Counterfeiting and inverse engineering of security and confidential documents, such as banknotes, passports, national cards, certificates, and valuable products, has significantly been increased, ...which is a major challenge for governments, companies, and customers. From recent global reports published in 2017, the counterfeiting market was evaluated to be $107.26 billion in 2016 and forecasted to reach $206.57 billion by 2021 at a compound annual growth rate of 14.0%. Development of anticounterfeiting and authentication technologies with multilevel securities is a powerful solution to overcome this challenge. Stimuli-chromic (photochromic, hydrochromic, and thermochromic) and photoluminescent (fluorescent and phosphorescent) compounds are the most significant and applicable materials for development of complex anticounterfeiting inks with a high-security level and fast authentication. Highly efficient anticounterfeiting and authentication technologies have been developed to reach high security and efficiency. Applicable materials for anticounterfeiting applications are generally based on photochromic and photoluminescent compounds, for which hydrochromic and thermochromic materials have extensively been used in recent decades. A wide range of materials, such as organic and inorganic metal complexes, polymer nanoparticles, quantum dots, polymer dots, carbon dots, upconverting nanoparticles, and supramolecular structures, could display all of these phenomena depending on their physical and chemical characteristics. The polymeric anticounterfeiting inks have recently received significant attention because of their high stability for printing on confidential documents. In addition, the printing technologies including hand-writing, stamping, inkjet printing, screen printing, and anticounterfeiting labels are discussed for introduction of the most efficient methods for application of different anticounterfeiting inks. This review would help scientists to design and develop the most applicable encryption, authentication, and anticounterfeiting technologies with high security, fast detection, and potential applications in security marking and information encryption on various substrates.
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Light-responsive polymers, especially photochromic ones, are among the most interesting classes of stimuli-responsive materials. Photochromic polymers can show different ...stimuli-chromic properties depending on the applied stimuli, chemical structure, and the surrounding media. Such polymers are commonly prepared by incorporation of photochromic compounds in polymer matrices to exhibit stimuli-chromic behavior. Photochromic compounds used in advanced materials include spiropyran, spiroxazine, azobenzene, and diarylethenes, while the recent studies have focused on their response to various stimulants. Stimulants may be classified into three types, physical, chemical, or biochemical, according to their effects on stimuli-chromic materials. Stimuli-chromic polymers that change color on stimulation may responds to light (photochromism), pH (acidochromism and basochromism), temperature (thermochromism), stress (mechanochromism), electrical potential (electrochromism), gelation (gelochromism), solvation (solvatochromism), pressure (piezochromism), water (hydrochromism), and also two or more stimulants (multi-stimuli-chromism). Chemosensors based on stimuli-chromic materials have received considerable attention as they may be used to sense a wide range of chemicals and targets, such as polarity, pH, temperature, positive ions, negative ions, stress, pressure, water, and also biomolecules. Studies focused on stimuli-responsive polymers based on photochromic compounds and different stimuli-chromic phenomena are comprehensively reviewed in the following. Effects of a photochromic compound on its polymeric substrate, matrix or carrier, and the converse effects are carefully investigated to further understanding of different stimuli-chromism phenomena. In addition, the most frequently used synthesis methods to prepare photochromic compounds and their corresponding stimuli-chromic polymers are investigated in detail. Photochromic properties may considerably be influenced by interactions of a photochromic compound with its surrounding media. Incorporation of photochromophores to the polymeric or non-polymeric matrices without decrease of photochromic properties, photofatigue resistant, photoswitchability, and photostability, in addition to removal of negative photochromism are the most significant challenges. This review presents new strategies to overcome these problems and new applications as optical and non-optical chemosensors in the future for a large family of photochromic compounds and its related stimuli-chromic polymers.
Increase of safety in security documents by using anticounterfeiting inks based on fluorochromic and photochromic compounds has attracted a great deal of attention in the recent years. Herein, we ...developed novel functionalized stimuli-responsive latex particles containing spiropyran (1 wt %) by semicontinuous emulsifier-free emulsion polymerization, which are usable as anticounterfeiting inks for marking on security documents and also photopatterning on cellulosic papers. The size and morphology of the latex particles were characterized by scanning electron microscopy and dynamic light scattering and their functionality was characterized by Fourier-transform infrared spectroscopy. All the stimuli-responsive latexes are composed of spherical particles with different hydroxyl, epoxy, and carboxylic acid functional groups, and the size of the particles varies in the range of 400–900 nm. Additionally, the latex particles undergo a remarkable light-induced size variation (aggregation–disaggregation) upon UV illumination (365 nm), depending on the functional group type, as a result of π–π stacking interactions and also electrostatic attractions between the different particles. The photochromic behavior, kinetics of the SP ⇌ MC isomerization, photoswitchability, and photofatigue-resistant characteristics of the prepared latexes were extensively investigated. The results display that the photochromic behavior and SP ⇌ MC isomerization can significantly be influenced by the polar interactions between the functional groups and MC molecules. As a novel application, the prepared stimuli-responsive latexes were used as anticounterfeiting inks for writing on cellulosic paper and also security marking on several monies, where the written phrase displayed red fluorescence emission and coloration under and after UV illumination (365 nm), respectively. Additionally, the latexes were sprayed on cellulosic papers to prepare stimuli-responsive papers for investigation of their photopatterning ability under UV irradiation and different masking. The presence of functional groups and large particle sizes are the main effective factors for stabilization of the latex particles on cellulosic papers. This is the first report on application of functionalized stimuli-responsive latex particles containing spiropyran as anticounterfeiting inks for security marking and photopatterning on cellulosic papers, directly and without using further additives.
