Quantifying and manipulating chirality and amplification of nanomaterials in liquid crystals

手性，最简单的描述是没有镜像对称，在自然界中随处可见，甚至可能在宇宙中。手性一词由开尔文勋爵于1894年提出，并由巴斯德等人大力推进。手性在化学、生物学、物理学、宇宙学和材料科学等领域都具有重要意义。被Wagniere描述为“普遍不对称”的同手性生命的起源是最核心的科学问题之一。手性的扩增支撑了大多数描述自然的同手性的理论，即只使用糖和氨基酸的一种对映体（单手性）来构建从简单到复杂的所有生命形式。这个项目由美国国家科学基金会的固态和材料化学项目以及凝聚态物理项目支持，它推进了最近的发现，即手性来自于被单层手性分子覆盖的纳米级颗粒，在液晶中比有机分子手性对应物产生更强烈的反应。与手性一样普遍存在于自然界的液晶态，在这里作为一个强大的测试平台，可以建立控制手性通过空间放大的尺寸-性质和形状-性质关系。肯特州立大学的这项研究产生的数据促进了对纳米级手性的理解，并为纳米级材料作为手性传感器、可调手性超材料和手性催化剂的新应用铺平了道路。学生体验多学科的训练环境，利用最先进的设备，并成为在展示他们的研究同行精通。该项目作为几个拓展活动的平台，包括高中学生的培训，社区大学生的动手讲座和实验室研究，以及科学研讨会。只有当人们能够通过空间和长度尺度检测、测量、可视化、调节和转移纳米材料的手性时，才有可能在理解和应用纳米材料的独特特征方面取得重大进展。为了研究这一点，无处不在的液晶状态为纳米材料手性的基础理论和应用实验研究提供了无与伦比的机会，允许在不同长度尺度上进行手性放大的可视化和量化。一系列成像技术，如偏振光学显微镜，荧光共聚焦显微镜和透射电子显微镜被用来研究这些系统。在赝标量手性指数的第一性原理理论计算的指导下，本实验还确定了纳米尺度上的手性放大如何取决于纳米材料的类型、尺寸、形状和纵横比。该团队在向列液晶中合成、表征和研究了手性配体外壳装饰的手性配体覆盖的金属纳米棒、纳米圆盘、纳米星形、纳米三角形和纳米笼，并将螺旋扭曲力的实验数据与计算的手性指数的理论值进行了比较。为了测试如何应用手性放大，我们创建了类似于节肢动物或复眼的手性向列微透镜阵列，并使用磁场与分散在向列液晶相中的手性分子覆盖的磁性纳米颗粒相结合。后者试图了解液晶宿主和分散的磁性纳米颗粒的相互竞争的弹性和磁力如何分别转化为运动。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。

NON-TECHNICAL SUMMARYChirality, most simply described by the absence of mirror symmetry, can be found everywhere in nature and probably in the universe. Established as a term by Lord Kelvin in 1894, and significantly advanced by Pasteur and others, chirality has significant implications in Chemistry, Biology, Physics, Cosmology, and Materials Science alike. Described as "universal asymmetry" by Wagniere, the origin of homochirality of life is one of the most central scientific questions. Amplification of chirality underpins most theories proposed to describe nature's homochirality, i.e. the use of exclusively one enantiomer (one handedness) of sugars and amino acids to build all life forms, from simple to complex. This project, supported by the Solid State and Materials Chemistry program as well as the Condensed Matter Physics program at NSF, advances recent findings that chirality emanating from nanoscale particles capped with a monolayer of chiral molecules is uniquely able to generate more intense responses in liquid crystals than their organic molecular chiral counterparts. The liquid crystalline state, pervasive in nature just like chirality, here serves as a powerful test platform to establish size-property and shape-property relationships governing the amplification of chirality through space. This research at Kent State University generates data that advance the understanding of nanoscale chirality and paves the way for new applications of nanoscale materials as chirality sensors, tunable chiral metamaterials, and chiral catalysts. Students experience a multidisciplinary training environment, utilize state-of-the-art equipment, and become proficient in presenting their research to peers. The project serves as a platform for several outreach activities including training of high school students, hands-on lectures and lab research for community college students, and a scientific symposium.TECHNICAL SUMMARYSignificant advances in the understanding and application of the unique features of nanomaterial chirality are only possible if one can detect, measure, visualize, tune, and transfer nanomaterial chirality through space and across length scales. To study this, the ubiquitous liquid crystalline state offers unrivaled opportunities for both fundamental theoretical and applied experimental research on nanomaterial chirality, by permitting the visualization as well as quantification of chirality amplification at different length scales. A range of imaging techniques such as polarized optical microscopy, fluorescence confocal microscopy, and transmission electron microcopy are used to study these systems. Guided by first principle theoretical calculations of a pseudoscalar chirality index, this experimental work also establishes how chirality amplification at the nanoscale depends on the nanomaterial type, size, shape, and aspect ratio. The team synthesizes, characterizes, and studies chiral ligand-capped metal nanorods, nanodiscs, nanostars, nanotriangles, and nanocages decorated with chiral ligand shells in nematic liquid crystals, and compares experimental data of the helical twisting power to theoretical values of the calculated chirality index. To test how chirality amplification can be applied, chiral nematic microlens arrays similar to arthropod or compound eyes are created, and the use of magnetic fields in combination with anisometric chiral molecule-capped magnetic nanoparticles dispersed in nematic liquid crystal phases examined. The latter seeks to understand how competing elastic and magnetic forces of liquid crystal host and dispersed magnetic nanoparticles, respectively, can be translated into motion.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.