Liquid crystal, wedge disclinations

Figure 8. Wedge disclinations, with rotational strength -it, in a cubic crystal and in a liquid crystal. Note that the molecular scale of the liquid crystal is much larger than the atomic scale of the cubic crystal.

The Cano wedge can be used to measure the cholesteric pitch. Two substrates are wedged by a small angle 2y. The cholesteric liquid crystal between the substrates is homogeneously aligned. Under polarized microscopy, the equally spaced disclinations appear at the middle of the wedge. The separation of the lines 2d is associated with the pitch P... 

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