Study of some cyanobiphenyls by dielectric spectroscopy

Abstract

ABSTRACT The dielectric properties of some liquid crystalline cyanobiphenyls were investigated using dielectric spectroscopy methodsin a wide frequency range from iOHz to iOHz. There are several significant parameters that can be obtained using thismethod, such as dielectric permittivity and electrical conductivity. Additionally, nature of the tested material at a givenfrequency range and for a given electric field range (to 7 104V/m) was investigated. This nature seems to be rather resistive.However, a capacitive nature becomes significantly responsible for the material behaviour in low frequency range - below 1Hz.Keywords: liquid crystals, conductivity, permittivity, resistive material, capacitive material 1. INTRODUCTION In a classical sense, Poisson's equation together with an equation of continuity and at appropriate boundary conditionsappear sufficient to describe a behaviour of the space charge in dielectrics. It is a macroscopic view of a behaviour of thedielectric materials1'2. However, there is microscopic (and sub-microscopic) length scale of problems. The questions toanswer, at microscopic level of physical processes, are as follows. How and where excess charges are accumulated indielectric, how dielectric responds to an applied electrical field, how charges move and as well as how charges enter andleave dielectrics? How the magnitude and polarity of the net induced dipole moment depend on the dielectric properties ofthe surrounding medium, as well as of the various components of the particle?Dielectric spectroscopy is an important tool in a study of various materials. Dielectric spectroscopy method observes thedynamics of polar entities such as molecules, ionic aggregations, as well as the transport of charge carriers and the effects ofspace charge polarisation.