It has been shown that the temperature behavior of dielectric permittivity ($\varepsilon$) in the isotropic phase of nematogens can be described in the same way as in critical binary solutions. Hence, using a relation with the critical exponent $\phi =1-\alpha =0.5\mathrm{}\pm 0.03$ it was possible to portray the results of $\varepsilon \mathrm{}\left(T\right)\mathrm{}$ measurements in the isotropic phase of 5-heptyl-2-(4′-cyanobiphenyl)-pyrimidine and 4,4-$n$-octylcyanobiphenyl. The influence of the position of the permanent dipole moment on the results was tested by additional measurements in $n$-($p$-methoxybenzylidene)-$p^{\prime }$-butylaniline. It also has been shown that a fluidlike analogy can be applied to the nonlinear dielectric effect (NDE), which describes changes of dielectric permittivity induced by a strong electric field. Measurements were conducted for the lowest frequency used in NDE studies ($f=67\mathrm{}$ kHz), so the condition $\tau f\ll 1$ (with $\tau$ the relaxation time) was always fulfilled. Values of discontinuities of the isotropicnematic phase transition from both the analysis of $\varepsilon \mathrm{}\left(T\right)\mathrm{}$ measurements and NDE studies are in good agreement.

• Received 4 June 1996

DOI:https://doi.org/10.1103/PhysRevE.54.6452