Showing papers by "Sylwester J. Rzoska published in 1995"

Time-scale dependence of the critical exponent for the nonlinear dielectric effect in a critical binary solution

Abstract: Low frequency [(300 kHz) results for the nonlinear dielectric effect (NDE)] (variation in electric permittivity of liquids induced by a strong, steady electric field) in a critical, binary solution have been obtained. Their comparison with NDE measurements for 9 and 6 MHz indicate that the appearance of a mean-field region near the critical consolute temperature (${\mathit{T}}_{\mathit{C}}$) and the crossover to the nonclassical behavior remote from ${\mathit{T}}_{\mathit{C}}$ could be associated not only with the degree of elongation of critical fluctuations but also with the time scale involved. This behavior is possibly due to the correlation between the relaxation time of critical fluctuations and the measurement frequency. The result obtained supplements the analysis given in Phys. Rev. E 48, 1136 (1993) plus Phys. Rev. E 47, 1445 (1993) and Phys. Rev. E 50, 5234 (1994) of the behavior near a critical consolute point of two effects immanently associated with the application of a strong, steady electric field: the electro-optical Kerr effect and nonlinear dielectric effect. (c) 1995 The American Physical Society

The equivalence of density and field variables for the pretransitional effect in the isotropic phase of nematogens

Abstract: The nonlinear dielectric effect (NDE) is described with reference to the concentrational, isothermal approach to the weakly discontinuous phase transition point from the isotropic to the nematic phase in MBBA (n-4-methoxybenzylidene-4-butylaniline)-benzene solution (nematogen-nonmesogenic component). It was ascertained that the dependence of the pretransitional effect as a function of benzene concentration (‘density’ variable) may be described, as with temperature or pressure (‘field’ variables) studies in pure MBBA, by the mean-field theory.

The Nonlinear Dielectric Effect in the Isotropic Phase of Nematogens

Abstract: Results are presented of studies of the nonlinear dielectric effect (NDE) for two frequencies (300 kHz and 61 MHz) of the weak measuring field in the isotropic phase of 4 heptyl 4′ cyanobiphenyl (7CB) For the smaller frequency the NDE increases markedly towards positive values on approaching the clearing point. For the higher frequency the increase is negative Despite this difference both pretransitional effects exhibit similar, mean - field temperature character. The observed behaviour coincide with relations between the relaxation time of prenematic fluctuation and measurement frequencies.