Flexible Photonic Crystal Material for Multiple Anticounterfeiting Applications

Abstract

In this study, a nanoimprinting method was introduced to fabricate polycarbonate films with transparent and flexible photonic crystal (FPC) structures. The fabricated flexible polymer films display a full-color grating because of the nanohemispherical structures on the surface. Through the Bragg diffraction formula, it was confirmed that the FPC polymer films transfer a part of the light energy to the second-order diffraction spectrum. Furthermore, the full-color grating properties can be modulated through geometric deformation because of the film’s elasticity. Additionally, anticounterfeiting features were also successfully achieved when the polymer films were either engraved with drawings and bent or patterned with fluorophores, which can be revealed under ultraviolet light. The most important aspect of this research is that the preparation of this FPC-structured polymer film is inexpensive and convenient, enabling the mass production of a new generation of smart materials.

Robust and Flexible Colloidal Photonic Crystal Films with Bending Strain–Independent Structural Colors for Anticounterfeiting

“…One is that the anticounterfeiting materials can change color as viewing angle changes. [ 15,24–26 ] The other type of PC anticounterfeiting materials usually consists of patterns that are invisible under normal circumstances but can be revealed under specific external stimulations (e.g., water, vapor, lighting, magnetic or electric field). [ 8,20,27–31 ] Although these unique anticounterfeiting characteristics make them high‐level security, their poor flexibility greatly limits their applications to curved surfaces or flexible objects, such as banknotes.…”

“…For example, Wang's group introduced the polycarbonate with high flexibility for the preparation of the PC‐based anticounterfeiting material via a novel nanoimprinting method. [ 25 ] Ge's group fabricated a patterned composite PC film for security purposes by introducing the mixture of poly(ethylene glycol) methacrylate and ethylene glycol (EG) into the colloidal PC system and subsequently selectively crosslinking it, where the patterns on the film are hidden in a normal state and can be revealed by a slight deformation due to the high softness. [ 36,37 ] Despite the good robustness and flexible stability of PC‐based anticounterfeiting materials in the above research, their structural colors will change with the bending curvature and viewing angle.…”

“…[ 36,37 ] Despite the good robustness and flexible stability of PC‐based anticounterfeiting materials in the above research, their structural colors will change with the bending curvature and viewing angle. [ 25,36,37 ] As a result, the film will undergo unpredictable and complex color changes when it is bent, making it difficult to reproduce a specific structural color in their practical applications. Therefore, it is essential to develop PC films with bending strain–independent structural colors to improve the recognition degree under bending.…”

“…Therefore, it is essential to develop PC films with bending strain–independent structural colors to improve the recognition degree under bending. [ 25 ]…”

Hydrocipher: Bioinspired Dynamic Structural Color‐Based Cryptographic Surface

“…Due to these advantages, the diffraction gratings with straight line, spiral, and butterfly‐like 2D patterns have been employed to develop diffraction colors in the banknote . Recently, a hexagonal array of hemispherical nanodomes on a flexible polymer substrate was prepared by nanoimprinting and used to develop angle‐dependent full rainbow colors . However, the encryption of a structural color pattern in the grating structure has not been reported to the best of our knowledge.…”