Twist-bend nematic phase in biphenylethane-based copolyethers
Twist-bend nematic phase in biphenylethane-based copolyethers
复制标题
联苯乙烷共聚醚中的扭转弯曲向列相
DOI：
10.1039/c7sm02525d
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发表时间：
2018
期刊：
影响因子：
3.4
通讯作者：
Goran Ungar
中科院分区：
文献类型：
--
作者：
Warren Stevenson;Jianggen An;Xiang-bing Zeng;Min Xue;Heng-xing Zou;Yongsong Liu;Goran Ungar
主链液晶（LC）共聚醚，其中向列相-液晶相转变是第一次实验观察到的重新审视和重新表征。掠入射X-射线散射表明，低-T（Ntb）相可以通过剪切高度对齐，比以前研究的弯曲LC二聚体。这是证明了四点广角X射线散射图案，这源于两个倾斜分布的卷积。通过强度模拟，计算了与每种分布相关的取向序参量，以及Ntb相的锥角。关于聚合物链构象的信息是使用偏振红外光谱法获得的。研究结果表明，平均构象的链是一个螺旋，和弯曲角介晶单元之间的温度呈负相关。所有的实验证据，包括双折射率在Ntb-Nm 2（N）相变处的跳跃，表明共聚醚样品反映了弯曲LC二聚体在相变期间的行为。这证实了共聚醚中的低T_c相确实与LC二聚体中的相同，现在已知为. Ntb。本文讨论了用调制DSC实验得到的复热容中过渡峰的异常加宽现象。
The main-chain liquid crystal (LC) copolyethers in which the nematic–nematic phase transition was first experimentally observed were revisited and re-characterised. Grazing incidence X-ray scattering revealed that the low-T nematic (Ntb) phase could be highly aligned by shearing, more so than in previously studied bent LC dimers. This was evidenced by a four-point wide-angle X-ray scattering pattern, which originates from convolution of two tilt distributions. Through intensity simulation the orientational order parameter associated with each of the distributions, as well as the conical angle of.the Ntb phase, was calculated. Information regarding the polymer chain conformation was obtained using polarised infrared spectroscopy. The findings suggest the average conformation of the chains is a helix, and that the bend angle between mesogenic units is inversely related to temperature. All.experimental evidence, including a jump in birefringence at the Ntb–nematic (N) phase transition, shows that copolyether samples mirror the behaviour of bent LC dimers over the transition. This confirms that the low-T nematic phase in copolyethers is indeed the same as that in LC dimers, now known to be the.Ntb. The unusual broadening of transition peaks in complex heat capacity, obtained by modulated DSC experiments, is discussed.