Relaxation time distribution, electric polarization

The electrical properties of nail resemble those of SC and hair. However, note that the low-frequency susceptance plateau in Figure 4.24 represents a deviation from a simple model with a distribution of relaxation times for a single dispersion mechanism (cf. Section 9.2), and it must be due to another dispersion mechanism such as, for example, electrode polarization, skin layers, etc. The admittance of nail is also logarithmically dependent on water content, as shown in Figure 4.25 (Martinsen et al., 1997c). 

The second term on the right of (7.28) i.e. the dipole disorienting factor describes the relaxation of dipoles due to a finite temperamre. The multiplier may be considered as a numerical coefficient k 2/3, as if the distribution function is spherical even in the electric field. In fact, a more precise value was found by Debye by averaging the Fe value over 9 with the field-induced dipole distribution function shown qualitatively in Fig. 7.11. Since the thermal motion of dipolar molecules destroys the field induced polar order, we introduce a thermal relaxation time Td, as the first (linear) approximation of the relaxation rate. In order to find this time, we should exclude from the kinetic equation. 

Many polymeric materials consist of dipoles (chemical bonds which have an unbalanced distribution of charge in a molecule) and traces of ionic impurities. If a polymer containing polar groups is heated so that an immobile dipole becomes mobile, an increase in permittivity is observed as the dipole starts to oscillate in the alternating electric field. This effect is referred to as a dipole transition and has a characteristic relaxation time (t) associated with it (76). When exposed to an electric field, the dipoles tend to orient parallel to the field direction and the ions move toward the electrodes, where they form layers. The dipole relaxation time... 

Applied electric fields, whether static or oscillating, distort (polarize) the electron distribution and nuclear positions in molecules. Much of this volume describes effects that arise from the electronic polarization. Nuclear contributions to the overall polarization can be quite large, but occur on a slower time-scale than the electronic polarization. Electronic motion can be sufficiently rapid to follow the typical electric fields associated with incident UV to near IR radiation. This is the case if the field is sufficiently off resonance relative to electronic transitions and the nuclei are fixed (see ref 5 for contributions arising from nuclear motion). Relaxation between states need not be rapid, so... 

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