Some Experiments on Electric Field Induced Structural Changes in a Mixed Liquid Crystal System
Electric field induced cholesteric to nematic structure changes have been investigated in mixtures of primary active amyl p-(4-cyanobenzylideneamino) cinnamate and the structurally similar nematics, cyano substituted benzylidene anilines. The high dielectric anisotropy of the latter materials plus their effect on the pitch of the cholesteric system enables the structure change to take place at fields as low as 2.5x104 V/cm. Studies of the transient behavior of the structure change show that the rise time over a limited range is proportional to exp α E−2. This is suggestive of a nucleation dominated switching process. The relaxation back to the nematic state is independent of the cell thickness and depends only on the temperature and the percentage of nematic material present in the liquid.
The ability of an electric field to switch the bright yellow iridescence of the cholesteric compound is a potentially useful display effect. Reflective contrast ratios of greater than 10:1 can be achieved if a black background is used. This is required since the material is transparent in its nematic state.
KeywordsNematic Liquid Crystal Cholesteric Liquid Crystal Dielectric Anisotropy Critical Electric Field Nematic State
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