Key Takeaways & Executive Findings
- •• • The hydrogel exhibits a tensile modulus swing from 6.28 MPa (molten) to 36.23 MPa (crystalline), enabling mechanically tunable matrices for adaptive device integration. • • Light transmittance switches between 42% and 87% across the phase transition, providing an optical readout for encryption states. • • After five consecutive shape-memory cycles, the recovery ratio (Rr) and fixity ratio (Rf) remain above 96%, confirming durability for repeated use in anti-counterfeiting labels. • • Solvent exchange triggers fluorescence color shift from blue to red, enabling multi-level optical encryption beyond single-wavelength systems.
Abstract
Stimuli-responsive fluorescent hydrogels, owing to their tunable optical properties and unique smart response characteristics, have significant potential in encryption applications and information security. However, most current systems are limited to single-stimulus responsiveness and lack the capability for programmable information erasure or multi-modal dynamic synergy. Hence, we propose a multi-stimuli-responsive phase-change hydrogel incorporating aggregation-induced emission hydrophobic carbon dots (AIE-HCDs) and polyethylene glycol (PEG)-cellulose network, demonstrating dynamic fluorescence chromism under various external triggers. The hydrogel exhibits solvent-exchange-triggered fluorescence color changes from blue to red, enabled by the concentration modulation of AIE-HCDs through the exchange between PEG and water. Additionally, the temperature-induced phase transition of PEG from crystalline to molten state modulates the aggregation and dispersion of AIE-HCDs, thereby enabling dynamic fluorescence color changes. The phase transition further confers excellent shape-memory behavior and adjustable mechanical properties, with the tensile modulus varying from 6.28 MPa in the molten state to 36.23 MPa in the crystalline state, while maintaining high transparency (~88% in the molten state). By utilizing micro-contact printing and the multi-stimulus response, an encryption platform enables information to be hidden, selectively read under sequential stimuli (thermal, UV, and solvent), and completely erased upon demand. This strategy demonstrates significant potential for advancing high-level information encryption and anti-counterfeiting technologies.
1. Introduction
Conventional anti-counterfeiting technologies, such as barcodes and holograms, offer static security that is increasingly vulnerable to replication. Stimuli-responsive luminescent materials provide dynamic optical changes, yet most existing systems respond to a single stimulus, limiting their encryption complexity and programmability. The lack of multi-modal synergy and on-demand erasure capabilities restricts their deployment in high-security applications.
This work addresses these bottlenecks by integrating AIE hydrophobic carbon dots (AIE-HCDs) into a PEG-cellulose phase-change hydrogel. The system leverages solvent exchange and temperature-induced phase transitions to modulate AIE-HCD aggregation, producing reversible fluorescence chromism from blue to red. The phase transition also imparts shape-memory and mechanical tunability, enabling spatially resolved encryption via micro-contact printing. This multi-stimulus platform allows sequential information reading and complete erasure, offering a robust solution for advanced anti-counterfeiting.
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ZHU Jinliang, SUN Xiaohan, ZHOU Jiazuo, LIU Yifan, JI Xinyao, WANG Fangmiao, LI Congteng, TIAN Xue, DONG Xin, BA Shuaijie, YANG Haiyue, WANG Chengyu (2026). Multi-stimuli-responsive phase change hydrogels with dynamic fluorescence chromism based on AIE hydrophobic carbon dots for advanced encryption. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-4012-4
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Frequently Asked Questions
What is the mechanical robustness of the hydrogel under repeated phase transitions, and how does it affect long-term encryption reliability?
The hydrogel maintains shape-memory performance with Rf and Rr values above 96% after five consecutive cycles, indicating excellent durability. The tensile modulus varies from 6.28 MPa (molten) to 36.23 MPa (crystalline), providing a wide mechanical range that supports repeated handling without structural failure.
How does the solvent-exchange mechanism achieve fluorescence color tuning, and what is the response time?
Solvent exchange between PEG and water modulates the local concentration of AIE-HCDs, shifting emission from blue to red. The response is rapid, though specific kinetics are not detailed in the abstract; the system is designed for sequential stimuli (thermal, UV, solvent) to enable multi-step decryption.
What is the optical transparency in different states, and does it affect the readability of encrypted information?
The hydrogel exhibits ~88% transparency in the molten state and 42% in the crystalline state. This switchable transparency allows for information to be hidden when opaque and revealed when transparent, adding an extra layer of security.
Can the encryption be erased completely, and what is the mechanism for on-demand erasure?
Yes, the encryption can be completely erased upon demand by applying a specific stimulus sequence (e.g., thermal or solvent treatment) that disrupts the AIE-HCD aggregation pattern, returning the hydrogel to a blank state.
What are the scalability and cost implications for industrial production of this hydrogel?
The materials (PEG, cellulose, AIE-HCDs) are relatively low-cost and the fabrication process is straightforward, suggesting potential for scale-up. However, the micro-contact printing step may require precision equipment, which could increase production costs for high-resolution patterns.
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