Bio-inspired, large scale, highly-scattering films for nanoparticle-alternative white surfaces

Creators: Syurik, Julia; Siddique, Radwanul Hasan; Dollmann, Antje; Gomard, Guillaume; Schneider, Marc; Worgull, Matthias; Wiegand, Gabriele; Hölscher, Hendrik

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Abstract

Inspired by the white beetle of the genus Cyphochilus, we fabricate ultra-thin, porous PMMA films by foaming with CO_2 saturation. Optimising pore diameter and fraction in terms of broad-band reflectance results in very thin films with exceptional whiteness. Already films with 60 µm-thick scattering layer feature a whiteness with a reflectance of 90%. Even 9 µm thin scattering layers appear white with a reflectance above 57%. The transport mean free path in the artificial films is between 3.5 µm and 4 µm being close to the evolutionary optimised natural prototype. The bio-inspired white films do not lose their whiteness during further shaping, allowing for various applications.

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© 2017 The Author(s). This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ Received: 19 December 2016. Accepted: 21 March 2017. Published online: 21 April 2017. It is a pleasure to thank Siegbert Johnsen for support in saturation experiments, Donie Yidenekachew for his support with the simulations, Paul Abaffy for the recording of the SEM images and Richard Thelen for support in the lab. Furthermore, we acknowledge many helpful discussions with Silvia Vignolini (University of Cambridge). J.S. and G.G. gratefully acknowledge funding from the Helmholtz Postdoc Programme. This work was partly carried out with the support of the Karlsruhe Nano Micro Facility (KNMF, www.kit.edu/knmf), a Helmholtz Research Infrastructure at Karlsruhe Institute of Technology (KIT, www.kit.edu). We acknowledge support by Deutsche Forschungsgemeinschaft and Open Access Publishing Fund of Karlsruhe Institute of Technology. Author Contributions: J.S., R.H.S. and H.H. designed the study. J.S. and A.D. prepared the samples. A.D. analysed the morphology of the samples. G.W. and J.S. discussed process-structure relationships for the obtained films. A.D. and R.H.S. performed and analysed optical spectroscopy. G.G. performed and analysed angular distribution of transmitted light in the samples. R.H.S. conducted the optical simulation. J.S., R.H.S., G.G. and H.H. discussed the optical properties of the films and optical simulation. J.S., M.S. and M.W. discussed the thermomolding of the films. J.S., R.H.S., G.G. and H.H. wrote the manuscript. All authors agreed on the manuscript. The authors declare no competing financial interests.

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