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

81%
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.
6
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Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase

81%
Wolarz E., Bauman D., Jadżyn J., Dąbrowski R.
Acta Physica Polonica A
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2011
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vol. 120
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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.
7
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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.
8
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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.
9
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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.
10
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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.
11
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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.
|
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.
12
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Guest-Host Interactions in Nematic p-Cyano-p'-Alkylphenylcyclohexanes

81%
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.
13
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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.
14
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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.
15
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Gelation Process of Toluene-Based bis-Urea in Cyclohexane Studied with Magnetic Resonance Imaging

71%
Tritt-Goc J., Boguszyńska J., Szwaj M., Boutellier L., Jadżyn J.
Acta Physica Polonica A
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2005
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vol. 108
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issue 1
81-87
EN
Magnetic resonance imaging was used for studies of the gelation and swelling processes of toluene-based bis-urea prepared in a form of cylindrical tablet and immersed in cyclohexane. The processes were investigated with the use of Bruker AVANCE (300 MHz) spectrometer equipped with a micro imaging probe head. The images were taken for cyclohexane protons within the bis-urea gel formed around the sample dry core at different intervals of the immersion. The mobility of the solvent molecules was estimated from the spatially resolved distribution of the spin-spin relaxation time T_2 and the spin densitiesρ, calculated on the basis of the images obtained. It was shown that the time-evolution of the thickness of the gel layer can be well described by the power equation with an exponent equal to 0.47 (±0.04), indicating the Fickian nature of the diffusion of cyclohexane molecules.
16
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Modeling of the Viscosity Behavior in the Interface Area of Two Miscible Liquids

71%
Szwajczak E., Stragaczyński R., Herba H., Świergiel J., Jadżyn J.
Acta Physica Polonica A
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2009
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vol. 115
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issue 5
905-908
EN
The paper presents the results of the share viscosity (η) investigations performed for binary mixtures composed of the liquids of extremely different viscosities: a high-viscous α-tocopherol acetate (η ≈ 10 Pa s) is mixed with 4-n-propylcyclohexyl-4'-n-pentylphenyl (η ≈ 10 mPa s) and mesitilene (η ≈ 1 mPa s), the two low-viscous solvents composed of the non-polar molecules of an essentially different shape. It was found that the viscosities of the mixtures, disregarding the molecular shape of the non-polar admixture, exhibit a strong nonlinear dependence on tocopherol mole fraction and, at a given temperature, the dependence can be described with an exponential function. For a constant tocopherol concentration in the mixtures, the viscosity temperature dependences are well described with the Vogel-Fulcher-Tammann relation. The results can be considered as a model of the viscosity behavior related to the laminar flow of miscible liquids of a different viscosity being in contact to each other.
17
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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.
18
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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.
19
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The Structural Phase Transitions in 6CB-Based Ferronematics

62%
Tomašovičová N., Koneracká M., Kopčanský P., Timko M., Závišová V., Tomčo L., Jadżyn J.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
336-338
EN
The structural transitions in ferronematics based on the thermotropic nematic liquid crystal 4-cyano-4'-hexylbiphenyl were studied. The ferronematic samples were prepared by doping with magnetic suspension consisting of Fe_3O_4 particles (10 nm in diameter) coated with oleic acid as a surfactant with different volume concentrations of magnetic particles (from 10^{-5} to 10^{-3}). Freedericksz transitions were studied in combined electric and magnetic fields. The experimental results indicated soft anchoring with perpendicular initial orientation between the magnetic moment of the magnetic particles and director.
20
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Magnetic Field Induced Structural Transitions in 6CHBT-Based Ferronematics

52%
Tomašovičová N., Timko M., Koneracká M., Závišová V., Jadżyn J., Beaugnon E., Chaud X., Kopčanský P.
Acta Physica Polonica A
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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.
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