Liquid Crystal Surfaces and Symmetry

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TECHNICAL SUMMARY Chirality at a surface can have important consequences on a wide variety of properties near an interface, and even in the bulk via long range dispersive/elastic interactions. This is especially true of liquid crystals (LCs). Based on Rosenblatt's recent development of techniques both to image LC orientation on nanoscopic length scales and to create controlled chirality at surfaces using inherently achiral alignment materials, he proposes to examine LC phenomena in which chirality is localized near a surface - and whose "strength" is even forced to vary spatially along the surface. The proposed work supported by the Condensed Matter Physics and Solid State and Materials Chemistry Programs in the Division of Materials Research has several objectives interconnected by the common theme of chirality localized to an interface and its effect on LCs. Among the issues to be addressed are: how chirality affects the anchoring of a LC at a substrate, especially the appearance of odd order (linear, cubic, etc.) terms in the surface free energy expansion of the interaction potential; how a chiral alignment layer induces enantiomeric resolution in a racemic LC mixture near the interface and the spatial extent over which this segregation occurs; how and to what extent a chiral alignment layer (of variable thickness) transmits its chirality into an otherwise achiral LC; and the effects of chiral colloidal inclusions on the bulk chiral properties of the LC. By exploiting the PI's ability to create chiral substrates of controlled strength from achiral materials and his ability to image LC orientation on volumetric scales 1/1000th that of confocal microscopy, this work will transform our conceptions about, and methodology toward, surface chirality and its effects on anisotropic fluids. To accomplish the proposed goals, the PI, his students, and postdocs will utilize a wide battery of experimental tools, including (but not limited to) traditional optical microscopy and optical nanotomography, atomic force microscopy, ellipsometry, photolithography, and a variety of electrooptic techniques.NON-TECHNICAL SUMMARYChirality is the absence of mirror symmetry, i.e., the inability to superimpose an object onto its mirror image by rotation and translation. One's hands - left and right - are chiral, as they are mirror images of each other; this is the origin of the term "chiral handedness". Chirality plays a central role in both large scale and small scale systems. On large scales, technologies such as the mechanical screw date back to antiquity. On microscopic and nanoscopic scales, chirality plays a central role in physics, chemistry, biology, and medicine, and is crucial for the existence of life (e.g., DNA is chiral). Although chirality most often is thought of as 3D, it also can exist at a surface as a quasi-two-dimensional phenomenon: For example, think of a multi-turn or multi-arm spiral. In this work, supported by the Condensed Matter Physics and Solid State and Materials Chemistry Programs, Rosenblatt will mechanically create chiral patterns on surfaces on nanoscopic length scales, and will use liquid crystals (LCs) to explore how one can control the "strength" of the chirality, how the chirality is transmitted into nonchiral molecules, how to separate molecules (especially pharmaceuticals) of opposite "handedness", and to discover new and useful electrooptic phenomena that can be deduced from chirality confined to a narrow region near a surface. Student training is an essential component of the proposal. The PI's students - postdocs, graduate, undergraduate, and high school students - work in teams, and will see their results incorporated into courses at both the undergraduate and graduate levels. Moreover, they will interact with the PI's international partners the Universitá della Calabria (Italy), Université Pierre et Marie Curie (France), and Nagaoka University of Technology (Japan), with a concomitant enhancement of our technological infrastructure: The students will eventually join the PI's former students and postdocs who now are actively employed in the R&D field at laboratories such as IBM, Motorola, Teledyne, Intel, and Apple Computer, and are faculty members at universities in the U.S. and around the world.