Ferroelectricity and the nematic liquid crystal phase

向列相(N)是最无序的液晶相，其中棒状分子的长轴或多或少沿同一方向排列，称为指向矢，而它们的质量中心是随机分布的。这个阶段很容易复制，只需往盒子里扔一把火柴，然后摇晃它。如果有足够的匹配，那么，出于打包的原因，它们都将在同一方向上排成一排，实际上你有一个向列相。假设火柴是随机扔进盒子里的，那么将有相同数量的火柴指向一个方向和另一个方向。这正是传统向列相的情况，分子同样有可能沿着指向矢指向任何一个方向，并且相被描述为非极性的。传统的N阶段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，首次有人提出可能存在一个向列相，在这个相中，所有的分子都可以沿同一方向排列。这相当于从分子上把火柴扔进盒子里，摇动它，然后发现所有的火柴现在都是头朝同一个方向。这被称为极性有序，该相被称为铁电向列相(NF)。最近，一种新的向列相被发现，它具有显著的性质，有人认为这是长期追求的纳米相。从根本和技术角度来看，这都有可能成为一项意义重大的发现。与传统的N相相比，NF相中的极性有序使其对电场的敏感性大大提高，这将显著提高液晶显示器件的速度和功耗性能。此外，对这一新阶段的研究有可能产生革命性的新的基础化学、物理和生物学。例如，40多年前就有人预测，为了减少静电能量，NF相将发生扭曲，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。这样的观察对于理解手性的起源可能具有巨大的意义。有人提出，当将传统的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，有一种强烈的结晶倾向。然而，如果这可以被抑制，那么应该形成相同数量的具有相反极化的磁区，由磁区壁分隔。施加电场将消除这种简并性，具有有利极性的磁区将增长，而不利的磁区将缩小。该计划的目的是开始了解观察核因子阶段所需的分子特征。一段时间以前，计算机模拟表明，不对称或锥形形状与纵向偶极矩相结合，促进了极秩序，可获得的非常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晶性的理解。该计划具有非常实际的潜力，可以提供将导致变革性的新的基础化学、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.