Polarization Maxwell-Wagner interfacial

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... 

Maxwell-Wagner interfacial polarization theory explains relaxations in a double layer of colloidal particles as a result of ionic species current conductance in parallel with capacitance. As a result of these processes in the double layer of a colloidal particle, the particle interface is charged by conductivity. 

Figure 2.10 Dielectric spectra of chitin films with Maxwell-Wagner (MW) polarization at low frequency and high temperatnre. Interfacial polarization can be detected by the appearance of an extra semicircle. Source Reprodnced with permission from Gonzalez-Campos JB, Prokhorov E, Luna-Barcenas G, Mendoza-Galvan A, Sanchez IC, Nuno-Donlucas SM, Garcia-Gaitan B, Kovalenko Y. J Polym Sci B Polym Phys 2009 47 932 [5]. Copyright 2009 John Wiley and Sons, Inc.

Another type of polarization arises from a charge build-up in the contact areas or interfaces between different components in heterogeneous systems. This phenomenon is also known as interfacial polarization and is due to the difference in the conductivities and dielectric constants (see below) of the materials at interfaces. The accumulation of space charge is responsible for field distortions and dielectric loss and is commonly termed Maxwell-Wagner polarisation . 

The interfacial or Maxwell-Wagner-Sillars (MWS) polarization is characteristic of heterogeneous systems. It is due to the piling up of space charges near the interfaces between zones of different conductivities. 

Interfacial polarization in biphasic dielectrics was first described by Maxwell (same Maxwell as the Maxwell model) in his monograph Electricity and Magnetism of 1892.12 Somewhat later the effect was described by Wagner in terms of the polarization of a two-layer dielectric in a capacitor and showed that the polarization of isolated spheres was similar. Other more complex geometries (ellipsoids, rods) were considered by Sillars as a result, interfacial polarization is often called the Maxwell-Wagner-Sillars (MWS) effect. 

The electrical conductivity measurements on powdered compacts suffer from 2 major difficulties the boundaries between the microcrystals introduce a supplementary energy barrier to current transport known as the interfacial polarization or Maxwell-Wagner effect, and the current is limited by an electrode polarization caused by the imperfect contact between the electrode and pellet surfaces and by the rate of discharge of the cations at the electrodes. 

In the interpretation of the loss factor tg 8, it is not easy to make a distinction between a dipole relaxation and the interfacial polarization. With metallic electrodes, both effects are superposed on the ionic part of the dielectric loss and not necessarily distinguishable from it. With blocking electrodes, the relative intensity of the dipole relaxation and the Maxwell-Wagner effect depends on the ratio of the thickness of the blocking layers and the zeolite pellets (15). 

Dielectric relaxation and dielectric losses of pure liquids, ionic solutions, solids, polymers and colloids will be discussed. Effect of electrolytes, relaxation of defects within crystals lattices, adsorbed phases, interfacial relaxation, space charge polarization, and the Maxwell-Wagner effect will be analyzed. Next, a brief overview of... 

Figure 17. Evidence of the Maxwell-Wagner-Sillars effect in the real permittivity of the composite system nematic E7 dispersed over hydroxypropylcellulose-type matrix. The interfacial polarization can be described by a double-layer arrangement. At lower frequencies and higher temperatures, the real permittivity increases further due to electrode polarization.

In Section 7.5, we analyze the double layer charge in a solution as a function of the perpendicular distance from the solid surface. No double layer formations are considered in the Maxwell—Wagner theory (Section 3.5.1). However, in wet systems and in particular with a high volume fraction of very small particles, the surface effects from counter-ions and double layers usually dominate. This was shown by Schwan et al. (1962). By dielectric spectroscopy, they determined the dispersion for a suspension of polystyrene particles (Figure 3.10). Classical theories based on polar media and interfacial Maxwell—Wagner theory could not explain such results the measured permittivity decrement was too large. The authors proposed that the results could be explained in terms of surface lateral) admittance. 

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 ... 

To study the effects of interaction of starch with silica, the broadband DRS method was applied to the starch/modified silica system at different hydration degrees. Several relaxations are observed for this system, and their temperature and frequency (i.e., relaxation time) depend on hydration of starch/silica (Figures 5.6 and 5.7). The relaxation at very low frequencies (/< 1 Hz) can be assigned to the Maxwell-Wagner-Sillars (MWS) mechanism associated with interfacial polarization and space charge polarization (which leads to diminution of 1 in Havriliak-Negami equation) or the 5 relaxation, which can be faster because of the water effect (Figures 5.8 and 5.9). 

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