Maxwell-Wagner polarization

The behavior of the relaxation times as a function of temperature for aniline in CPG of 7,5 nm pore size are depicted in Fig. 3. For temperatures greater than 246 K (melting point inside the pores), there are two different relaxations. The longer component of the relaxation that is of the order of lOx 10" s is divided into three regions. The response in the region T > 267K is due to Maxwell-Wagner polarization. 

The three phase dielectric system backbone-waterlayer-air of a real RF aerogel is reduced to a two layer system. The third phase (air) is neglected because of its relative low influence (compared to the other two phases) on the compound dielectric permittivity according to its own material parameters e and k. In order to explain the measured spectra by Maxwell-Wagner polarization processes due to the absorbed water we propose the following model. ... 

Maxwell-Wagner polarization (20-23) arises in heterogeneous specimens containing domains of different conductivity and/or dielectric constant. This phenomenon can be distinguished by low-frequency impedance dispersions that extend over several decades of frequency. In addition, the magnitude and frequency dependence of Maxwell-Wagner polarization is related to spatial fluctuations of dielectric... 

This is the well-known Maxwell-Wagner polarization. It always arises when two media are in contact and have differing electrical properties. A strong field and a disparity of charges arises at the juncture, leading to the possibility of high effective polarizations. These are ubiquitous in biology. 

Yeo LY, Lastochkin D, Wang S-C, Chang H-C (2004) A new ac electrospray mechanism by Maxwell-Wagner polarization and capillary resonance. Phys Rev Lett 92 133902... 

Interfacial or Maxwell-Wagner polarization is a special mechanism of dielectric polarization caused by charge build-up at the interfaces of different phases, characterized by different permittivities and conductivities. The simplest model is the bilayer dielectric [1,2], (see Fig. 1.) where this mechanism can be described by a simple Debye response (exponential current decay). The effective dielectric parameters (unrelaxed and relaxed permittivities, relaxation time and static conductivity) of the bilayer dielectric are functions of the dielectric parameters and of the relative amount of the constituent phases ... 

Keywords dielectric relaxation, dielectric strength permittivity, dipole moment, polarization, relaxation, conductivity, relaxation time distribution, activation energy, Arrhenius equation, WLF-equation, Maxwell-Wagner polarization. 

The dependence of the ER effect on the dispersed particle conductivity has been comprehensively investigated. As shown earlier, the strongest ER effect was found to occur at the conductivity about 10 S/m for the polyaceneqiiinones/cereclor suspension fllS], and tliere was no detectable ER activity observed once the conductivity shifts far away from this value. A similar result was obtained in oxidized polyacrylonitrilc/siliconc oil suspension and interpreted in view of Maxwell-Wagner polarization [119, 120]. The effect of the particle conductivity on the ER activity was also theoretically analyzed [121-123]. A conduction model was presented for understanding ER phenomena and ER mechanism [124]. The current density of an ER fluid is obviously a very important parameter that scales energy consumption in practical devices. Both the current density and ER activity... 

Without electrolyte, the dielectric property of non-aqueous suspension will be mainly governed by the Maxwell-Wagner polarization, which will be discussed in detail in this section. 

T is the relaxation time of the Maxwell-Wagner polarization, and can be expressed as ... 

Direct differentiation on the contribution of the Debye or the Wagner-Maxwell polarization to the ER effect was carried out by Hao [35]. The strategy employed in Hao s paper is to compare the temperature dependence difference of the dielectric loss tangent maximum values of commonly encountered thrcc-lypc polarizations, the ionic polarization, the Debye polarization, and the interfacial polarization. As shown in Eq.(147) in Chapter 7, for the Maxwell-Wagner polarization (also called the interfacial polarization) the dielectric loss tangent can be expressed as follows if the particle conductivity Op is much larger than that of the medium... 

Limitations in charge mobility can be of two kinds. Firstly, the charge may migrate to boundaries over which further transport is either restricted or totally inhibited. Under this category, the boimdary may delineate the mdecule as is the case for electronic polarizability, or extend further in for example the ion atmosphere of a polyelectroiyte in solution, or constitute a phase boundary semi- or impermeable to charge in a solid material. For the last two examples the phenomenon is termed interfacial or Maxwell-Wagner polarization. The second type of restricted mobility occurs when dipoles are present which can cause pcdarization by a redistribution of their inclinations relative to the field direction. Such orientation polarization need not involve complete rotatory diffusion of the dipole even a restricted rotation or libration can affect polarization by this mechanism. 

The macroscopically observed transport is based on the quantum-mechanical interaction between the electron waves in neighboring quantum metal particles, which is probably facilitated by the Maxwell-Wagner polarization and thermally stimulated. Instead of hopping, the expression tunneling may approximate more closely the quantum-mechanical fundamentals of this process. 

In addition to the Debye model for dielectric bulk materials, other dielectric relaxations expressed according to Maxwell-Wagner or Schwartz "interfacial" mechanisms exist. For example, the Maxwell-Wagner "interfacial" polarization concept deals with processes at the interfaces between different components of an experimental system. Maxwell-Wagner polarization occurs... 

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