Effects of Electric Fields on Mixtures of Nematic and Cholesteric Liquid Crystals
This work involves nematic materials mixed with small amounts of cholesteryl acetate. It is assumed that the structures for these mixtures are similar to the cholesteric structure. The dielectric constant of p-methoxybenzylidene-p-cyanoaniline is greatest in a direction parallel to the long axes of the molecules; therefore, the structure for mixtures of this material with a cholesteric material can be changed to a nematic structure by applying external electric fields. NMR techniques and measurements of the dielectric loss at a microwave frequency are used to obtain information about the cholesteric-nematic phase transition as the external electric field and the concentration of cholesteryl acetate are varied. Although mixtures of p-[n-(p-methoxybenzylidene)-amino]-phenyl acetate and cholesteryl acetate cannot be changed to a nematic phase by employing electric fields because of the negative dielectric anisotropy, an ordering can be obtained with the screw axis of the helix parallel to a 300 kHz electric field.
KeywordsNematic Phase Cholesteric Liquid Crystal Side Peak Dielectric Anisotropy Phenyl Acetate
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