Dielectric spectroscopy Concept

This chapter concentrates on the results of DS study of the structure, dynamics, and macroscopic behavior of complex materials. First, we present an introduction to the basic concepts of dielectric polarization in static and time-dependent fields, before the dielectric spectroscopy technique itself is reviewed for both frequency and time domains. This part has three sections, namely, broadband dielectric spectroscopy, time-domain dielectric spectroscopy, and a section where different aspects of data treatment and fitting routines are discussed in detail. Then, some examples of dielectric responses observed in various disordered materials are presented. Finally, we will consider the experimental evidence of non-Debye dielectric responses in several complex disordered systems such as microemulsions, porous glasses, porous silicon, H-bonding liquids, aqueous solutions of polymers, and composite materials. 

In this contribution we present some concepts of modern dielectric spectroscopy. We are going to illustrate these ideas by experimental examples related to... 

Following the general plan of our chapter, we will discuss here a universal view of scaling which is widely employed in modem dielectric spectroscopy. We will show how this concept can be applied to the description of disordered materials and how these ideas can be useful in the determination of the topological parameters of these systems. 

First, we give an introduetion to the basic concepts underlying the measuring teehnique, before the technique itself is reviewed. Finally, experimental work is presented. The experimental part has three main sections, i.e., one section covers equilibrium systems, in the seeond non-equilibrium systems are regarded and the last one is on the application of dielectric spectroscopy to biological systems. 

Samouillan et al. (2011) studied the dielectric properties of elastin at different degrees of hydration and specifically at the limit of freezable water apparition. The quantification of freezable water was performed by DSC. Two dielectric techniques were used to explore the dipolar relaxations of hydrated elastin dynamic dielectric spectroscopy (DDS), performed isothermally with the frequency varying from 10 to 3 x 10 Hz, and the TSDC technique, an isochronal spectrometry running at variable temperature, analogous to a low-frequency spectroscopy (10 to 10 Hz). A complex relaxation map was evidenced by the two techniques. Assignments for the different processes can be proposed by the combination of DDS and TSDC experiments and the determination of the activation parameters of the relaxation times. As already observed for globular proteins, the concept of solvent-slaved protein motions was checked for the fibrillar hydrated elastin (Samouillan et al. 2011). 

Sample Preparation and Dielectric Spectroscopy Measurements. Dielectric relaxation spectra were collected using a Novocontrol GmbH Concept 40 broadband dielectric spectrometer over the frequency range 0.01 Hz - 3 MHz and over the temperature range of 0 to 100° C. The temperature stability of the instrument was controlled to within 0.2° C. 

The reflectivity of bulk materials can be expressed through their complex dielectric functions e(w) (i.e., the dielectric constant as a function of frequency), the imaginary part of which signifies absorption. In the early days of electroreflectance spectroscopy the spectra were often interpreted in terms of the dielectric functions of the participating media. However, dielectric functions are macroscopic concepts, ill suited to the description of surfaces, interfaces, or thin layers. It is therefore preferable to interpret the data in terms of the electronic transitions involved wherever possible. 

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