Józef Żmija

Investigation of The Biased Rotation of Chiral Molecule Around its Long Molecular Axis in the Ferroelectric Liquid Crystal Mixture

Abstract Spontaneous polarization (Ps), tilt angle (θ), helical pitch (p) and densytometric (ρ) characteristics versus temperature and concentration of chiral dopant have been measured for FLC mixture. On the base of computer modelling the molecular dipole moment (μ), transverse (αt) and longitudinal (α1) molecular polarizabilities as well as angle (γ and Φ0) between the vector μ and main long n and short 1 molecular axes of inertia have been calculated. Knowing the molecular parameters μ, αt, αl, γ and Φ0 and state parameters θ, p, spontaneous polarization Ps has been calculated as the vector sum of the components of molecular dipole moment μ1 perpendicular to the tilt direction. To do it the Zeks1 rotational potential modified by us2 has been used. After comparing spontaneous polarization Ps taken from experimental and obtained from theoretical approximation the biased rotation parameter η has been calculated.

On the Consistency and Applicability of Internal Field Models in Nematics

Abstract Information on anisotropy of the local field of light wave in nematics is obtained mainly from refractivity measurements. Such investigations, supplemented by those concerning thermal dependence of density ρ(T), allow for determining optical polarizability anisotropy of nematogenic molecules, as well as their orientational order parameter. This paper discusses, on the basis of extensive experimental data, the following problems: • applicability of approximate relations between refractive indices of nematic liquid crystals (NLCs) and their molecular parameters for describing optical properties of nematic mesophase has been estimated; • anisotropy of the local field factor Fk has been investigated, as well as its influence on calculated anisotropy of molecular polarizability. Influence of various extrapolation procedures on calculated molecular parameters of the NLCs has been investigated.

How to Choose the Proper Polymer to PDLC Prepare

Abstract Polymer dispersed liquid crystals exhibit some advantages in applications and also interesting physical properties. In this contribution we present general rules of choosing a proper polymer, which fulfill all basic requirements, for PDLC preparation.

Optical Investigation of the Vector Field of Directors in the L. C. Boundaried Nematic Medium Under Electric and Magnetic Fields

Abstract We have measured both phase difference decrease δ between ordinary and extraordinary rays passing through liquid crystal cell and dielectric constants ϵ of 4-trans-n-hexyl-cyclohekxyl-isothiocyanatobenzene (6CHBT). The results of the studies for different alignment and thicknesses under various electric measuring and magnetic fields are presented. The exposed experimental technique and data processing allows K11 and K33 determination. Determination Θ(z) is derived from continuum theory so it is not purely experimental determination but semiempirical method.

Determination of the Nematic Liquid Crystal (NLC)-Substrate Interaction Potential by Means of Semiempirical Method of Self-Consistent Director Field

Abstract A semi-empirical method is proposed for determination of the nematic liquid crystal-substrate interaction potential. Employing results of the dielectric constant e and phase shift δ measurements, presented for 4-trans-4′-n-hexyl-cyclo-hexyl-isothiocyanatobenzene (6CHBT) and applying the selfconsistent director field method, interaction potentials (6CHBT-polyimide) and (6CHBT-lecithin) have been estimated.

On the Effect of Neutron Radiation on Mesogenic Cholesteryl Esters

Abstract The influence of ionizing radiation on the mesogenic properties of cholesterogens has been studied by several authors. The main conclusions of these works were: 1. The temperature of S-Ch transition and consequently the temperature of color response have been lowered after being irradiated linearly with an absorbed dose (and non-linearly with sufficiently high doses [6]) for all systems studied. 2. The above have been caused by products of radiolysis of cholesterogen which acts as a dopant of CLC. The majority of these works were concerned with the influence of gamma-radiation on the solutions of mesogenic cholesteryl esters in organic solvents. In this paper, we present some interesting results of the preliminary studies on the effect of neutron radiation on the mesogenic properties of cholesteryl esters.

Attempt to Apply Liquid-Crystal Thermography in Prick Test Allergy Diagnosis

Abstract Prick tests are commonly used in allergy diagnosis but in some cases obtained results are difficult for objective interpretation. Application of liquid-crystal contact thermography improves this kind of diagnosis especially in case of coloured or sick skin.

Thickness Dependence of Dielectric Properties of a Ferroelectric Liquid Crystal

Abstract A room temperature ferroelectric liquid crystal has been studied by means of dielectric measurements. The results of the studies of the complex electric permittivities for aligned samples of different thicknesses and for the different electric measuring fields are presented. We discuss how dielectric properties depend on boundary conditions, thicknesses of the samples and the magnitude measuring electric fields. The obtained experimental results and the discussion make it possible to determine the spontaneous polarization from dielectric measurements.

Technical aspects of measurement of elastic constants and diamagnetic anisotropy of nematic liquid crystals

Abstract We have measured the critical values of electric Ec and magnetic Hc fields in different types of Freedericksz transitions for 4-trans-n-hexyl-cyclohexyl- isothiocyanatobenzene (6CHBT). Capacitive and optical methods have been employed to detect these transitions. In the case of twist-type deformation we have proposed a new interference method for threshold fields determination. On the basis of these measurements diamagnetic anisotropy Δχ splay K11, twist K22 and bend K33 elastic constants have been calculated for cells of various thickness, coated with different polyimides.