Their approach centers on engineering nanoscale naphthyl-rich, aromatic hydrocarbon domains that can simultaneously deliver mechanical strength, exceptional fluorescence, and long-lived charge storage within a single material system.
Wearable sensors must endure repeated stretching, bending, and occasional damage, but still provide reliable optical and electronic signals.
Traditional composite approaches, such as mixing conductive fillers into elastomers, often weaken mechanical performance or compromise healing.
Aromatic thermoplastic elastomers containing naphthalene units, on the other hand, have long exhibited strong photoluminescence and charge-trapping behavior due to excimer formation, but integrating these properties into a fully self-healing elastomer has been challenging.
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Polymer-Constrained Excimer Strategy
The team first synthesized a series of 1-vinylnaphthalene isoprene copolymers designed to form highly ordered naphthyl nanodomains within the flexible polyisoprene material.
By using controlled polymerization techniques, they created copolymers with tunable monomer ratios and precisely distributed aromatic units. NMR, FTIR, SAXS, and TEM confirmed random copolymerization and uniform nanoscale segregation.
This structure successfully constrained the mobility and spacing of naphthalene groups, stabilizing excimers in the solid state.
Photoluminescence measurements revealed an ultra-high quantum yield exceeding 98 %, while computational excited-state analyses pinpointed the favored excimer separation at around 3.2 Å. This is particularly notable as such efficient excimer formation usually requires rigid hosts or solvent environments, rather than soft elastomers.
Mechanical and Self-Healing Performance
Mechanical testing showed that copolymers with ~30 mol% 1-vinylnaphthalene struck the best balance between flexibility and toughness, with elongations above 2000 % and tensile strengths approaching 1 MPa. Higher molecular weight versions reached strengths up to 25 MPa while remaining stretchable.
These materials also display rapid, intrinsic self-healing. A cut sample could be rejoined and partially healed within minutes at room temperature, achieving near-complete recovery after several hours.
The authors attribute this behavior to the mobility of the cis-1,4-polyisoprene segments and the reversible π-π interactions that drive naphthyl groups to re-aggregate at damage sites.
Optical and Electret Properties
The transparent elastomers exhibited strong solid-state fluorescence dominated by excimer emission.
Fluorescence increased at lower temperatures, consistent with suppressed non-radiative decay. The copolymers’ photoluminescent performance outperformed most other reported fluorescent polymer systems.
Charge storage tests further demonstrated that the naphthyl nanodomains function as electret sites, retaining stable surface charges for over 30 days at room temperature.
Further characterization using SEM imaging confirmed that this behavior arises from molecular aggregation rather than porosity, highlighting the effectiveness of the microphase-separated architecture.
Sensor Demonstrations
To test its practical integration, the researchers created self-healing electromechanical sensors using the copolymer and a conductive ionic gel. They found that the device maintained stable output signals after being cut and healed, validating its ability to recover mechanically and electronically.
Mounted on robotic fingertips, the sensors captured bending motions with high resolution and wirelessly transmitted the data to a mobile device.
Under ultraviolet light, the copolymer’s fluorescence enabled optical motion tracking. Such tracking is an additional sensing modality uncommon in conventional soft electronics and useful for applications ranging from electronic skin to human–machine interfaces.
Conclusion
The study demonstrates that the ordering of nanoscale naphthyl into microphase separation can unify mechanical toughness, autonomous self-healing, high-efficiency fluorescence, and long-lived charge storage in a single elastomer platform.
By using a polymer-constrained excimer mechanism, the work opens promising directions for future systems that may benefit from both electrical and optical readouts.
Journal Reference
Zheng S., et al. (2025). Polymer-constrained excimer enables flexible and self-healable optoelectronic elastomer for mechanical sensor. Nature Communications 16, 10500. DOI: 10.1038/s41467-025-65539-9