Mechanochromic and Solvomechanochromic Fluorescent Photonic Crystals for Dual-Mode Modulating Fluorescence and Multilevel Anticounterfeiting

Structurally-colored adhesives for sensitive, high-resolution, and non-invasive adhesion self-monitoring

Polymeric adhesives are critical in many applications, from daily life to implantable devices and soft robotics. Monitoring adhesion in a real-time and convenient manner before premature failure is essential yet challenging. Herein, we present structurally-colored adhesives for sensitive, high-resolution, and non-invasive adhesion self-monitoring via distinct color change for detecting subtle deformation and debonding. The structurally-colored adhesives are designed by integrating one-dimensional photonic nanochains into exemplified acrylate-copolymer-based adhesives and demonstrate distinct color-changing capability through a unique tilting mechanism of nanochains under shear. Our structurally-colored adhesives can be customized as pressure-sensitive and structural adhesives, exhibiting ultrafast response (<60 ms), high sensitivity, and high resolution (~120 μm). Moreover, predicting adhesion states and premature failure can be achieved assisted by imaging systems and machine learning algorithms with an average accuracy of up to 97.2%. Our structurally-colored adhesives are expected to offer a practical paradigm for structural health monitoring in the Internet of Things era.

Dual-Mode Multicolor Display Based on Structural and Fluorescent Color CdS Photonic Crystal Hydrogel

In this study, we prepared a multicolor structural-fluorescent CdS-PEGDA photonic crystal hydrogel (SFC-CPH) with a dual display mode, which has two different optical states: structural color mode and fluorescent color mode. SFC-CPH displays structural color mode under visible light and fluorescent color mode under ultraviolet light. Initially, monodisperse CdS colloidal particles were synthesized via a hydrothermal method, leading to the self-assembly of a photonic crystal template. The high refractive index of CdS contributes to the photonic crystals' low-angle dependence and vivid structural colors. Then, a variety of fluorescent molecules were doped into poly(ethylene glycol) diacrylate (PEGDA) hydrogel and combined with photonic crystals with distinct structural colors to prepare three distinct colors of SFC-CPH. We also investigated the optical characteristics and surface properties of these photonic crystal hydrogels. Based on these dual-mode display characteristics, we designed several dual-mode display patterns and a method for information encoding. The unique property of this photonic crystal hydrogel material suggests its substantial potential for applications in information storage, security, and encoding, offering innovative avenues in the realm of information display.

Metal-organic framework photonic crystals with bidisperse particles-based brilliant structural colors and high optical transparency for elaborate anti-counterfeiting

Photonic crystals (PCs) have attracted great interest and wide applications in displays, printing, anti-counterfeiting, etc. However, two main challenges significantly hinder their applications: 1) the tradeoff between high optical transparency across the whole visible range and brilliant colors requiring a large refractive index contrast (Δn), and 2) the way of regulating structural colors by altering tens of different sizes. To address these issues, a new type of metal-organic framework (MOF)-based transparent photonic crystal (TPC) has been fabricated through self-assembling MOF particles into three-dimensional ordered structures which were then infiltrated by polydimethylsiloxane (PDMS). Compared to conventional PCs, these TPCs exhibit 1) both brilliant forward iridescent structural colors and high transmittance (>75 %) across the whole visible spectra range, and 2) conveniently adjustable colors based on bidisperse particles. The unique color-generating mechanism of the light diffraction by each plane lattice and the small Δn between MOF particles and PDMS are the keys to TPCs' characteristics. Moreover, the prepared invisible anti-counterfeit labels can reversibly hide-reveal patterns with elaborate and exchangeable color contrast in a non-destructive way, showing potential applications in anti-counterfeiting, information encryption, and optical devices.