Yunusa Muhammad, Adaka Alex, Aghakhani Amirreza, Shahsavan Hamed, Guo Yubing, Alapan Yunus, Jákli Antal, Sitti Metin
Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569, Stuttgart, Germany.
Materials Science Graduate Program, Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH, 44242, USA.
Adv Mater. 2021 Sep;33(38):e2104807. doi: 10.1002/adma.202104807. Epub 2021 Aug 1.
Understanding the origin of structural ordering in supercooled liquid gallium (Ga) has been a great scientific quest in the past decades. Here, reflective polarized optical microscopy on Ga sandwiched between glasses treated with rubbed polymers reveals the onset of an anisotropic reflection at 120 °C that increases on cooling and persists down to room temperature or below. The polymer rubbing usually aligns the director of thermotropic liquid crystals (LCs) parallel to the rubbing direction. On the other hand, when Ga is sandwiched between substrates that align conventional LC molecules normal to the surface, the reflection is isotropic, but mechanical shear force induces anisotropic reflection that relaxes in seconds. Such alignment effects and shear-induced realignment are typical to conventional thermotropic LCs and indicate a LC structure of liquid Ga. Specifically, Ga textures obtained by atomic force and scanning electron microscopy reveal the existence of a lamellar structure corresponding to a smectic LC phase, while the nanometer-thin lamellar structure is transparent under transmission polarized optical microscopy. Such spatial molecular arrangements may be attributed to dimer molecular entities in the supercooled liquid Ga. The LC structure observation of electrically conductive liquid Ga can provide new opportunities in materials science and LC applications.
在过去几十年里，了解过冷液态镓（Ga）中结构有序性的起源一直是一项重大的科学探索。在此，对夹在经摩擦聚合物处理的玻璃之间的镓进行反射式偏振光学显微镜观察发现，在120°C时出现各向异性反射，该反射在冷却时增强，并一直持续到室温或更低温度。聚合物摩擦通常会使热致液晶（LC）的指向矢平行于摩擦方向排列。另一方面，当镓夹在使传统液晶分子垂直于表面排列的基板之间时，反射是各向同性的，但机械剪切力会诱导出在数秒内松弛的各向异性反射。这种排列效应和剪切诱导的重新排列是传统热致液晶的典型特征，表明液态镓具有液晶结构。具体而言，通过原子力显微镜和扫描电子显微镜获得的镓织构揭示了对应于近晶液晶相的层状结构的存在，而纳米级薄的层状结构在透射偏振光学显微镜下是透明的。这种空间分子排列可能归因于过冷液态镓中的二聚体分子实体。对导电液态镓的液晶结构观察可为材料科学和液晶应用提供新的机遇。
