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1

Dynamics of the Molecules in Solid Phases of Few Chosen Schiff Bases Compounds

100%

Bąk A., Massalska-Arodź M.

Acta Physica Polonica A

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2004

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vol. 105

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issue 5

467-474

EN

The dielectric relaxation processes observed in solid phases of MBBA, OH-MBBA, and EBBA belonging to the homologous series of the Schiff bases are discussed. The data are compared with the results completed by the present authors for EBPA compound. The uniform interpretation of the temperature changes of relaxation for all mentioned compounds is proposed.

2

Guest Effect on Nematic-Isotropic Phase Transition Temperature of Liquid Crystal 6CHBT

100%

Bauman D., Solczyński J., Chrzumnicka E.

Acta Physica Polonica A

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1997

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vol. 92

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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.

3

Study of Magnetic Fredericksz Transition in Ferronematics

100%

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.

4

Molecular Dynamics of n-p-(Ethoxybenzylidene) P'-Propylaniline in Nematic and Solid Phases as Studied by Dielectric Relaxation Spectroscopy

100%

Bąk A., Massalska-Arodź M., Urban S.

Acta Physica Polonica A

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2000

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vol. 97

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issue 2

323-330

EN

The complex dielectric permittivity ε*(ν,T) = ε'(ν,T) - iε''(ν,T) of n-p-(ethoxybenzylidene) p'-propylaniline has been measured in the frequency range from 1 Hz to 13 MHz and temperature range from 360 K to 180 K on heating and on cooling the sample. Dielectric relaxations have been found in nematic and solid phases. A detailed analysis of the observed processes has been performed and the parameters describing molecular dynamics have been evaluated. The comparison of results with those obtained for the other Schiff bases is discussed.

5

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

100%

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.

6

Viscosity Behavior at the Nematic to Smectic A Phase Transition in Freely Flowing Compounds

80%

Jadżyn J., Czechowski G.

Acta Physica Polonica A

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2004

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vol. 105

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issue 5

459-465

EN

The paper shows that the shear viscosity at the nematic to smectic A phase transition in freely flowing n-hexyloxycy$ $anobiphenyl + n-octyloxycyanobiphenyl mixtures (a system exhibiting the reentrant nematic phase) corresponds to the Mięsowicz η_3 viscosity coefficient and its temperature behavior is analogous (but strongly enhanced) to that observed for the η_2 viscosity coefficient at the isotropic to nematic phase transition.

7

Orientational Ordering for System of Ellipsoidal Molecules Dispersed in Cubic Lattice

80%

Mejdani R.

Acta Physica Polonica A

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1996

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vol. 90

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issue 6

1127-1141

EN

We represent here some results for a model of migrating and nonmigrating ellipsoidal molecules dispersed in a cubic lattice, describing: the orientational ordering in nematics, the possibility of a biaxial ordered liquid state, the orientational ordering in solid hydrogen (orto-H_{2} or para-D_{2}) or the orientational glassy structure (the "higher rank"glass state). Through this kind of molecular ensemble (in the case of the system of ellipsoidal and spherical molecules) it is also possible to study the orientational and positional orderings in binary mixtures and to obtain the so-called plastic state.

8

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

80%

Chrzumnicka E., Bauman D., Jadżyn J.

Acta Physica Polonica A

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2002

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vol. 102

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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.

9

Scaling in 2-d Distribution of Topological Defects in a Liquid Crystal

80%

Massalska-Arodź M.

Acta Physica Polonica A

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1998

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vol. 94

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issue 1

41-47

EN

Distribution of the topological point defects observed microscopically by Nagaya, Hotta, Orihira and Ishibashi in Schlieren texture of N-(4-n-methoxy benzylidene) 4'-n'-butylaniline has been analyzed. The same fractal dimensionality D_{f}=1.4 has been estimated for several sets of defects obtained in subsequent stages of evolution of the nematic sample after the transition from the isotropic liquid phase.

10

Correlation Length in PBnA Liquid Crystal Family

80%

El Guermai K., Ayadi M., El Boussiri K.

