PATTERN FORMATION AND SYMMETRY OF FIELDS IN ELECTROHYDRODYNAMICSS IN LIQUID CRYSTALS

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The electrohydrodynamic instability (EHD) in nematic liquid crystals is investgated using homeotropically aligned systems where the nematic director orients perpendicular to the electrodes. In homeotropically aligned EHD the system has a continuously rotational symmetry as well as a translational one. This symmetry leads to additional new Goldstone modes at onset of convections and dramatically changes the bifurcation properties as well as observed patterns. The obtained results in the present study are as follows.1) In the system with additional Goldstone modes due to continuous rotational symmetry, a direct transition from nonconvective states to spatiotemporal chaos is observed.2) The bifuration at onset occurs supercritically. The correlation time of macroscopic randam motions becomes longer inversely proportional to the deviation from the onset, that is, a critical slowing down phenomenon is observed. From this behavior the spatiotemporal chaos has been named the soft mode turbule … More nce (SMT) .3) The stability of additional Goldstone modes can be controlled by application of magnetic field since magnetic fields induce the prefered axis and suppress the generation of the Goldstone modes. Therefore under superimposing strong magnetic fields periodic patterns are observed.4) New type of zig-zag patterns are found out which are not predicted in currently available thcories.5) It is clarified from these findings that driving forccs which result in SMT are induced by non-parallel orientation between the director and the wavevector of covective rolls.6) Depending on the strength of magnetic fields there are two types of spatiotemporal chaos. The transition between them is clearly defined by looking the spatial power spectra of patterns and distribution functions of roll orientations.7) The rolls exist either in all directions or only in the prefered directions induced by magnetic fields. Then the formet one is called SMT and the latter the defect turbulence.Thus excess of symmetry can result in chaos and the intrinsic mechanism for direct transition to chaos from a spatially uniform state is destabilization of short-wavelength modes due to coupling with Goldstone modes of the spectrum. Based on these results, new theory will be expected in EHD. Less