Dynamics and the mesomorphic properties of a novel antiferroelectric liquid crystalline thiobenzoate MHPSBO10: thermal, optical and dielectric spectroscopy study.
The complementary studies of the mesomorphic properties of a novel antiferroelectric liquid crystal (AFLC) (S)-2-octile 4-S-(4'decyloxybiphenyl-4-tiocarboxy)benzoate, known under MHPSBO10 acronym have been undertaken. The polymorphism has been complementary studied in details by Differential Scanning Calorimetry (DSC), Transmitted Light Intensity (TLI) and Polarization Microscopy (POM). The switching characteristics along with multiple macroscopic parameters describing the mesomorphic properties were determined by using electro-optic measurements, both upon cooling and heating. Frequency domain dielectric spectroscopy (DS), covering a wide frequency range, has been applied to characterize the molecular motions. Several collective modes, including the low frequency processes in the condensed hexatic phase were detected, analyzed in details and followed with the temperature. The presented studies deliver a wide report of the phase transitions, molecular dynamics and the macroscopic properties of the novel antiferroelectric thiobenzoate.
Mesomorphic properties of (S)-MHPSBOn series
Abstract This article reports new results on synthesis and mesomorphic properties of the homologous series of ( S )-1-methylheptyl-4-(4′-alkyloxybiphenylthiocarboxy)-benzoates, referred to as ( S )-MHPSBO n , where n varies from 7 to 10 and denotes the number of carbon atoms in the alkyl chain. These compounds are sulphur analogous to a liquid crystal known as MHPOBC, where the central ester bridge was replaced with the –COS– connecting group. The ( S )-MHPSBO n homologous series possesses enantiotropic SmA*, SmC*, Sm C A * and monotropic SmI* phases for n  = 7–10. The ( S )-MHPSBO7 compound has also smectic chiral subphases: Sm C α * and Sm C γ * . Their mesomorphic properties were investigated by means of polarizing optical microscopy (POM), differential scanning calorimetry (DSC), transmittance light intensity (TLI), X-ray diffraction and electro-optic (EO) measurements.
A possible structural model of the SmC*beta phase
The so-called chiral smectic C-beta (SmC*beta) phase has been reported as distinct from the SmC* phase in several materials that exhibit antiferroelectric liquid crystal mesophases and subphases. The SmC*beta phase is known to be chiral, tilted and to exhibit ferrielectric switching, but no structure had been suggested which explains these effects. This paper presents a possible structure for the SmC*beta phase which can explain the ferrielectric properties. The model is proposed on the basis of complementary optical, electric and X-ray diffraction studies of a chiral liquid crystal. The layer spacing, optical and steric tilt and spontaneous polarization over the temperature range of the SmC*beta phase are described. The complementary experimental techniques used reveal the occurrence of inversion phenomena, on which this model is based.