Acta Physica Polonica A

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1998

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vol. 94

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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.

11

Dynamics of 4-(2-hexyloxy-ethoxy) 4'-cyanobiphenyl Molecules on Approaching a Glass Transition as Studied by Dielectric Spectroscopy

80%

Massalska-Arodź M., Witko W., Gorbachev V., Hartmann L., Kremer F.

Acta Physica Polonica A

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2003

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vol. 104

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issue 6

527-536

EN

The complex dielectric permittivity of 4-(2-hexyloxy-ethyloxy) 4'-cyano-biphenyl measured in the frequency range from 0.03 Hz to 10^9 Hz is presented. Monotropic sequence of thermodynamic phases was found with two stable phases (isotropic and crystal) and three metastable states (supercooled isotropic phase, its glass and a smectic phase observed only on heating the sample first cooled rapidly to the liquid nitrogen temperature). In isotropic and supercooled isotropic phases the temperature dependence of the dielectric relaxation time was described by the same Vogel-Fulcher-Tammann formula while in a smectic phase it was of the Arrhenius type. In the transition from a supercooled isotropic phase to a smectic phase the relaxation rate of molecular motions around the short axes increases by two decades. Comparison of the relaxation behaviour and polymorphism of 4-(2-hexyloxy-ethyloxy) 4'-cyano-biphenyl of linear molecules with two chiral cyanobiphenyls is discussed.

12

Molecular Dynamics of 4-(trans-4'-n-Heptylcyclohexyl)- Isothiocyanatobenzene Studied with Dielectric Relaxation Spectroscopy

80%

Bauman D., Czechowski G., Jadżyn J., Legrand C., Douali R.

Acta Physica Polonica A

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2000

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vol. 98

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issue 1-2

71-81

EN

Dielectric relaxation study was carried out for the nematic and isotropic phases of 4-(trans-4'-n- heptylcyclohexyl)isothiocyanatobenzene in the frequency range from 100 kHz to 1 GHz. In the nematic phase two relaxation processes were recorded for the electric permittivity component measured parallel to the molecular orientation (director n) and three relaxation processes - for the perpendicular permittivity component. The strength of the nematic potential and the nematic order parameter were estimated.

13

Singular Elastic Properties of Mixtures with the Re-entrant Nematic Phase

80%

Czechowski G., Jadżyn J.

Acta Physica Polonica A

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2004

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vol. 106

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issue 4

475-485

EN

The paper presents temperature behavior of the splay and bend elastic constants measured for n-hexyloxycyanobiphenyl and n-octyloxycyanobiphenyl mixtures - a system exhibiting the re-entrant nematic phase. It was shown that singularities in the elastic properties of the system concern not only the nematic phase (the well-known pre-smectic effects) but first of all - the smectic A phase, in which the splay and bend deformations, normally not allowed for the layered structures, can be induced.

14

Nonlinear Dielectric Relaxation in Solutions of the Polar Mesogenic Molecules in the Isotropic Phase

80%

Kędziora P.

Acta Physica Polonica A

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2003

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vol. 104

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issue 1

45-53

EN

The nonlinear spectra of 4,4'-n-hexylcyanobiphenyl (C_6H_{13}-Ph-Ph-CN) in benzene solutions were recorded in the frequency range of 300~kHz-100~MHz in the presence of the strong static electric field E_0=1.1×10^7 V/m, at 25˚C. The dynamic pretransitional phenomena revealed for polar C_6H_{13}-Ph-Ph-CN were interpreted in the frame of the Landau-de Gennes theory. The identical concentration-dependent behavior of nonlinear relaxation time in the vicinity of the transition from the isotropic to the nematic phase for polar and nonpolar compounds was discussed.

15

Dielectric, Viscous, and Elastic Properties of Mesogenic 4-n-Hexyloxy-4'-Cyanobiphenyl

80%

Czechowski G., Jadżyn J.

