Dipolar polarization, Debye term

The SoSoo term corresponds to the instantaneous response of the material to the electric field, whereas the so(s,-8oo) (t) term is related to the slower response assigned to dipolar polarization, where the dielectric function 0(0 describes the temporal development of the dipole orientation. The decay function, < )(0=1-O(0, accoimts for the decrease of polarization after removing the electric field, ( )(0)=1 and < >(oo)=0. In the model of Debye the polarization process follows a first-order kinetics, where its time variation is proportional to the equilibrium value ... 

P. J. W. Debye, Polar Molecules (Dover, New York, reprint of 1929 edition) presents the fundamental theory with stunning clarity. See also, e.g., H. Frohlich, "Theory of dielectrics Dielectric constant and dielectric loss," in Monographs on the Physics and Chemistry of Materials Series, 2nd ed. (Clarendon, Oxford University Press, Oxford, June 1987). Here I have taken the zero-frequency response and multiplied it by the frequency dependence of the simplest dipolar relaxation. I have also put a> = if and taken the sign to follow the convention for poles consistent with the form of derivation of the general Lifshitz formula. This last detail is of no practical importance because in the summation Jf over frequencies fn only the first, n = 0, term counts. The relaxation time r is such that permanent-dipole response is dead by fi anyway. The permanent-dipole response is derived in many standard texts. 

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. 

For some time it was thought that the Keesom dipole-dipole interactions should be treated separately from the Debye sind London interactions. Because of the dipolar nature of the Keesom phenomenon, the term polar was applied to these interactions, in contrast to the apolar Debye and London interactions. This distinction between all three apolar electrodynamic forces impeded progress in the search for the true polar surface interactions. After Chaudhury (1984) showed that the three, apolar, electrodynamic forces are simply additive, and should be treated as a single entity, the LW interactions, it became possible to examine the nature of the polar (Lewis) properties of surfaces as an entirely separate phenomenon from their electrod3mamic (LW) properties. 

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