Bioinspired Dynamic Camouflage in Programmable Thermochromic‐Patterned Photonic Films for Sophisticated Anti‐Counterfeiting

Abstract

Although the encrypted anti-counterfeiting technology based on infiltrationcontrolled photonic crystals has attracted widespread attention, the information has only hidden and display states. The more diverse and complex encryption effect requires a continuous and programmable color transformation. Inspired by the dynamic camouflage in chameleons and cephalopods, a programmable thermochromic patterned photonic film is developed for encrypted anti-counterfeiting, which is constructed by infiltrating thermoresponsive poly(oligo ethylene glycol acrylate) copolymers in SiO 2 -coated ZnS photonic crystals. The responsive temperature range is determined by the lower critical solution temperature of filled copolymers, which is tunable by controlling the ratios of different monomers in copolymerization. Based on this, the responsive range is adjusted to 5-55 °C and decoding temperature is set at 20 °C. The pattern is hidden either when the water temperature is >55 °C or <5 °C. Only when the water temperature accurately matches the decoding temperature (20 °C), do the different areas display the preset colors, resulting in the complete pattern being revealed. The design of this programmable thermochromic patterned photonic film indicates a new direction for the encrypted anti-counterfeiting technology, which can carry more abundant information and encrypt them more complex and sophisticated.

Preparation of novel authentication film by screen printing of anthocyanin biomolecular extract: Thermochromism and vapochromism

“…The term “smart products” is used to describe materials that can alter one or more of their physical characteristics, such as color, responding to external stimuli. Thermochromic materials, for instance, can alter their appearance in response to heat [20, 21]. Thermochromic anti‐counterfeiting paper documents have lately attracted more interest because of their potential usage in several sectors, such as sensors and security alerts.…”

“…The term "smart products" is used to describe materials that can alter one or more of their physical characteristics, such as color, responding to external stimuli. Thermochromic materials, for instance, can alter their appearance in response to heat [20,21].…”

“…A material thermochromism indicates its capacity to alter its hue in response to exposure to temperature increase. Some applications of thermochromic materials include anti‐counterfeiting composites for use in creating security barcodes [20]. The exposure to a heat source causes a reversible color shift in this security authentication barcode.…”

Nacre-inspired layered composite gels with broad tunable mechanical strength and structural color for stress visualization

“…Mimicking these natural nanostructures, a large number of artificial-structural-colored materials have been developed based on the assembly of colloidal microspheres, cellulose, block copolymers, or two-dimensional (2D) nanosheets. [4][5][6][7][8] Among these, structural color switching in gels can be mechanically triggered by inducing changes in lattice space or diffraction angles. Structural-colored gels can provide visual feedbacks for changes and distribution of strain/ stress, which make them promising in fields of mechanochromic sensor, health monitor, anti-counterfeit labels, display, etc.…”

Rewritable Structurally Colored Paper Based on Hollow SiO2–Polyurethane Composite Photonic Crystal Film

“…By tuning the lattice constant or refractive index, full spectral ranged reflected colors are easily achieved on a responsive photonic crystal film. Such a stimuli-sensitive photonic crystal has been widely used in structure color display, , chemical and physical colorimetric sensor, − anti-counterfeiting, ,− encryption, , and green printing. − It is worth noting that rewritable photonic crystal paper as a kind of green printing material, in which the structural colored pattern can be reversibly printing and erase under external stimuli, has recently become prevalent, since paper is still the most important media for mankind to record information and spread the civilization. Moreover, photonic crystal paper with dye free character is more durable than traditional pigments and dyes, which can lessen the heavy environmental burden brought about by traditional paper industry.…”