Color-changing organogel stretches 46 times its size and self-heals
Sanjukta Mondal
contributing writer
Sadie Harley
scientific editor
Robert Egan
associate editor
Scientists from Taiwan have developed that can stretch up to 4,600% of its original length before breaking. Even if it does break, gently pressing the pieces together at room temperature allows it to heal, fully restoring its shape and stretchability within 10 minutes.
The sticky and stretchy polyurethane (PU) organogels were designed by combining covalently linked cellulose nanocrystals (CNCs) and modified mechanically interlocked molecules (MIMs) that act as artificial molecular muscles.
The muscles make the gel sensitive to external forces such as stretching or heat, where its color changes from orange to blue based on whether the material is at rest or stimulated. Thanks to these unique properties, the gels hold great promise for next-generation technologies鈥攆rom flexible electronic skins and soft robots to anti-counterfeiting solutions.
The findings are in Advanced Functional Materials.
MIMs, such as rotaxanes and daisy chains, are promising because their molecular motion enhances toughness and flexibility. MIMs have also opened up the world of mechanochromic materials鈥攕ubstances that fluoresce or change colors in response to a stimulus.
These materials contain molecular switches called mechanophores, which respond to force by breaking and reforming chemical bonds, leading to small but dramatic structural shifts.
Studies show that even small amounts of MIMs can greatly enhance the stretchability and toughness of polymers. While mechanophores are commonly used for temperature and force sensing, incorporating them into self-healing systems has proven challenging.
To address this, the researchers experimented with a range of compositions to develop novel PU organogels. They achieved their desired strength, stretch, self-repair, adhesion, and color-changing properties in organogels by incorporating MIMs modified with special fluorescent groups called DPAC and cellulose nanocrystals via a step-growth polymerization process.
The PU organogels containing about 1.5 wt.% MIMs exhibited excellent toughness of 142 MJ/m3 and stretchability 46 times its own size. The organogels emitted orange or blue fluorescence depending on how stretched the material was.
When relaxed, DPAC units in the material vibrated in an unconstricted way with a frequency of 603 nm, resulting in orange light. Stretching applied force that drove the DPAC units to slide, constraining the vibrations and shifting the emission to blue at 451 nm.
The gels autonomously self-healed at room temperature, recovering more than 90% of their original strength and stretchability. This self-repair was supported by hydrogen bonding introduced through cellulose nanocrystals.
Scaled for mass production, this material could enable sustainable technologies by signaling repairs and extending product lifetimes.
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More information: Tu Thi Kim Cuc et al, Effective Sliding Motions of Vibration鈥怚nduced Emission Stoppers in Mechanically Interlocked Molecules as Artificial Muscle Tougheners and In Situ Molecular Shuttling Sensors for Self鈥怘ealable Mechano鈥怓luorescent Polyurethane Organogels, Advanced Functional Materials (2025).
Journal information: Advanced Functional Materials
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