Showing papers by "Jan Jadżyn published in 2009"

Conductivity dynamics and static dielectric permittivity of highly conducting molecular liquids studied with impedance spectroscopy. Formamides

Abstract: Impedance spectroscopy was used for studies of the frequency dependence of the electric conductivity of two highly conducting liquid amides: N-methylformamide (NMF), strongly self-associated via the hydrogen bonds C=O...N-H, and N,N-dimethylformamide (DMF), which is not able to self-organize by hydrogen bonding. The studies were performed in the frequency range f = 50 kHz-100 MHz and in the temperature range T = 278.15-363.15 K. It was found that, at a given temperature, NMF exhibits static conductivity (sigma(0)) of 2 orders of magnitude higher, and conductivity relaxation time (tau(sigma)) of 2 orders of magnitude shorter, than those of DMF. On the basis on sigma(0) and tau(sigma) values, the static dielectric permittivity (epsilon) was calculated for both liquids studied and the values obtained perfectly agree with those measured with the classical dielectric methods. An empirical equation for epsilon(T) dependence for NMF and DMF is proposed.

Influence of the molecular structure of thermotropic liquid crystals on their ability to form monolayers at interface

Abstract: Langmuir and Langmuir–Blodgett (LB) films of some thermotropic liquid crystals of rod-like shape have been studied. It has been found that the compounds with the terminal isothiocyanato (–NCS) group are not able to form a compressible monolayer at the air–water interface. Very short and very long alkyl or alkoxy chains attached to the rigid molecular core also hinder the creation of the stable films. The Langmuir films have been characterised by the surface pressure-area and surface potential-area isotherms and by Brewster angle microscopy (BAM). The analysis of the isotherms and the BAM images suggests that the organisation of the mesogenic molecules on the water surface is dependent on their structure and to some extent reflects their ability to form an appropriate mesophase in the bulk. For the LB films of the liquid crystals the electronic absorption spectra have been recorded. On the basis of these spectra the conclusions about the creation of the self-aggregates by mesogenic molecules at the air-sol...

Dielectric properties of nematic liquid crystals with Fe3O4 nanoparticles in direct magnetic field

Abstract: Researched within the frequency range 10 -1 -10 6 Hz were dielectric properties of pure 6CHBT liquid crystals and 6CHBT ones with the impurity of Fe3O4 nanoparticles that have the mean diameter 5 nm and weight concentration 10 -4 %. The study was performed without and under the influence of direct magnetic field with the induction 0.45 and 0.60 T. It has been shown that the magnetic field influences on the parameters of the near-electrode area of liquid crystal. In the case of liquid crystal with magnetic nanoparticles, the parameter changes caused by the magnetic field depend on the induction value.

Pretransitional dielectric properties of nematogenic 4-cyanophenyl-4′-n-heptylbenzoate

Abstract: This article presents results of the static and dynamic dielectric studies performed for mesogenic 4-cyanophenyl-4′-n-heptylbenzoate in the isotropic (I) and nematic (N) phases. Pretransitional phenomena are observed in the vicinity of I–N phase transition as an anomalous temperature behavior of both the static and the dynamic dielectric properties of the compound. The temperature dependence of the static permittivity is correlated with the entropy change induced by the probing electric field while an anomalous behavior of the dielectric relaxation directly points out for a subdiffusional Brownian rotation of mesogenic molecules in the vicinity of the phase transition.

The Structural Phase Transitions in 6CB-Based Ferronematics

Abstract: 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 Fe3O4 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.

Viscous and dielectric properties of α-tocopherol and α-tocopherol acetate

Abstract: This article presents the results of the shear viscosity and the dielectric relaxation measurements performed for α-tocopherol and α-tocopherol acetate, two principal compounds from the vitamin E group. The temperature dependence of the viscosity and dielectric relaxation time of the compounds can be very well reproduced with the Vogel–Fulcher–Tammann equation. It was found that for both tocopherols, the viscosity and the relaxation time attain their infinite high value (solid-like state) at the temperature of ∼60 K below the transition to the glass state.

Shear Viscosity of Mixtures of α-Tocopherol with Nonpolar Solvents†

Abstract: Shear viscosities (η) of the binary mixtures of α-tocopherol (vitamin E) with 4-n-propylcyclohexyl-4′-n-pentylphenyl and mesitilene, two nonpolar solvents composed of the molecules of essentially different shape, have been measured in the temperature range from (278 to 353) K. In the whole concentration range of α-tocopherol in both solvents, the dependence of η on T can be well described by the Vogel−Fulcher−Tammann equation. The viscosity deviations from the additive behavior are strongly negative, and their concentration dependence was fitted to the Redlich−Kister equation.

The structural transitions in a nematic liquid crystals doped with magneticaly labeled carbon nanotubes

Abstract: Z. Mitróová, N. Tomašovičová, M. Koneracká, V. Závǐsová, M. Timko, J. Kováč, P. Kopčanský, L. Tomčo, N. Éber, K. Fodor-Csorba, T. Tóth-Katona, A. Vajda, J. Jadzyn, E. Beaugnon, X. Chaud 1 Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Košice, Slovakia 2 Faculty of Aeronautics, Technical University, Rampova 7, 041 21 Košice, Slovakia 3 Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, H-1525 Budapest, Hungary 4 Institute of Molecular Physics, Polish Academy of Sciences, Smoluchovskiego 17, 60179 Poznan, Poland 5 Grenoble High Magnetic Field Laboratory, Centre National de la Recherche Scientifique, 25 Avenue des Martyrs, Grenoble, France

Viscosity of Mixtures of α-Tocopherol Acetate + Mesitylene

Abstract: The paper presents results of the share viscosity measurements performed as a function of temperature and concentration for mixtures of α-tocopherol acetate (vitamine E acetate) and mesitylene, two liquids of essentially different viscosity (four order of magnitude difference at 280 K). The viscosity/temperature dependence for pure α-tocopherol acetate as well as for the mixtures studied can be well described with the Vogel-Fulcher-Tammann equation. The viscosities of the mixtures exhibit a strong negative deviation from the rule of additive dependence on concentration and for increasing temperature the maximum value of the deviation shows an exponential decreasing.

Liquid crystals doped with magnetic nanoparticles

Abstract: The paper presents an overview of the observations of structural transitions in ferronematics based on thermotropic nematics 4-cyano-4'octylbiphenyl (8CB) and 4-trans-4’-n-hexyl-cyclohexyl-isothiocyanato-benzene (6CHBT). The determination of the surface density of anchoring energy of nematic molecules on magnetic particles surfaces by the observations of the structural transitions in external fields is demonstrated on the example of the 8CB-based ferronematic. The ferronematic droplets were observed in solutions of nematogenic 6CHBT dissolved in phenyl isothiocyanate and doped with fine magnetic particles. The phase diagram of the transitions from the isotropic phase to the nematic phase via droplets was found. The magneto-dielectric measurements of various structural transitions in this new system enabled to estimate the type of anchoring of nematic molecules on magnetic particles surfaces in droplets.

Modeling of the Viscosity Behavior in the Interface Area of Two Miscible Liquids

Abstract: 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.