Direct observation of a twist mode in electroconvection

I report on the direct observation of a uniform twist mode of the director field in electroconvection in the nematic liquid crystal I52. Recent theoretical work suggests that such a uniform twist mode of the director field is responsible for a number of secondary bifurcations in both electroconvection and thermal convection in nematics. I show here evidence that the proposed mechanisms are consistent with being the source of the previously reported stationary oblique roll pattern identified as the SO2 state of electroconvection in the liquid crystal I52. The same mechanisms also contribute to a tertiary Hopf bifurcation that I observe in electroconvection in the liquid crystal I52. There are quantitative differences between the experiment and calculations that only include the twist mode. These differences suggest that a complete description must include effects described by the weak-electrolyte model of electroconvection.