Adlem K, Čopič M, Luckhurst G R, Mertelj A, Parri O, Richardson R M, Snow B D, Timimi B A, Tuffin R P, Wilkes D
Merck Chemicals Ltd., Chilworth Technical Centre, University Parkway, Southampton SO16 7QD, United Kingdom.
Phys Rev E Stat Nonlin Soft Matter Phys. 2013 Aug;88(2):022503. doi: 10.1103/PhysRevE.88.022503. Epub 2013 Aug 12.
Here we report the chemical induction of the twist-bend nematic phase in a nematic mixture of ether-linked liquid crystal dimers by the addition of a dimer with methylene links; all dimers have an odd number of groups in the spacer connecting the two mesogenic groups. The twist-bend phase has been identified from its optical texture and x-ray scattering pattern as well as NMR spectroscopy, which demonstrates the phase chirality. Theory predicts that the key macroscopic property required for the stability of this chiral phase formed from achiral molecules is for the bend elastic constant to tend to be negative; in addition the twist elastic constant should be smaller than half the splay elastic constant. To test these important aspects of the prediction we have measured the bend and splay elastic constants in the nematic phase preceding the twist-bend nematic using the classic Frederiks methodology and all three elastic constants employing the dynamic light scattering approach. Our results show that, unlike the splay, the bend elastic constant is small and decreases significantly as the transition to the induced twist-bend nematic phase is approached, but then exhibits unexpected behavior prior to the phase transition.
在此，我们报告了通过添加具有亚甲基连接的二聚体，在醚连接的液晶二聚体的向列相混合物中化学诱导扭曲弯曲向列相；所有二聚体在连接两个介晶基团的间隔基中具有奇数个基团。扭曲弯曲相已通过其光学织构、X射线散射图案以及核磁共振光谱得以识别，核磁共振光谱证明了相的手性。理论预测，由非手性分子形成的这种手性相稳定性所需的关键宏观性质是弯曲弹性常数趋于为负；此外，扭曲弹性常数应小于展曲弹性常数的一半。为了检验该预测的这些重要方面，我们使用经典的弗雷德里克斯方法测量了扭曲弯曲向列相之前的向列相中的弯曲和展曲弹性常数，并使用动态光散射方法测量了所有三个弹性常数。我们的结果表明，与展曲不同，弯曲弹性常数较小，并且随着向诱导的扭曲弯曲向列相的转变临近而显著降低，但在相变之前表现出意想不到的行为。
