been investigated in the SmA phase close to the SmA-SmCα* transition point in antiferroelectric liquid crystals MHPOBC and MHPOCBC. We have developed a Landau theory taking into account the fluctuations and shown that there are two contributions to the Kerr effect. On the basis of theoretical results, the experimental results obtained in MHPOBC and MHPOCBC were discussed and a clear evidence of the fluctuation-induced Kerr effect was presented.

Linear and non-linear electro-optic studies of the smectic-A: Smectic-Cα* phase transition

Abstract Electro-optical measurements have been performed around the SmA-SmCα* phase transition point in antiferroelectric liquid crystals MHPOBC and MHPOCBC. In both materials the soft mode condensation is clearly seen in addition to the partial softening of the ferroelectric soft mode. The Curie Weiss law is observed. The comparison of the slopes of these modes shows that MHPOBC and MHPOCBC should be close to the critical point. In addition to these soft modes, a low frequency mode was detected.