Instantaneous, Simple, and Reversible Revealing of Invisible Patterns Encrypted in Robust Hollow Sphere Colloidal Photonic Crystals,Advanced Materials

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Instantaneous, Simple, and Reversible Revealing of Invisible Patterns Encrypted in Robust Hollow Sphere Colloidal Photonic Crystals
Advanced Materials ( IF 27.4 ) Pub Date : 2018-05-04 , DOI: 10.1002/adma.201707246
Kuo Zhong ₁ , Jiaqi Li ₂ , Liwang Liu ₃ , Stijn Van Cleuvenbergen ₁ , Kai Song ₄ , Koen Clays ₁

Affiliation

The colors of photonic crystals are based on their periodic crystalline structure. They show clear advantages over conventional chromophores for many applications, mainly due to their anti‐photobleaching and responsiveness to stimuli. More specifically, combining colloidal photonic crystals and invisible patterns is important in steganography and watermarking for anticounterfeiting applications. Here a convenient way to imprint robust invisible patterns in colloidal crystals of hollow silica spheres is presented. While these patterns remain invisible under static environmental humidity, even up to near 100% relative humidity, they are unveiled immediately (≈100 ms) and fully reversibly by dynamic humid flow, e.g., human breath. They reveal themselves due to the extreme wettability of the patterned (etched) regions, as confirmed by contact angle measurements. The liquid surface tension threshold to induce wetting (revealing the imprinted invisible images) is evaluated by thermodynamic predictions and subsequently verified by exposure to various vapors with different surface tension. The color of the patterned regions is furthermore independently tuned by vapors with different refractive indices. Such a system can play a key role in applications such as anticounterfeiting, identification, and vapor sensing.

中文翻译：

瞬时，简单和可逆的揭示在坚固的空心球体胶体光子晶体中加密的不可见图案

光子晶体的颜色基于其周期性的晶体结构。在许多应用中，它们显示出优于常规生色团的明显优势，这主要是由于其抗光漂白和对刺激的响应能力。更具体地，将胶体光子晶体和不可见图案相结合对于用于防伪应用的密写术和水印术是重要的。这里提出了一种方便的方法，可以在空心二氧化硅球的胶体晶体中刻印出坚固的不可见图案。尽管这些模式在静态环境湿度（甚至高达100％相对湿度）下仍不可见，但它们会立即（约100毫秒）显示出来，并通过动态湿流（例如人的呼吸）完全可逆地显示出来。它们由于图案化（蚀刻）区域的极高润湿性而显露出来，如接触角测量所证实。通过热力学预测来评估引起润湿（露出已印制的不可见图像）的液体表面张力阈值，然后通过暴露于具有不同表面张力的各种蒸汽中进行验证。此外，图案化区域的颜色由具有不同折射率的蒸气独立地调节。这样的系统可以在诸如防伪，识别和蒸气感测之类的应用中发挥关键作用。

更新日期：2018-05-04

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