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

这项国际合作由英国赫尔大学和肯特州立大学的科学家组成，他们拥有互补的专业知识，重点是理解与双轴性有关的现象——在所谓的液晶（lc）的向列相中自发出现的两个不同的光轴。虽然双轴向列图是在38年前提出的假设，但直到最近，双轴向列图在实际材料中被证明是相当难以捉摸的——事实上，几乎所有的向列图都是光单轴的，几乎所有的lc应用都局限于对单个光轴的操纵。双轴向列相在由本质上是双轴形状的分子（或分子聚集体）组成的lc中是预期的，例如，板状或弯曲核（香蕉形）分子。形成双轴向列的另一种重要可能性出现在盘状和棒状分子的混合物中，这已经成为了几项激烈理论研究的主题。根据这些成分分子的纵横比和浓度，我们可以期待三个向列相，两个单轴和一个双轴，具有相图的特定拓扑和相变性质的有趣演变。英国首席研究员Georg Mehl教授和他的团队率先合成了兼容的棒状和圆盘状系统，这些系统形成稳定的溶液，并表现出明显的向列相（可能包括双轴相）。美国研究人员将在具有双轴形分子和棒盘混合物的系统中，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。在这个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LC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采用最先进的技术，如动态光散射、同步加速器x射线衍射、共聚焦和原子力显微镜以及光电测量。该项目的成果可能会通过新显示技术的出现和光学双轴流体的其他应用对行业产生变革性影响。本科生、研究生和博士后将在具有影响光子学、电信和网络基础设施领域潜力的领域进行培训。初级研究人员将有机会与先进光子源的英国研究小组成员和其他国际学者进行互动和建立长期的专业联系。美国研究生和博士后将能够多样化他们的技能和科学经验，并以对材料开发和物理特性的深刻理解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.