Negative viscosity of liquid crystals in the presence of turbulence: Conductivity dependence, phase diagram, and self-oscillation
Negative viscosity of liquid crystals in the presence of turbulence: Conductivity dependence, phase diagram, and self-oscillation
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存在湍流时液晶的负粘度：电导率依赖性、相图和自振荡
DOI：
10.1103/physreve.101.022702
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
T. Nagaya
中科院分区：
文献类型：
--
作者：
F. Kobayashi;Y. Sasaki;S. Fujii;H. Orihara;T. Nagaya
最近，我们报道了在存在由交流电场诱导的湍流的情况下发现了双折射液晶的巨大负粘度，这使得我们能够观察到与负粘度相关的独特现象，例如自发剪切流动、流动曲线中的滞后和自振荡[Oriharaet al.，Phys. Rev. E 99，012701（2019）10.1103/PhysRevE.99.012701]。在本文中，我们报告了另一种双折射液晶的流变性质，这是一个同系物的前一个。本发明液晶的性质强烈依赖于电导率。通过改变离子掺杂剂的量制备了三种具有不同电导率的样品。结果发现，没有掺杂剂的最低电导率的样品显示没有负粘度，而其他离子掺杂的样品表现出负粘度与强烈的依赖于交流电场的频率，与微观观察一致。在振幅和频率平面上的负和正粘性状态的相图被构造来显示电导率效应。此外，我们提出了一个模型来重现另一种类型的自振荡在本研究中发现。
Recently, we reported the discovery of enormous negative viscosity of a nematic liquid crystal in the presence of turbulence induced by ac electric fields, which enabled us to observe unique phenomena related to the negative viscosity, such as spontaneous shear flow, hysteresis in flow curves, and self-oscillation [Oriharaet al., Phys. Rev. E 99, 012701 (2019)10.1103/PhysRevE.99.012701]. In the present paper, we report the rheological properties of another nematic liquid crystal, which is a homologue of the previous one. The properties of the present liquid crystal are strongly dependent on electrical conductivity. Three samples with different conductivities were prepared by changing the amount of an ionic dopant. It was found that the lowest-conductivity sample without dopant shows no negative viscosity whereas the other ion-doped samples exhibit negative viscosity with strong dependence on the frequency of the ac electric field, consistent with microscopic observations. Phase diagrams of the negative- and positive-viscosity states in the amplitude and frequency plane are constructed to show the conductivity effect. Furthermore, we propose a model to reproduce another type of self-oscillation found in the present study.