Electroconvection in a Freely Suspended Film of Smectic a Liquid Crystal
Liquid crystals in the smectic A phase have a layered structure . They are liquid—like in the plane of the layers, but act like a soft solid in the perpendicular direction. A film of smectic A, supported only at its edges, forms a nearly two—dimensional liquid . We observe that such a film can be driven into convection by an electric field applied in the plane of the film . Two types of convection are observed; one which requires the injection of charge at the electrodes [4,5] and one which is due to charged impurities already present in the material [6,7]. The director orientation is unaffected by the motion of the liquid. In contrast to the behaviour of nematic or isotropic films [8,9], we find that the free surfaces of the smectic are not deformed by the flow. No significant hysteresis is observed at the bifurcation to the convecting state. The flow patterns, shown if Fig. 1, resemble two-dimensional versions of conventional convection rolls. This instability is an interesting new example of a low dimensional pattern-forming system .
KeywordsLiquid Crystal Critical Voltage Critical Amplitude Charged Impurity Roll Pattern
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