NSF/DMR-BSF: Liquid Crystals as a Paradigm for Chirality and Topological Defects

摘要：手性是指物体不能与其镜像重合，其中左手和右手可能是最著名的例子。当系统固有的“特征”（科学上称为“顺序参数”）不能在点、线或面上唯一地描述时，就会出现拓扑缺陷。这两种现象在自然界普遍存在，往往是相互关联的，是科学和技术中心问题的基础。一些例子包括量子光学、半导体二极管和生物材料中的手性——DNA是最著名的；手性转移，即如何在非手性材料中诱导手性；以及多个拓扑缺陷的相互作用。本项目以液晶为范例，重点研究手性和拓扑缺陷。由于液晶的长尺度和新的光学性质，许多相关现象可以可视化和定量测量。这使得我们对手性和拓扑缺陷有了一般的了解，而这是研究其他材料所无法做到的。技术摘要：由于液晶具有较大的光学、电学和磁各向异性，液晶是研究凝聚态及其他多种现象的理想试验台。这项工作的中心主题是利用液晶来探索手性和拓扑缺陷的开创性问题，这些问题可以影响更广泛的科学事业。PI利用他的纳米级技术来创建和图像控制手性和表面缺陷-有时两者结合。项目包括：在生物相关的手性纳米胶囊中进行手性转移，以实现“圣杯”，即测量手性诱导长度；手性多极的产生；手性拓扑缺陷、诱导双轴性和skyrminons；线路缺陷的多稳态“重接线”；用于纳米光子学和半导体的手性自组装单层膜；以及高度复杂的油性和皂状条纹液晶缺陷。PI的团队使用了一系列实验工具，包括光学显微镜、共聚焦荧光显微镜、光学纳米层析成像、原子力显微镜、原子力显微镜、原子力显微镜纳米光刻和椭偏仪。大部分工作是与耶路撒冷希伯来大学的化学家David Avnir教授和他的同事合作完成的。通过利用PI的能力来创建精细定制的纳米级手性和拓扑缺陷易轴模式，并将液晶方向成像到50 x 50 x 2nm的x，y，z尺寸，这项工作正在改变我们对手性，缺陷，两者如何在各向异性流体中耦合以及凝聚态中更广泛问题的概念和方法。特别是，PI的工作正在导致对非手性材料的诱导手性的理解、量化和开发，以及对手性和非手性拓扑缺陷、它们的操作和光学和电子领域的潜在应用的更深入的了解。研究的问题跨越了多个学科，因为手性和缺陷的后果出现在生物学、化学、物理学、医学、药理学和材料科学中。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Abstract:Chirality is the inability of an object to coincide with its mirror image, where the left and right hands are perhaps the best-known example. A topological defect occurs when the system's inherent "character", scientifically called its "order parameter", cannot be described uniquely at a point, line, or surface. Both phenomena are pervasive throughout nature, often are coupled, and are fundamental to central questions in science and technology. A few examples include chirality in quantum optics, semiconductor diodes, and biomaterials - DNA is the best known; chirality transfer, i.e., how chirality can be induced in an otherwise non-chiral materials; and interactions of multiple topological defects. This project focuses on chirality and topological defects using liquid crystals as a paradigm. Because of the long length scales and novel optical properties of liquid crystals, many of the associated phenomena can be visualized and measured quantitatively. This permits a general understanding of chirality and topological defects that would not be possible by studying other materials.Technical Abstract:Owing to their large optical, electrical, and magnetic anisotropies, liquid crystals are an ideal test bed for a multitude of phenomena in condensed matter and beyond. The central theme of this work is to exploit liquid crystals to explore seminal issues of chirality and topological defects that can impact the broader scientific enterprise. The PI utilizes his nanoscale techniques to create and image controlled chirality and defects at surfaces - sometimes in combination. Projects include: chirality transfer in biologically-relevant chiral nanocapsules to achieve the Holy Grail, viz., a measure of the chiral induction length; the creation of chiral multipoles; chiral topological defects, induced biaxiality, and skyrmions; multistable "rewiring" of line defects; chiral self-assembled monolayers for nanophotonics and semiconductors; and highly complex oily and soapy streak liquid crystalline defects. The PI's team employs a battery of experimental tools, including optical microscopy, confocal fluorescence microscopy, optical nanotomography, atomic force microscopy, AFM nanolithography, and ellipsometry. Much of the work is performed in collaboration with chemist Prof. David Avnir and his colleagues at the Hebrew University of Jerusalem. By exploiting the PI's ability to create exquisitely tailored nano-scale chiral and topological defect easy axis patterns, and to image liquid crystal orientation down to x,y,z dimensions of 50 x 50 x 2 nm, this work is transforming our conceptions about - and methodology toward - chirality, defects, how the two can be coupled in anisotropic fluids, and broader issues in condensed matter. In particular, the PI's work is leading to the understanding, quantification, and exploitation of induced chirality in otherwise achiral materials, as well as a deeper knowledge of chiral and achiral topological defects, their manipulation, and potential applications in optics and electronics. The issues studied cut across multiple disciplines, as consequences of chirality and defects appear throughout biology, chemistry, physics, medicine, pharmacology, and materials science.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.