Development of Mechanically Reliable and Transparent Photochromic Film Using Solution Blowing Spinning Technology for Anti-Counterfeiting Applications

Recent advances in photoresponsive printing inks for security encoding applications

Counterfeiting of banknotes, important documents, and branded goods continues to be a major worldwide problem for governments, businesses, and consumers. This problem has serious financial, security, and health implications. Due to their stability for printing on various substrates, the photochromic anticounterfeiting inks have received important interest. There have been various photochromic agents, such as polymer nanoparticles, quantum and carbon dots, and organic and inorganic fluorophores and luminophores, which have been broadly used for antiforging applications. In comparison to organic agents, inorganic photochromic materials have better stability under reversible/long-term light illumination. Recently, the remarkable optical characteristics and chemical stability of photoluminescent and photochromic agents have led to their extensive usage anticounterfeiting products. There have been also several strategies to tackle the rising problem of counterfeiting. Both of solvent-based and water-based inks have been developed for security encoding purposes. Additionally, the printing methods, including screen printing, labeling, stamping, inkjet printing, and handwriting, that have been used to apply anticounterfeiting inks onto various surfaces are discussed. The limitations of photoluminescent and photochromic agents and the potential for their future preparation to combat counterfeiting were discussed. This review would benefit academic researchers and industrial developers who are interested in the area of security printing.

A Heat-Resistant Polymer Based on the Reversible Change in Polymer Skeleton Structure for Self-Anticounterfeiting

Heat-resistant polymer materials have been widely used in many fields, but their anticounterfeit is still a significant challenge. This work has successfully constructed a heat-resistant polymer material that can achieve self-anticounterfeit. In response to changes in the external environment, the color of polymer changes from yellow-green to red reversibly, which is due to the fact that polymer material's backbone undergoes isomerization. Therefore, this high-performance polymer material can not only be used in a high-temperature environment for a long time but also achieve its anticounterfeit and be used in advanced security applications.

Green syntheses of silk fibroin/wool keratin-protected AuAg nanoclusters with enhanced fluorescence for multicolor and patterned anti-counterfeiting

Counterfeiting is a serious worldwide issue that threatens human health and economic security. How to apply anti-counterfeiting techniques to textile materials remains a great challenge. Herein, we report bimetallic AuAg nanoclusters (NCs) synthesized by one-step reduction of chloroauric acid (HAuCl4) and silver nitrate (AgNO3) with wool keratin (WK) as reducer and silk fibroin (SF) as stabilizer. The strongest orange-red fluorescence under ultraviolet light as well as the highest zeta potential absolute values of -27.97 mV were simultaneously realized in the optimal proportion Au-AgNCs2 (WK/SF is 3/2), which was further processed to a series of anti-counterfeiting films by blending with SF, silk sericin (SS), and polyvinyl alcohol (PVA). After successfully being numbered into fifteen colors, a dark blue-orange-dark red-dark blue cyclic fluorescent anti-counterfeiting color chart was designed. In addition, a two-Maxwell-unit model was constructed to assist with the microstructure analysis, which found that the formation of hydrogen bonds and the secondary structure transition from α-helices to β-sheets during stretching were responsible for improving the mechanical properties and the two-staged fracture curves of films, respectively. Finally, a patterned and multicolor fluorescence anti-counterfeiting fabric application was demonstrated by combining the color chart and screen printing, indicating the great potential in textile anti-counterfeiting.

Preparation of photoluminescent nanocomposite ink for detection and mapping of fingermarks