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•Preparation of photochromic chemosensors based on spiropyran.•Stimuli-responsive papers with pH-responsivity.•Chemical modification of cellulosic papers with functionalized acrylic ...latex particles.•Study on photo-switchablity, photofatigue resistant and kinetic of photoisomerization.
Photochromic chemosensors based on spiropyran have attracted great attentions in recent years. Here, stimuli-responsive papers were prepared by chemical attachment of epoxy functionalized latex particles containing spiropyran moieties on the cellulose fibers by a new strategy for design and preparation of an acrylic copolymer pH-sensor. pH-Responsivity, photo-switchablity, photofatigue resistant and kinetic of photoisomerization were investigated by soaking of the papers in water with different pHs and they were analyzed by solid-phase UV–vis spectroscopy. Photoisomerization rate constants were measured for the wet papers in acidic and basic media (kc = 0.11–0.14 s−1) and they were much faster than in the dry state (kc = 0.08 s−1). Remarkable photochromic properties with no negative photochromism were observed here and also not influenced by hydrogen bondings and dipolar interactions. SEM images and contact angle measurements revealed high resistance of such papers against their surrounding environment. Moreover, the immediate response to pH changes was accompanied with different distinct colors.
Incorporation of chromophores into a polymer chain results in prominent photoreversibility and fatigue resistance, photostability over the long term, and restriction of the internal conversion (IC). ...Here, we report the copolymerization of two photoactive monomers with methyl methacrylate via emulsion polymerization in order to obtain photoswitchable dual-color fluorescent nanoparticles. For this purpose, azocarbazole ethyl acrylate (AzoCzEA) and spiropyran ethyl acrylate (SPEA) were synthesized and the fluorescence polymeric latex nanoparticles were prepared correspondingly. FT-IR and 1HNMR spectra were used to confirm the structure of novel fluorescent AzoCzEA. UV–vis studies of the obtained nanoparticles displayed the spectral features of both AzoCzEA and SPEA under stimuli-irradiation and inclusion of these chromophores into the polymer particles. DSC analysis revealed an increase in T g of the prepared copolymer, indicating covalently incorporation of the photoactive monomers into the polymer chains. The optimum ratio of two chromophores to achieve complete quenching and highest energy transfer was determined by UV–vis spectroscopy. DLS and SEM results demonstrated particle size distribution of 40–80 nm with spherical morphology. Fluorescence spectra revealed remarkable fluorescence resonance energy transfer (FRET) from AzoCzEA to SPEA after UV irradiation at 365 nm and dual-color characteristic of the prepared nanoparticles. Besides, an enhancement in the photoreversibility, photostability, prevention of IC, dye leakage, and aggregation were studied elaborately. The obtained results were attributed to the involvement of such chromophores into the polymeric matrix via covalent bonding. Labeling and tracking of living cells and rewriteable patterning are potential applications for such dual-color fluorescent nanoparticles.
Meta-heuristic algorithms have been effectively employed to tackle a wide range of optimisation issues, including structural engineering challenges. The optimisation of the shape and size of ...large-scale truss structures is complicated due to the nonlinear interplay between the cross-sectional and nodal coordinate pressures of structures. Recently, it was demonstrated that the newly proposed Marine Predator Algorithm (MPA) performs very well on mathematical challenges. The MPA is a meta-heuristic that simulates the essential hunting habits of natural marine predators. However, this algorithm has some disadvantages, such as becoming locked in locally optimal solutions and not exhibiting high exploratory behaviour. This paper proposes two hybrid marine predator algorithms, Nonlinear Marine Predator (HNMPA) and Nonlinear-Chaotic Marine Predator Algorithm (HNCMPA), as improved variations of the marine predator algorithm paired with a hill-climbing (HC) technique for truss optimisation on form and size. The major advantage of these techniques is that they seek to overcome the MPA's disadvantages by using nonlinear values and prolonging the exploration phase with chaotic values; also, the HC algorithm has been used to avoid locally optimum solutions. In terms of truss optimisation performance, the proposed algorithm is compared to fourteen well-known meta-heuristics, including the Dragonfly Algorithm (DA), Henry Gas Solubility optimisation (HGSO), Arithmetic optimisation Algorithm (AOA), Generalized Normal Distribution Optimisation (GNDO), Salp Swarm Algorithm (SSA), Marine Predators Algorithm (MPA), Neural Network Algorithm (NNA), Water Cycle Algorithm (WCA), Artificial Gorilla Troops Optimiser (GTO), Gray Wolf Optimiser (GWO), Moth Flame Optimiser (MFO), Multi-Verse Optimiser (MVO), Equilibrium Optimiser (EO), and Cheetah Optimiser (CO). Furthermore, seven algorithms were chosen to test HNCMPA performance on benchmark optimisation sets, including MPA, MVO, PSO, MFO, SSA, GWO, and WOA. The experiment results demonstrate that the optimisation techniques surpass previously established meta-heuristics in the field of optimisation, encompassing both traditional and CEC problems, by a margin of over 95% in terms of attaining a superior ultimate solution. Additionally, with regards to solving truss optimisation difficulties as a large-scale real-world engineering challenge, the outcomes indicate a performance boost of over 65% in obtaining significantly better solutions for problems involving 260-bar and 314-bar; conversely, in the case of 340-bar issues, the improvement rate is slightly lower at almost 25%.