Acta Physica Polonica A

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2001

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vol. 99

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issue 5

579-591

EN

The paper presents the results of measurements of the static and dynamic electric permittivity, the shear viscosity, and the splay and bend elastic constants for 4-n-hexyloxy-4' -cyanobiphenyl (C_6H_{13}O-Ph-Ph-C≡N). On the basis of the static values of the nematic principal permittivities, ε_ǁ (T) and ε_(T), the angle between the dipole moment vector and the long axis of 4-n-hexyloxy-4'-cyanobiphenyl molecule, the apparent dipole moment and the nematic order parameter were determined. From the temperature dependences of the dielectric relaxation time (corresponding to the molecular rotation around the short axis) and the shear viscosity, the strength of the nematic potential and the effective length of 4-n-hexyloxy-4'-cyanobiphenyl molecule (in isotropic phase) were estimated. The K_{11} and K_{33} elastic constants were determined from the voltage dependence of the capacitance of the planar nematic cell with the method proposed by Gruler et al. and Uchida et al.

16

Singular Pretransitional Behavior of the Electric Field-Dependent Part of the Thermodynamic Quantities of Strongly Polar Mesogenic Liquids in the Isotropic Phase

80%

Jadżyn J., Déjardin J., Czechowski G.

Acta Physica Polonica A

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2007

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vol. 111

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issue 6

877-884

EN

A new interpretation of the pretransitional temperature behavior of the static dielectric permittivity and its derivative in terms of the basic thermodynamic quantities: the internal energy, the entropy, and the Helmholtz free energy is presented. It was shown that in the case of strongly polar mesogenic compounds (as the homologous series of alkylcyanobiphenyls) the electric field-induced increments of both the internal energy and the entropy exhibit a critical-like temperature dependence in the vicinity of transition from the isotropic liquid to the nematic phase. As a most important pretransitional effect, it is shown that at a temperature of about 10 degrees before the phase transition, an electric field applied to the isotropic liquids induces an increase in the entropy (Δ S>0) instead of its decrease, as observed far from the phase transition or for the non-mesogenic dipolar liquids.

17

Dynamics of Nematogenic Molecules with Transverse Component of Dipole Moment

80%

Douali R., Czechowski G., Legrand C., Jadżyn J.

Acta Physica Polonica A

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2004

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vol. 105

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issue 4

365-371

EN

The paper presents the results of studies of the dielectric relaxation of nematic 4'-butyloxy-3-fluoro- 4-isothiocyanatotolane, performed for different values of the angle between the probing electric field E and the macroscopic orientation of the sample (the director n) forced by the magnetic field B. Due to a relatively large transverse component of the dipole moment of 4'-butyloxy- 3-fluoro-4-isothiocyanatotolane, the studies allowed one to interpret consistently the dielectric relaxation spectra connected with the molecular rotation around the long axis.

18

Viscous Behavior of Binary Mixtures of Mesogenic Solvent/Non-Mesogenic Solute

80%

Jadżyn J., Czechowski G., Laskowski S.

Acta Physica Polonica A

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2006

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vol. 109

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issue 6

723-730

EN

The paper presents results of the shear viscosity measurements performed on diluted binary mixtures of mesogenic solvent n-hexylcyanobiphenyl (C_6H_{13}PhPhC≡N,6CB) and two non-mesogenic admixtures: (i) n-heptylcyanophenyl (C_7H_{15}PhC≡N,7CP), composed of the molecules of the same polarity as the solvent molecules but of a slightly shorter length, and (ii) 4-n-propylcyclohexyl-4'-n-pentylphenyl (C_3H_7CyHxPhC_5H_{11},3CyP5), composed of the non-polar molecules but of a length very close to that of the mesomorphic solvent molecules. The experiment showed that the concentrational depression of the clearing temperature and the temperature extent of the isotropic + nematic (I + N) two-phase region in the mixtures are significantly smaller, i.e. the nematic phase is more thermodynamically stable, when the admixture molecular length is compatible to that of the mesogenic solvent, regardless of the polarity of the admixture molecules. The activation energy for freely flowing mixtures in the isotropic, nematic, and two-phase I + N regions was determined and discussed.

