Lipophilic Magnetic Photonic Nanochains for Practical Anticounterfeiting

Magnetic photonic crystals (PCs) possess attractive magnetic orientation, flexible pattern designability, and abundant angle-dependent colors, providing immense potential in anticounterfeiting field. However, all-solid magnetic PCs-based labels generally suffer from incompatibility with screen printing techniques, and inferior environmental endurance and mechanical properties. Herein, by developing a selective concentration polymerization method under magnetic field (H) in microheterogenous dimethyl sulfoxide-water binary solvents, individual tens-of-micrometer-length lipophilic magnetic photonic nanochains (PNCs) of full-width at half-maxima below 30 nm are fabricated, which, after simply dispersed in solvent-free cycloaliphatic epoxy resin, can be formulated as photonic inks to print robust anticounterfeiting labels through an H-assisted screen-printing technology. The as-printed labels possess vivid optically variable effects (OVEs) associated with the spatial distribution of H directionality, which are easy to identify by the naked eye but difficult to imitate and duplicate, while they show excellent environmental resistance and mechanical properties, promising practical applications in banknotes and high-grade commodities. The polymerization mechanism of the lipophilic PNCs is elucidated, and the OVEs are deciphered in numerical simulation. Besides an efficient way to build organic-inorganic hybrid nanostructures, the work provides advanced structural color pigments to achieve the practical application of magnetic PCs in such an anticounterfeiting field.