Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 11, Issue 48, Pages 45256-45264Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.9b18995
Keywords
photonic crystal; soaking-revealed; invisible pattern; macroporous; polyurethane
Funding
- National Natural Science Foundation of China [21671067, 21972046]
- Shuguang Program - Shanghai Education Development Foundation [15SG21]
- Shanghai Municipal Education Commission
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Invisible photonic crystal (PC) pattern with encrypted and discoverable information is potentially useful for anti-counterfeiting labels, but it is still a big challenge to realize strict invisibility, fast response, and convenient triggering. Here, a new kind of soaking-revealed invisible PC pattern is fabricated by the regional coating of ethylene glycol-ethanol ink on a collapsed inverse opaline macroporous polyurethane (IOM-PU) film, followed by a quick thermal treatment. During the above process, wet heating retains the collapsed but recoverable IOM structure, but dry heating disables the recovery of ordered IOM structure due to the adhesion of macropore walls, which render the pattern and the background with different optical responses to the solvent. In the dry state, the pattern was invisible because both the collapsed IOM-PU film and the adhesive PU film are colorless and transparent. Once the sample is soaked in ethanol-water mixtures, the invisible pattern appears immediately because only the wet-heated region recovers the ordered macroporous structure and shows color, which forms a significant contrast in color to the dry-heated region. Compared to the previously invisible PC pattern, the current material has many superior properties, such as high invisibility, large color contrast in showing, excellent recyclability, and good toughness in bending and stretching.
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