Ferroelectricity and the nematic liquid crystal phase

向列相(N)是最不有序的液晶相，其中棒状分子的长轴或多或少沿同一方向排列，称为指向性，而它们的质心是随机分布的。这个阶段很容易复制，扔一把火柴到一个盒子里，然后摇晃它。如果有足够的匹配，那么出于包装的原因，它们将会在同一个方向上排列，这样你就有了一个向列相。假设火柴被随机扔进盒子里，将会有相同数量的火柴头指向一个方向。这正是传统的向列相的情况，分子沿着方向指向任意一个方向的可能性是相等的，这个相被描述为非极性的。传统的N相支撑着液晶显示技术，预计到2025年，液晶显示技术的市场价值将增长到近2000亿美元。100多年前，人们首次提出向列相可以存在，其中所有的分子可以沿同一方向排列。这是一个分子等效的过程，把火柴扔进盒子里，摇晃它，然后发现所有的火柴现在都是头朝向同一个方向。这被称为极性有序，相称为铁电向列相（NF）。最近发现了一种新的向列相，它具有非凡的性质，有人认为这是人们长期追求的NF相。从基础和技术的角度来看，这都有可能成为一个巨大的重大发现。NF相的极性排序使其对电场的敏感性大大高于传统的N相，这将极大地提高液晶显示设备在速度和功耗方面的性能。此外，对这一新相的研究有可能产生革命性的新基础化学、物理和生物学。例如，四十多年前就预测到，为了减少静电能量，NF相会扭曲形成极性胆甾相，自发手性通过非手性分子之间的空间和静电相互作用来控制。这一发现对于理解手性的起源具有重要意义。有人提出，在将传统的N相冷却到NF相时，分子偶极子将自发地沿单一方向排列。在这一点上有很强的结晶倾向。然而，如果这可以被抑制，具有相反极化的相同数量的畴应该形成，由畴壁分开。电场的应用将消除这种简并，具有有利极性的畴将增长，而具有不利极性的畴将缩小。本课程的目的是开始了解观察NF相需要哪些分子特征。不久前，计算机模拟表明，不对称或锥形的形状与纵向偶极矩相结合，促进了极序，并且早期的实验数据支持这一观点。为了实现我们的目标，我们需要加强我们对如何通过分子静电和空间相互作用来操纵液体结晶度的理解。该计划具有提供材料的真正潜力，这些材料将导致变革性的新基础化学，物理和生物学，以及包括下一代显示设备在内的新技术。

The nematic phase (N) is the least ordered liquid crystal phase, and in which the long axes of the rod-like molecules are more or less aligned in the same direction, known as the director, whereas their centres of mass are randomly distributed. This phase is easily replicated by throwing a handful of matches into a box and shaking it. Providing there are enough matches, then, for packing reasons, they will all line-up in the same direction and effectively you have a nematic phase. Providing the matches were thrown into the box randomly, there will be an equal number of matches pointing with their heads in one direction as in the other. This is exactly the case for the conventional nematic phase, and the molecules are equally likely to be pointing in either direction along the director, and the phase is described as being non-polar. The conventional N phase underpins liquid crystal display technology which has a market value predicted to grow to almost $200 billion by 2025. Over 100 years ago, it was first suggested that a nematic phase could exist in which all the molecules could align in the same direction. This is the molecular equivalent of taking the matches, throwing them into the box, shaking it, and discovering that all the matches now lay with their heads pointing in the same direction. This is known as polar ordering and the phase is called the ferroelectric nematic (NF) phase. Very recently a new nematic phase was discovered having remarkable properties, and it has been suggested that this is the long sought after NF phase. This has the potential to be a hugely significant discovery from both fundamental and technological viewpoints. The polar ordering in the NF phase makes it vastly more sensitive to an electric field than the conventional N phase, and this will dramatically improve the performance of liquid crystal display devices in terms of both speed and power consumption. In addition, the study of this new phase has the potential of generating transformative new fundamental chemistry, physics and biology. For example, it was predicted over forty years ago that the NF phase, in order to reduce electrostatic energy, will twist giving a polar cholesteric phase, the spontaneous chirality being controlled through steric and electrostatic interactions between achiral molecules. Such an observation could have huge significance in understanding the origins of chirality. It has been proposed that on cooling the conventional N phase into the NF phase, the molecular dipoles will align spontaneously in a single direction. At this point there is a strong tendency towards crystallisation. If this can be suppressed, however, equal numbers of domains having opposite polarisations should form, separated by domain walls. The application of an electric field will remove this degeneracy and domains having favourable polarity will grow and unfavourable will shrink. The aim of this programme is to begin to understand what molecular features are required to observe the NF phase. Some time ago computer simulations suggested that an asymmetric or tapered shape combined with a longitudinal dipole moment promote polar order, and the very early experimental data available support this view. To achieve our aim, we will need to enhance our understanding of how to manipulate liquid crystallinity though molecular electrostatic and steric interactions. This programme has the very real potential to deliver materials that will lead to transformative new fundamental chemistry, physics and biology, and new technologies including the next generation of display devices.