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In practice, additional efforts are necessary to maintain the ‘supertwisted’ structure with a twist angle θ ＞ 90° .
An ordinary nematic liquid crystal would optimize its elastic energy by ‘flipping back’ to ξ − 180° which has the smaller absolute value.
Therefore, it’s necessary to ‘pre-twist’ the material. This is done by admixing a small amount of a chiral nematic ( cholesteric ) liquid crystal.
