Kim Young-Ki, Cukrov Greta, Vita Francesco, Scharrer Eric, Samulski Edward T, Francescangeli Oriano, Lavrentovich Oleg D
Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242, USA.
Dipartimento di Scienze e Ingegneria della Materia, dell'Ambiente ed Urbanistica and CNISM, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy.
Phys Rev E. 2016 Jun;93(6):062701. doi: 10.1103/PhysRevE.93.062701. Epub 2016 Jun 1.
The possibility of biaxial orientational order in nematic liquid crystals is a subject of intense current interest. We explore the tendencies toward local and global biaxial ordering in the recently synthesized trimethylated oxadiazole-based bent-core mesogens with a pronounced asymmetric (bow-type) shape of molecules. The combination of x-ray diffraction and optical studies suggests that the biaxial order is expressed differently at the short- and long-range scales. Locally, at the scale of a few molecules, x-ray-diffraction data demonstrate biaxial packing. However, above the mesoscopic scale, the global orientational order in all three compounds is uniaxial, as evidenced by uniform homeotropic alignment of the nematic phase which is optically tested over the entire temperature range and by the observations of topological defects induced by individual and aggregated colloidal spheres in the nematic bulk.
向列型液晶中双轴取向有序的可能性是当前人们密切关注的一个课题。我们研究了最近合成的基于三甲基化恶二唑的弯曲核液晶基元中局部和全局双轴有序的趋势，这些分子具有明显的不对称（弓形）形状。X射线衍射和光学研究的结合表明，双轴有序在短程和长程尺度上的表现不同。在局部，在几个分子的尺度上，X射线衍射数据表明存在双轴堆积。然而，在介观尺度以上，所有三种化合物的全局取向有序都是单轴的，这通过向列相在整个温度范围内的均匀垂直排列以及对向列相中单个和聚集的胶体球诱导的拓扑缺陷的观察得到了证实。
