Self-Assembly of Twisted Monolayer Cholesteric Films via Surface Tension Local Anisotropy
Abstract
Colorful, cholesteric patterns are ubiquitous in the bodies of insects and fishes. Bioinspired materials may be employed in smart coatings for optical communication, signaling, and camouflage. However, due to the fundamental challenges associated with such applications, the development of adaptive monolayers with continuous, hierarchical nanoscale and micrometer-scale structures, as found in nature, and design simplicity has not been fully explored. We show that controlling the local anisotropy of surface tension during the self-assembly of a twisted cholesteric oligomer can lead to the appearance of distinct coexisting colors in monolayer films. The reflection wavelength, which is proportional to the helical pitch, is tuned by forming transparent, surface-active films on the free side of a cholesteric film with a pitch gradient. Reflective colors are related to the internal nanoscale structure, as demonstrated by transmission electron microscopy. Open and self-sustaining bicolor tags are created. The surface design of these films allows the manipulation of their bulk chiral self-organization on a variety of substrates. Smart, reflective multicolor tags, including self-guiding systems for autonomous vehicles, functional facades, camouflage skins for robots, and anticounterfeiting labels, are the intended application.
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