Ferroelectricity and the nematic liquid crystal phase

液晶相（N）是最不有序的液晶相，并且其中棒状分子的长轴或多或少在相同方向上对齐，称为指向矢，而它们的质心随机分布。这个阶段很容易复制，只要把一把火柴扔到盒子里，然后摇晃它，如果有足够的火柴，那么，出于包装的原因，它们都会朝着同一个方向排列，有效地你有一个混合阶段。假设火柴是随机扔到盒子里的，那么将有相同数量的火柴头指向一个方向和另一个方向。这正是常规的双极性相的情况，分子同样可能沿着指向矢指向沿着任一方向，并且该相被描述为非极性的。传统的N相是液晶显示技术的基础，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，可能存在一种所有分子都可以沿同一方向排列的双相。这就相当于把火柴扔进盒子里，摇晃它，发现所有的火柴都指向同一个方向。这被称为极性有序，并且该相被称为铁电体非晶（NF）相。最近发现了一种新的具有显著性能的纳米晶相，并且已经表明这是长期以来一直在寻找的纳米晶相。从基础和技术角度来看，这有可能成为一个非常重要的发现。NF相中的极性有序性使其对电场的敏感性大大高于常规的N相中的极性有序性，这将显著改善液晶显示装置在速度和功耗方面的性能。此外，这一新阶段的研究有可能产生变革性的新基础化学，物理学和生物学。例如，四十多年前就预测，为了减少静电能，NF相将扭曲，产生极性胆甾相，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。这样的观察对于理解手征性的起源有着巨大的意义。有人提出，在将常规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，有强烈的结晶倾向。然而，如果这可以被抑制，则应该形成由畴壁分隔的具有相反偏振的相等数量的畴。电场的应用将消除这种简并性，并且具有有利极性的畴将生长而不利极性的畴将收缩。该计划的目的是开始了解观察NF阶段所需的分子特征。不久前的计算机模拟表明，不对称或锥形的形状与纵向偶极矩相结合，促进了极序，而早期的实验数据支持这一观点。为了实现这一目标，我们需要进一步理解如何通过分子静电和空间位阻相互作用来调控液晶性。该计划具有非常真实的潜力，可以提供将导致变革性的新基础化学，物理学和生物学以及包括下一代显示设备在内的新技术的材料。

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.