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1
Content available remote

Effects of Order on Spectral Properties of Discotic Liquid Crystal Heptyloxydibenzopyrene

100%
Uznański P.
Acta Physica Polonica A
|
1998
|
vol. 94
|
issue 5-6
825-834
EN
The spectral properties of discotic heptyloxydibenzopyrene were studied by UV-VIS absorption, fluorescence, and infrared spectroscopy as a function of temperature in two different types of spectroscopic cells. The molecule was found to be a sensitive spectroscopic probe of molecular orientation on a surface. Capillary-filled cells caused the liquid crystal to assume a parallel orientation with respect to the surface, whereas spin-coating caused the orientation of columns to be statistically more nonuniform. It was shown from the spectroscopic studies that the molecular orientation changed on going from crystal to liquid crystalline state and a conclusion was drawn that bulk molecular alignment of columnar phase was defined by an interface imposed by an external surface.
2
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Investigations of Director Field Arrangement Induced in Tunable Liquid Crystalline Waveguide

100%
Walczak A.
Acta Physica Polonica A
|
1998
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vol. 94
|
issue 5-6
813-823
EN
Measurements of the refractive index profile have been made to provide data for obtaining local optical axis arrangement in the waveguide cross-section. Liquid crystalline planar waveguide tuned with the electric field has been used. A new approach is proposed to accomplish refractive index profile measurements in a direct way. The modal line method is presented as a tool that allows one to do it and to improve the attenuated total reflection disadvantages as well. The obtained results maintain applicability of the modal line method for a direct refractive index profile measurement. To verify the method, nematic 6CHBT (4-trans-4-n-hexyl-cyclohexyl- isothiocyanatobenzene) described earlier in the literature has been examined. A nematic mixture W602 contained 6CHBT as a main component has been examined too.
3
Content available remote

New Method for Analysis of Liquid Crystal Elasticity

100%
Walczak A.
Acta Physica Polonica A
|
1998
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vol. 94
|
issue 5-6
803-812
EN
Orientational elastic constant k_{11}, k_{33} and k_{13} of liquid crystals are determined by a new way. Liquid crystalline waveguide is applied to measure refractive index profile across the waveguide layer. Results of the measurements allow one to find local director field within the liquid crystalline layer. Director field is applied to transform the Frank-Oseen equations into a form of an overdetermined algebraic system of equations with elastic constants as unknown variables. A solution of those equations has been found by the orthogonal decomposition method. Elastic constants for nematic mixture, W602, and main component of it, 6CHBT (4-trans-4-n-hexyl-cyclohexyl-isothiocyanatobenzene), have been obtained as well as anchoring energy values
4
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Guest Effect on Nematic-Isotropic Phase Transition Temperature of Liquid Crystal 6CHBT

63%
Bauman D., Solczyński J., Chrzumnicka E.
Acta Physica Polonica A
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1997
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vol. 92
|
issue 6
1151-1161
EN
The polarized absorption spectra of seven dichroic azo dyes dissolved in the nematogenic liquid crystal host 6CHBT have been recorded as a function of temperature. On the basis of these spectra, the guest order parameter has been determined. Moreover, the influence of the dye addition on the behaviour of the guest-host mixture in the vicinity of the nematic- isotropic phase transition has been examined. The experimental results have been compared in some details with the calculations done on the basis of the mean field theory for binary mixtures.
5
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Orientational Behaviour of the Guest-Host Systems in the Smectic A and Nematic Phases

63%
Bauman D., Moryson H., Wolarz E.
Acta Physica Polonica A
|
1992
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vol. 81
|
issue 4-5
559-570
EN
The measurements of the polarized absorption and fluorescence components spectra for the guest-host mixtures have been used to study the long orientational order in the uniaxial phases of the liquid crystal. The temperature dependence of the order parameters, ⟨P_{2}⟩ and ⟨P_{4}⟩, has been investigated and the molecular distribution function has been determined. On the basis of the ⟨P_{2}⟩ and ⟨P_{4}⟩, values some conclusions about the molecular orientation in the smectic A and nematic phases of the liquid crystalline samples have been drawn. It has been also found that the fluorescence spectroscopy is a sensitive method for determination of the phase transition temperatures of the liquid crystal doped with the fluorescent dye.
6
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Study of Magnetic Fredericksz Transition in Ferronematics

