All-in-one photoluminescent Janus nanoparticles for smart technologies: Organic light-emitting diodes, anticounterfeiting, and optical sensors

In this study, a new category of amphiphilic nanoparticles based on random copolymers was prepared by polymerization of the methyl methacrylate (MMA) with methacrylamide (MAAm) in emulsion media to develop functionalized nanoparticles containing amide polar groups in different concentrations, and also the size of nanoparticles is in the range of 47-145 nm. Subsequently, the physical modification of amide groups on the surface of functionalized amphiphilic nanoparticles by using oxazolidine derivative (OXOH) with a concentration of 5 wt% led to the development of photoluminescent copolymer nanoparticles (PLCNPs). The MAAm monomer was used to functionalize polymer nanoparticles with amide groups acting as electron donor groups for oxa-zolidine molecules and their stability on the surface of the polymer nanoparticles by hydrogen bonding. To investigate of optical properties, the PLCNPs samples containing different concentrations of amide groups (0-20 wt%) were studied by photoluminescence and UV-Vis spectroscopy. Obtained results indicate that the emission and absorbance bands (intensity and wavelength) can be influenced significantly by the concentration of amide groups located on the surface of amphiphilic nanoparticles, and most importantly the local polarity. Investigation of the color change of photoluminescence emission for PLCNPs samples as a function of amide group concen-tration by CIE colorimetric diagrams displayed regular shifts in color position by the increase of local polarity, which observed color shifts are in agreement with results of photoluminescence and UV-Vis spectra. It was observed that PLCNPs samples displayed suitable adhesion to the surface and stable optical properties when deposited or coated on substrates that have polar surfaces, such as thermoset/thermoplastic polymer sheets and also cellulose papers. Hence, the PLCNPs samples were used directly as the colloid solution to develop photo-luminescence organic light emitting diodes, water-based and ecofriendly anticounterfeiting inks, and the portable sensor for the detection of artificially created scratches on the surface of the polycarbonate sheet by fluorescence imaging. The results displayed that printed security tags and encrypted information on cellulose papers have orange fluorescence emission with remarkable intensity because the size of latex particles is in the range of nanoscale (below 100 nm) which led to a reduction of light scattering and an increase of light ab-sorption. In a new approach and for the first time, a solution of poly(vinyl alcohol) (PVA)/PLCNPs was deposited on LED (has blue light emission with a wavelength of 365 nm) to change the color of photoluminescence emission from blue to orange-purple by excitation of an organic photoluminescent polymer layer with UV light of LED (365 nm). On the other hand, the PLCNPs solutions were sprayed on the substrate to detect created scratches on the polycarbonate sheet under irradiation with UV light (365 nm) and fluorescence imaging. The advantages of developed water-based PLCNPs samples resulted in to use as an all-in-one nanomaterial in a different and wide range of applications, such as photoluminescent inks for ecofriendly anticounterfeiting technologies, photo-luminescence OLEDs, and also a portable detector for optical visualization of scratches and micro-cracks on various substrates.