Maxwell-Wagner effects

The low frequency absorption II originates from the Maxwell-Wagner effect already observed in dehydrated X-type zeolites (8). In the presence of water the enhanced cationic mobility intensifies this effect. This interpretation disagrees with that of Matron et al. (10). They ascribed their low frequency a-process to cations on site I and site II. This is improbable in view of the correspondence with the Maxwell-Wagner effect in dehydrated X-type zeolites, observed by us (8). 

Dominant contributions are responsible for the a, fi, and y dispersions. They include for the a-effect, apparent membrane property changes as described in the text for the fi-effect, tissue structure (Maxwell-Wagner effect) and for the y-effect, polarity of the water molecule (Debye effect). Fine structural effects are responsible for deviations as indicated by the dashed lines. These include contributions from subcellular organelles, proteins, and counterion relaxation effects (see text). 

The dielectric properties of tissues and cell suspensions will be summarized for the total frequency range from a few Hz to 20 GHz. Three pronounced relaxation regions at ELF, RF and MW frequencies are due to counterion relaxation and membrane invaginations, to Maxwell-Wagner effects, and to the frequency dependent properties of normal water at microwave frequencies. Superimposed on these major dispersions are fine structure effects caused by cellular organelles, protein bound water, polar tissue proteins, and side chain rotation. 

For non-conducting fibers, such as glass, the matrix resin is the more conductive phase, at least early in cure, and one would expect some internal polarization effects to be visible in parallel-plate data. However, in spite of a large body of literature on glass fiber composites (see Sect. 5), we have found no clearly documented cases of Maxwell-Wagner effects in fiber-reinforced composites. We speculate that... 

The a process appears most clearly at the higher frequencies whereas at the lower frequencies it is hidden by the rapid increase in both dielectric constant and loss due to the Maxwell-Wagner effect The p process on the other hand is easily revealed in the whole frequency range. 

C yielded a loss mechanism in the mHz region in polyethylene and in the kHz region for polycarbonate that was Interpreted as a Maxwell-Wagner 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). 

Space charge polarization occurs when the material contains free electrons whose displacement is restricted by grain boundaries. Hence, entire macroscopic regions of the material become either positive or negative. This mechanism is often called the Maxwell-Wagner effect and it takes place in low frequency fields. 

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... 

Maxwell model A mechanical model for simple linear viscoelastic behavior that consists of a spring of Young s modulus E) in series with a dashpot of coefficient of viscosity (ri). It is an isostress model (with stress 8), the strain (e) being the sum of the individual strains in the spring and dashpot. This leads to a differential representation of linear viscoelasticity as stress relaxation and creep with Newtonian flow analysis. Also called Maxwell fluid model. See stress relaxation viscoelasticity. Maxwell-Wagner efifect See dielectric, Maxwell-Wagner effect. 

M. Iwamoto, The Maxwell-Wagner Effect, in Encyclopedia of Nanoscience and Technology, ed. B. Bhushan (Ed.), Encyclopedia of Nanoscience and Technology, Springer Reference,... 

---