Relative relaxation times of polarization

The relaxation time of those polarizations are governed by different factors. For the electronic polarization the relaxation time is comparable to the speed of light. Tlie relaxation time of atomics (ions) is comparable to the vibration frequency of each ion. The relaxation time of the Debye polarization is controlled by the potential barrier between two equilibrium positions where the dipole would orientate from one to other [10[. The relaxation time of the Debye polarization, tj, can be expressed as [10]  

For electrode polarization, the relaxation time should be controlled by the time of building up the elcetrical double layer. Suppose that the cations and anions have a same diffusion coeillcient D ol the dimension area/second, the ion velocity vi in an electrical double layer of thickness k can be expressed as  

The time needed for building up an electrical double layer is  

The diffusion coefficient D of ion can be expressed by the Stokes-Einstein equation  

(32) indicates that the relaxation time of the electrode polarization decreases with the number concentration of ions and increases witli the size of ions, the dielectric constant and the viscosity of medium. Detailed discussion on the electrode polarization will be given further on. 

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