Comparative analysis of anisotropic material properties of uniaxial nematics formed by flexible dimers and rod-like monomers
Comparative analysis of anisotropic material properties of uniaxial nematics formed by flexible dimers and rod-like monomers
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DOI：
10.1080/02678292.2016.1240248
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发表时间：
2017-01-01
期刊：
影响因子：
2.2
通讯作者：
Lavrentovich, Oleg D.
中科院分区：
文献类型：
--
作者：
Cukrov, Greta;Golestani, Youssef Mosaddeghian;Lavrentovich, Oleg D.
我们报告温度依赖性的材料性能，如介电各向异性，双折射，splay（K-11），扭曲（K-22），和弯曲（K-33）的弹性常数的单轴取向（N）相形成的柔性二聚体的DTC 5C 9和比较其行为的相应的单体MCT 5。DTC 5C 9在低于N相的温度下形成扭曲向列相（N-tb）。MCT 5的各向异性性质是典型的棒状介晶。特别地，双折射随着温度降低而增加，遵循Haller描述的经典行为。弹性常数也遵循标准行为，它们的比值实际上与温度无关。相比之下，DTC 5C 9显示出与标准情况的显著偏离。Bi_2O_3随温度非单调变化，在接近N-N-tb相变时减小。K-33在N-N-tb跃迁附近强烈降低到0.4 pN，但仍然是有限的。DTC 5C 9的弹性常数的比率显示出强烈的温度依赖性，可以与弯曲引起的取向分布函数的变化。所测量的弹性性质与二聚体分子采用弯曲构型的趋势一致，所述弯曲构型产生N-tb相。[图形]。
We report temperature dependencies of material properties such as dielectric anisotropy, bire-fringence, splay (K-11), twist (K-22), and bend (K-33) elastic constants of the uniaxial nematic (N) phase formed by flexible dimers of DTC5C9 and compare their behaviour to that of a corresponding monomer MCT5. DTC5C9 forms a twist-bend nematic (N-tb) at temperatures below the N phase. Anisotropic properties of MCT5 are typical of the rod-like mesogens. In particular, birefringence increases as the temperature is reduced, following the classic behaviour, described by Haller. The elastic constants also follow the standard behaviour, with their ratios being practically temperature independent. In contrast, DTC5C9 shows a dramatic departure from the standard case. Birefringence changes non-monotonously with temperature, decreasing on approaching the N-N-tb phase transition. K-33 decreases strongly to 0.4 pN near the N-N-tb transition, although remains finite. The ratios of the elastic constants in DTC5C9 show a strong temperature dependence that can be associated with the bend-induced changes in the orientational distribution function. The measured elastic properties are consistent with the tendency of the dimeric molecules to adopt bent configurations that give rise to the N-tb phase.[GRAPHICS].