Chapter 11 - Dielectric Behavior in Liquids: Critical Mixtures and Liquid Crystals

Abstract

This chapter discusses dielectric properties of liquids focusing on the application of the dielectric spectroscopy of phase-separating liquid mixtures and of liquid crystals. The dielectric response of a material is usually described by the dielectric constant. However, no known material medium can be described correctly by a dielectric constant; that is, having a polarization that is strictly proportional to the electric field, and always independent of the field strength, frequency, temperature, and pressure. A general theoretical background appropriate for liquids and (dense) gases is presented in the chapter. Static properties, dynamic dielectric response are then discussed. The chapter also outlines the contributions of dielectric investigations to progress in better understanding of phase transitions and critical phenomena in phase-separating binary liquid mixtures. The basic feature that distinguishes the liquid crystalline phase from other condensed phases is the presence of orientational order of the nonspherical molecules, while, additionally, the positional order of the centers of mass of the molecules is either absent or reduced. Dielectric spectroscopy is a powerful technique for studying the orientational order and the dynamics of molecular relaxation phenomena in liquid crystals. Apart from being interesting for the fundamentals of molecular behavior in liquid crystals, the technique provides essential information for high technical applications.