Danuta Bauman

The Study of the Guest Effect on the Nematic Phase Stabilization

Abstract The effect of azo-dye on some optical and thermodynamical properties of the liquid crystal 5CB are examined. The relation between molecular geometry of the guest, guest and host order parameters and nematic-isotropic transition temperature of the azo-dye/liquid crystal mixtures is determined. The experimental results are compared in some detail with calculations done on the basis of the molecular mean-field theory and predictions of the lattice models as well. It has been found that good agreement between experiment and theory can be obtained taking into account not only the molecular sizes of the solute and the guest-host interaction, but also the concentration dependence of the dye order parameter and the flexibility of the end-chain of the liquid crystal molecules.

Guest-host interactions in dichroic dye-liquid crystal mixtures in smectic A and nematic phases

Abstract The polarized absorption spectra of six azo dyes dissolved in the liquid crystals 8CB and 8OCB have been measured as a function of temperature in the smectic A and nematic phases. On the basis of these spectra the order parameter of the dyes oriented in the liquid crystalline host has been determined. The guest order parameter has been compared with that of the host, obtained from the optical birefringence measurements. Moreover, the influence of the dichroic dye on the phase transition temperatures of the pure liquid crystal has been studied. A correlation between the orientation of the guest molecules in the uniaxial liquid crystalline phases, the guest molecular geometry and the nematic-isotropic transition temperature of the dye-liquid crystal mixture has been discussed.

Derivatives of 4-amino-N-ethylnaphthalimide for use in nematic liquid crystals

Abstract The order parameters of some dichroic fluorescent dyes {derivatives of 4-amino-N-ethylnaphthalimide} in three nematic liquid crystal mixtures (W52, E7 and ZLI 2359) have been determined by means of optical spectroscopy methods and the influence of the dye addition on the nematicisotropic phase transition temperature has also been investigated. The voltages characterizing the impact of the electric field on the dye-liquid crystal mixtures have been estimated. It was found that the dyes can be utilized in guest-host liquid crystal display devices.

Spectral properties of fluorescent dyes in nematic liquid crystals

Abstract The basic spectral properties and the orientation of some dichroic fluorescent dyes (derivatives of 4-amino-(N-ethylnaphthalimide)) in several nematic liquid crystal matrices have been studied. Moreover, the temperature of the nematic—isotropic phase transition for the dye—liquid crystal mixtures has been determined. It has been found that the dyes investigated are characterized by parameters which make them applicable to both passive and active “guest—host” liquid crystal display devices.

Dichroism and polarized fluorescence of chlorophyll a, chlorophyll c and bacteriochlorophyll a dissolved in liquid crystals

Three photosynthetic pigments were studied: chlorophyll a, chlorophyll c and bacteriochlorcphyll a in nematic liquid crystal matrixes. The polarized absorption and fluorescence spectra as a function of the electric field have been measured. From the polarized components of the absorption A( parallel) and A( perpendicular) of the pigments in liquid crystals two reduced components A(x) and A(y) are calculated (x and y are the direction of the axis which is going through the second, fourth pyrrol rings, and the first, third rings, respectively). From these results the orientation of chlorophylls in liquid crystals and the configuration of the transition moments in the skeleton of the pigment molecules were determined.

Influence of the alkyl chain length of some mesogenic molecules on their Langmuir film formation ability

Langmuir films of members of two homologous series, the 4‐n‐alkyl‐4′‐cyanobiphenyls (nCB) for n = 2–14 and trans‐4‐n‐alkyl(4′‐cyanophenyl)cyclohexanes (PCHn) for n = 2–12, have been studied by recording surface pressure/area isotherms and by Brewster angle microscopy. It has been found that the compounds with very short chains (n⩽3) and very long chains (n>12 for nCB, n>10 for PCHn) are unable to form compressible monolayers at the air–water interface. Other members of both series can form stable Langmuir films, but both their rigidity and stability as well as the molecular packing vary with the alkyl chain length. The isotherms and BAM images imply that the organization of the liquid crystal molecules in the films is to some extent correlated with their ability to form corresponding mesophase in the bulk: nematogenic compounds tend to form rounded droplet‐like domains, whereas smectogenic compounds tend to form flat domains.

Optical spectroscopy study of some 3,4,9,10-tetra-(n-alkoxy-carbonyl)-perylenes in Langmuir–Blodgett films

Abstract Langmuir (L) and Langmuir–Blodgett (LB) films of some 3,4,9,10-tetra-( n -alkoxy-carbonyl)-perylenes have been studied. On the basis of the surface pressure–mean molecular area isotherms, the molecular alignment on the air–water interface has been estimated. The optical spectroscopic study of the LB films has allowed conclusions to be drawn about the arrangement of the molecules on the quartz slides. The fluorescence spectra of the LB films of the perylene-derivatives investigated have revealed the formation of excited dimers.

Fluorescent 3-oxy benzanthrone dyes in liquid crystalline media

Abstract The behaviour of novel 3-oxy benzanthrone derivatives of intense fluorescence emission in liquid crystalline media has been studied with regard to their potential for display application. The optical properties of the dyes were examined both in organic solvents, nematic liquid crystal (LC) and polymer film. The influence of the dyes upon the phase transition temperatures and the electro-optical properties of LC in dye/LC systems was investigated in surface-stabilised display cells. The dichroism D(λ) and the orientational order parameters SA and SF of the dyes in LC were determined from absorption and fluorescence anisotropy. The effect of a polymer component added to the dye/LC systems upon the transition temperatures of LC was established.

Polarized Fluorescence Studies of Orientational Order in Some Nematic Liquid Crystals Doped with Stilbene Dye

Abstract The measurements of the polarized fluorescence intensity for a stilbene guest molecule dissolved in nematic liquid crystals (5CB, 7CB and PCH7) have been used to study the molecular orientational order in thin aligned samples. The temperature dependence of the order parameters ⟨P2⟩ and ⟨P4⟩ have been investigated. The attempt for the explanation of the different behaviour of ⟨P4⟩ parameter in the various liquid crystals has been undertaken. On the basis of the experimental ⟨P2⟩ and ⟨P4⟩ values some information about the orientational distribution of molecules in guest-host mixture have been obtained.

Spectral properties of chlorophyll a in liquid crystal.

Solution of chlorophyll a in liquid crystals mixture (MBBA + EBBA) was investigated. Chl molecules are in LC in low electric field oriented. They can be divided into two groups: one strongly interacting with LC and subjected to reorientation by the electric field, and another weakly interacting with the solvent and insensitive to the voltage applied. The emission spectrum of the first type of chlorophyll is strongly perturbed. At higher voltages, the pigment molecules orientation in the plane of the electrode is another. Pigment absorption and emission anisotropy provides information about the reorientation of LC molecules. Even at high (10(-3)M) Chl concentration and regular pigment array, the interaction between the pigment and solvent exceeds pigment-pigment interaction because the solvent appears to have a stronger influence on the Chl spectrum.