Materials World Network: Structure, Dynamics and Critical Phenomena in Biaxial Liquid Crystals

英国赫尔大学和肯特州立大学的科学家开展了这项具有互补专业知识的国际合作，重点是了解与双轴性相关的现象，双轴性是指两个不同的光轴自发出现在所谓的液晶向列相(LCS)中。尽管大约38年前提出了假设，但直到最近，双轴向列相在真实材料中一直被证明是相当难以捉摸的--事实上，几乎所有向列相都是光学单轴的，并且LCS的几乎所有应用都被限制在操纵单个光轴上。在由本质上是双轴形状的分子(或分子聚集体)组成的LCS中，预期会出现双轴向列相，例如板状或弯曲芯(香蕉形)分子。另一种形成双轴向列相的重要可能性出现在盘状和棒状分子的混合物中，这是几个密集的理论研究的主题。根据这些组分分子的长径比和浓度的不同，人们可以预期三个向列相，两个单轴和一个双轴，具有特定的相图拓扑和有趣的相变性质的演变。英国首席研究员Georg Mehl教授和他的团队率先合成了相容的棒状和盘状系统，这些系统形成了稳定的溶液，并显示出明显的向列相(可能包括双轴相)。美国研究人员将探索不同向列相之间几个有趣的相变的结构、光学和其他物理性质、动力学和临界行为，无论是在具有双轴形分子的系统中，还是在棒-盘混合系统中都是如此。在该项目下获得的结果和数据将有助于测试当前理论的有效性，并为新型液晶材料的物理和化学提供重要的见解。研究人员将在他们的研究中使用最先进的技术，如动态光散射、同步X射线衍射、共焦显微镜和原子力显微镜，以及光电测量。该项目的结果可能会通过一种新的显示技术的出现和光学双轴流体的其他应用对该行业产生革命性的影响。本科生、研究生和博士后将在一个可能影响光子学、电信和网络基础设施领域的领域接受培训。初级研究人员将有机会与研究小组在英国的成员和高级光子源的其他国际学者进行互动并建立长期的专业联系。美国研究生和博士后将能够使他们的技能和科学经验多样化，并在深刻理解材料开发和物理表征的基础上开始他们的职业生涯。

This international collaboration, between scientists at the University of Hull, UK and Kent State University having complementary expertise, focuses on understanding phenomena associated with biaxiality - the spontaneous occurrence of two distinct optical axes - in the so-called nematic phase of liquid crystals (LCs). Although it was hypothesized about 38 years ago, biaxial nematics have, until recently, proven quite elusive in real materials - indeed, virtually all nematics are optically uniaxial and virtually all applications of LCs have been restricted to the manipulation of a single optical axis. The biaxial nematic phase is expected in LCs composed of molecules (or, molecular aggregates) that are intrinsically biaxial in shape, e.g., plank-like or bent-core (banana-shaped) molecules. Another important possibility for formation of a biaxial nematic, which has been the subject of several intense theoretical investigations, arises in mixtures of disk- and rod-shaped molecules. Depending on the aspect ratios of these component molecules and on the concentration, one can expect three nematic phases, two uniaxial and one biaxial, with a specific topology of the phase diagram and interesting evolution of the nature of phase transitions. The principal investigator in the UK, Professor Georg Mehl, and his team have pioneered the synthesis of compatible rod- and disk-like systems, which form stable solutions and exhibit distinct nematic phases (possibly including a biaxial phase). The US researchers will probe the structure, optical, and other physical properties, the dynamics, and critical behavior at several interesting phase transitions between different nematic phases, both in systems with biaxial-shaped molecules and in rod-disc mixtures.The results and the data acquired under this project will help test the validity of the current theories and provide important insight into the physics and chemistry of novel LC materials. The researchers will employ state-of-the-art techniques such as dynamic light scattering, synchrotron x-ray diffraction, confocal and atomic force microscopies, and electro-optical measurements in their investigations. The results of this project are likely to have transformative impact on the industry via the emergence of a new display technology and other applications of optically biaxial fluids. Undergraduate and graduate students and postdocs will be trained in an area that has the potential of impacting the fields of photonics, telecommunications, and cyber infrastructure. Junior researchers will have opportunities to interact and forge long-term professional contacts with members of the research group in the UK and other international scholars at the Advanced Photon Source. US graduate students and postdocs will be able to diversify their skills and scientific experience and begin their careers with a profound appreciation for materials development as well as physical characterization.