Lorentz-Lorenz internal field

The calculation of the intrinsic birefringence for a given molecular organization is almost impossible at present. It involves both molecular and macroscopic polarizability and the form of the Lorenz-Lorentz or internal fields relation relevant to an anisotropic molecular organization. The orientation parameter is given by ... 

I) Lorentz-Lorenz, Onsager internal field factors (QM(g), Continuum)... 

For the discussion of the results it has to be emphasized that the Kuhn-Griin relation is based on the application of the Lorenz-Lorentz-equation. It has already been discussed earlier that the assumption of a spherical internal field could not be valid for extended non-spherical statistical segments of polymer chains The strong influence of different internal fields on the sign of the stress optical coefficient has been described by Pietralla The same problem arises for liquid crystalline phases and has been discussed in detail for low molar mass LCs whereby the validity of the Lorenz -Lorentz equation in the isotropic state still has been assumed... 

Applying the well known formula of Lorentz-Lorenz one finds a less good agreement. This formula is based on a theory which does not account for the influence of the internal field. The Gladstone and Dale equation is a purely empirical relation which seems to cover the actual behaviour of systems of this kind very satisfactorily. 

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