J. Kędzierski

Some Physical Properties of Mesogenic 4-(trans-4′-n-Alkylcyclohexyl) Isothiocyanatobenzenes

Abstract Temperature dependences of density, refractive indices, and dielectric constants have been measured for mesogenic compounds of as for some of their cyano-analogues: and . The effects of substituting a phenyl ring by a cyclohexyl ring, as well as of a –CN group by an –NCS group have been analyzed. The results lead to the following conclusions: (i) the above exchange of rings leads to mesogens the long molecular axes of which do not coincide with the axes of the terminal groups, –CN or –NCS; (ii) antiparallel correlation of molecular dipoles found for cyano-mesogens does not occur in the case of isothiocyanato-mesogens.

Refractive Indices of the MHPB(H)PBC and MHPB(F)PBC Antiferroelectric Liquid Crystals

MHPB(H)PBC and MHPB(F)PBC were studied by means of refractometric measurements. The refractive indices: n “ (T), n Á (T) and n I (T) were measured using combined methods, applying both appropriately prepared Abbe refractometer and interference wedge. Values of the n “ (T), n Á (T) for the Sm A*, Sm C* and Sm C A * phases are related to the optical axis perpendicular to the proper smectic planes. The results of the optic measurements were discussed.

The Origin of High Optical Tilt in a Homologous Series of Fluorinated Antiferroelectric Liquid Crystals

The compounds from the fluorinated nF6B (n = 1,2,3,4,5,6,7) homologous series were investigated by means of optical, electrooptical, refractometrical, dielectric, densytometric, X-ray and IR spectroscopy methods. For some compounds being a subject of investigations a computer simulation of molecular properties were done. In our opinion high value of optical tilt Θo angle in comparison with a tilt angle obtained from X-ray measurements can be interpreted in terms of de Vries model of SmA* phases as well as of dimers creation process.

Determination of ordinary and extraordinary refractive indices of nematic liquid crystals by using wedge cells

A new accurate and fast interference method for determining ordinary and extraordinary refractive indices of nematic liquid crystals is presented and discussed. The method relies on microscopic measurements of distances between interference fringes appearing in polarised parallel coherent monochromatic light beam transmitted normally to the surfaces through a wedge cell filled with a nematic. Both glass plates confining the cell are coated with a partly transparent thin film of metal which is deposited by evaporation in vacuum. Owing to the multiple reflections between the surfaces and a small edge angle, the interference fringes observed near the wedge apex edge are sharp and equidistant. To apply this method one needs only small amount of an investigated liquid crystal. Basic mathematical formulae and results of an experiment are briefly discussed.

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.

Synthesis and Some Physical Properties of Unsymmetrical 4,4′-Dialkylazoxybenzenes

Abstract Two series of unsymmetrical 4,4′-dialkylazoxy compounds: have been obtained, where K = C m H2m+l with m = 2 to 10. The method of their synthesis and the results of measurements of the phase transition temperatures, dielectric constants, refractive indices and densities are presented. Compounds I and in a lesser degree compounds II are low-melting nematics with a small positive anisotropy of the dielectric constant. In both series a strong alteration was observed of clearing point, dielectric constant anisotropy Δe and birefringence Δn with the number in ofcarbon atoms in the alkyl radical.

An Influence of a Single Fluorine Atom Position in the Molecular Rigid Core on Physical Properties of Orthoconic Antiferroelectric Liquid Crystal

The homologous series of mesogenic (S)-4″[n-(perfluoroalkanoyloxy)hexyl-1-oxy]-4-(1-metylheptyloxy-carbonyl)terphenyl compounds exhibiting low temperature, wide range, near orthoconic antiferroelectric phase has been synthesized [1]. Compounds of the homologous series differ from each other by a position of a single fluorine atom substituted at the phenyl ring of the molecular rigid core. This affects the mesogenic behavior. Moreover, the molecular dipole moment of the compound as well as the physical parameters of the antiferroelectric phase are changed. The importance of the molecular dipole moment orientation and magnitude for the mesogenic behavior and physical parameters of the orthoconic antiferroelectric phase is discussed.

Apparent Tilt Angle and Structural Investigations of the Fluorinated Antiferroelectric Liquid Crystal Material for Display Application

Recently the investigation in the field of display technology has been boosted by the availability of new materials. The mostly promised solution for that looks to be based on an antiferroelectric liquid crystalline materials (AFLC). The new group of materials consisting of a fluorinated terminal chain has been recently synthesized in Poland [1]. Such key factors as the optical indices, apparent tilt angle, and structural properties and electrooptical performance of these materials have been studied. The effect of the bend (hockey stick like) molecular shape has been assumed as a factor leading to an high apparent optical tilt angle. The relation between the apparent optical tilt angle and the tilt measured using XRD method and its change with the temperature has been explained.

Electrically Tunable Liquid Crystal Filters

This paper presents tunable liquid crystal filter consists of three interference filters (LC – cells) with different cell thicknesses. These filters use nematic liquid crystal (with high birefringence). Such design allows to select precisely (using the electric field) the wavelength of outgoing light.

On the Importance of the Molecular Core Interactions on the Induction of the High Optical Tilt Angle

Two smectogens being structural analogs with the opposite space orientation of the COO ester group in the molecular core exhibit extremely different tilt angles. A molecular mechanism of the induction of the high optical tilt angle is searched on the basis of extensive investigations of those compounds. Computer modeling of molecules and investigations of physical parameters of smectic phases were done. Different molecular aggregates forming smectic phases were observed. The size and shape of those aggregates are estimated on the basis of measurements and calculations. The different values of the tilt angles in studied compounds were discussed.