Structure and Properties of the Twist-Bend Nematic Phase

非技术摘要。液晶带来了一场信息呈现方式的革命，使整个液晶显示器（LCD）行业成为可能。 从智能手机到笔记本电脑屏幕和平板电视机的现代设备都采用了LCD，其中所谓的液晶在电场的作用下重新排列，从而改变像素化屏幕的光学外观。多年来，唯一已知的顺时针排列类型是具有单一直轴的分子取向。 这个项目的重点是一个新发现的螺旋序，其中的分子取向遵循一个非平凡的几何形状的斜螺旋，扭曲和弯曲在一个非常小的尺度纳米。 该项目将确定新型液晶的基本性质，确定其结构和性质，并探索如何将新材料用于LCD等实际应用。技术摘要 液晶（LC）代表了一种特殊的物质状态，结合了固体晶体和各向同性流体的性质。 最广为人知的LC类型是所谓的平行排列，其中棒状分子彼此平行排列，但可以自由滑过它们的邻居。 有序性、流动性和对电场的强烈响应性的微妙结合，为我们今天呈现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，即所谓的指向矢，被认为是由非手性分子构成的唯一可能的方向。 然而，Meyer和Dozov的理论模型假设，可能存在指向矢弯曲和扭曲的向列线。 2013年，在具有二聚体分子的材料中证明了扭曲-弯曲的NNTb的存在，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，基态指向矢不是一条直线，而是一个具有纳米级间距的斜螺旋面。 该项目的目标是探索Ntb的详细结构和物理性质。 纳米尺度调制的指向矢应该对诸如温度和电场等弱驱动力敏感，这可能与经典LC的应用相媲美。 该项目将建立对Ntb结构的基本理解，该结构在从纳米到数百微米的广泛不同的长度尺度上具有自发破缺的手性对称性，并确定形成Ntb的材料的物理特性，例如弹性和对电磁场的响应性。 这些目标将通过应用一系列成像和表征技术来实现，从冷冻TEM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.