On Travelling Waves in Electrohydrodynamic Convection in Nematics

Abstract

Electrohydrodynamic convection (EHC) in a thin layer of nematic liquid crystals has advanced to a paradigm for anisotropic pattern forming systems during the last few years. It exhibits a number of novel features of current interest.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 Due to an axial anisotropy in nematics the orientation of convection rolls is not arbitrary. Therefore one has a transition from convection-rolls which are obliquely oriented to the anisotropy, to normal oriented ones.2, 3, 4, 5, 6 EHC cells can be prepared with rather big aspect ratios (~ 103 ) and therefore it was possible in EHC to investigate without boundary effects static and stationary properties of single disclocations with fairly high precission.15 Travelling waves (TW) often appear in EHC supercritical instead of those in binary fluid convection(TW).9, 10, 11 This allows to compare results on the amplitude equation level with the observations. Multiplicative noise is easily superimposed to the deterministic part of the externally applied voltage and it was therefore EHC where very general properties of multiplicative noise action could be investigated for the first time.7 Recent studies on the transition to turbulence turn out to have strong similarities to the turbulence-turbulence transition in superfluid He II,17, 18 in EHC however one has the great advantage that most of the physical properties in the convection cell are visible under a microscope.