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Structure and optical function of amorphous photonic nanostructures from avian feather barbs: a comparative small angle X-ray scattering (SAXS) analysis of 230 bird species

DOI: 10.1098/rsif.2012.0191 DOI Help

Authors: Vinod Kumar Saranathan (University of Oxford) , Jason Forster (Center for Research on Interface Structures and Phenomena (CRISP), Yale University) , Heeso Noh (Center for Research on Interface Structures and Phenomena (CRISP), Yale University) , Seng-Fatt Liew (Center for Research on Interface Structures and Phenomena (CRISP), Yale University) , Simon Mochrie (Center for Research on Interface Structures and Phenomena (CRISP), Yale University) , Hui Cao (Center for Research on Interface Structures and Phenomena (CRISP), Yale University) , Eric Dufresne (Center for Research on Interface Structures and Phenomena (CRISP), Yale University) , Richard Prum (Center for Research on Interface Structures and Phenomena (CRISP), Yale University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The Royal Society Interface , VOL 9 (75) , PAGES 11101-11106

State: Published (Approved)
Published: August 2012
Diamond Proposal Number(s): 6905

Abstract: Non-iridescent structural colours of feathers are a diverse and an important part of the phenotype of many birds. These colours are generally produced by three-dimensional, amorphous (or quasi-ordered) spongy β-keratin and air nanostructures found in the medullary cells of feather barbs. Two main classes of three-dimensional barb nanostructures are known, characterized by a tortuous network of air channels or a close packing of spheroidal air cavities. Using synchrotron small angle X-ray scattering (SAXS) and optical spectrophotometry, we characterized the nanostructure and optical function of 297 distinctly coloured feathers from 230 species belonging to 163 genera in 51 avian families. The SAXS data provided quantitative diagnoses of the channel- and sphere-type nanostructures, and confirmed the presence of a predominant, isotropic length scale of variation in refractive index that produces strong reinforcement of a narrow band of scattered wavelengths. The SAXS structural data identified a new class of rudimentary or weakly nanostructured feathers responsible for slate-grey, and blue-grey structural colours. SAXS structural data provided good predictions of the single-scattering peak of the optical reflectance of the feathers. The SAXS structural measurements of channel- and sphere-type nanostructures are also similar to experimental scattering data from synthetic soft matter systems that self-assemble by phase separation. These results further support the hypothesis that colour-producing protein and air nanostructures in feather barbs are probably self-assembled by arrested phase separation of polymerizing β-keratin from the cytoplasm of medullary cells. Such avian amorphous photonic nanostructures with isotropic optical properties may provide biomimetic inspiration for photonic technology

Subject Areas: Chemistry


Instruments: I22-Small angle scattering & Diffraction

Other Facilities: Advanced Photon Source

Added On: 11/01/2013 09:01

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