Nonstandard electroconvection and flexoelectricity in nematic liquid crystals

Agnes Buka ,Alexei Krekhov ,Werner Pesch ,Nandor Eber ,Tibor Toth-Katona

Research Institute for Solid State and Optics, Hungarian Academy of Sciences
Physikalisches Institut, Universitat Bayreuth

For many years it has been commonly accepted that electroconvection (EC) as primary instability in nematic liquid crystals for the ''classical'' planar geometry requires a positive anisotropy of the electric conductivity, $\sigma_a$, and a slightly negative dielectric anisotropy, $\epsilon_a$. This firm belief was supported by many experiments and theoretical studies. Recent experiments, which have surprisingly revealed EC patterns at negative conduction anisotropy as well, have motivated new theoretical studies in this paper. It will be demonstrated that including the usually neglected flexoelectric effect into the standard EC model, provides a natural explanation for EC in the "nonstandard" case $\sigma_a<0$. The theoretical results and the experiments match very well.

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