Optical anti-counterfeiting with cholesteric liquid crystal emulsions: preparation, properties, and applications

Abstract

Creating sophisticated anti-counterfeiting tags with unique optical characteristics and detailed security attributes is a highly desirable objective to establish a robust authentication capacity across different stimulus modalities. The ability of structured photonic materials to periodically alter their refractive index enables selective diffraction of specific wavelengths and the tuning of optical density states, leading to the discovery of novel optical properties. This fine-tuning is advantageous for numerous optical applications. Using emulsion templates, microparticles with photonic structures have been created, offering enhanced features and functionalities beyond those of standard films. In this realm, cholesteric liquid crystal (LC) emulsions have recently attracted significant interest. Their inherent periodic structures and modifiable optical signals, responsive to external stimuli, present unique benefits and a broad spectrum of applications in optical anti-counterfeiting. This review explores the preparation techniques of cholesteric LC emulsions, the latest developments in cholesteric LC droplets for various anti-counterfeiting intensities, and the range of optical anti-counterfeiting effects achievable with these droplets under different stimulus conditions. It also provides a brief overview of the existing challenges and prospective future applications of cholesteric LC droplets in anti-counterfeiting systems. The aim of this review is to offer fresh insights and suggestions for enhancing optical anti-counterfeiting strategies through the application of cholesteric LC emulsions.