We consider electroconvection as a response of nematic liquid crystals to an external electric AC field, in the absence of free charge carriers. Previous experimental and theoretical results emphasized charge carriers as a necessary precondition of electroconvection because free-charges in the fluid can respond to an external electric field. Therefore, ionized molecules are considered as responsible for the driving of electroconvective flows. In experiments, finite conductivity is achieved by adding charge-carrying dye molecules or in non-dyed liquid crystals by impurities of the samples. The phenomenon of electroconvection is explained by the Carr–Helfrich theory, supported by numerical simulations. In the present paper, we show that electroconvection may occur also in pure nematic liquid crystals. By means of particle-based numerical simulations we found that bound charges emerge by alignment of polarized liquid crystal molecules in response to the external electric field. In our simulations we could reproduce the characteristic features of electroconvection, such as director-flow patterns, the phase-transition in the voltage-frequency diagram, and dislocation climb/glide motion, which are well known from experiments and hydrodynamic simulations under the assumption of free charge carriers.

中文翻译：

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纯向列液晶的电对流，无自由载流子

在没有自由载流子的情况下，我们认为电对流是向列液晶对外部交流电场的响应。先前的实验和理论结果都强调电荷载体是电对流的必要前提，因为流体中的自由电荷可以响应外部电场。因此，电离分子被认为是驱动电对流的原因。在实验中，通过添加带有电荷的染料分子或样品中的杂质在未染色的液晶中获得有限的电导率。电对流现象由Carr–Helfrich理论解释，并得到了数值模拟的支持。在本文中，我们表明在纯向列型液晶中也可能发生电对流。通过基于粒子的数值模拟，我们发现响应于外部电场，极化液晶分子的排列会产生束缚电荷。在我们的模拟中，我们可以重现电对流的特征，例如导向流模式，电压-频率图中的相变以及位错爬升/滑移运动，这在实验和流体动力学模拟中在以下条件下是众所周知的：免费的运营商。