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Electrooptic and dielectric measurements were done for B phases of two banana-shaped homologues 1,3-phenylene bis(4-[(4-nonyloxybenzoyl)sulfanyl]benzoate (9OSOR) and 1,3-phenylene bis(4-[(4-dodecyloxybenzoyl) sulfanyl]benzoate (12OSOR). Polarizing microscopy allowed to identify B1 phase for 9OSOR and B2 phase for 12OSOR on the basis of texture observation. Spontaneous polarization measurements were performed using reversal current method. The current response to applied triangular voltage shows that B1 phase is a ferroelectric and B2 phase antiferroelectric one for which two well separated peaks were observed. Polarization for phase B1 of 9OSOR is rather small and its temperature dependence is unusual for ferroelectric liquid crystals it increases with temperature. Spontaneous polarization for B2 phase of 12OSOR compound is of about 600 nC/cm2. Dielectric spectra measured with bias field for B2 phase of 12OSOR show two well separated relaxation processes. In the low frequency range the relaxation process is connected with fluctuations of ferroelectric domains. The relaxation process in the high frequency range appearing also without bias field is connected with molecular reorientation. The dielectric spectra measured for B1 phase of 9OSOR with and without bias voltage showed only one dielectric relaxation process connected with molecular reorientation around the short axis. [ABSTRACT FROM AUTHOR]

1,3-Phenylene bis{4-[(4-dodecyloxybenzoyl) sulfanyl] benzoate} (12OSOR) possessing banana-like achiral molecules has been studied by complementary methods to investigate linear dielectric as well as antiferroelectric properties of its B2 phase. To this end, the following experimental methods were used: differential scanning calorimetry, polarizing microscopy, dielectric spectroscopy and reversal current method. As found, 12OSOR compound with bent-core molecules exhibits only B2 phase that happens to be antiferroelectric. Dielectric spectra have been measured using the dielectric spectrometer based on Agilent 4294A impedance analyzer. The measurements have been done using HG 5 µm cells (giving homogeneous orientation) with gold electrodes. Thermal, dielectric, and electro-optic properties of 12OSOR are discussed. [ABSTRACT FROM AUTHOR]

In this article two examples of hexatic phases have been presented to show that the highly ordered phases can be either the ferro- or antiferroelectric ones. Some of them display a well-developed helicoidal structure, very high spontaneous polarization and low conductivity in contrast to liquid-like phases in higher temperature. On the other hand, some of their electrooptic parameters are not so useful for practical applications. First of all their alignment, i.e. a  uniformly aligned mono-domain, is difficult in commercial cells. There are two kinds of smectic C*-hexatic transitions where the spontaneous polarisation changes either continuously or discontinuously in spite of the fact that from the thermodynamic standpoint both transitions are of the first order. The thermal, dielectric and electrooptic properties of the hexatic phases, studied by the DSC calorimetry, polarising microscopy, dielectric spectroscopy, texture observation and reversal current method have been presented for an exemplary fluorinated compound and discussed in the light of the existing theories. The compound shows an enantiotropic hexatic phase which exhibits large spontaneous polarisation. [ABSTRACT FROM AUTHOR]

Complementary methods were used to study one of the MHPOBC analogues: 4-(1-methylheptyloxycarbonyl)phenyl-4 ′ nonylbiphenyl-4-carboxylate (MHPNBC). The substance shows rich phase polymorphism. In addition to the para-, ferro- and antiferroelectric phases it exhibits three sub-phases (two ferri- and alpha sub-phase) and a highly ordered room temperature phase. Typical Goldstone mode in the whole temperature range of the SmC * phase and the soft mode in the vicinity of the SmC *– SmA * transition were observed in the dielectric spectra. In the phase two relaxation processes were found: the non-cancellation mode (NCM) and the reorientation around the short molecular axis (S-process). There is only one dielectric relaxation process observed in a highly ordered phase. It is most probably the NCM, whereas the S-process seems to be frozen out. [ABSTRACT FROM AUTHOR]

Abstract: Two chiral liquid crystalline compounds have been investigated, namely 4-(1-methylheptyloxycarbonyl) phenyl-4′nonylbiphenyl-4-carboxylate (MHPNBC), 3-(2-fluor-octyloxy)-6-(4octyl-phenyl) pyridine (FOOPP) to study the SmA∗–SmC∗ transition. For both substances strong electroclinic effect is observed in the SmA∗ phase what indicates that it is the so-called de Vries SmA∗ phase. To study the paralectric-ferroelectric de Vries type transition electrooptic, dielectric as well as SAXS methods have been applied. [Copyright &y& Elsevier]