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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.

Temperature-dependent dielectric spectroscopy of resynthesized discotic compounds, rufigallol hexa-n-alkoxylates for n ¼ 6, 7, 8, 9 having wide temperature range (470 C) hexagonal columnar mesophase has been carried out in the frequency range of 10 Hz to 10 MHz. The mesophase and their transition temperatures have been determined by using polarizing microscope and differential scanning calorimeter. Dielectric permittivity parallel (" 0 jj ) and perpendicular (" 0 ? ) to column have been determined. Using these data, dielectric anisotropy (Á" ¼ " 0 jj À " 0 ? ) has been found to be positive throughout the entire range of the Col h phase for all of the four compounds of this series. No relaxation phenomenon is found in the frequency range of 10 Hz to 10 MHz. The DC conductivity of these compounds has been found to be rather low ($10 À10 -10 À11 S-m À1 ). All the electrical parameters show odd-even effect with the variation of n.

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