Mizukami Masashi, Ohta Noboru, Tomita Kazuhito, Yanagimachi Takuya, Shibuya Yuuta, Yagi Naoto, Kurihara Kazue
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan.
Phys Chem Chem Phys. 2021 Jan 6;23(1):131-138. doi: 10.1039/d0cp04266h.
The orientational behavior of a smectic-A liquid crystal (4-cyano-4'-octylbiphenyl, 8CB) confined between mica surfaces as well as between silica surfaces with a nanometer scale thickness was investigated by synchrotron X-ray diffraction measurement. The crystallographic axes of two confining mica sheets were adjusted parallel to each other to induce the preferential orientation of 8CB molecules along their crystallographic axis. The silica surfaces, which were hydrophilic and amorphous and had nanometer level smoothness, were prepared on mica surfaces using a sputtering technique. The X-ray diffraction measurement revealed that the 8CB molecules, confined between mica surfaces (DHW = 1.7 nm) and between silica surfaces (DHW = ca. 2 nm), took a planar orientation (oriented its long axis parallel to the surface) and formed a lamellar structure. However, the in-plane orientation of the confined 8CB changed depending on the confining surfaces. The lamellar axis of the 8CB confined between mica surfaces uniaxially oriented most probably due to the preferential alignment of its long axis along the principal crystallographic a-axis of the mica. On the other hand, 8CB between the silica surfaces formed lamellar domains in which the lamellar axis of 8CB omnidirectionally oriented in-plane. The effect of the shear on the orientation of the nano-confined 8CB was also investigated. The lamellar axis, corresponding to the long axis of the 8CB molecules confined between the mica surfaces, rotated only ca. 3 degrees within the plane parallel to the surface by perpendicularly applying shear to the axis. The lamellar axis of the 8CB molecules between the silica surfaces showed no noticeable change by applying the shear. These results indicated that the effect of shear to align the 8CB molecules was significantly suppressed due to the confinement effect which significantly reduces the mobility of molecules as well as the alignment effect along the crystallographic axis in the case of mica. We also observed a change in the orientation of nano-confined 8CB after shear treatment at large D (= 3.3 μm).
通过同步加速器X射线衍射测量，研究了限制在云母表面之间以及具有纳米级厚度的二氧化硅表面之间的近晶A液晶（4-氰基-4'-辛基联苯，8CB）的取向行为。调整两个限制云母片的结晶轴彼此平行，以诱导8CB分子沿其结晶轴优先取向。使用溅射技术在云母表面制备亲水性、无定形且具有纳米级光滑度的二氧化硅表面。X射线衍射测量表明，限制在云母表面（DHW = 1.7 nm）和二氧化硅表面（DHW = 约2 nm）之间的8CB分子呈平面取向（其长轴平行于表面取向）并形成层状结构。然而，受限8CB的面内取向因限制表面而异。限制在云母表面之间的8CB的层状轴最有可能单轴取向，这可能是由于其长轴沿着云母的主结晶a轴优先排列。另一方面，二氧化硅表面之间的8CB形成层状畴，其中8CB的层状轴在面内全方位取向。还研究了剪切对纳米受限8CB取向的影响。对应于限制在云母表面之间的8CB分子长轴的层状轴，通过垂直于该轴施加剪切，在平行于表面的平面内仅旋转了约3度。二氧化硅表面之间的8CB分子的层状轴在施加剪切后没有明显变化。这些结果表明，由于限制效应，显著降低了分子的迁移率以及在云母情况下沿结晶轴的排列效应，剪切使8CB分子排列的效果受到显著抑制。我们还观察到在大D（= 3.3μm）下进行剪切处理后纳米受限8CB的取向发生了变化。
