SYNTHESIS AND PROPERTIES OF NEMATIC LIQUID CRYSTALS EXHIBITING A POSITIVE DIELECTRIC ANISOTROPY

Des séries de cristaux liquides comportant des groupements benzonitrile et cinnamonitrile en position para ont été préparées. Leurs températures de transition et leurs constantes diélectriques ont été déterminées. L'introduction dans des cristaux liquides d'un groupe nitrile en position para ne change pas de manière significative leurs stabilités thermiques, mais augmente considérablement leurs anisotropies diélectriques. L'adjonction d'une double liaison dans des mésomorphes accroît leurs stabilités thermiques mais joue très peu sur leurs anisotropies diélectriques.A series of liquid crystalline materials comprising 4-substituted benzonitriles and cinnamonitriles were prepared, and their transition temperatures and dielectric constants were investigated. The introduction of a 4-cyano group in a liquid crystal (LC) molecule is not accompanied by significant changes in mesophase thermal stabilities but it leads to materials with a considerable positive dielectric anisotropy. Introduction of an additional double bond in LC molecules increases mesophase thermal stabilities without significant changes in their dielectric anisotropies

Experimental verification of the theory of electrohydrodynamic instability in nematic liquid crystals

Williams domains threshold voltage are given as functions of dielectric and conductivity anisotropy. Experimental data confirm the theory of electrohydrodynamic (EHD) instability in nematic liquid crystals (NLC) based on Helfrich's model and taking into account the boundary conditions. © 1975