A Fluid Liquid-Crystal Material with Highly Polar Order
A Fluid Liquid-Crystal Material with Highly Polar Order
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DOI：
10.1002/adma.201702354
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发表时间：
2017-11-20
影响因子：
29.4
通讯作者：
Kikuchi, Hirotsugu
中科院分区：
文献类型：
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作者：
Nishikawa, Hiroya;Shiroshita, Kazuya;Kikuchi, Hirotsugu
对于在介晶核（DIO）中具有1，3-二氧杂环己烷单元的液晶化合物，在观察到高流动性的中间相温度范围（MP相）中发现了接近10（4）的非常大的介电常数。在此温度范围内，在小和宽的布拉格角都没有观察到尖锐的X射线衍射峰，类似于α相;然而，通过偏光显微镜观察到不均匀的桑迪织构或破碎的纹影织构，不同于常规α相。DIO表现出具有大偏振值的偏振切换，即，P = 4.4 μ C cm（-2），在MP相中存在平行四边形的极化-电场磁滞回线。当发生场致极化转换时，在没有电场的情况下，非均匀排列的DIO沿着所施加的电场沿着采取均匀取向。此外，足够大的二次谐波产生观察到DIO在MP阶段。二次谐波产生干涉术清楚地表明，当MP中所施加的电场的+/-符号反转时，偏振的意义被反转。这些结果表明，一个单向的，铁电性的平行极性排列的分子产生沿着在MP相的导演。
An anomalously large dielectric permittivity of approximate to 10(4) is found in the mesophase temperature range (MP phase) wherein high fluidity is observed for a liquid-crystal compound having a 1,3-dioxane unit in the mesogenic core (DIO). In this temperature range, no sharp X-ray diffraction peak is observed at both small and wide Bragg angles, similar to that for a nematic phase; however, an inhomogeneous sandy texture or broken Schlieren one is observed via polarizing optical microscopy, unlike that for a conventional nematic phase. DIO exhibits polarization switching with a large polarization value, i.e., P = 4.4 mu C cm(-2), and a parallelogram-shaped polarization-electric field hysteresis loop in the MP phase. The inhomogeneously aligned DIO in the absence of an electric field adopts a uniform orientation along an applied electric field when field-induced polarization switching occurs. Furthermore, sufficiently larger second-harmonic generation is observed for DIO in the MP phase. Second-harmonic-generation interferometry clearly shows that the sense of polarization is inverted when the +/- sign of the applied electric field in MP is reversed. These results suggest that a unidirectional, ferroelectric-like parallel polar arrangement of the molecules is generated along the director in the MP phase.