The huge advancement in the field of communication has pushed the innovation pace toward a new concept in the context of Internet of Things (IoT) named IoT for Financial Technology applications ...(IoT-FinTech). The main intention is to leverage the businesses' income and reducing cost by facilitating the benefits enabled by IoT-FinTech technology. To do so, some of the challenging problems that mainly related to routing protocols in such highly dynamic, unreliable (due to mobility), and widely distributed network need to be carefully addressed. This article, therefore, focuses on developing a new trustworthy and efficient routing mechanism to be used in routing data traffic over IoT-FinTech mobile networks. A new nonlinear Lévy Brownian generalized normal distribution optimization (NLBGNDO) algorithm is proposed to solve the problem of finding an optimal path from source to destination sensor nodes to be used in forwarding FinTech's related data. We also propose an objective function to be used in maintaining the trustworthiness of the selected relay-node candidates by introducing a trust-based friendship mechanism to be measured and applied during each selection process. The formulated model also considering node's residual energy, experienced response time, and internode distance (to figure out density/sparsity ratio of sensor nodes). Results demonstrate that our proposed mechanism could maintain very wise and efficient decisions over the selection period in comparison with other methods.
Chemical incorporation of epoxy-modified graphitic layers in epoxy/novolac phenolic resin matrices was carried out through co-curing of epoxy and novolac resins using triphenylphosphine as catalyst. ...First, (3-glycidyloxypropyl) trimethoxysilane (GPTMS) was grafted on graphene oxide (GO) surface to obtain epoxidized GO layers. Then epoxy resin and GPTMS-modified GO were incorporated into thermosetting reaction using novolac resin in the presence of triphenylphosphine. Covalent attachment of GPTMS-modified GO to the resin matrices resulted in a hybrid composite with high thermal characteristics. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction, and Raman spectroscopy were used for approving modification of GO with GPTMS. The images resulted from scanning and transmission electron microscopies exhibited GO layers with lots of creases turning to smooth layers with a few thin ripples after modification with GPTMS. TGA results showed that thermal characteristics of resins were improved by the addition of GPTMS-modified GO. Char residue of the hybrid composites containing 0.5 and 1 wt% of GPTMS-modified GO reached 28.1 and 34.3%, respectively. Also, their maximum thermal degradation temperature was also increased by the incorporation of GPTMS-modified GO.
Investigation of developed photoactive security inks and anticounterfeiting technologies in recent years indicates significant challenges for future of this research area, such as increase of ...security, fast responsivity, and facile authentication. Here, amine-functionalized latex nanoparticles were synthesized by emulsion copolymerization of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). Size of the latex nanoparticles was increased as a function of poly(dimethylaminoethyl acrylate) (PDMAEMA) contents, and also a decrease of particle size was obtained in response to an increase of temperature from 25 to 70 °C, above the lower critical solution temperature (LCST) of PDMAEMA. Surface physical modification of the functional latex nanoparticle with spiropyran photoswitches led to the development of anticounterfeiting nanoinks that have multilevel security and photochromic/fluorescence properties with a higher intensity and also brightness. The photoluminescent nanoinks were made of spiropyran latex nanoparticles and used for printing of the encoded optical security tags on cellulosic papers and banknotes. The results displayed that an increase of the particle size above 100 nm and an increase of the PDMAEMA contents led to a remarkable decrease of printability, fluorescent emission, brightness, intensity of photochromism, and also resolution of the printed security tags. As a significant advantage of the developed security inks, the printed security tags could be authenticated easily and fast upon sunlight irradiation by means of photochromism. The responsivity of encoded tags from the invisible to visible state is immediate upon sunlight irradiation for some seconds, whose intensity of coloration is appropriate and detectable clearly by naked eyes. The security anticounterfeiting inks based on spiropyran with multilevel security have been reported for the first time for applying in printing of encoded security tags on cellulosic papers, banknotes, and other documents, where the printed marks are detectable on sunlight exposure.
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