Simple and efficient detection and mapping method based on a strong turn-on fluorescent pigment was developed for fingerprint analysis. We present a phosphor powder characterized by strong emission which is useful to achieve better fingerprint detection on multicolored or photoluminescent surfaces, such as currency notes characterized by optically changeable inks and highly fluorescent positions, because it offers better contrast and reduce the difficulty of background interference. Novel photochromic ink was prepared to establish a fingerprinted colorless film onto cellulose documents with green emission for anticounterfeiting applications as illustrated by photoluminescence spectra. Inorganic/organic nanoscale composite ink was prepared from rare-earth doped aluminate phosphor nanoparticles (PNPs; 27-49 nm) dispersed in a polyacrylic acid binding agent. PNPs were dispersed efficiently in polyacrylic acid to generate a colorless mark. The produced photochromic inks were spray-coated onto off-white paper sheets enclosing invisible fingermarks, and then exposed to thermofixation. Photochromic film was detected on paper surface presenting a transparent appearance under visible daylight and switchable to green under UV light. The CIE Lab parameters and photoluminescence spectra were studied under visible light and ultraviolet irradiation. The fingerprinted sheets showed fluorescence band at 517 nm upon excitation at 366 nm, showing a bathochromic shift and reversible photochromism without fatigue. The morphologies of pigment phosphor particles and fingerprinted sheets were inspected. The rheological properties of ink and mechanical behavior of the fingerprinted paper samples were explored. HIGHLIGHTS: Novel smart ink with alkaline-earth aluminate and polyacrylic acid was developed. Dual-mode fluorescent photochromism was presented for latent fingerprint analysis. Off-white fingerprinted films under daylight showed color change to green under UV. Fluorescence band monitored at 517 nm upon excitation at 366 nm. Fluorescent fingermark on paper sheets demonstrated good photostability.

Solution blowing spinning of polylactate/polyvinyl alcohol/ZnO nanocomposite toward green and sustainable preparation of wound dressing nanofibrous films

The outstanding biodegradability, biocompatibility, affordability, and renewability of polylactic acid have made it a prominent biomaterial. Herein, an innovative, easy, and eco-friendly technique is used to prepare sodium polylactate (SP)-based nanofibers. Solution blowing spinning (SBS) was used to create fibrous mats of SP and polyvinyl alcohol (PVA). SBS's SP nanfibers were crosslinked using an aqueous solution of calcium chloride to produce moisture-resistant calcium polylactate nanofibrous spun mats. Both of UV-visible absorption spectra and transmission electron microscopy were utilized to study the produced zinc oxide (ZnO) nanoparticles (NPs) to indicate a diameter of around 15-23 nm with a high intensity absorption intensity at 370 nm. New polylactate copolymer was synthesized and characterized by infrared and NMR spectroscopic techniques. In order to prepare SP/PVA/ZnO nanocomposite nanofibers, various ZnO ratios were used. The morphologies of the composite nanofibers were investigated by infrared spectroscopy (FTIR), energy-dispersive X-ray analyzer, and scanning electron microscopy. The cytotoxicity tests of the prepared mat were studied by conducting experiments with L-929 cells at various time intervals. The prepared composite SP/PVA/ZnO nanofibers were subjected to cytotoxicity tests to determine their cytocompatibility. Results showed that those with ZnO concentrations between 0.5% and 2% were found to be less harmful than those with higher concentrations. A variety of bacterial species, including Bacillus pumilus and Staphylococcus aureus, as well as Klebseilla pneumoniae and Escherichia coli, were used to test the antibacterial properties of SP/PVA/ZnO spun mats. The ZnO NPs integrated in the SP/PVA fibrous mats were responsible for their antibacterial properties. After finding the appropriate concentration of ZnO that is least harmful while yet giving a satisfactory antibacterial activity, this biomaterial might be perfect for wound dressing applications. HIGHLIGHTS: New eco-friendly biodegradable sodium polylactate (SP) copolymer was synthesized. Zinc oxide nanoparticles (ZnO NPs) with a diameter of 15-23 nm were prepared. High antibacterial SP/PVA/ZnO fibers were prepared by solution blowing spinning. SP/PVA/ZnO nanofibers (180-220 nm) with various ratios of ZnO were presented. Cytotoxicity results showed that the cell viability decreases with increasing ZnO.

