Origin of traveling rolls in electroconvection of nematic liquid crystals

Electroconvection in nematic liquid crystals exhibits a Hopf bifurcation to traveling rolls for a wide parameter range. The model normally used to describe electroconvection fails to predict this. A recent theoretical extension, the weak-electrolyte model, incorporates the dissociation-recombination reaction of the ionic dopant in the sample and does predict a Hopf bifurcation for a range of parameter values. We present a quantitative experimental test of this theory using the nematic liquid crystal I52. Measured Hopf frequencies at the onset of convection agree well with the theory.