Thermally and magnetically stimulated shape memory polyurethane (PU) nanocomposites were synthesized for intravascular stent applications. For this end, Fe3O4 magnetic nanoparticles (MNPs) were ...modified with octadecyl isocyanate (OD) to increase their affinity with the PU matrix by formation of the covalent urea linkages. The results showed that the OD‐grafted MNPs were replaced instead of carbonyl groups of polycaprolactone (PCL) soft segments in hydrogen bond formation with the urethane linkages. This led to higher phase separation degrees among the soft and hard phases, thereby PCL chains could reveal higher crystallization potential. Mechanical studies showed that the nanocomposites had high mechanical strength, Young's modulus, and elongation at break, which improve their practical applications. The nanocomposites showed thermo‐responsive shape memory behavior with a high shape recovery and shape fixity ratios due to the presence of the crystallizable PCL segments. The nanocomposite containing 10 wt% of the OD‐grafted MNPs could recover its original shape (during 90s) in a relatively weak alternating magnetic field (350 kHz and 12.9 kA/m). These results indicated that the prepared nanocomposites could be used to normalize the narrowed blood vessels through the remotely and magnetically‐controllable restricted shape recovery process.
Restricted shape recovery process in the presence of an alternating magnetic field.
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.
Fe3O4 magnetic nanoparticles (MNPs) are subsequently modified with (3‐aminopropyl) triethoxysilane (APTES) and octadecyl isocyanate (OD) to yield MNPs‐g‐OD. Fourier‐transform infrared (FTIR), X‐ray ...diffraction (XRD), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM) verified successful modification of MNPs with three different ratios of OD. Shape memory polyurethane (SMPU) nanocomposites containing 4 wt% of the neat, APTES‐grafted, and OD‐grafted MNPs are prepared through solution casting, where a strong correlation is achieved between the microstructure, crystallinity, thermal, and mechanical properties of the nanocomposites. Phase mixing degree of the soft and hard phases is increased by hydrogen bonding between the OD and polyurethane (PU) chains, causing to decrease of crystallization ability of PU chains. Field‐emission scanning electron microscopy (FE‐SEM) images show that high dispersion of MNPs‐g‐OD reduces the number and size of their aggregation sites in the PU matrix. The nanocomposites show high Young's modulus, because of increasing hydrogen bonding index of carbonyl groups with incorporation of MNPs‐g‐OD into the PU matrix. The nanocomposites show lower Young's modulus with increasing the degree of crystallinity. Shape memory studies indicated that all the samples have considerable shape memory abilities at 50 °C and room temperature. However, shape fixity ratios show a close dependence on the degree of crystallinity at room temperature.
The formation of hydrogen bonds among urea linkages on octadecyl isocyanate‐grafted Fe3O4 magnetic nanoparticles (OD‐grafted MNPs) with polyurethane (PU) chains improves their dispersion in organic matrix and increases phase mixing degree of soft and hard phases. The improved interaction of magnetic nanoparticles with PU matrix manipulates different properties of PU nanocomposites.
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.
Optical chemosensors and ionochromic cellulosic papers based on oxazolidine chromophores were developed for selective photosensing of metal ions and information encryption as security tags, ...respectively. The oxazolidine molecules have been displayed highly intense fluorescent emission and coloration characteristics that are usable in sensing and anticounterfeiting applications. Obtained results indicated that oxazolidine molecules can be used for selective detection of pb
(0.01 M), and photosensing of Fe
, Co
and Ag
metal ion solutions by colorimetric and fluorometric mechanisms with higher intensity and sensitivity. Also, oxazolidine derivatives were coated on cellulosic papers via layer-by-layer method to prepare ionochromic papers. Prepared ionochromic papers were used for printing and handwriting of optical security tags by using of metal ion solutions as a new class of anticounterfeiting inks with dual-mode fluorometric and colorimetric securities. The ionochromic cellulosic papers can be used for photodetection of metal ions in a fast and facile manner that presence of metal ions is detectable by naked eyes. Also, key-lock anticounterfeiting technology based on ionochromic papers and metal ion solution as ink is the most significant strategy for encryption of information to optical tags with higher security.
(3-Aminopropyl) triethoxysilane was grafted at the surface of GO in low and high different graft densities to yield GOHAL and GOHAH, respectively. Subsequently, ...2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (RA) was attached at the surface of GOHAL and GOHAH by an amidation reaction to yield GOHRL and GOHRH, respectively. Then, GOHRL and GOHRH were used in grafting from RAFT polymerization of styrene.
•A RAFT agent grafted GO was used in grafting from RAFT polymerization of styrene.•The efficiency of RAFT agent attachment at the surface of GO is 41.12% for high density sample.•Polystyrene molecular weight is decreased by the addition of graphene content and also graft density of RAFT agent.
(3-Aminopropyl) triethoxysilane was grafted at the surface of GO in low and high different graft densities to yield GOHAL and GOHAH, respectively. Subsequently, 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (RA) was attached at the surface of GOHAL and GOHAH by an amidation reaction to yield GOHRL and GOHRH, respectively. Then, GOHRL and GOHRH were used in grafting from RAFT polymerization of styrene. Grafting of APTES and RA was approved by Fourier transform infrared spectroscopy, X-ray photo electron spectroscopy, and Raman spectroscopy. Expansion of graphene interlayer by oxidation and functionalization processes was evaluated by X-ray diffraction. Conversion values of styrene were calculated using gas chromatography. Molecular weight and PDI values of attached polystyrene (PS) chains were studied by size exclusion chromatography. Thermogravimetric analysis was also used to investigate the degradation temperatures, char contents, and graft contents of modifiers and PS chains. GOHRH and GOHRL reach to char content of 55.3 and 45.2% at 600°C, which shows that weight ratio of modifier (APTES and RA moieties) is 15.3 and 5.2%, respectively. Scanning and transmission electron microscopies show that graphite layers with flat and smooth surface wrinkled after oxidation and turned to opaque layers by grafting PS.
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