Simple Preparation of Multifunctional Luminescent Textile for Smart Packaging

Linen has been a significant material for textile packaging. Thus, the application of the simple spray-coating method to coat linen fibers with a flame-retardant, antimicrobial, hydrophobic, and anticounterfeiting luminescent nanocomposite is an innovative technique. In this new approach, the ecologically benign room-temperature vulcanizing (RTV) silicone rubber was employed to immobilize the environmentally friendly Exolit AP 422 (Ex) and lanthanide-doped strontium aluminum oxide (RESAO) nanoscale particles onto the linen fibrous surface. Both morphological properties and elemental compositions of RESAO and treated fabrics were examined by transmission electron microscopy (TEM), scanning electron microscopy (SEM), wavelength-dispersive X-ray fluorescence (WD-XRF), Fourier transform infrared (FTIR) spectroscopy, and energy-dispersive X-ray spectroscopy (EDX). In the fire resistance test, the treated linen fabrics produced a char layer, giving them the property of self-extinguishing. Furthermore, the coated linen samples' fire-retardant efficacy remained intact after 35 washing cycles. As the concentration of RESAO increased, so did the treated linen superhydrophobicity. Upon excitation at 366 nm, an emission band of 519 nm was generated from a colorless luminescent film deposited onto the linen surface. The coated linen displayed a luminescent activity by changing color from off-white beneath daylight to green beneath UV source, which was proved by CIE Lab parameters and photoluminescence spectral analysis. The photoluminescence effect was identified in the treated linen as reported by emission, excitation, and decay time spectral analysis. The comfort properties of coated linen fabrics were measured to assess their mechanical and comfort features. The treated linen exhibited excellent UV shielding and improved antimicrobial performance. The current simple strategy could be useful for large-scale production of multifunctional smart textiles such as packaging textiles.

Optical Detection of Acetone Using "Turn-Off" Fluorescent Rice Straw Based Cellulose Carbon Dots Imprinted onto Paper Dipstick for Diabetes Monitoring

Persistent bad breath has been reported as a sign of serious diabetes health conditions. If an individual's breath has a strong odor of acetone, it may indicate high levels of ketones in the blood owing to diabetic ketoacidosis. Thus, acetone gas in the breath of patients with diabetes can be detected using the current easy-to-use fluorescent test dipstick. In another vein, rice straw waste is the most well-known solid pollutant worldwide. Thus, finding a simple technique to change rice straw into a valuable material is highly important. A straightforward and environmentally friendly approach for reprocessing rice straw as a starting material for the creation of fluorescent nitrogen-doped carbon dots (NCDs) has been established. The preparation process of NCDs was carried out via one-pot hydrothermal carbonization using NH₄OH as a passivation substance. A testing strip was developed on the basis of cellulose CD nanoparticles (NPs) immobilized onto cellulose paper assay. The NCDs demonstrated a quantum yield of 23.76%. A fluorescence wavelength was detected at 443 nm upon applying an excitation wavelength of 354 nm. NCDs demonstrated remarkable selectivity for acetone gas as their fluorescence was definitely exposed to quenching by acetone as a consequence of the inner filter effect. A linear correlation was observed across the concentration range of 0.5-150 mM. To detect and measure acetone gas, the present cellulose paper strip has a "switch off" fluorescent signal. A readout limit was accomplished for an aqueous solution of acetone as low as 0.5 mM under ambient conditions. The chromogenic fluorescence of the cellulose assay responsiveness depends on the fluorescence quenching characteristic of the cellulose carbon dots in acetone. A thin fluorescent cellulose carbon dot layer was deposited onto the surface of cellulose strips by a simple impregnation process. CDs were made using NP morphology and analyzed using infrared spectroscopy and transmission electron microscopy. The carbon dot distribution on the paper strip was evaluated by scanning electron microscope and energy-dispersive X-ray analysis. The absorption and fluorescence spectral analyses were investigated. The paper sheets' mechanical qualities were also examined.

Simple preparation of novel photochromic polyvinyl alcohol/carboxymethyl cellulose security barcode incorporated with lanthanide-doped aluminate for anticounterfeiting applications