63%
Kopčanský P., Koneracká M., Jadżyn J., Czechowski G., Żywucki B.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
437-440
EN
The magnetic Fredericksz transition in ferronematics (thermotropic nematic liquid crystals 7CB and MBBA combined with fine magnetic particles of a size 10 nm) as a function of concentration of magnetic particles was studied by using simple dielectric measurements. The increase of the threshold magnetic field is observed in 7CB based ferronematic while the decrease of threshold field in MBBA based ferronematic is observed when the concentration of magnetic particles is increased. Experimental results are discussed in the framework of Brochard, de Gennes and Burylov, Raikher theories.
7
Content available remote

Guest-Host Interactions in Nematic p-Cyano-p'-Alkylphenylcyclohexanes

63%
Bauman D., Moryson H., Jadżyn J.
Acta Physica Polonica A
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1994
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vol. 85
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issue 3
553-562
EN
Studies of the temperature dependence of the guest order parameter for binary mixtures of the dichroic azo dye in the homologous series of the p-cyano-p'-alkylphenylcyclohexane were performed. Odd-even effect for the order parameter value was observed. A correlation between the shift in the nematic-isotropic transition temperature after dye addition and the orientation of the guest molecules in the nematic host was discussed.
8
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Magnetic Field Induced Structural Transitions in 6CHBT-Based Ferronematics

51%
Tomašovičová N., Timko M., Koneracká M., Závišová V., Jadżyn J., Beaugnon E., Chaud X., Kopčanský P.
Acta Physica Polonica A
|
2012
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vol. 121
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issue 5-6
1276-1278
EN
Ferronematics are stable colloidal suspensions of magnetic particles in nematic liquid crystals. The presence of the magnetic particles enhances the magnetic susceptibility of ferronematics, in comparison with pure liquid crystals. In this work the thermotropic liquid crystal 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanato-benzene (6CHBT) and 6CHBT dissolved in phenyl isothiocyanate were doped with spherical magnetic nanoparticles with aim to increase the sensitivity of the liquid crystal on an external magnetic field. The volume concentration of the magnetic particles was 5 × 10^{-4}. The phase transition temperature from isotropic to nematic phase in the external magnetic field up to 12 T was monitored by precise capacitance measurements in the capacitance cells filled with nematic sample as well as with the prepared ferronematic sample. There was no observable shift in the transition temperature in the case of pure 6CHBT, 6CHBT doped with spherical particles and 6CHBT dissolved in phenyl isothiocyanate while in the case of 6CHBT dissolved in phenyl isothiocyanate doped with spherical magnetic particles the shift in the temperature about 9C of the phase transition from isotropic to droplet state at the external magnetic field 12 T was observed.
9
Content available remote

Dielectric Properties of Lyotropic Magnetic Liquid Crystal

51%
Kopčanský P., Tomčo L., Jadzyn J., Swiergiel J., Majorošová J., Kubovčíková M., Timko M., Rajňák M., Šipošová K., Gažová Z., Bednariková Z., Hu C.-K., Hayryan S., Studenyak I., Kovalchuk T., Kovalchuk O.
Acta Physica Polonica A
|
2015
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vol. 127
|
issue 2
632-634
EN
An important feature of lyotropic liquid crystals is the self-assembly of the amphiphilic molecules as supermolecular structures. We have studied the formation of nematic liquid crystal phase in solutions containing lysozyme amyloid fibrils and magnetic nanoparticles using oscilloscopic method. Interaction of fibrils with magnetic nanoparticles under the external magnetic field resulted in fibril re-arrangement. The analysis of the obtained results suggests that the decrease in conductivity of solutions in presence of magnetic field is due to decrease of the ion mobility caused by re-arrangement of structures in the solution. The obtained results allow determination of the optimum ratio of the components which can lead to preparation of solutions with a more ordered structure in presence of magnetic field.
10
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The Current Phenomenon in the Indium-Tin Oxide-Alignment Layer-Liquid Crystal Structure

51%
Mykytyuk Z., Fechan A., Sushynsky O., Yasynovska O., Kotsun V.
|
|
issue 1
248-250
EN
This work is connected to investigation of frequency dependences of conductive value and dielectric conductivity of the indium-tin oxide-alignment layer-liquid crystal structure which allows to find new ways in formation of the electrically stabilized structure of liquid crystal materials for the optoelectronic devices.
11
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Molecular Interactions in Monolayers οf Azo Dye/Liquid Crystal Mixtures at Interfaces

