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Title: Tunable nano-wrinkling of chiral surfaces: Structure and diffraction optics

Periodic surface nano-wrinkling is found throughout biological liquid crystalline materials, such as collagen films, spider silk gland ducts, exoskeleton of beetles, and flower petals. These surface ultrastructures are responsible for structural colors observed in some beetles and plants that can dynamically respond to external conditions, such as humidity and temperature. In this paper, the formation of the surface undulations is investigated through the interaction of anisotropic interfacial tension, swelling through hydration, and capillarity at free surfaces. Focusing on the cellulosic cholesteric liquid crystal (CCLC) material model, the generalized shape equation for anisotropic interfaces using the Cahn-Hoffman capillarity vector and the Rapini-Papoular anchoring energy are applied to analyze periodic nano-wrinkling in plant-based plywood free surfaces with water-induced cholesteric pitch gradients. Scaling is used to derive the explicit relations between the undulations’ amplitude expressed as a function of the anchoring strength and the spatially varying pitch. The optical responses of the periodic nano-structured surfaces are studied through finite difference time domain simulations indicating that CCLC surfaces with spatially varying pitch reflect light in a wavelength higher than that of a CCLC’s surface with constant pitch. This structural color change is controlled by the pitch gradient through hydration. All these findings provide amore » foundation to understand structural color phenomena in nature and for the design of optical sensor devices.« less
Authors:
;  [1] ;  [2]
  1. Department of Chemical Engineering, McGill University, 3610 University Street, Montreal, Quebec H3A 2B2 (Canada)
  2. Department of Mechanical Engineering, McGill University, 817 Sherbrook West, Montreal, Quebec H3A 0C3 (Canada)
Publication Date:
OSTI Identifier:
22489619
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 143; Journal Issue: 11; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 77 NANOSCIENCE AND NANOTECHNOLOGY; ANISOTROPY; CHIRALITY; COLLAGEN; DIFFRACTION; EXOSKELETON; GLANDS; HYDRATION; INTERACTIONS; LIQUID CRYSTALS; NANOSTRUCTURES; SENSORS; SIMULATION; SURFACE TENSION; SURFACES; WAVELENGTHS