Structure and Properties of the Twist-Bend Nematic Phase

非技术抽象。液晶带来了一场革命，我们现在如何呈现信息，使整个行业的液晶显示器（lcd）。从智能手机到笔记本电脑屏幕，再到平板电视等现代设备都采用了lcd，这种所谓的向列液晶在电场作用下重新排列，从而改变了像素化屏幕的光学外观。多年来，唯一已知的向列排列类型是分子取向的单一直轴。该项目专注于新发现的向列序，其中分子取向遵循倾斜螺旋面的非平凡几何形状，在非常小的纳米尺度上扭曲和弯曲。该项目将建立新型向列液晶的基本性质，确定其结构和性质，并探索如何将新材料用于液晶显示器等实际应用。技术文摘。液晶是一种结合固体晶体和各向同性流体特性的特殊物质状态。最广为人知的LCs类型是所谓的向列型，其中棒状分子彼此平行排列，但可以自由地滑过相邻的分子。向列图将有序、流动性和对电场的灵敏响应巧妙地结合在一起，给我们展示信息的方式带来了一场革命，使整个便携式液晶显示器（lcd）行业成为可能。几十年来，分子取向的单轴，即所谓的指向性，被认为是唯一可能由非手性分子构成的向列。然而，Meyer和Dozov的理论模型假设，可能存在导演弯曲和扭曲的向列式。2013年，扭曲-弯曲向列Ntb的存在在二聚体分子材料中得到了证明，二聚体分子代表由柔性脂肪链连接的两个刚性核心。在Ntb中，基态指向器不是一条直线，而是沿着一个纳米级螺距的斜螺旋。该项目的目标是探索Ntb的详细结构和物理性质。纳米级调制的导流器应该对温度和电场等弱驱动力敏感，有望与经典的导流器相媲美。该项目将建立对Ntb结构的基本理解，并在从纳米到数百微米的广泛不同的长度尺度上自发破断手性对称，并确定形成Ntb的材料的物理性质，如弹性和对电磁场的响应性。该目标将通过应用一系列成像和表征技术来实现，从低温透射电镜到3D光学显微镜。

NON-TECHNICAL ABSTRACT. Liquid crystals brought a revolution in how we present information nowadays, enabling the entire industry of Liquid Crystal Displays (LCDs). Modern devices ranging from smart phones to laptop screens and flat-panel TV sets are all featuring the LCDs, in which so-called nematic liquid crystals realign under the action of the electric field, thus changing the optical appearance of the pixelated screen. For many years, the only known type of nematic alignment was the one with a single straight axis of molecular orientation. This project focuses on a newly discovered nematic order, in which the molecular orientation follows a nontrivial geometry of an oblique helicoid, with twists and bends at a very small scale of nanometers. The project will establish the basic properties of the new nematic liquid crystals, determine their structure and properties and explore how the new materials can be used in practical applications such as LCDs.TECHNICAL ABSTRACT. Liquid crystals (LCs) represent a peculiar state of matter combining properties of solid crystals and isotropic fluids. The most widely known type of LCs is the so-called nematic, in which rod-like molecules are aligned parallel to each other, but have the freedom to glide past their neighbors. The subtle combination of order, fluidity, and eager responsiveness to the electric field featured by the nematics brought a revolution in the way we present information nowadays, enabling an entire industry of portable LC displays, or LCDs. For many decades, the single axis of molecular orientation, the so-called director, was considered as the only possible nematic made of non-chiral molecules. Theoretical models by Meyer and Dozov hypothesized, however, that there might be nematics in which the director bends and twists. In 2013, the existence of the twist-bend nematic Ntb was proven in materials with dimeric molecules, representing two rigid cores connected by a flexible aliphatic chain. In Ntb, the ground-state director is not a straight line, but follows an oblique helicoid with a nanoscale pitch. The goal of this project is to explore the detailed structural and physical properties of Ntb. The nanoscale-modulated director should be sensitive to weak driving forces such as temperature and electric field, promising applications that might rival those of the classic LCs. The project will establish a fundamental understanding of the Ntb structure with spontaneously broken chiral symmetry at the widely disparate length scales from nanometers to hundreds of microns and determine the physical properties of materials forming Ntb, such as elasticity and responsiveness to electromagnetic fields. The goals will be achieved by applying a battery of imaging and characterization techniques, ranging from cryo-TEM to 3D optical microscopy.