Nonstandard electroconvection with Hopf bifurcation in a nematic liquid crystal with negative electric anisotropies.

Research paper by Tibor T Tóth-Katona, Aude A Cauquil-Vergnes, Nándor N Eber, Agnes A Buka

Indexed on: 07 Aug '07Published on: 07 Aug '07Published in: Physical review. E, Statistical, nonlinear, and soft matter physics


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 nonstandard 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.