Debye polarisation equation

The complete expression (Debye equation) for the molar polarisation is then ... 

The usefulness of Frohhch s formula (2.53) is mainly restricted by our ignorance of the correlation factor g, which necessarily depends on the shapes of molecules and the disposition of the permanent dipoles within them, the anisotropy of pOlarisability and the presence of charge distributions of higher orders of symmetry. The theory gives us a good general understanding of the behaviour of polar materials, but deviations from the simple Debye equation (2.44) can often only be discussed in qualitative terms. 

The double layer thickness is decisive for the retarding impact of double layer polarisation on the electrophoretic motion. Equation (2.42) yields simple linear relationships only for the two limiting cases of very thin double layers (ka oo) and infinitely thick ones (kg 0). The correction function/(/ca) then simplifies to a constant value of 3/2 and 1, respectively (Fig. 2.21 von Smoluchowski 1903 Debye and Hiickel 1924 O Brien and White 1978). 

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