Unusual electric-field-induced transformations in the dark conglomerate phase of a bent-core liquid crystal
Unusual electric-field-induced transformations in the dark conglomerate phase of a bent-core liquid crystal
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DOI：
10.1080/02678292.2014.885602
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发表时间：
2014-03
期刊：
影响因子：
2.2
通讯作者：
Mamatha Nagaraj;K. Usami;Zhaopeng Zhang;V. Görtz;J. Goodby;H. Gleeson
中科院分区：
文献类型：
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作者：
Mamatha Nagaraj;K. Usami;Zhaopeng Zhang;V. Görtz;J. Goodby;H. Gleeson
本文描述了在恶二唑基非手性弯核液晶中看到的暗砾岩（DC）相的不寻常行为，这在其他液晶的DC相中尚未报道。在偏光光学显微镜下，我们看到在直流相的基态中没有相反的手性域。然而，当电场作用于系统时，它表现出不同寻常的变化。随着电场的增大，首先相反手性的畴变得可见，然后它们的大小逐渐增大，慢慢地样品转变为单手性或单手性形式，然后在非常高的电场下变为非手性状态。实现这些变化所需的阈值电场与温度有关，并且无论施加电场的频率（100 Hz至5 kHz），波形类型（正弦，方形和三角形）以及厚度（1.5 μm至15 μm）或所使用器件的几何形状（平面和扭曲），都可以看到转换。此外，即使在器件上施加足够大的电场（~22 V/μm），也没有观察到场致高双折射织构。行为的性质是通过各种技术，如光学显微镜，conoscopy，圆二色和拉曼光谱，电光学和介电光谱研究。详细讨论了这些变化背后可能存在的物理现象。
Unusual behaviour of the dark conglomerate (DC) phase seen in an oxadiazole-based achiral bent-core liquid crystal, which has not previously been reported for the DC phase of other liquid crystals, is described. Under polarising optical microscopy, we see no domains of opposite handedness in the ground state of the DC phase. However, it shows unusual transformations when an electric field is applied to the system. On increasing the electric field, at first the domains of opposite handedness become visible and then they grow in size and slowly the sample transforms to a monochiral or single-handed form which is followed by a nonchiral state at very high fields. The threshold electric fields required to achieve these changes are temperature dependent and the transformations are seen irrespective of the frequency of the applied electric field (100 Hz to 5 kHz), type of the waveform (sine, square and triangular) and the thickness (1.5 μm to 15 μm) or the geometry (planar and twisted) of the device used. Further, there is no field-induced high birefringence texture observed even though sufficiently large electric field (~22 V/μm) has been applied across the devices. The nature of the behaviour is investigated by various techniques such as optical microscopy, conoscopy, circular dichroic and Raman spectroscopies, electro-optics and dielectric spectroscopy. The possible physical phenomena behind these changes are discussed in detail.