Turning a Material Flaw Into a Feature: Information Encryption and Readout via the Mullins Effect

ABSTRACT The Mullins effect, a stress‐softening phenomenon in elastomers, has long been considered a critical bottleneck for mechanoluminescent (ML) devices, undermining the reproducibility and intensity of their light emission. Herein, this paradigm is challenged by transforming the detrimental Mullins effect into a functional asset. Highly deformable elastic films, composed of polydimethylsiloxane (PDMS) and copper‐doped zinc sulfide (ZnS: Cu), are fabricated to elucidate the complex interplay between the stress softening and the ML intensity. Counter‐intuitively, it is discovered that while stress softening diminishes ML intensity at large, fixed strains, it paradoxically enhances the luminescent response in the small strain regime. This nuanced understanding is leveraged to design a novel inverse encryption strategy, where information is securely concealed after a pre‐stretching or pre‐pressing “key”. The versatility of the platform is demonstrated by multilevel data encryption as well as Personalized and Randomized Pattern Customization (PRPC), where the stored information can be read out for over 1000 cycles and preserved for more than six months. This work not only redefines the role of the Mullins effect in functional materials but also unlocks new design principles for sophisticated ML devices in anti‐counterfeiting, soft robotics, and neuromorphic systems capable of associative learning.