Showing papers by "Sylwester J. Rzoska published in 1996"

Isothermal and high-pressure studies of dielectric relaxation in supercooled glycerol

Abstract: Measurements of isothermal (), high-pressure behaviour (up to 270 MPa) of complex electric permittivity in supercooled glycerol are presented. The observed peaks of relaxation in absorption curves show increasing relaxation time with increasing pressure. The behaviour of can be reproduced by the pressure version of an Arrhenius relation or by a modified Vogel - Fulcher - Tammann equation. The data obtained can be superimposed by applying the scaling form used by Dixon et al 1990 Phys. Rev. Lett. 65 1108.

High-pressure and temperature dependence of dielectric relaxation in supercooled di-isobutyl phthalate

Abstract: Results are presented for isothermal, high-pressure (up to p=300 MPa), and temperature (under atmospheric pressure) measurements of complex dielectric permittivity in supercooled di-isobutyl phthalate. The relaxation times determined from the temperature study obey the temperature Vogel-Fulcher-Tammann (VFT) law. The pressure dependence of relaxation times describes the relation \ensuremath{\tau}=${\mathrm{\ensuremath{\tau}}}_{0}$exp[B/(p-${\mathit{p}}_{0}$)]. This equation gives the same ideal glass transition pressure ${\mathit{p}}_{0}$ as the generalized VFT formula proposed by Leyser et al. [Phys. Rev. E 51, 5899 (1995)]. For isobaric and isothermal absorption curves, the scaling behavior has been also tested. \textcopyright{}1996 The American Physical Society.

Mean-field behaviour of the low frequency non-linear dielectric effect in the isotropic phase of nematic and smectic n-alkylcyanobiphenyls

Abstract: Results are presented of studies on the low frequency (f' 250 kHz) non-linear dielectric effect on approaching the nematic and smectic A phases in 4′-cyano-4-n-alkylbiphenyls (nCB, for n = 6, 7, 8, 10, 11, 12). In all cases, the mean-field behaviour was valid up to the clearing temperature. In the case of the isotropic-nematic transition (6CB, 7CB, 8CB), a quantitative agreement with the relation based on the Landau-de Gennes model was also ascertained. The specific feature of the research method applied was that the characteristic time introduced by the measurement field (T′ ≊ 1/f) was always greater than the relaxation time τ, i.e. the condition: (T′/τ)>1 was satisfied up to T c.

A new application of the nonlinear dielectric method for studying relaxation processes in liquids

Abstract: The measurement setup for studying changes of electric permittivity induced in liquids by a strong electric field nonlinear dielectric effect, (NDE) is presented. The construction is based on the idea of frequency modulation of an LC generator (with an inductance L and a capacitance C in resonant circuit), proposed by Malecki [J. Chem. Soc. Faraday Trans. II 72, 104 (1976)]. The strong electric field is applied in the form of rectangular pulses (typically 1–4 ms). The setup enables measurements in a broad range of frequencies (80 kHz–12 MHz) and contains a new calibrating system, minimizing the influence of systematic error on the measured NDE values. We also indicate menthol as a standard, reference liquid in NDE studies. New applications of the NDE technique for studying relaxation processes in critical solution are also presented. They are based on the time resolved analysis of NDE decay after switching off the strong electric field.

Influence of high hydrostatic pressure on a nitrobenzene-dodecane critical solution

Abstract: Results are presented of high-pressure (up to p = 200 MPa) miscibility studies in a nitrobenzene-dodecane critical solution. It was found that the important parameter dTc/dp, characterising the rate of change of the critical temperature (Tc ) with pressure (p), increases linearly with pressure. Its value for the atmospheric pressure limit is: dTc/dp = 0.0071 ± 0.0005 K × MPa−1. The possible influence of the pressure on the critical concentration has also been discussed. The coexistence curve has been determined for pressure p = 100 MPa. The critical exponent β which describes its shape, within the limit of the experimental error, is the same as for a binodal under atmospheric pressure.