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.
On the temperature dependence of the tilt and spontaneous polarisation in high tilt antiferroelectric liquid crystals
The temperature-dependent physical properties of four related liquid crystalline materials are reported. The materials differ chemically only in the degree of fluorination of one of the core aromatic rings and all materials exhibit both chiral smectic-C (ferroelectric) and antiferroelectric liquid crystal phases. The steric tilt angles, calculated from the layer spacing, are relatively low, saturating at a maximum of 25°, while the optical tilt angles are much higher, achieving values of 42.5°. Most obviously, the tilt angle and spontaneous polarisation exhibit very different temperature dependencies, the former appearing to be discontinuous at the orthogonal to tilted transition, while the latter follows a simple power law. It is noted that this behaviour has been observed in other similar materials, but that it is not in agreement with the simple coupling between spontaneous polarisation and tilt that is often assumed in ferroelectric liquid crystals. A theoretical explanation is given for the different temperature dependence of these two physical quantities, suggesting that the biaxial order parameter, not directly determined by the tilt angle, is important in these systems.
Geomagnetic micropulsations due to the motion of ocean waves
When sea waves move in the magnetic field of the earth, electric currents are generated in the water volume. These currents give rise to a small magnetic field which perturbs the earth's field. For plane trochoidal waves, this perturbing field decays exponentially with altitude and lies in a vertical plane which is oriented in the direction of wave propagation. The magnitude of the perturbing field also depends upon the magnitude and dip angle of the earth's field, and upon the height, wavelength, and propagation direction of the sea waves. For north-south waves, sea state 5, and an altitude of 100 feet, the perturbation is of the order of 0.1 gamma.