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1
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Viscosity Behavior at the Nematic to Smectic A Phase Transition in Freely Flowing Compounds

100%
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.
2
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Singular Elastic Properties of Mixtures with the Re-entrant Nematic Phase

100%
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.
3
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Dielectric, Viscous, and Elastic Properties of Mesogenic 4-n-Hexyloxy-4'-Cyanobiphenyl

100%
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.
4
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Temperature Dependence of the Viscosity of Isotropic Liquids

81%
Jadżyn J., Czechowski G., Lech T.
Acta Physica Polonica A
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2002
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vol. 101
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issue 4
495-503
EN
Temperature dependence of the shear viscosity measured for isotropic liquids belonging to the three homologous series: 4-(trans-4'-n-alkylcyclohexyl) isothiocyanatobenzenes (C_n H_{2n+1} CyHx Ph NCS; nCHBT, n=0÷12), n-alkylcyanobiphenyls (C_nH_{2n+1} Ph Ph CN; nCB, n=2÷12) and 1,n-alkanediols (HO(CH_2)_nOH; 1,nAD, n=2÷10) were analysed with the use of Arrhenius equation and its two modifications: Vogel-Fulcher and proposed in this paper. The extrapolation of the isothermal viscosity of 1,n-alkanediols (n=2÷10) to n=1 leads to an interesting conclusion concerning the expected viscosity of methanediol, HOCH_2OH, the compound strongly unstable in a pure state.
5
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Singular Pretransitional Behavior of the Electric Field-Dependent Part of the Thermodynamic Quantities of Strongly Polar Mesogenic Liquids in the Isotropic Phase

81%
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.
6
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Dynamics of Nematogenic Molecules with Transverse Component of Dipole Moment

81%
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.
7
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Viscous Behavior of Binary Mixtures of Mesogenic Solvent/Non-Mesogenic Solute

81%
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.
8
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Dielectric Relaxation of 4-Cyanophenyl 4'-n-Decyloxybenzoate in the Isotropic, Nematic, and Smectic A Phases

81%
Ginovska M., Czechowski G., Andonovski A., Jadżyn J.
Acta Physica Polonica A
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2000
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vol. 98
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issue 6
715-720
EN
The paper presents the results of the dielectric relaxation study performed for the isotropic, nematic, and smectic A phases of 4-cyanophenyl 4'-n-decyloxybenzoate (C_{10}H_{21}O-Ph-COO-Ph-C≡ N, CP10DB) in the frequency range from 100 kHz to 100 MHz. In the nematic and smectic A phases the permittivity was measured with the probing electric field E parallel to the macroscopic molecular orientation (the director n). The recorded dielectric spectra correspond to the rotation of CP10DB molecules around the short axis and can be quite well described in the framework of the Debye model. It was found that the values of the activation energy for the molecular reorientations in the isotropic and smectic A phases of CP10DB are quite close to each other, whereas in the nematic phase the energy is remarkably higher.
9
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Dielectric Relaxation in Hydrogen Bonded Urea-Based Supramolecular Polymer N,N'-di(2,2-dipentylheptyl)urea

81%
Jadżyn J., Bouteiller L., Déjardin J., Czechowski G.
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EN
Results of the dielectric relaxation studies, performed for supramolecular polymer formed by N,N'-di(2,2-dipentylheptyl)urea dissolved in carbon tetrachloride, are presented. The measurements were done for N,N'-di(2,2-dipentylheptyl)urea concentration up to about 7% (in mole fraction) in the frequency region from 100 kHz to 100 MHz and at the temperatures from 5ºC to 50ºC. The analysis of the experimental data were performed with the Havriliak-Negami equation. In the studied range of N,N'-di(2,2-dipentylheptyl)urea concentration and temperature, the obtained values of exponentsα andβ of the Havriliak-Negami equation are equal to 0.9±0.1 and 0.7±0.1, respectively, showing an anomaly in the dielectric relaxation behavior close to the Davidson-Cole type. Two examples of the modeling of dielectric properties of the supramolecular polymer solutions were presented.
10
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Study of Magnetic Fredericksz Transition in Ferronematics

71%
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.
11
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Molecular Dynamics of 4-(trans-4'-n-Heptylcyclohexyl)- Isothiocyanatobenzene Studied with Dielectric Relaxation Spectroscopy

71%
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.
12
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Anomalous Dielectric Relaxation in Binary Mixtures of Mesogenic Solvent/Non-Mesogenic Solute

71%
Jadżyn J., Bauman D., Déjardin J., Ginovska M., Czechowski G.
Acta Physica Polonica A
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2005
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vol. 108
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issue 3
479-489
EN
Dielectric relaxation studies for mixtures of strongly polar and mesogenic n-heptylcyanobiphenyl with non-polar and non-mesogenic carbon tetrachloride (CCl_4) were performed. The absorption band broadening due to fractional diffusion was observed. A correlation between the non-mesogenic admixture concentration and the anomalous diffusion exponent was found.
13
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Dielectric and Optical Studies of Homologous Series of Bicyclo[2,2,2]octane Derivatives with -NCS Terminal Group

62%
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
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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.
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