RESUMO
Precise solutions for the threshold voltage U(c) and wave number q(c) that feature the appearance of longitudinal flexoelectric domains of Vistin'-Pikin-Bobylev at strong anchoring have been derived. Based on the formulated expressions, we present and analyze computer calculations for a planar nematic layer with anisotropic elasticity and both negative and positive dielectric anisotropy under the action of a homogeneous flexoelectrically deforming d.c. electric field. The obtained relations allow a selection of particular values of physical parameters, in order to improve the performance of devices exploiting flexoelectrcity in nematics.
Assuntos
Cristais Líquidos/química , Cristais Líquidos/efeitos da radiação , Modelos Químicos , Modelos Moleculares , Anisotropia , Simulação por Computador , Módulo de Elasticidade , Campos EletromagnéticosRESUMO
We report on the converse flexoelectric effect in two bent-core nematic liquid crystals with opposite dielectric anisotropies. The results are based on electro-optic investigations of inplane field-driven distortions in homeotropic samples (the Helfrich method). They are interpreted by an extension of the Helfrich theory that takes into account the higher order distortions. The bend flexocoefficient for both the compounds is of the usual order of magnitude as in calamitics, unlike in a previously investigated bent-core nematic for which giant values of the bend flexocoefficient are reported. In order to resolve this discrepancy, we propose a molecular model with nonpolar clusters showing quadrupolar flexoelectricity. The study also includes measurements on surface polarization instabilities in the dielectrically positive material; the splay flexocoefficient thereby deduced is also of the conventional order.