Materials by design: Using architecture in material design to reach new property spaces
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Introduction Materials with architected microstructures, such as butterfly wings and diatoms, are often found in nature. Structures on multiple length scales allow for a variety of novel nanoscale properties to propagate on to macroscopic structures. For example, the nanoscale architecture of a butterfly wing interacts with light to create iridescent, colorful wings, and smallscale ceramic building blocks are the key behind the unique material properties of nacre.1 Materials scientists and engineers have utilized the idea of architecture and hierarchy to create different kinds of novel metamaterials, taking inspiration from nature. Architecture, here referred to an arrangement of beam elements into a three-dimensional (3D) structure such as a truss or lattice, has been used for many years to improve the efficiency of large engineered structures. Consider the Great Pyramid of Giza and the Eiffel Tower, two structures with vastly different architectures. The Great Pyramid is analogous to common bulk engineering materials, whereas the Eiffel Tower is analogous to a structural metamaterial, in which the lattice-based architecture spans length scales down to the material microstructure, which determines its strength. Structural metamaterials gain unique mechanical properties
from the hierarchical ordering of length scales within the material, from the microstructure of the constituent material to large-scale structural ordering. As the external dimensions of materials are reduced to the nanoscale, their mechanical behavior changes.14 These structural metamaterials have unique properties that stem from the linked behavior of the constituent material and the structure at small dimensions, rather than from either one independently. Three-dimensional architecture and periodicity on the nano- and microscales allow novel control over properties such as the propagation of photons, phonons, and electrons through the structure. Photonic crystals (PhCs) are architected materials composed of repeating structural units with varying indices of refraction that selectively reflect light of wavelengths commensurate with their periodicity. PhCs underlie many striking coloration effects seen in natural systems. The iridescent colors found in opals, beetle scales, peacock feathers, and even the skin of certain cephalopods are the result of periodic geometries that can be as complex as the double gyroid and the kagome lattice or as relatively simple as close-packed spherical particles, cylinders, and lamellae.1,2
Lauren Montemayor, Jet Propulsion Laboratory, USA; [email protected] Victoria Chernow, California Institute of Technology, USA; [email protected] Julia R. Greer, California Institute of Technology, USA; [email protected] DOI: 10.1557/mrs.2015.263
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MRS BULLETIN • VOLUME 40 • DECEMBER 2015 • www.mrs.org/bulletin
© 2015 Materials Research Society
MATERIALS BY DESIGN: USING ARCHITECTURE IN MATERIAL DESIGN TO REACH NEW PROPERTY SPACESS
Similarly, phononic crystals (PnCs) are artificial periodic structures com
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