Dynamic anticounterfeiting polymeric inks for multipurpose time-dependent encryption with a high level of security

Abstract

Development of dynamic anticounterfeiting inks with time-dependent photochromism and photoluminescence characteristics has become highly interesting in advanced encryption systems. These inks are applicable in different fields, such as tracking UV rays and gas leakage and also quality monitoring. In this study, semi-continuous copolymerization of butyl acrylate and methyl methacrylate in the heterogeneous miniemulsion medium was used to synthesize colloidal nanoparticles with different flexibilities and polarities. Then, hydroxyl-functional spiropyran (SPOH) was physically incorporated into the nanoparticles to prepare photochromic and photoluminescent inks. The nanoparticles showed low light reflectance due to their small size, which makes them applicable in photoresponsive and sensing applications. In addition, the nanoparticles exhibited different glass transition temperature (Tg) that affects their photoresponsivity. Microscopic analysis revealed that all the latex samples have spherical nanoparticles with a mean size of about 70 nm and a low polydispersity index. UV–vis absorption and fluorescence emission spectra, isomerization kinetics, and photofatigue resistance of the photochromic latex nanoparticles were studied, which depend on chain polarity and flexibility of the latex nanoparticles. The optical properties of the photochromic materials are closely related to the structure and composition of the latex samples. Time-dependent features of the inks originate from their spiropyran molecules which gradually turns into the merocyanine form upon visible light induction. Photochromic inks with advanced encryption and dynamic characteristics were developed from the SPOH-doped colloidal latex nanoparticles. Different polarities and Tg of the inks result in their different dynamic chromism, which show their high level of information encryption technology. By virtue of these unique time-dependent properties, the encryption capabilities of these inks are significantly improved. These inks achieved unprecedented advances in the field of information security and encryption because of their innovative features.