Showing papers by "Jan Jadżyn published in 2014"

Concentration Evolution of the Dielectric Response of Hydrogen-Bonded Supramolecular Polymers Formed by Dialkylurea in Non-Polar Medium

Abstract: Theoretical predictions on the dielectric response of different dynamic models of supramolecular chain polymers [J. Chem. Phys. 2006, 125, 184905], have been experimentally verified for the strongly hydrogen-bonded linear polymers formed by N,N′-di(2-ethylhexyl)urea (EHU), R·NH·CO·NH·R, R = CH2CH(C4H9)C2H5, dissolved in nonpolar medium. Within evolution of the dielectric response upon the urea concentration, one can recognize the basic theoretical results presented in the cited paper. Namely, in diluted and not too concentrated solutions, where the degree of the urea self-association and the viscosity of solutions are relatively low, the dielectric relaxation spectra have rather a complex form (the Davidson–Cole type), as predicted for the frozen Rouse (unbreakable) chains. However, with increasing of the urea concentration, followed by an essential rise of the solutions viscosity, i.e., together with increasing of the complexity of the system, the dielectric spectra become more and more simple. From the ...

Electrical Conductivity in Dimethyl Sulfoxide + Potassium Iodide Solutions at Different Concentrations and Temperatures

Abstract: The direct current conductivity of DMSO + KI solutions was determined with the use of the impedance spectroscopy. The measurements were performed in the whole solubility range of KI and in the temperature range from (293.15 to 323.15) K. The limiting molar conductivities Λo(T) and λI–o(T), as well as the constant KA of ionic association, K+ + I–, were determined at different temperatures with the use of the Fuoss-Onsager method. The obtained data on KA, together with the literature data referred to the K+ + I– association in different solvents, allowed us to formulate an empirical dependence of KA on the molecular dipolar polarizability of the solvent used, KA ∝ exp(−μi2), where μi is the dipole moment of the molecules of ith solvent.

Compliance of the Stokes-Einstein model and breakdown of the Stokes-Einstein-Debye model for a urea-based supramolecular polymer of high viscosity.

Abstract: Impedance spectroscopy was used for the study of the static and dynamic behavior of the electrical conductivity of a hydrogen-bonded supramolecular polymer of high viscosity. The experimental data are discussed in the frame of the Stokes–Einstein and Stokes–Einstein–Debye models. It was found that the translational movement of the ions is due to normal Brownian diffusion, which was revealed by a fulfillment of Ohm’s law by the electric current and a strictly exponential decay of the current after removing the electric stimulus. The dependence of the dc conductivity on the viscosity of the medium fulfills the Stokes–Einstein model quite well. An extension of the model, by including in it the conductivity relaxation time, is proposed in this paper. A breakdown of the Stokes–Einstein–Debye model is revealed by the relations of the dipolar relaxation time to the viscosity and to the dc ionic conductivity. The importance of the CO⋯H–N hydrogen bonds in that breakdown is discussed.

Phase Transitions in Liquid Crystal Doped with Magnetic Particles of Different Shapes in Combined Electric and Magnetic Fields

Abstract: We have studied the influence of electric and magnetic fields on the orientational structure of ferronematics based on a thermotropic nematic 4-trans-4\(^{\prime }\)-n-hexylcyclohexyl-isothiocyanato-benzene (6CHBT). The 6CHBT liquid crystal has been dissolved in phenyl isothiocyanate and doped with rod-like or chain-like magnetic particles. In such a mixture, the phase transition from an isotropic to a nematic phase is via a droplet state, i.e., coexistence of nematic and isotropic phases. The obtained results showed that a combination of the electric and magnetic fields can change the character of a phase transition from the isotropic to the nematic phase via the droplet state in such systems. Moreover, magneto-dielectric measurements of structural transitions showed the magnetic field induced a shift of the phase transition temperature from the isotropic to the droplet state.

Increasing the magnetic sensitivity of liquid crystals by rod-like magnetic nanoparticles

Abstract: Magnetic Freedericksz transition was studied in ferronematics based on the nematic liquid crystal 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). 6CHBT was doped with rod-like magnetic particles of different size and volume concentration. The volume concentrations of magnetic particles in the prepared ferronematics were $\phi_1$ = 10$^{-4}$ and $\phi_2$ = 10$^{-3}$. The structural changes were observed by capacitance measurements that demonstrate a significant influence of the concentration, the shape anisotropy, and/or the size of the magnetic particles on the magnetic response of these ferronematics.

Sensitivity of 6CHBT Liquid Crystal Doped with Ferroelectric or Magnetic Particles to Electric and Magnetic Fields

Abstract: or Magnetic Particles to Electric and Magnetic Fields J. Majoro2ováa,∗, N. Toma2ovi£ová, M. Timko, M. Koneracká, I.P. Studenyak, O.V. Kovalchuk, S.O. Kovalchuk, J. Jad»yn, P. Kop£anský Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Ko2ice, Slovakia Uzhorod National University 46 Pidhirna St., Uzhorod 88000, Ukraine Institute of Physics, National Academy of Science of Ukraine,46, prospect Nauky, 03028 Kyiv, Ukraine Taras Shevchenko National University of Kyiv 64, Volodymyrs'ka St., 01601 Kyiv, Ukraine Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60179 Poznan, Poland