Helical twist distortions, chiral nematics

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.

Systems that lack inversion symmetry (for example, because of addition of chiral constituents) can form liquid crystal phases with a spontaneous helical distortion to the direction of molecular alignment. One of these phases is the cholesteric, also called a twisted nematic. It is similar to a nematic, but the alignment... 

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