image: The hydrogel transforms from rubbery softness to rigid armor in seconds when heated—and just as quickly reverts to its flexible state when cooled.
Credit: ©Science China Press
A team from Donghua University has engineered a groundbreaking hydrogel that transforms from rubbery softness to rigid armor in seconds when heated—and just as quickly reverts to its flexible state when cooled. Published in National Science Review, this “high-entropy” hydrogel addresses a long-standing bottleneck in thermal-responsive materials: slow recovery.
Why It Matters
Traditional thermal-stiffening hydrogels, which harden upon heating, often take over 30 minutes to soften again due to slow phase dissolution. This delay limits their use in real-time applications like impact-resistant wearables or soft robots. The new hydrogel slashes recovery time to 28 seconds while maintaining exceptional stiffness (760-fold modulus increase at 80°C).
The Science Behind the Speed
The key lies in a high-entropy phase-separation design. By incorporating hydrophilic acrylamide (AAm) units into a calcium acrylate polymer network, the team disrupted dense clusters of calcium-crosslinked chains. This created a disordered, porous structure that allows rapid water diffusion during cooling.
“Think of it like loosening tightly packed Lego blocks with marbles in between,” explains co-author Shengtong Sun. “The high-entropy topology lowers energy barriers, letting the material ‘melt’ back to softness almost instantly.”
Performance Highlights
- Soft state (20°C): Stretches over 20x its length, conforms to human hand.
- Rigid state (80°C): Supports 1 kg weight, resists impact at 474 J/m.
- Ultrafast recovery: Transitions from glassy to rubbery in 28 seconds (vs. 23 minutes for conventional hydrogels).
Applications on the Horizon
The material’s rapid switching dynamics make it ideal for:
- Adaptive armor: Hardens on impact, softens for comfort.
- Soft robotics: Enables heat-triggered shape changes for precise tasks.
- Smart fabrics: Adjusts stiffness based on body temperature.