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

• DOI: 10.1038/s42004-019-0202-8
• Publication Date: 2019-08-29T10:04:46Z
• Authors: Stephanie L. Burg; Adam Washington; David M. Coles; Antonino Bianco; Daragh McLoughlin; Oleksandr O. Mykh...; Julie Villanova; Andrew J. C. Denn...; Christopher J. Hill; Pete Vukusic; Scott Doak; Simon J. Martin; Mark Hutchings; Steven R. Parnell; Cvetelin Vasilev; Nigel Clarke; Anthony J. Ryan; Will Furnass; Mike Croucher; Robert M. Dalgliesh; Sylvain Prevost; Rajeev Dattani; Andrew Parker; Richard A. L. Jones; J. Patrick A. Fai...; Andrew J. Parnell
• Keywords: 600; 02 engineering and technology; 540; 0210 nano-technology

AbstractCyphochilus 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.