Propagative Structures and Localization in the Convection of a Liquid Crystal
Fluids driven to convection under an external forcing can exhibit above some threshold a well-defined ordered spatial structure. Usually the obtained state is stationary. The Rayleigh-Bénard rolls in a small rectangular box, or the Taylor-Couette vortices are classical examples of isotropic systems. Convection in a nematic liquid crystal, under either an electric field or a thermal gradient, provides a particularly interesting example of an anisotropic system. With respect to the former, this system possesses an intrinsic preferred direction which imposes a unique direction for the wavevector of the basic roll structure over the whole plane of the layer [l]. Then the experiments can be performed in very extended layers where the boundary effects can be neglected. We present here experimental results which show that, inside some other range in frequency, the basic structure at threshold is no longer stationary and homogeneous in space, but appears as localised domains of traveling waves. We analyse the fluid motion in the propagating pattern and we suggest some elements for an interpretation of the travelling wave and for the localisation. Our results show some similarity with those found in the Rayleigh-Bénard convection of binary mixtures [2,3]. However, our observations indicate clearly that the localization inside small domains is not due to finite size effects induced by solid lateral boundaries.
KeywordsNematic Liquid Crystal Molecular Orientation Normal Roll Convective Roll Anisotropic System
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