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

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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.