Jerzy Kedzierski

Novel high birefringent isothiocyanates based on quaterphenyl and phenylethynyltolane molecular cores

We report the synthesis of new laterally alkyl substituted high birefringent quaterphenyl and phenylethynyltolane liquid crystals with isothiocyanate terminal group. The thermal and optical properties such as birefringence are measured and discussed based on their molecular structures. The compounds exhibit birefringence (Δn) in the range of 0.44–0.63, and are expected to be appropriate components of high birefringent nematic mixtures for various applications.

Preparation and evaluation of polyimide layers as materials for nematic liquid crystal orientation

Abstract Ten polypyromellitimides, seventeen poly(imide esters) and six poly(imide amides) have been synthesized. The stability of 0.5% solutions of the poly(amic acids) in DMF, and the hardness, adhesion to glass and quality of nematic liquid crystal alignment of the polyimide layers using the interference wedge method have been tested. The relationship between the chemical structure of polyimides and their properties, especially the alignment depth, is discussed.

Dielectric investigation of the diamagnetic anisotropy and elasticity of 4-trans-4′-n-hexyl-cyclohexyl-isothiocyanatobenzene (6CHBT)

Abstract We have measured the dielectric constants of 6CHBT. The results from studies of various alignments and thicknesses measured under different electric and magnetic fields are presented. We discuss how the dielectric properties depend on boundary conditions, sample thickness and the magnitudes of electric and magnetic fields. Experimental results and discussion in the terms of continuum theory make it possible to compute the diamagnetic anisotropy (Δχ), as well as the splay and bend elastic constants (K 11, K 33) of 6CHBT.

Homologous series of fluorinated antiferroelectric liquid crystals: a comparative study of physical properties and the electro-optical performance

Recently the investigation in the field of LCD technology has been boosted by the availability of new materials. The new group of fluorinated mesogens has been recently synthesized in Poland. In this work we have been focused on investigations of properties of materials having the broad temperature range of antiferroelectric phase. Such key factors as apparent tilt angle and structural properties and electro-optical performance have been studied by means of electro-optical and X-ray methods. The bend molecular shape and the presence of fluorinated tail has been assumed as a factor leading to an extremely high apparent optical tilt. The length of the fluorinated chain seems to affect th mesogenic behavior.

Composite Method for Determination of Liquid Crystal Material Parameters

Abstract A stable method for the determination of the nematic liquid crystal material parameters, such as the splay and bend elastic constants, the anisotropy of diamagnetic susceptibility, the electric permittivities and either the coupling between the nematic molecules and the substrate at the planar liquid crystal cell boundary (i.e. the director field boundary value), is presented in the work. The method consists of two stages: firstly the effective electric permittivity of planar nematics cell is measured as a function of external electric and magnetic fields, secondly the coefficient inverse problem is solved numerically using the experimental data to determine the values of material parameters. The coefficient inverse problem is posed in a variational way as a problem of nonlinear mean-square fit of the calculated nematics layer characteristics to the measured ones. The description of phenomena is based on Ericksens - Leslies theory. The unknown material parameters serve in this approach as the fit parameters, the best values of which corresponding to the best possible approximation of the experimental data by the refined mathematical model are to be found. The method was successfully used for the determination of the material parameters of PCB and can be applied to every nematics.

Interference Method for Determining Dispersion of Refractive Indices of Liquid Crystals

An efficient, quick and pretty accurate interference method for determining dispersions of ordinary n o and extraordinary n e refractive indices and optical anisotropy of nematic liquid crystals, i.e., ne(λ), no(λ) and Δn(λ) ≡ n e (λ)–no(λ), as functions of wavelength λ (in visible and near infrared region), is presented. The method relies on measurements of positions of interference fringes in spectrogram produced by a flat-parallel nematic liquid crystal cell in only one run.

Nematic liquid crystal mixtures for 3D active glasses application

ABSTRACT Methods of 3D imaging present on the market can be divided into two basic groups: autostereoscopic and stereoscopic. At the stereoscopic methods of 3D imaging it is necessary to use special glasses for separation of images constituting stereo-pair. The most commonly used active glasses consist of two electro-optical transducers based on twisted nematic or other electro-optical effects. Here the evaluation of liquid crystal mixtures is designed intentionally for 3D active glasses in order to eliminate drawbacks of active glasses available on the contemporary market. Material parameters of new designed liquid crystal mixtures such as: elastic constants, viscosity, refractive indices, dielectric and spectral properties as well as response times have been determined. In addition to the symmetrisation of the switching times of 3D active glasses, a dual frequency nematic liquid crystal has been proposed. GRAPHICAL ABSTRACT

Method for Determining Material Constants of Nematic Liquid Crystals by Use of Wedge Cells

A wedge cell of the wedge angle of order of few milliradians was used to measure the phase shift between ordinary and extraordinary rays of transmitted light, for the Fréedericksz transition induced by a magnetic or an electric field. A nematic liquid crystal, PCB, filling the cell, was of the planar alignment enforced by the treatment of the flat boundary plates. A polyimide, MK8–poly (amic acid), was used as aligning substance. A system of interference fringes appeared in the cell placed in normally incident light between the analyser and the polariser crossed. In the neighbourhood of each fringe the cell can be considered as a flat-parallel one and hence it is equivalent to a system of flat cells of different precisely determined thickness. The dependence of the phase shift on applied external fields was measured for several interference fringes. The nematic liquid crystal material parameters (the splay and bend elastic constants, the anisotropy of diamagnetic susceptibility and the boundary tilt angle as a function of the torque) were determined by fitting the calculated characteristics to the measured ones.

Composite Method for Measurement of Splay, Twist and Bend Nematic Elastic Constants by Use of Single Special In-Plane-Switched Cell

A method for quick and pretty accurate measurements of splay, twist and bend elastic constants of nematic liquid crystals is proposed. The main concept relies on exploiting only electric field in a plane-parallel liquid crystal cell of special configuration with thin transparent comb-like electrodes on one cover and usual transparent plane electrode on the other. Rubbing in direction parallel to comb electrode stripes enforces homogeneous planar or homeotropic orientation of nematic molecules. Fréedericksz’ transition of pure splay, twist or bend form is initialised by applying voltage between the electrodes appropriately. The method was tested with three different comb-like electrode configurations and three nematics: 4-pentyl-4′-cyanobiphenyl, 4-trans-4′-n-hexyl-cyclohexyl-isothiocyanatobenzene and Demus’ esters.

Determiniation of nematic liquid crystal material parameters by solving inverse problems for different planar cells

The practical application of the composite method of the determination of nematic liquid crystal material parameters (namely the splay and bend elastic constants, the anisotropy of diamagnetic susceptibility and the boundary tilt angle) is presented. The description of phenomena is based on the Ericksen-Leslie theory of nematics. The director field value at the nematics cell boundaries is described as a function of the torque transmitted from the deformed bulk, modeling the coupling between a nematics and a substrate. The method is based on approximate solving the coefficient inverse problem. The applied procedure of the determination of material parameters may be divided into three stages. The first one was the preparation of flat-parallel nematics cells, made of the same nematics and with the same treatment of the glass plate surfaces. The second one was the measurements of the optical response of the cells influenced by an external electric field (a voltage). Such cell characteristics contain information about the unknown magnitudes of material parameters. The final stage was the determination of the magnitudes of liquid crystal material parameters as solutions of coefficient inverse problems with measured cell characteristics as input data. The method was applied to study a system nematics PCB - polyimide PI10.