Chirality, 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.
Significant 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.