TRAVELING WAVES IN ELECTROCONVECTION OF THE NEMATIC PHASE-5 - A TEST OF THE WEAK ELECTROLYTE MODEL

We investigated travelling Naves appearing as the primary pattern-form ing instability in the nematic Phase 5 (Merck) in the planar geometry in order to test the recently developed weak electrolyte model of ac-d riven electroconvection [1]. Travelling waves are observed over the fu ll conductive range of applied frequencies for three cells of differen t layer thickness d. We also measured the elastic constants, the elect ric conductivity, and the dielectric constant. The other parameters of Phase 5 are known, apart from the (relatively unimportant) viscosity alpha(1) and the two parameters of the weak electrolyte model that are proportional to the geometric mean of the mobilities, and the recombi nation rate, respectively. Assuming a sufficiently small recombination rate, the predicted dependence of the frequency of the travelling wav es at onset (Hopf frequency) on d and on the applied frequency agreed quantitatively with the experiments, essentially without fit parameter s. The absolute value of the Hopf frequency implies that the geometric mean of the mobilities amounts to 1.1 x 10(-10) m(2)/(Vs).