Forgery and low-quality products pose a danger to the society. Therefore, there are increasing demands for the production of easy to recognize and difficult to copy anti-counterfeiting materials. Products with smart photochromic and fluorescent properties can change color and emission spectra responding to a light source. In this context, we devised a straightforward preparation of luminescent polyvinyl alcohol/carboxymethyl cellulose (PVA/CMC) nanocomposite to function as a transparent labeling film. The lanthanide-doped aluminate (LdA) was prepared in the nanoparticle form to indicate diameters of 35-115 nm. Different ratios of the lanthanide-doped aluminate (LdA) were physically dispersed in the PVA/CMC nanocomposite label film to provide photochromic, ultraviolet protection, antimicrobial activity and hydrophobic properties. Fluorescence peaks were detected at 365 and 519 nm to indicate a color change to green. As a result of increasing the phosphor ratio, improved superhydrophobic activity was achieved as the contact angle increased from 126.1° to 146.0° without affecting the film original physical and mechanical properties. Both UV protection and antibacterial activity were also investigated. The films showed quick and reversible photochromic response without fatigue. The current strategy reported the development of photochromic smart label that is transparent, cost-effective and flexible. As a result, numerous anticounterfeiting products can benefit from the current label for a better market. LdA-loaded PVA/CMC films demonstrated antibacterial activity between poor, good, very good and outstanding as the percentage of LdA in the film matrix increased. The current film can be applied as a transparent photochromic security barcode for anticounterfeiting applications and smart packaging.

Simple Preparation of Photoluminescent and Color-Tunable Polyester Resin Blended with Alkaline-Earth-Activated Aluminate Nanoparticles

A simple inorganic/organic nanocomposite was used to generate long-lasting phosphorescent pebbles for easy commercial manufacturing of smart products. An organic/inorganic nanocomposite was made from low-molecular-weight unsaturated polyester and rare-earth-activated strontium aluminum oxide nanoparticles doped with europium and dysprosium. The polyester resin was mixed with phosphorescent strontium aluminate oxide nanoparticles and methylethyl ketone peroxide as a cross-linking agent to create a viscous mixture that can be hardened in a few minutes at room temperature. Before adding the hardener catalyst, the phosphorescent strontium aluminate nanoparticles were dispersed throughout the polyester resin in a homogeneous manner to ensure that the pigment did not accumulate. Long-lasting, reversible luminescence was shown by the photoluminescent substrates. The emission was reported at 515 nm upon exciting the pebble at 365 nm. In normal visible light, both blank and luminescent pebbles had a translucent appearance. As a result of UV irradiation, the photoluminescent pebbles produced an intense green color. The three-dimensional CIE Lab (International Commission on Illumination) color coordinates and luminescence spectra were used to investigate the color changing characteristics. Photophysical characteristics, including excitation, emission, and lifetime, were also investigated. Scanning electron microscopy, wavelength-dispersive X-ray fluorescence spectroscopy, and energy-dispersive X-ray analysis were employed to report the surface morphologies and elemental content. Without impairing the pebbles' original physico-mechanical characteristics, the pebbles showed improved superhydrophobic activity. The current simple colorless long-lasting phosphorescent nanocomposite can be applied to a variety of surfaces, like ceramics, glassware, tiles, and metals.

Development of a Fluorescent Nanofibrous Template by In Situ SNAr Polymerization of Fluorine-Containing Terphenyls with Aliphatic Diols: Self-Assembly and Optical and Liquid Crystal Properties

Stimulus-responsive supramolecular organogels have been broadly studied, but the assembly of a liquid crystalline organogel with a thermoreversible response remains a challenge. This could be attributed to the difficulty of designing organogelators with liquid crystalline properties. Nucleophilic aromatic substitution (S_NAr) has been utilized to produce a diversity of pentafluorobenzene-containing aromatics, which are very regioselective to para positions. Those pentafluorobenzene-functionalized aromatics have been ideal compounds for the preparation of calamitic liquid crystals. In this context, novel fluoroterphenyl-containing main-chain polyether (FTP@PE) was synthesized using in situ S_NAr polymerization as a convenient and effective synthetic strategy toward the development of fluorescent liquid crystals bearing fluoroterphenyl and ether groups. The fluoroterphenyl unit was synthesized by Cu(I)-supported decarboxylation cross-coupling of potassium pentafluorobenzoate and 1,4-diiodobenzene. The chemical structures of FTP@PE were studied with ¹H/¹³C/¹⁹F nuclear magnetic resonance and infrared spectra. The liquid crystal mesophases were determined with differential scanning calorimetry and polarizing optical microscopy. Ultraviolet-visible absorbance and emission spectral profiles showed solvatochromic activity. The nanofibrous morphologies were studied with a scanning electron microscope. The organogels of FTP@PE were developed in a number of solvents via van der Waals attraction forces of aliphatic moieties and π stacking of fluoroterphenyl groups. They demonstrated thermoreversible responsiveness.