Stephanie Burg, University of  Sheffield - Liquid-liquid phase separation morphologies in ultra-white beetle scales and a synthetic equivalent

Presentation - pdf

Stephanie L. Burg, Adam Washington, David M. Coles, Antonino Bianco, Daragh McLoughlin, Oleksandr O. Mykhaylyk, Julie Villanova, Andrew J. C. Dennison, 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 Dalgliesh, Sylvain Prevost, Rajeev Dattani, Andrew Parker, Richard A. L. Jones, J. Patrick A. Fairclough, Andrew J. Parnell

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.


From  Georgina Zimbitas : I was wondering wether you could suspend your films/scales in resin and allow to harden, FIB cut the resin and then examine (e.g. via SEM)? The resin might compress the material, but you could determine the degree of that and extrapolate.

Answer: So, anytime as soon as you cut the scale, that is it… that will giving fractions that were double what we measured with tomography. As far as I know, you have to measure them intact.

From  Georgina Zimbitas : I meant keep the scales intact - resin on the outside and then cut.
Answer: I don’t think it would support the inner structure, that would give support to the outer structure. The fibres are not very connected, and just touching the top and bottom and you support the outside and cut it you will still get some distortion.

From  Simon Gibbon : Where you saw the round fibres like structures (Cyphochilus), versus the non-fibrillar (L stigma) does this suggest a different mechanisms of formation (different evolutionary biology)?  Or do you know the physical parameters which control the difference in the same spinodal decomposition?
Answer: This is a good question and if you run a spinodal simulation under flow, meaning that there is a direction of liquid flow in one direction you can actually elongate and create a stretch spinodal structure and if you remember from the way the beetles was, that could create this structure but that is another piece of work.