Critical behavior of dielectric permittivity and nonlinear dielectric effect in the isotropic phase of nematogens

TLDR: In this paper, it was shown that the behaviour of dielectric permittivity and its changes in a strong electric field can be described in the way analogous to that applied in critical binaiy solutions.

Abstract: The paper shows that the behaviour of dielectric permittivity (e) and its changes in a strong electric field (nonlinear dielectric effect NDE) can be described in the way analogous to that applied in critical binaiy solutions. Basing onmeasurement in 4,4n4iexylcyanobiphenyl (6CB) and 4,4n4etracyanobipheny1 (4CB) it was possible to portray thetemperature behavior of s and NDE from T up to T + 50 K. In the case of 4CB the satisfied description was possible despite the fact that the sample erystallises before reaching the clearing point. NDE tests was conducted for the measurement frequencyf= 70 kHz, what allowed to avoid the influence of relaxation processes on results.Keywords: Isotropicnematic transition, critical phenomena, dielectric pernnttivity, nonlinear dielectric effect. 1. INTRODUCTION Experimental studies of nonlinear dielectric effect (NDE) in liquid dielectrics determine changes of dielectric pernlittivity induced by a strong electric AE E '; E E2 (I)where I and care dielectric permittivitites in a strong and weak electric field E, respectively.Yet first experimental studies in the isotropic phase in MBBA2 in 1978 showed that NDE exhibits near the isotropicnematic (FN) phase transition the same type of the pretransitional behavior as the Kerr effect (ICE) ,