title: Revealing Invisible Photonic Inscriptions: Images from Strain.
abstract: Photonic structural materials have received intensive interest and have been strongly developed over the past few years for image displays, sensing, and anticounterfeit materials. Their "smartness" arises from their color responsivity to changes of environment, strain, or external fields. Here, we introduce a novel invisible photonic system that reveals encrypted images or characters by simply stretching, or immersing in solvents. This type of intriguing photonic material is composed of regularly arranged core-shell particles that are selectively cross-linked by UV irradiation, giving different strain response compared to un-cross-linked regions. The images reversibly appear and disappear when cycling the strain and releasing it. The unique advantages of this soft polymer opal system compared with other types of photonic gels are that it can be produced in roll to roll quantities, can be vigorously deformed to achieve strong color changes, and has no solvent evaporation issues because it is a photonic rubber system. We demonstrate potential applications together with a fabrication procedure which is straightforward and scalable, vital for user take-up. Our work deepens understanding of this rubbery photonic system based on core-shell nanospheres.
authors.affiliation: †Nanophotonics Centre, Cavendish Laboratory, University of Cambridge, CB3 0HE Cambridge, United Kingdom.|‡Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, CB3 0FS Cambridge, United Kingdom.
authors.forename: Tao
authors.initials: T
authors.lastname: Ding
authors.affiliation: §Hushes Hall College, University of Cambridge, Wollaston Road, CB1 2EW Cambridge, United Kingdom.
authors.forename: Guoshuai
authors.initials: G
authors.lastname: Cao
authors.affiliation: ∥Ernst-Berl Institut für Technische und Makromolekulare Chemie, Technische Universität Darmstadt, Alarich-Weiss-Straβe 4, 64287 Darmstadt, Germany.
authors.forename: Christian G
authors.initials: CG
authors.lastname: Schäfer
authors.affiliation: †Nanophotonics Centre, Cavendish Laboratory, University of Cambridge, CB3 0HE Cambridge, United Kingdom.
authors.forename: Qibin
authors.initials: Q
authors.lastname: Zhao
authors.affiliation: ∥Ernst-Berl Institut für Technische und Makromolekulare Chemie, Technische Universität Darmstadt, Alarich-Weiss-Straβe 4, 64287 Darmstadt, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Gallei
authors.affiliation: ‡Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, CB3 0FS Cambridge, United Kingdom.
authors.forename: Stoyan K
authors.initials: SK
authors.lastname: Smoukov
authors.affiliation: †Nanophotonics Centre, Cavendish Laboratory, University of Cambridge, CB3 0HE Cambridge, United Kingdom.
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Baumberg
keywords: patterns; photonic crystals; strains; structural colors; tunable