Many physical phenomena create colour: spectrally selective light absorption by pigments and dyes1,2, material-specific optical dispersion3 and light interference4,5,6,7,8,9,10,11 in micrometre-scale and nanometre-scale periodic structures12,13,14,15,16,17. In addition, scattering, diffraction and interference mechanisms are inherent to spherical droplets18, which contribute to atmospheric phenomena such as glories, coronas and rainbows19. Here we describe a previously unrecognized mechanism for creating iridescent structural colour with large angular spectral separation. Light travelling along different trajectories of total internal reflection at a concave optical interface can interfere to generate brilliant patterns of colour. The effect is generated at interfaces with dimensions that are orders of magnitude larger than the wavelength of visible light and is readily observed in systems as simple as water drops condensed on a transparent substrate. We also exploit this phenomenon in complex systems, including multiphase droplets, three-dimensional patterned polymer surfaces and solid microparticles, to create patterns of iridescent colour that are consistent with theoretical predictions. Such controllable structural colouration is straightforward to generate at microscale interfaces, so we expect that the design principles and predictive theory outlined here will be of interest both for fundamental exploration in optics and for application in functional colloidal inks and paints, displays and sensors.
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All relevant data generated or analysed for this study are included in this published article (and its Supplementary Information files).
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L.D.Z., A.E.G., C.H.M., A.P.S. and S.C. acknowledge support from the Department of Materials Science and Engineering, the Department of Chemistry, and the Materials Research Institute at The Pennsylvania State University. S.N. and M.K. were supported in part by the US Army Research Office through the Institute for Soldier Nanotechnologies at MIT, under contract number W911NF-13-D-0001. A.E.G., S.N., M.K. and L.D.Z. acknowledge support by the National Science Foundation’s CBET programme on “Particulate and Multiphase Processes” under grant numbers 1804241 and 1804092. C.H.M. acknowledges support from the Thomas and June Beaver Fellowship and A.P.S. received support from the Office of Science Engagement at The Pennsylvania State University. Sandia National Laboratories is a multimission laboratory managed and operated by the National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc. for the US Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in this paper do not necessarily represent the view of the US Department of Energy or the United States Government.
Nature thanks Kenneth Chau, Lorne Whitehead and the other anonymous reviewer(s) for their contribution to the peer review of this work.