The Cholesteric Domain Texture

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Abstract
When a large pitch cholesteric is held between parallel glass plates a distance d apart, near the isotropic transition, a characteristic striped pattern appears. The distance between stripes is about the half pitch p oo/2 (providing d > p oo) and the texture has no measurable optical rotatory power. It does not appear if d ≤ p oo. Assuming that the molecules lie in planes perpendicular to the glass plates and twist uniformly in the interior of the sample about an axis parallel to the glass plates, we have solved the Frank equation(1) when tangential (or homoeotropic) boundary conditions are applied. The solution predicts a lattice of χ(2) disclinations at the surface of the sample, the distance between the χ's being related to the half-pitch. We have found that this configuration is not stable within a distance p o/4 (d∼p o) of the disclination and we suggest that this results in the splitting of the χ into a λ and a τ.(2) This latter configuration appears to adequately explain the experimentally observed features of the cholesteric domain texture. The same type of instability occurs when a χ is parallel to the cholesteric axis, and leads also to a splitting into a λ; and τ. A complete calculation is presented for this case.

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