Showing papers by "Jan Jadżyn published in 2002"

Dynamics of the nonlinear dielectric properties of a nematogenic compound dissolved in a nonpolar medium.

Abstract: The nonlinear dielectric spectra of ${4\ensuremath{-}(trans\ensuremath{-}4}^{\ensuremath{'}}\ensuremath{-}n\ensuremath{-}\mathrm{h}\mathrm{e}\mathrm{x}\mathrm{y}\mathrm{l}\mathrm{c}\mathrm{y}\mathrm{c}\mathrm{l}\mathrm{o}\mathrm{h}\mathrm{e}\mathrm{x}\mathrm{y}\mathrm{l})\mathrm{i}\mathrm{s}\mathrm{o}\mathrm{t}\mathrm{h}\mathrm{i}\mathrm{o}\mathrm{c}\mathrm{y}\mathrm{a}\mathrm{n}\mathrm{a}\mathrm{t}\mathrm{o}\mathrm{b}\mathrm{e}\mathrm{n}\mathrm{z}\mathrm{e}\mathrm{n}\mathrm{e}$ $({\mathrm{C}}_{6}{\mathrm{H}}_{13}\mathrm{CyHx}\mathrm{}\mathrm{Ph}\mathrm{}\mathrm{NCS},$ 6CHBT) in benzene solutions were recorded in the whole concentration range up to an appearance of the two-phase isotropic and nematic region (0.82 mole fraction of 6CHBT, at $25\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}).$ Two electric fields: (i) the field of high strength (110 kV/m) and low frequency (85 Hz) causing the dielectric nonlinearity, and (ii) the probing field of low strength and high frequency (100 kHz--3 GHz), were used. At about of 0.2 mole fraction of 6CHBT the nonlinear dielectric increment becomes positive. With increasing of 6CHBT concentration the dynamics of the increment shows a critical-like behavior, which can be interpreted in terms of the reorientation of the growing pseudonematic domains in the solutions studied.

Viscosity of a series of 1,2-alkanediols

Abstract: This paper presents the viscosity data for the series of 1,2-alkanediols, H(CH2)n-2CH(OH)CH2(OH), for n = 3 to 6, 8, 10, and 12. The results are compared with those obtained for 1,n-alkanediols.

Reorientational dynamics of the pseudonematic domains studied with nonlinear dielectric spectroscopy.

Abstract: Nonlinear dielectric spectroscopy was used for studies of the reorientational dynamics of the pseudonematic domains in the isotropic phase of the mesogenic substance in the vicinity of the isotropic to nematic phase transition. The results were interpreted in the frame of the Landau--de Gennes theory.

Non-linear dielectric effect in superpressed chiral isopentylcyanobiphenyl (5∗CB)

Abstract: Results are presented of linear and non-linear dielectric studies in pressurized isopentylcyanobiphenyl (5 ∗ CB). Temperature studies of linear dielectric relaxation in 5 ∗ CB showed the Vogel–Fulcher–Tammann evolution of relaxation times and the broadening of loss curves on cooling [J. Chem. Soc. Farad. Trans. 94 (1998) 387; Phys. Chem. Chem. Phys. 1 (1999) 4843]. The behavior characteristic for glassy liquids was also found in the presented preliminary tests of dielectric relaxation in pressurized 5 ∗ CB. For pressure dependencies for maxima of loss curves and for the static dielectric permittivity additional pretransitional anomalies was found. They may be associated with premesomorphic fluctuation (inhomogeneities) in the isotropic (fluid-like) surrounding. The stationary response of strong electric field induced changes of dielectric permittivity (NDE) also exhibited a singular behavior. It was found that NDE decreased strongly towards negative values on pressuring. This is a novel behavior which can be hardly explained by classic models developed for normal liquids [Dielectric Physics, PWN–Elsevier, Warsaw, 1980 and 1993].

Dielectric, viscous and elastic properties of nematogenic 1-(4- trans -propylcyclohexyl)-2-(4-cyanophenyl)ethane

Abstract: This paper presents the results of measurements of the static and dynamic electric permittivity, the shear viscosity of a freely flowing sample, and the splay and bend elastic constants for 1-(4-trans -propylcyclohexyl)-2-(4-cyanophenyl)ethane (C3H7-CyHx-CH2CH2-Ph-C=N) (3CCPE). The static permittivity of the isotropic phase shows pre-nematic critical behaviour which is discussed in the frame of the fluid-like model of Mukherjee. From the temperature dependence 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 the 3CCPE molecule (in the isotropic phase), were estimated. The splay and bend elastic constants were determined from the voltage dependence of the capacitance of a planar nematic cell.

Temperature Dependence of the Viscosity of Isotropic Liquids

Abstract: 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 2 n + 1 CyHx Ph NCS; nCHBT, n = 0 + 12), n-alkylcyanobiphenyls (C n H 2 n + 1 Ph Ph CN; nCB, n = 2 + 12) and 1, n-alkanediols (HO(CH 2 ) n OH; 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 2 OH, the compound strongly unstable in a pure state

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

Abstract: 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 dyeswas 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.

Linear and Non-linear Dielectric Pretransitional Behavior Near the Isotropic-nematic Phase Transition for 4-cyano-4-n-pentylbiphenyl (5CB)

Abstract: Linear and non-linear dielectric permittivity measurements for n-pentylcyanobiphenyl 5CB are presented. By two different experimental methods the same value of the temperature discontinuity for the isotropic-nematic transition was obtained. Broadband dielectric relaxation tests showed a significant influence of the pretransitional behavior on the dynamic properties above and below the nematic clearing temperature (T 1 - N ). The form of the loss curves is clearly non-Debye'an and can be portrayed within the Cole-Davidson approximation (CD). In the isotropic and nematic phases the CD parameter β C D drops on approaching the clearing temperature. This is connected with the broadening of the dielectric absorption width.