Session QC28 - Topics in Pattern Formation and Nonlinear Dynamics.
ORAL session, Wednesday morning, March 24
Room 168W, GWCC
Over a wide range of conditions, the bifurcation to electro-convection in the nematic liquid crystal I52 is a Hopf bifurcation to travelling waves. These waves form a number of different spatial structures. Of these, localized states known as worms, as well as spatiotemporal chaos (STC), are perhaps the most interesting.(M. Dennin, D.S. Cannell, and G. Ahlers, Phys. Rev. E 57), 638 (1998). Worms and STC appear right above onset and can be described by complex Ginzburg-Landau equations.(H. Riecke and G.D. Granzow, Phys. Rev. Lett. 81), 333 (1998). The observed patterns depend on the voltage amplitude V_0 and frequency f applied to the sample, and on the electrical conductivity \sigma of the sample. \sigma is determined by doping with iodine. Moderate doping leads to \sigma(f,T) which depends on f and on the temperature T. We present measurements of \sigma(T) at small f and modest doping over the range 30 \alt T \alt 60^\circC. For a given sample, \sigma depends also slightly upon the time t. We found that it decreases with t in a medium temperature range, whereas it increases at lower and higher T. Finally we observed that very high doping leads to a much weaker dependence of \sigma on f, and that in this range stationary patterns replace STC right above the onset to the convecting state.