Unusual physical properties in B phase of polar bent-core thioester compound

Bent-core compound, 4-chloro-1,3-phenylene bis4-[(n-undecyloxybenzoyl)-sulfanyl]benzoate, has been studied by dielectric spectroscopy, DSC calorimetry, and electro-optic methods. As found, the spontaneous polarization of the B phase is by one order of magnitude smaller than for B 2 phases of nOSOR series studied by us before. Its temperature dependence is characteristic for B 1 phase, observed for shorter homologues of nOSORs. Measurements of the complex electric permittivity were carried out in the frequency range from 40 to 15 MHz using gold-coated electrodes. Electro-optic studies have been done applying AWAT HG 1.9 µm cells with strongly rubbed polymer layers. Such cells facilitate inhomogeneous planar alignment, which under strong electric field transforms into a mono-domain exhibiting switching behavior. Dielectric and electro-optic data of bent-core compounds will be discussed taking into account molecular structure and phase structure as well

Dielectric and Electrooptic Investigations of B Phases οf Banana-Shaped Thioesters

Electrooptic and dielectric measurements were done for B phases of two banana-shaped homologues 1,3-phenylene bis{4-[(4-nonylo-xy-benzoyl)sulfanyl]benzoate (9OSOR) and 1,3-phenylene bis{4-[(4-dodecylo-xy-benzoyl)sulfanyl]benzoate (12OSOR). Polarizing microscopy allowed to identify $B_{1}$ phase for 9OSOR and $B_{2}$ 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 $B_{1}$ phase is a ferroelectric and $B_{2}$ phase - antiferroelectric one for which two well separated peaks were observed. Polarization for phase $B_{1}$ of 9OSOR is rather small and its temperature dependence is unusual for ferroelectric liquid crystals - it increases with temperature. Spontaneous polarization for $B_{2}$ phase of 12OSOR compound is of about 600 nC/$cm^{2}$. Dielectric spectra measured with bias field for $B_{2}$ 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 $B_{1}$ phase of 9OSOR with and without bias voltage showed only one dielectric relaxation process connected with molecular reorientation around the short axis

Polymorphism of chiral thioester studied by dielectric spectroscopy

(S)-(+)-4'-[(4-(1-methylheptyloxycarbonylphenyl) thiocarbonylphenyl]-decyloxybenzoate (in short 10.OPOSMH) was studied by complementary methods. The substance shows rich polymorphism. In addition to ferroelectric and antiferroelectric smectic C^{*} phases it possesses three ferrielectric sub-phases. Phase transitions between the phases were revealed by differential scanning calorimetry and static dielectric permittivity measurements. The aim of this paper was to study phase transitions and differences in dielectric spectra shown by different phases. Collective and molecular dynamics of all phases shown by 10.OPOSMH will be discussed in terms of theoretical models. Dielectric spectra of antiferroelectric phase show two characteristic dielectric relaxation modes: one connected with the molecular process (reorientation around the short axis) and the other originating from fluctuations of antiferroelectric order parameters