Field-Induced Distortions in Chiral Nematics

The starting point is to reconsider Eqs. (1) and (2). In the presence of an external field, the free energy density is modified by a term involving the coupling between the electro-magnetic (or other) bulk anisotropic property and the field (see Eq. 69). This leads to reorientation of the director n in order to minimize this addition- 

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Fig. 7.3. The deviation of the optic axis in a cholesteric (hard-twisted chiral nematic, p <, where p is the cholesteric pitch and A is the wavelength of light) when an electric field E is applied perpendicular to the helical axis. The cholesteric geometry allows a fiexoelectric polarization to be induced in the direction of E. The plane containing the director, which is perpendicular to the page in the middle figure and is shown in the lower figure, illustrates the splay-bend distortion and the corresponding polarization that arises. (After Rudquist, inspired by Meyer and Patel.

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