51%
Bauman D., Płóciennik A., Inglot K.
Acta Physica Polonica A
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2009
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vol. 116
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issue 2
203-210
EN
A study of azo dye/liquid crystal mixtures in monolayers formed at an air-water interface (the Langmuir films) and at a solid surface (the Langmuir-Blodgett films) has been performed. Five azo dyes with various molecular structure and the liquid crystal 4-octyl-4'-cyanobiphenyl (8CB) have been used. The dyes have been added to the liquid crystal at various molar fractions. Surface pressure and surface potential versus mean molecular area isotherms for the Langmuir films have been recorded and information about intermolecular interactions at the air-water interface has been obtained. On the basis of electronic absorption measurements for the Langmuir and Langmuir-Blodgett films the conclusions about the ability of dyes molecules to form self-aggregates at the interfaces have been drawn. The influence of the dye molecular structure and its concentration on aggregates' geometry has been found.
12
Publication available in full text mode
Content available

Optical Order Parameter of Dichroic Azo-Dyes in Liquid Crystalline Side-Chain Polysiloxanes

51%
Chrzumnicka E., Bauman D., Jadżyn J.
Acta Physica Polonica A
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2002
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vol. 102
|
issue 6
767-780
EN
Polarized light absorption spectra of seven dichroic azo-dyes dissolved in mesogenic side-chain polysiloxanes were recorded as a function of temperature. On the basis of the spectra the optical order parameter of the dyes was determined. The influence of the dye on the phase transition temperatures of polysiloxanes was examined. The results obtained for polysiloxanes were compared with the data for low molecular weight liquid crystal.
13
Content available remote

How to Enhance Sensitivity of Liquid Crystals to External Magnetic Field?

51%
Kopčanský P., Tomašovičová N., Gdovinová V., Timko M., Éber N., Tóth-Katona T., Jadzyn J., Honkonen J., Chaud X.
Acta Physica Polonica A
|
2015
|
vol. 127
|
issue 2
157-162
EN
Liquid crystals, due to their large dielectric anisotropy, respond very sensitively to application of an external electric field, whereas they are only weakly sensitive to the magnetic field. A possible way of improving that sensitivity is doping liquid crystals with magnetic nanoparticles. As a result, stable colloidal suspensions of liquid crystals with relatively low concentrations of magnetic nanoparticles (called ferronematics, ferrocholesterics, ferrosmectics, etc.) can be produced. We illustrate some examples of the influence of the magnetic field, as well as of a superposition of magnetic and electric fields on the structural transitions (e.g. on the Fréedericksz transition) in ferronematics based on the calamitic liquid crystal 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). It is shown that the samples respond to the applied magnetic field of low strength. The effects of the magnetic particles and magnetic field on the nematic to isotropic phase transition temperature are discussed as well.
14
Content available remote

Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase

51%
Wolarz E., Bauman D., Jadżyn J., Dąbrowski R.
Acta Physica Polonica A
|
2011
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vol. 120
|
issue 3
447-454
EN
Dielectric relaxation study of nematogenic 4-n-alkyl-4'-cyanobiphenyls (nCB, n = 5, 6), 4-(trans-4'-n-alkylcyclohexyl)isothiocyanatobenzenes (nCHBT, n = 6, 8), 4-cyanophenyl-4'-n-alkylbenzoates (nCPB, n = 6, 8), 4-cyano-3-fluorophenyl-4'-n-octyloxybenzoate (8OCFPB), and 4-cyanophenyl-4'-n-octyloxy-3'-fluorobenzoate (8OCPFB) was performed in the frequency range from 50 kHz to 100 MHz in the nematic and isotropic phases. The static permittivity and the relaxation process related to the rotation of molecules around their short axis was analyzed. For some of these liquid crystals anomalous temperature dependence of static permittivity in the pretransitional region of the isotropic phase was observed. Based on the Meier-Saupe-Martin model of molecular diffusion in nematics, the orientational order parameter 〈P_2〉 was determined from dielectric relaxation times and retardation factor. The values of 〈P_2〉 calculated from the dielectric relaxation data were compared with the results obtained from measurements of polarized electronic absorption. Correlations between the magnitude of the dielectric pretransitional effect and the orientational order in the nematic phase were discussed.
15
Content available remote

