Dielectric response of electric-field distortions of the twist-bend nematic phase for LC dimers

Wide band dielectric spectroscopy of bent-shaped achiral liquid-crystal dimers 1′′-n′′-bis(4-cyanobiphenyl-4′-yl) n-alkanes (CBnCB n = 7, 9, 11) has been investigated in a frequency range 0.1 Hz–100 MHz using planar-aligned cells of sample thicknesses ranging from 2 to 10 (μm) over a temperature range that covers both nematic and twist bend nematic phases. Two peaks in the dielectric spectrum in the higher frequency range are assigned to the molecular relaxation processes. The peak at the highest frequency, ∼40 to 80 MHz, is assigned to an internal precessional rotation of a single unit of the dimer around the director. The mode in the next lower frequency range of 2–10 MHz is assigned to the spinning rotation of the dimer around its long axis. This involves fluctuations of the dipole moment of the bent-shaped conformation that is directed along its arrow direction of the bow shape formed by the dimer. The peak in the frequency range 100 kHz–1 MHz can be assigned to the collective fluctuations of the local director with reference to the helical axis of the NTB structure. The dependence of its frequency on temperature is reminiscent of the soft mode observed at the SmA∗ to SmC∗ phase transition. This result clearly corresponds to the electroclinic effect—the response of the director to the applied electric field in an electro-optic experiment. The lowest frequency mode, observed in the frequency range of 0.1 Hz–100 Hz, is identified with the Goldstone mode. This mode is concerned with the long range azimuthal angle fluctuations of the local director. This leads to an alternating compression and expansion of the periodic structure of the NTB phase

Electrical switching of a chiral lasing from polariton condensate in a Rashba-Dresselhaus regime

Efficient optical classical and quantum information processing imposes on light novel requirements: chirality with low threshold non-linearities. In this work we demonstrate a chiral lasing from an optical modes due to emerging photonic Rashba-Dresselhaus spin-orbit coupling (SOC). For this purpose we developed a new electrically tunable device based on an optical cavity filled with birefringent liquid crystal (LC) and perovskite crystals. Our novel method for the growth of single crystals of CsPbBr$_3$ inorganic perovskite in polymer templates allows us to reach a strong light-matter coupling regime between perovskite excitons and cavity modes, and induce polariton condensation. The sensitivity of the LC to external electric fields lets us to tune the condensate energy in situ and induce synthetic SOC. This shapes the condensate between a single linearly polarized or two circularly polarized separated in momentum, emitting coherent light. The difference in the condensation thresholds between the two SOC regimes can be used to switch on and off the chiral condensate emission with a voltage.Comment: 8 pages, 5 figure

Identifying of thermotropic liquid crystal phase and its influence on lubricity of ionic liquids

In this article there is discussed a possibility of forming the liquid crystal structure in ionic liquids and its influence on performance characteristics, especially tribological, of these liquids. Formation of such thermal phase might influence on, among other things, easier creation of the boundary lubricating film, which is characterized by high viscous anisotropy. The results of tribological tests showed better lubricity of selected ionic liquids than modern PFPE oils. Identification of mesophase in ionic liquids was necessary. This method is described in the paper. Biolar PL polarizing interference microscope with thermal stabilizing table, with birefraction system, and Brüker Discover 8 powder diffraction instrument with a Cu lamp and monochromator were used. There was being searched the state characterized simultaneously by optical anisotropy properties and liquid state of aggregation. For identification of phase transition temperature, the additional calorimetric tests were carried out during the cycle of heating and cooling. These researches were carried out within the framework of the development and research project no. PBR 15-249/2007/WAT-OR0002904, financed by Ministry of Science and Higher Education during 2007-2011

A Study Of A Binary Liquid-Crystalline Mixtures With The Wide Antiferroelectric Phase

Binary mixtures of fluorinated materials having broad antiferroelectric phase have been prepared. A set of phase parameters (phase transition temperatures and enthalpies, the spontaneous polarization and the tilt angle) of pure antiferroelectric components and mixtures prepared using them have been studied. Electrooptical investigations of obtained mixtures have been conducted. An influence of mole mixing ratio of two components on evolution of electrooptical switching from tristable through V-shaped to W-shaped characteristics has been observed. The thresholdless switching of a mixture with specific mixing ratio has been ascribed as the result of the formation of frustrated phase in the medium. Copyright © Taylor & Francis Group, LLC