Kerr Constant

Most solutions are isotropic.  That is, there is no order as the molecules are free to rotate in solution. However, when an electric field is applied, it may induce the molecules to align which generates anisotropy in the solution.  Light traveling through this solution will have a different refractive index for the two orthogonal polarizations.  This birefringence may be measured using a PEM-based Exicor® instrument equipped with a Kerr cell to apply the high voltage (up to 30 kV) across the liquid.

The measured birefringence (Δn) is related to the Kerr constant (K) by the following equation:

Δn = λKE2


Δn is the birefringence
λ is the wavelength of light used
K is the Kerr constant of the solution
E is the strength of the electric field

Measuring polymer tacticity is one application in which the Kerr constant measurement application has been used.  This technique provides a unique tool for probing molecular structure in polymers.


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