FORMATION OF CHEVRONS IN THE DIELECTRIC REGIME OF ELECTROCONVECTION IN NEMATIC LIQUID-CRYSTALS

We present quantitative measurements of the scenario leading to chevro ns in the dielectric range of ac driven electroconvection in a planarl y aligned layer of the nematic liquid crystal Merck Phase 5. First, we demonstrate that the threshold of electroconvection is described corr ectly by the standard theory. Second, we characterize above threshold the appearance of chevrons out of the defect chaotic state by a rather sudden increase of the density of defects. Furthermore, we show that the spatial correlations between defects characterizing the chevrons s et in simultaneously. Finally, we give the onset curve of chevrons (vo ltage versus frequency) and also discuss briefly their further develop ment.