Photoelectrochemical Cell with Dye Molecules Oriented in Nematic Liquid Crystal

51%
Naser N. S., Planner A., Frąckowiak D.
Acta Physica Polonica A
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1997
|
vol. 92
|
issue 3
535-542
EN
A photoelectrochemical cell consisting of two semiconducting electrodes covered by orienting SiO_{x} layers and filled with merocyanine solutions in nematic liquid crystal was constructed. Dye molecules were oriented as a result of the guest-host effect. Generation of photocurrent by two components of polarized light gives different values of photocurrent amplitude but anisotropy of photocurrent is lower than that of absorption in the region of a free base form of dye. It is explained by dominant participation of a protonated form of dye in the photocurrent generation. The last form exhibits a lower degree of orientation than the free base form of dye.
16
Content available remote

Low Magnetic Field Response in Ferronematics

51%
Gdovinová V., Tomašovičová N., Závišová V., Éber N., Tóth-Katona T., Royer F., Jamon D., Jadzyn J., Kopčanský P.
Acta Physica Polonica A
|
2017
|
vol. 131
|
issue 4
934-936
EN
In this work the 4-n-hexyl-4'-cyanobiphenyl liquid crystal was doped with differently shaped magnetite nanoparticles. The structural changes were observed by capacitance measurements. Influence of the shape of magnetic particles on magnetic Fréedericksz transition depends on the type of anchoring, which is characterized by the density of the anchoring energy and by the initial orientation between the liquid crystal molecules and the magnetic moment of the magnetic particles. It was observed that in the case of doping with spherical particles, the critical magnetic field is shifted to higher values with increase of volume concentration of the magnetic nanoparticles but decreases with increase of biasing voltage. In the case of doping with rod-like particles, the critical magnetic field is almost independent of the volume concentration of the magnetic nanoparticles.
17
Content available remote

Correlation Length in PBnA Liquid Crystal Family

51%
El Guermai K., Ayadi M., El Boussiri K.
Acta Physica Polonica A
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1998
|
vol. 94
|
issue 5-6
779-784
EN
We present a study of the range molecular interactions inside layers in smectic phases A and I of PBnA (phenyl-4 benzylidene 4'-alkylaniline) liquid crystals family. The purpose of this work is to determine the correlation length of the molecules' gravity centers in existing domain of smectic phases and at the transition between them. We used X-rays in-plane peaks of the pattern diffraction of aligned sample by a magnetic field.
18
Content available remote

Dielectric and Optical Studies of Homologous Series of Bicyclo[2,2,2]octane Derivatives with -NCS Terminal Group

51%
Herba H., Żywucki B., Czechowski G., Bauman D., Wąsik A., Jadżyn J.
Acta Physica Polonica A
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1995
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vol. 87
|
issue 6
985-994
EN
The static dielectric constants and the optical birefringence for four members of the homologous series of bicyclo[2,2,2]octane derivatives with -NCS terminal group (pentyl to octyl) have been measured as a function of temperature. From the dielectric anisotropy, the optical birefringence as well as the polarized absorption spectra of the dichroic dye dissolved in the liquid crystalline host the order parameter has been determined. The results obtained by using various experimental methods have been compared with those calculated from the Maier-Saupe mean field theory. It has been found that the order parameter for the successive homologues shows alternation similar to that exhibited for the nematic-isotropic transition temperature.
19
Content available remote

Guest Influence on the Dipolar Association of the Nematic Liquid Crystal Host

51%
Bauman D., Fan Z.-X., Haase W.
Acta Physica Polonica A
|
1991
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vol. 80
|
issue 4
545-552
EN
X-ray diffraction method has been used to study the molecular organization in 4-n-pentyl-4'-cyano-p-terphenyl doped with guest dye molecules. It has been found that the dye with strong polar end group affects significantly the monomer to dimer ratio in the nematic phase of the liquid crystal studied.
20
Content available remote

The Influence of Magnetic Particles on the Nematic Droplets Formation in Liquid Crystal

51%
Majorošová J., Gdovinová V., Tomašovičová N., Juríková A., Závišová V., Jadzyn J., Kopčanský P.
Acta Physica Polonica A
|
2017
|
vol. 131
|
issue 4
955-957
EN
In this work the thermotropic nematic liquid crystal 4-trans-4'-n-hexyl-cyclohexyl-isothiocyanato-benzene (6CHBT) was dissolved in phenyl-isothiocyanate and doped with spherical magnetic particles with volume concentration ϕ₁=10¯⁴ and ϕ₂=10¯³. The influence of the volume concentration on the phase transitions from isotropic to nematic phase was studied by three experimental methods: optical microscopy, differential scanning calorimetry, and dielectric measurements. The obtained results confirmed the coexistence of isotropic and nematic phase, i.e. nematic or ferronematic droplets in isotropic phase in a wide temperature range between nematic and isotropic phase.
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