Electroconvection conductive

Abstract A systematic overview of various electric-field induced pattern forming instabilities in nematic liquid crystals is given. Particular emphasis is laid on the characterization of the threshold voltage and the critical wavenumber of the resulting patterns. The standard hydrodynamic description of nematics predicts the occurrence of striped patterns (rolls) in five different wavenumber ranges, which depend on the anisotropies of the dielectric permittivity and of the electrical conductivity as well as on the initial director orientation (planar or homeotropic). Experiments have revealed two additional pattern types which are not captured by the standard model of electroconvection and which still need a theoretical explanation. 

Electroconvection in nematics is certainly a prominent paradigm for nonequilibrium pattern-forming instabilities in anisotropic systems. As mentioned in the introduction, the viscous torques induced by a flow field are decisive. The flow field is caused by an induced charge density p i when the director varies in space. The electric properties of nematics with their quite low electric conductivity 10 (fl m) ] are well described within the electric quasi-static approximation, i.e. by charge conservation and Pois-... 

A. Buka, B. Dressel, W. Otowski, K. Camara, T. Toth-Katona, L. Kramer, J. Lindau, G. Pelzl and W. Pesch, Electroconvection in nematic liquid crystals with positive dielectric and negative conductivity anisotropy, Phys. Rev. E 66(5), 051713/1-8, (2002). doi 10.1103/PhysRevE.66.051713... 

Traditionally, the term electroconvection is used in at least four different physical contexts, of which three pertain to flows of liquid dielectrics. Thus, it is used to describe the electric field-induced flow of nematic liquid crystals, the flow of liquid dielectrics caused by the action of electric field on the space charge of ions of the appropriate sign injected in a low quantity into a fluid, or the effects of an electric field acting on the surface charge accumulated at the interface between two weakly conducting fluids. The latter process was studied by G. I. Taylor, who in the mid-1960s introduced the leaky dielectric model... 

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