Zofia Stolarz

Synthesis, mesomorphic and optical properties of isothiocyanatotolanes

The synthesis, mesomorphic properties and UV absorption spectra of laterally fluorine substituted, and the corresponding unsubstituted, 4′-alkyl-, 4′-alkoxy-, 4′-alkylcyclohexyl-, 4′-alkylbicyclo [2,2,2]octyl- and 4′-alkylcyclohexylethyl-4-isothiocyanatotolanes are described. Multicomponent broad range nematic mixtures with birefringence values higher than 0.4 and moderate viscosities are developed.

Low viscosity, high birefringence liquid crystalline compounds and mixtures

Two types of fast switching mixtures with high positive dielectric anisotropy were described. The first type, with a birefringence below 0.3, was designed for devices operating at room or lower temperatures and the second one, with a birefringence higher than 0.3 for devices operating at elevated temperatures.

Synthesis and Mesomorphic Characteristic of Bicyclo-(2,2,2)Octane Derivatives with the -NCS Terminal Group

Abstract Compounds containing in their molecule an alkyl substituted bicyclo(2,2,2)octane ring and the phenylisothiocyanato group bonded to it directly or via bridging group such as -COO-, -OCO-, -CH2-CH2- or -CH2O- have been synthesized. The phase transition temperatures, melting enthalpies and viscosities of these compounds have been determined and their suitability as components of nematic mixtures has been tested.

Studies of Helical Pitch in Antiferroelectric Compounds and Mixtures

The changes of the helical pitch in antiferroelectric phase of compound C 3 F 7 COO(CH 2 ) 6 OPhPhCOOPhCOOC*H(CH 3 )C 6 H 13 and homologous C n F 2n+1 COO(CH 2 ) 6 OPhC OOPhPhCOOC*H(CH 3 )C 6 H 13 versus temperature were measured based on selective reflection of the light. The first compound was mixed with achiral compounds, and compounds of second structure were mixed with their racemic mixtures. In all cases the dilution of pure compounds causes the increase of the helical pitch. Compounds having second structure have longer helical pitch than first one. The increase of the fluorinated part of the terminal chain of homologous series causes at first the increase next the decrease of the pitch.

Liquid Crystalline Cells for Fiber Optic Sensing of Low Hydrostatic Pressure

Abstract The paper presents a new approach to a low-pressure fiber-optic sensing employing pressure-induced deformation effects occurring in twisted nematic LC cells. This method is particularly suitable for measurement of pressures up to 2 MPa and utilizes strong rotatory power occurring in chiral nematic liquid crystals. The effect manifests itself in rotation of linear polarization of light coming through a LC cell and resides in detecting changes in helicoidal pitch of a chiral nematics under the pressure-induced deformation of the cell. Results indicate that this method of hydrostatic pressure measurement offers high response to pressure with reduced temperature sensitivity and, depending on the on the specific LC materials and on geometry of the LC cell used, can be pre-set for a required range of pressure.

PHOTOREFRACTIVE EFFECTS IN PURE MULTICOMPONENT ISOTHIOCYANATE LIQUID CRYSTALS UNDER LOW POWER ILLUMINATION

In this paper the relation between the diffraction efficiency in liquid crystal mixtures and DTWM (Degenerated Two Wave Mixing) systems is described. The aim of this work is to study the most important compound of the measured before LC mixture using diffraction efficiency system under low power illumination.

Influence of nematic liquid crystal with dye and cell construction parameters on dynamic holographic grating formation

We have described the relation between LC parameters and induced diffraction gratings recorded by light intensity pattern in dye-doped nematic liquid crystals sandwiched between two coating glass plates covered with ITO conductive and polyimide orientation layers. In our investigations we used the LC cells containing planary oriented nematic mixtures (low-angle rubbing, tilt 1.5 - 2%) doped with the antraquinone dyes (0.1 - 1% w/w). Nematic liquid crystal mixtures with different electrooptical threshold, optical anisotropy, viscosity and conductivity have been investigated. The influence of resistivity, optical anisotropy of LC mixtures and polyimide layers on diffraction efficiency and other parameters have been discussed.

Low-viscosity mixtures for TN and STN displays

Liquid crystalline isothiocyanatocompounds have been investigated as components of mixtures for TN as well as STN displays. It was shown that mixtures with low viscosities and short response time can be formulated for both kind of display modes.

Achromatic phase retarders using double-layer liquid crystal cells

Achromatic phase retarders can be designed by combining two layers of birefringent materials with different dispersion of birefringence. We synthesized and studied several liquid crystalline structures in order to find combinations giving the best performance in achromatic phase retarders. We found that birefringence dispersion of liquid crystals is approximated well by the single band mode. The best achromatism is achieved with material having a very low resonance wavelength and birefringence. However the required thickness of the liquid crystal layers is large in these cases so that a compromise has to be found. Liquid crystal combinations with high and nearly equal clearing point should be used for devices in order to compensate the temperature drifts of birefringence against each other, thereby extending the operating temperature range. Achromatic phase retarders based on these measurements and calculations were constructed and tested. It was necessary to install an electrooptic regulation circuit for stabilizing the phase retardance at a target value. Device performance is reported and compared to achromatic retarders made of crystalline materials.

Synthesis and mesomorphic properties fluoro- and chloro-substituted isothiocyanatotolanes

We report the synthesis procedures, phase transition temperatures, optical and dielectric properties of the fluoro and chloro -- substituted two rings and three rings isothiocyanatotolanes. Three eutectic mixtures comprising of these isothiocyanatotolane compounds showing a wide nematic range, low viscosity and high birefringence (~0.4) are formulated.