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Topologically non-equivalent textures generated by the nematic electrohydrodynamics
摘要： Some classes of nematic liquid crystals can be driven through turbulent regimes when forced by an external electric field. In contrast to isotropic fluids, a turbulent nematic exhibits a transition to a stochastic regime that is characterised by a network of topological defects. We study the deformations arising after the electric field has been switched-off. In contrast to the turbulent regime, the relaxation of this topological-defect regime involves the annihilation of an interlacement of defect lines. We show that these defect lines separate regions of the nematic having topologically non-equivalent textures.
关键词： Nematic liquid crystals,electrohydrodynamics,twist deformation,topological defects
更新于2025-09-23 15:22:29
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Transient electrohydrodynamics of a liquid drop in AC electric fields
摘要： The transient behavior of a leaky dielectric liquid drop under a uniform AC electric ?eld of small strength is investigated, using a closed form analytical solution. The drop settles to a quasi-steady state in a relaxation time that is set by the viscosities of the drop and the ambient ?uid and the surface tension, and oscillates around a mean deformation with a frequency that is twice the electric ?eld frequency. The mode of instantaneous deformation remains the same (oblate or prolate) or switches between oblate and prolate, depending on the relative importance of the time-periodic component of the deformation compared to that of the time-exponential. The structure of the ?ow ?eld and its evolution is studied for representative ?uid systems at a high and a low electric ?eld frequency. The individual contribution of the net tangential and normal electric stresses, which are the driving forces of the problem, on the ?ow structure and drop deformation is characterized. On the basis of the mean (time-independent) and time-periodic components of the driving forces, the ?ow ?eld is represented as the superposition of three di?erent ?ow patterns. It is shown that the interplay of these ?ow patterns leads to formation and destruction of toroidal vortices, and that the residence time of these vortices correlates inversely with the ?eld frequency.
关键词： liquid drop,AC electric ?elds,leaky dielectric,?ow ?eld evolution,transient electrohydrodynamics
更新于2025-09-09 09:28:46