Fabrication and Characterization of Angle-Independent Structurally Colored Films Based on CdS@SiO2 Nanospheres

Bioinspired Low-Angle-Dependent Photonic Crystal Elastomer for Highly Sensitive Visual Strain Sensor

Photonic crystals (PCs) possess unique photonic band gap properties that can be used in the field of sensors and smart displays if modulated on the micronano structure. Both nonclose-packed (NCP) structure and high refractive index (RI) contrast of PC play important roles in response sensitivity during stretching. Herein, we constructed an NCP-structured PC strain sensor with high RI by a novel coating-etching strategy. Stretch-induced changes in structural color correspond to the strength of the force, enabling the detection of the strength of the acting force by the naked eye. The flexible 3D cross-linked network constructed by poly(ethylene glycol) phenyl ether acrylate and pentaerythritol tetrakis(3-mercaptopropionate) endows the sensor with excellent elasticity and robustness. The designed PC strain sensor achieves high mechanochromic sensitivity (∼8.3 nm/%, 0.02 to 4.21 MPa) and a substantial reflection peak shift (Δλ = 249 nm). More importantly, the high RI contrast (Δn = 0.43) between CdS and polymers imparts isotropic optical properties, ensuring a broad viewing angle while avoiding misleading signals. The research provides a novel fabrication strategy to construct sensitive PC strain sensors, expanding the prospective applicability to human movement monitoring and secure message encryption.

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.

Structural Coloration of Polyester Fabrics with High Colorfastness by Copolymer Photonic Crystals Containing Reactive Epoxy Groups

Structural color as a revolutionary coloration strategy has been proposed to replace the traditional dyeing and printing process. However, the poor colorfastness and easy crack formation of structural colors on textile fabrics restrict their practical application at present. In this study, poly (tert-butyl acrylate-co-glycidyl methacrylate) (P(t-BA-co-GMA)) copolymers containing reactive epoxy groups with different mass ratios of tert-butyl acrylate (t-BA) and glycidyl methacrylate (GMA) were successfully synthesized, which were used to create structural colors on black polyester fabrics. The results showed that P(t-BA-co-GMA) nanospheres could form crack-free structural colors on polyester fabrics, and the colors vary with the mass ratio of t-BA and GMA to obtain five different colors. The different particle sizes of the different P(t-BA-co-GMA) nanospheres with different refractive indexes and the arrangement of short-range ordered and long-range disordered in microstructures may be the reason of different angle-independent structural colors on polyester fabrics. The P(t-BA-co-GMA) nanosphere structural colors on polyester fabrics possess good abrasion and washing colorfastness. This research provides the experimental basis for the development of crack-free amorphous photonic crystal structural color on fabrics with high colorfastness to promote the practical application of structural color in textile coloration.

Thermal Responsive Photonic Crystal Achieved through the Control of Light Path Guided by Phase Transition

Responsive photonic crystal is widely considered in the field of anti-counterfeiting and information encryption because of their structural color changes caused by external stimulation. However, the response signal is usually achieved by adjusting the periodic lattice constant based on Bragg's law with volume changes. Thus, it is a great challenge to achieve the response of photonic crystals by non-array parameter control. Herein, novel thermal responsive photonic crystal (TRPC) with low angle dependent structural color is fabricated by introducing poly(ethylene glycol) into the structure of low angle dependent SnO₂ inverse opal. The response is achieved through the control of light path guided by phase transition and the significant volume change caused by the change of traditional array parameters can be effectively avoided. Meanwhile, the low angle dependent structural color of TRPC can effectively reduce the interference of observation angle change to response signal caused by external thermal stimulation. Patterned responsive photonic crystals with temperature gradient response are easily obtained by combining confinement self-assembly and direct template method, and the patterns can be presented and hidden by the control of light path, showing great potential in anti-counterfeiting and information encryption fields.