Yadav Neelam, Panarin Yuri P, Jiang Wanhe, Mehl Georg H, Vij Jagdish K
Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland.
Department of Electrical and Electronic Engineering, TU Dublin, Dublin 7, Ireland.
Phys Chem Chem Phys. 2023 Mar 29;25(13):9083-9091. doi: 10.1039/d3cp00357d.
An achiral compound, DIO, known to exhibit three nematic phases namely N, N and N, is studied by polarizing microscopy and electro-optics for different surface conditions in confinement. The high temperature N phase assigned initially as a conventional nematic phase, shows two additional unusual features: the optical activity and the linear electro-optic response related to the polar nature of this phase. An appearance of chiral domains is explained by the spontaneous symmetry breaking arising from the saddle-splay elasticity and followed by the formation of helical domains of the opposite chirality. This is the first example of helical segregation observed in calamitic non-chiral molecules in the nematic phase. As reported previously, the ferronematic N shows strong polar azimuthal surface interaction energy which stabilizes a homogeneous structure in planar aligned LC cells rubbed parallel and exhibits a twisted structure in cells with antiparallel buffing. The transmission spectra are simulated using Berreman's 4 × 4 matrix method. The observed agreement between the experimental and the simulated spectra quantitatively confirms the presence of twisted structures in antiparallel rubbed cells.
一种非手性化合物DIO，已知其呈现三种向列相，即N、N和N，通过偏光显微镜和电光技术对其在受限条件下的不同表面状况进行了研究。最初被指定为常规向列相的高温N相，呈现出另外两个不寻常的特征：光学活性以及与该相极性相关的线性电光响应。手性畴的出现可通过鞍形展曲弹性引起的自发对称性破缺来解释，随后形成相反手性的螺旋畴。这是在向列相的棒状非手性分子中观察到螺旋分离的首个实例。如先前报道，铁电向列相N显示出很强的极性方位表面相互作用能，这使得在平行摩擦的平面取向液晶盒中稳定了均匀结构，而在反平行摩擦的盒中呈现扭曲结构。使用贝里曼4×4矩阵方法模拟了透射光谱。实验光谱与模拟光谱之间观察到的一致性定量地证实了反平行摩擦盒中存在扭曲结构。
