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Non-standard electroconvection with Hopf-bifurcation in a nematic with negative electric anisotropies

Tibor Toth-Katona ,Aude Cauquil-Vergnes ,Nandor Eber ,Agnes Buka

Research Institute for Solid State Physics and Optics

Electric field driven pattern formation has been investigated in a nematic liquid crystal with negative dielectric and conductivity anisotropies. Despite the fact that the standard Carr-Helfrich theory predicts no hydrodynamic instability for such compound, experiments reveal convection patterns which we call non-standard electroconvection (ns-EC). In this work, we characterize the ns-EC patterns by measuring the frequency-, thickness-, and temperature dependence of the threshold voltage, wave-number, roll orientation, etc., and compare them with the standard EC (s-EC) characteristics. For the first time, we report traveling rolls in ns-EC, and we give the dependence of the Hopf frequency on the driving frequency, temperature and sample thickness. Finally, we discuss possible sources for the existence of these patterns.

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