Dielectric spectroscopy of a binary mixture of liquid crystals showing wide temperature range twisted grain boundary phase with re-entrant cholesteric phase

Abstract

There are only few materials, which have shown long temperature range twisted grain boundary (TGB) phases. One such material is the chiral binary mixture of 7OCB and 5* CBB (mole ratio 0.8 and 0.2) which shows unique phase sequence of cholesteric ( N*) , a wide temperature range TGBA (approximately 31 degrees C) and reentrant cholesteric (N*re) phases. In the present work we are reporting the dielectric spectroscopy of the above mixture with a chiral analog of earlier reported nematic (N) , smectic- A (SmA) , and reentrant nematic (Nre) phase sequences [Phys. Rev. A 46, 7733 (1992)] for different conditions of molecular orientations. Two modes of dielectric relaxations have been detected in a homeotropically aligned sample with unusually low relaxation frequencies for one of them. Planar oriented molecules in the TGBA phase show a soft mode of relaxation and support the recently proposed theory for the soft mode relaxation of the TGBA phase [Phys. Rev. E 65, 11701 (2001)]. By applying the dc electric field on planar oriented molecules in the TGBA phase, it has been possible to obtain a helix free homeotropically aligned TGBA phase.

Dielectric spectroscopy of liquid crystals. Electrodes resistivity and connecting wires inductance influence on dielectric measurements

“…In many papers, difficulties with high frequency measure− ments are indicated which are related to finite conductivity of ITO electrodes in measuring cells [1][2][3][4][5][6][7][8][9]. In Ref.…”

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

“…At TGBA−TGBC * transition, ¢ e || increases rapidly by appreciable magnitude in the case of the first two members of the series (DC4−10 and DC4−11) and ¢ e || becomes constant at lower temperatures of TGBC * phase. Such behaviour has been observed in some other similar systems also [18,19,21]. In the case of DC4−12 [28], ¢ e || decreases continuously with decrease in the temperature throughout TGBC * phase [ Fig.…”

“…Dielectric studies of the phases are still in nascent stage and the data on the dielectric behaviour of TGB phases available in literature is not very comprehensive [10,[12][13][14][15][16][17][18][19][20][21] because most of the TGB phases exist over a very short tem− perature range due to their frustrated nature. Initial fre− quency dependent (dynamic) dielectric studies of the TGBA phase [12][13][14][15] show that electric field induces amplitude fluctuation of tilt angle like those of SmA * phase, leading to excitation of soft mode of dielectric relaxation.…”

Electron beam irradiation induced changes in liquid-crystal compound 5CB

“…The 10-kHz dielectric data has been taken as the 'static' value, as it is free from low-and high-frequency artifacts [9,10] and there seems to be no dispersion mechanism up to this frequency. Further details about the experimental techniques used for the dielectric measurements are given in our earlier publications [11,12].…”