Witold Drzewiński

Solution of the dark state problem in antiferroelectric liquid crystal displays

So far, it has proven impossible to achieve an acceptable dark state between crossed polarizers for antiferroelectric liquid crystals (AFLCs), which otherwise would have an enormous potential for electro-optic applications, in particular for high-resolution full color displays. The reason lies in static and dynamic spatial fluctuations of the optic axis. As both have intrinsic causes it is not likely that the problem is ever going to be solved by improvement in alignment and addressing methods. We show that if the directors in alternating layers are orthogonal to each other, the AFLC acquires new optical properties such that the problem is eliminated, and a dark state extinction is achieved which is only limited by the quality of the polarizers. After having synthesized such a material, we have been able to demonstrate the predicted unique electro-optical properties of this new class of AFLC materials.

Antiferroelectric liquid crystals with 45° tilt - a new class of promising electro-optic materials

Abstract Antiferroelectric liquid crystals with a tilt angle of 45 degrees have very interesting optical properties, which seem to have been overlooked so far - perhaps because such materials have hardly been available. We have prepared a four-component mixture of partially fluorinated compounds with a SmCa* phase in the interval between 27.4°C and 121.6°C, in which the tilt angle θ saturates at 45 degrees for T≤80°C, and we investigate the optical properties, theoretically and experimentally. One of the surprising features of 45 degree materials is that they permit a remarkably high contrast by virtue of an excellent dark-state, in spite of the fact that AFLC materials are notoriously difficult to align. This is because a 45° AFLC turns out to be (negatively) uniaxial instead of biaxial. We describe these properties and propose a number of potentially interesting new applications, including a polarizer-free display mode and a three-level “phase-only” modulator.

Comparison of mesomorphic properties in chiral and achiral homologous series of high tilted ferroelectrics and antiferroelectrics

Homologous series of chiral (S) 4-(1-methylheptyloxycarbonyl)-phenyl and achiral 4-(4-heptyloxycarbonylphenyl 4-(perfluoroalkanoyloxyhexyloxy)biphenylates or 4-(alkanoyloxyhexyloxy)biphenylates, chiral (S) and racemic (R,S) 4′-(1-methyl heptyloxycarbonyl)biphenyl-4-yl 4-(perfluoroalkanoyloxyhexyloxy)benzoates or 4 (alkanoyloxyhexyloxy)benzoates have been prepared and their phase transitions have been investigated by DSC and polarizing thermomicroscopic methods. Moreover the temperature dependence of interlayer spacing by a small angle X-ray diffraction method has been studied. The chiral and achiral members exhibit a SmC anti. phase, while racemic members only exhibit SmC phase. Fluorinated compounds have lower melting points, lower melting enthalpy and broader range of the SmC anti. phase than earlier prepared series with shorter spacer group (CH 2 ) m , m < 6. They are very useful components for the formulation of orthoconic (interlayer tilt 90°) antiferroelectric mixtures with temperature range from (−20°C) to 100°C.

New antiferroelectric compounds containing partially fluorinated terminal chains. Synthesis and mesomorphic properties

Abstract Methods for preparing optically active hydroxyesters: 1-hydroxy-4-(1-methylheptyloxycarbonyl)benzene and 4-hydroxy-4′-(1-methylheptyloxy-carbonyl)biphenyl, 4-(1-methylheptyloxycarbonyl)phenyl 4′-hydroxybiphenyl-4-carboxylate and 4′-(1-methylheptyloxy carbonyl)biphenyl-4-yl 4-hydroxybenzoate have been elaborated. These compounds were used as intermediates for preparing liquid crystalline homologous series of di- and triesters exhibiting tilted smectic phases CA* and C*. The phase transitions have been measured by DSC and thermomicroscopic methods and the smectic phases have been identified by microscopic textures and miscibility studies.

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.

Determination of molecular parameters of the MHPB(H)PBC and MHPB(F)PBC antiferroelectric liquid crystals

Abstract Two investigated antiferroelectric liquid crystals, MHPB(H)PBC and MHPB(F)PBC, were synthesized [1] and some their physical properties were described earlier [2]. Apart of the above, MHPB(H)PBC and MHPB(F)PBC have been studied by means of dielectric, densitometric, refractometric and X-ray measurements. Spontaneous polarization P s and tilt angle θ in ferro- (SmC*) and antiferroelectric (SmCA*) phases of MHPB(H)PBC and MHPB(F)PBC have also been investigated. Transverse α1 and longitudinal α1 molecular polarizabilities have been calculated from the ordinary n 0 and extraordinary n e refractive indices and density ρ of MHPB(H)PBC and MHPB(F)PBC, using Neugebauers, Vuks and Lorentz equations with both Haller and Subramhanyama extrapolation procedures. Effective values of the molecular dipole moment μ have been calculated from electric permittivity ε in the 1 phases of these compounds, using Maier and Meier equation.

Antiferroelectric Compounds with trifluoromethyl group in ω-Position of Terminal Chain

Abstract Chiral (S) 4-(1-methylheptyloxycarbonyl)phenyl 4′-(ω-trifluoroethoxyalcoxy)biphenyl-4-carboxylates and 4′-(ω-trifluoro-butanoyloxyalcoxybiphenyl)carboxylates were prepared and their phase transitions and the temperature dependence of the smectic layer spacings, tilt angle, spontaneous polarization, threshold and switching times for the antiferroelecrtic—ferroelectric transition were measured.

Synthesis and Mesomorphic Properties of Achiral and Chiral Esters with High Tilted Synclinic and Anticlinic Phases

Two series of three ring esters with chiral chain (derivative of (S)-octanol-2) and achiral chain (the swallow type) with high tilted synclinic and anticlinic phases were chosen to studies. The aim of presented studies was to find how the changes of different molecule units influence the mesomorphic properties of the compounds (temperatures, enthalpies and the sequence of phase transitions) and to find members with the best properties for mixture formulation. The compounds were studied by polarising microscope, differential scanning calorimetry, miscibility and X-ray diffraction methods.

Synthesis and mesomorphic properties of esters with swallow type terminal chain and their ability to enhance or induce anticlinic phases

Compounds with the terminal swallow tailed chain have been synthesized. The prepared compounds were studied by thermomicroscopy, differential scanning calorimetry, miscibility and X-ray diffraction methods.

Antiferroelectric Liquid Crystals Containing a Naphthoate Mesogenic Unit

Two homologous series of antiferroelectric liquid crystals have been synthesized and their mesomorphic behaviour investigated by DSC and polarized light microscopy is presented. The mesogenic group consists of a biphenyloate-naphthoate unit, the varied terminal chain being attached to this via a six-membered alkyl chain, as long chains promote high tilt angles. The terminal chain is either alkanoyloxy alkoxy or perfluoroalkanoyloxy alkoxy. The behaviour of these series are discussed and compared to two previously reported analogous series which have a benzoate group in place of the naphthoate group, and which exhibit an orthoconic SmC* A phase. The naphthoate unit leads to an increase in transition temperatures and a slight decrease in the stability of the SmC* A phase whilst enhancing the SmC* and SmA phases.