19

Dielectric Properties of Liquid Crystalline Isothiocyanato-tolane Derivatives with Fluorine Atom at Various Lateral Positions

80%

Czub J., Urban S., Dąbrowski R., Gestblom B.

Acta Physica Polonica A

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2005

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vol. 107

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issue 6

947-958

EN

Dielectric studies were performed for several isothiocyanato-tolane compounds having the F atom attached to the benzene rings at different lateral positions and the alkoxy or alkyl chain at the p-position. They form the nematic phase in broad temperature intervals. The static as well as dynamic properties of the compounds in the nematic and isotropic phases were studied. Tensor permittivity components: ε_ǁ, ε_⊥, Δε, as functions of temperature were measured. The complex dielectric permittivity, ε^*(f)=ε'(f)-iε''(f), was measured in the frequency range of 1 kHz - 3 GHz from which the relaxation times τ_ǁ and τ_⊥ were calculated. The order parameter S(T) was determined from the dielectric data. It was found that the close vicinity of the F atom and the alkoxy group results in blocking of the internal rotation of the wing around the O-phenyl bond.

20

Short-Range Order Fluctuation in the Isotropic Phase of Solutions of 4-trans-4'-n-dodecylcyanobiphenyl in Benzene Studied by Nonlinear Dielectric Spectroscopy

80%

Kędziora P.

Acta Physica Polonica A

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2005

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vol. 107

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issue 6

907-916

EN

Nonlinear dielectric spectroscopy is used to study the dynamics of the smectogenic compound 4-trans-4'-n-dodecylcyanobiphenyl in the isotropic phase as a function of its concentration in benzene. The results obtained reveal that the large, positive amplitude of the field-induced dielectric increment (Δε≈10^{-3}) and its frequency dependence observed in the nonlinear dielectric effect spectra, even far from the possible isotropic-smectic A type phase transition, are due to short range fluctuations of the electric moment. The nature of molecular formations as a result of the strong intermolecular orientational correlations is discussed.

Refine search results

Dynamics of the Molecules in Solid Phases of Few Chosen Schiff Bases Compounds

Guest Effect on Nematic-Isotropic Phase Transition Temperature of Liquid Crystal 6CHBT

Study of Magnetic Fredericksz Transition in Ferronematics

Molecular Dynamics of n-p-(Ethoxybenzylidene) P'-Propylaniline in Nematic and Solid Phases as Studied by Dielectric Relaxation Spectroscopy

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

Viscosity Behavior at the Nematic to Smectic A Phase Transition in Freely Flowing Compounds

Orientational Ordering for System of Ellipsoidal Molecules Dispersed in Cubic Lattice

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

Scaling in 2-d Distribution of Topological Defects in a Liquid Crystal

Correlation Length in PBnA Liquid Crystal Family

Dynamics of 4-(2-hexyloxy-ethoxy) 4'-cyanobiphenyl Molecules on Approaching a Glass Transition as Studied by Dielectric Spectroscopy

Molecular Dynamics of 4-(trans-4'-n-Heptylcyclohexyl)- Isothiocyanatobenzene Studied with Dielectric Relaxation Spectroscopy

Singular Elastic Properties of Mixtures with the Re-entrant Nematic Phase

Nonlinear Dielectric Relaxation in Solutions of the Polar Mesogenic Molecules in the Isotropic Phase

Dielectric, Viscous, and Elastic Properties of Mesogenic 4-n-Hexyloxy-4'-Cyanobiphenyl

Singular Pretransitional Behavior of the Electric Field-Dependent Part of the Thermodynamic Quantities of Strongly Polar Mesogenic Liquids in the Isotropic Phase

Dynamics of Nematogenic Molecules with Transverse Component of Dipole Moment

Viscous Behavior of Binary Mixtures of Mesogenic Solvent/Non-Mesogenic Solute

Dielectric Properties of Liquid Crystalline Isothiocyanato-tolane Derivatives with Fluorine Atom at Various Lateral Positions

Short-Range Order Fluctuation in the Isotropic Phase of Solutions of 4-trans-4'-n-dodecylcyanobiphenyl in Benzene Studied by Nonlinear Dielectric Spectroscopy