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Liquid–liquid phase separation morphologies in ultra-white beetle scales and a synthetic equivalent

Journal Article (2019)
Author(s)

Stephanie L. Burg (University of Sheffield)

Adam Washington (ISIS Neutron and Muon Source, University of Sheffield)

David M. Coles (University of Sheffield)

Antonino Bianco (University of Sheffield)

Daragh McLoughlin (AkzoNobel/International Paint Ltd)

Oleksandr O. Mykhaylyk (University of Sheffield)

Julie Villanova (European Synchrotron Radiation Facility)

Andrew J.C. Dennison (University of Sheffield)

Steven R. Parnell (TU Delft - RID/TS/Instrumenten groep)

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Research Group
RID/TS/Instrumenten groep
DOI related publication
https://doi.org/10.1038/s42004-019-0202-8 Final published version
More Info
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Publication Year
2019
Language
English
Research Group
RID/TS/Instrumenten groep
Journal title
Communications Chemistry
Issue number
1
Volume number
2
Article number
100
Downloads counter
286
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Institutional Repository
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Abstract

Cyphochilus beetle scales are amongst the brightest structural whites in nature, being highly opacifying whilst extremely thin. However, the formation mechanism for the voided intra-scale structure is unknown. Here we report 3D x-ray nanotomography data for the voided chitin networks of intact white scales of Cyphochilus and Lepidiota stigma. Chitin-filling fractions are found to be 31 ± 2% for Cyphochilus and 34 ± 1% for Lepidiota stigma, indicating previous measurements overestimated their density. Optical simulations using finite-difference time domain for the chitin morphologies and simulated Cahn-Hilliard spinodal structures show excellent agreement. Reflectance curves spanning filling fraction of 5-95% for simulated spinodal structures, pinpoint optimal whiteness for 25% chitin filling. We make a simulacrum from a polymer undergoing a strong solvent quench, resulting in highly reflective (~94%) white films. In-situ X-ray scattering confirms the nanostructure is formed through spinodal decomposition phase separation. We conclude that the ultra-white beetle scale nanostructure is made via liquid–liquid phase separation.