Functional Micro–Nano Structure with Variable Colour: Applications for Anti-Counterfeiting

Abstract

Colour patterns based on micro-nano structure have attracted enormous research interests due to unique optical switches and smart surface applications in photonic crystal, superhydrophobic surface modification, controlled adhesion, inkjet printing, biological detection, supramolecular self-assembly, anti-counterfeiting, optical device and other fields. In traditional methods, many patterns of micro-nano structure are derived from changes of refractive index or lattice parameters. Generally, the refractive index and lattice parameters of photonic crystals are processed by common solvents, salts or reactive monomers under specific electric, magnetic and stress conditions. This review focuses on the recent developments in the fabrication of micro-nano structures for patterns including styles, materials, methods and characteristics. It summarized the advantages and disadvantages of inkjet printing, angle-independent photonic crystal, self-assembled photonic crystals by magnetic field force, gravity, electric field, inverse opal photonic crystal, electron beam etching, ion beam etching, laser holographic lithography, imprinting technology and surface wrinkle technology, etc. This review will provide a summary on designing micro-nano patterns and details on patterns composed of photonic crystals by surface wrinkles technology and plasmonic micro-nano technology. In addition, colour patterns as switches are fabricated with good stability and reproducibility in anti-counterfeiting application. Finally, there will be a conclusion and an outlook on future perspectives.

Versatile Applications of Silver Nanowire-Based Electrodes and Their Impacts

“…AgNWs have unique optical and electrical properties, which can be used to create anti-counterfeiting labels and tags that are difficult to be replicated [ 54 , 55 ]. Anti-counterfeiting technologies use AgNW electrodes as a key component in the design of security features for products ( Figure 8 ).…”

“…AgNWs are highly conductive and can be used to create transparent electrodes with high conductivity, which can be used in several anti-counterfeiting applications. One example of an anti-counterfeiting technology that uses AgNW electrodes is the creation of transparent security tags [ 54 , 55 ]. These tags use AgNW electrodes to create unique electrical signatures, which can be used to authenticate the product.…”

“…Reproduced from Ref. [ 54 ] under the Creative Commons Attribution 4.0 International (CC BY 4.0) License.…”

Metasurface-Driven Optically Variable Devices

“…In addition to these print-based anticounterfeit technologies, chemical-based security inks and optically variable devices (OVDs) have been developed to introduce tunability to the devices. − Tunable security inks, such as luminescent ink, metameric ink, and thermochromic ink, utilize the chemical characteristics of inks to achieve their sensitivity. OVDs such as microlens labels, rainbow hologram stickers, and thin-film interference filters exhibit iridescent images using optical phenomena that come from the surface profile. Despite the development of anticounterfeit technology, the battle between manufacturers and counterfeiters continues.…”

A Physical Unclonable Function Based on Recyclable Polymer Nanoparticles to Enable the Circular Economy

“…The development of recyclable PUFs is a major challenge that can be overcome using advanced multifunctional polymer chemistry supported by nanotechnology. − In this paper, we focus on polyesters used in many fields of industry such as beverage bottles, food packaging, pharmaceutical containers, and cosmetic packaging . We present the use of polyester polymer nanoparticles for the design of a novel PUF-based optical identification system aimed to enable the circular economy.…”