Key Takeaways & Executive Findings
- •• • S-UD elastomer achieves elongation at break of ~3257% at −78 °C, 3.4× higher than PDMS controls and ~32% higher than M-UD (~2474%), enabling extreme stretchability for robotic joints in polar conditions. • • Autonomous self-healing efficiency at −78 °C reaches ~75.9% for S-UD after 24 h, versus ~34.3% for M-UD, demonstrating superior crack recovery critical for durable e-skin operation in harsh environments. • • PDMS backbone with Tg = −127 °C and Tb = −150 °C remains unfrozen at polar temperatures, mitigating brittleness and preserving flexibility down to −78 °C, a key design parameter for ultralow-temperature elastomers. • • DFT analysis shows S-UD has a deeper potential well at 0° convergence angle, indicating stronger thermodynamic driving force for chain reconfiguration, which underpins its superior cryogenic self-healing.
Abstract
Polar exploration demands robotic systems capable of operating at extreme low temperatures, yet existing electronic skins (e-skins) fail due to polymer brittleness and impaired self-healing. Here, we report a supramolecular elastomer strategy that enables highly stretchable, self-healing, and sensitive e-skins functional at −78 °C. The elastomers are based on a poly(dimethylsiloxane) (PDMS) backbone (Tg = −127 °C, Tb = −150 °C) functionalized with kinetically reversible quadruple hydrogen-bonding motifs (2-ureido-4[1H]-pyrimidone, UPy) in side chains (S-UD) or main chains (M-UD). At −78 °C, S-UD elastomers exhibit superior stretchability, with optimized S-U1.2D0.8 achieving elongation at break of ~3257%, 3.4 times that of PDMS controls and exceeding M-U1.2D0.8 (~2474%). Self-healing efficiency after 24 h at −78 °C reaches ~75.9% for S-UD versus ~34.3% for M-UD, with visual scratch disappearance only in S-UD. Density functional theory (DFT) analysis reveals that S-UD possesses more thermodynamically favorable chain convergence, enhancing cryogenic self-healing. The optimized S-UD elastomer serves as an excellent substrate for constructing ultralow-temperature-tolerant e-skins, addressing a critical bottleneck in polar robotics.
1. Introduction
Polar exploration demands robotic systems capable of operating at extreme low temperatures, yet existing electronic skins (e-skins) fail due to polymer brittleness and impaired self-healing. Standard elastomers lose flexibility below their glass transition temperature (Tg) or brittleness temperature (Tb), while dynamic bonds for self-healing become kinetically trapped. Flexible conductors such as liquid metals solidify, further complicating device integration. To date, no e-skin has been reported for polar robots, leaving a critical gap in human-robot interaction and autonomous exploration in Earth's coldest regions.
This work addresses the bottleneck by engineering supramolecular elastomers with a PDMS backbone (Tg = −127 °C, Tb = −150 °C) that remains unfrozen at polar temperatures, combined with kinetically reversible quadruple hydrogen-bonding UPy motifs. The side-chain architecture (S-UD) enhances chain mobility and thermodynamic driving forces for self-healing, achieving record stretchability (~3257% at −78 °C) and autonomous healing efficiency (~75.9% after 24 h). These quantitative improvements directly enable the construction of e-skins that maintain mechanical integrity and self-repair capability in ultracold environments, a prerequisite for reliable polar robotics.
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Wentong Gao, Cheng-Hui Li (2026). Side-chain quadruple H-bonds empower self-healing e-skins with ultralow-temperature tolerance. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3627-x
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Frequently Asked Questions
What is the maximum elongation at break for the optimized S-UD elastomer at −78 °C, and how does it compare to PDMS controls?
The optimized S-U1.2D0.8 achieves elongation at break of ~3257% at −78 °C, which is 3.4 times greater than PDMS controls and exceeds the M-UD analogue (~2474%). This indicates superior chain flexibility and energy dissipation in side-chain architectures.
How does the self-healing efficiency of S-UD at −78 °C compare to M-UD, and what is the underlying mechanism?
After 24 h autonomous healing at −78 °C, S-UD reaches ~75.9% healing efficiency versus ~34.3% for M-UD. DFT analysis shows S-UD has a deeper potential well at the most stable 0° convergence angle, indicating stronger thermodynamic driving forces and enhanced chain mobility, which facilitate bond reformation.
What are the key design parameters that enable ultralow-temperature flexibility in this elastomer system?
The PDMS backbone has a Tg of −127 °C and Tb of −150 °C, ensuring it remains unfrozen at polar temperatures. The incorporation of kinetically reversible quadruple H-bonding UPy motifs allows rapid bond dissociation and reformation, while side-chain placement (S-UD) enhances chain mobility compared to main-chain (M-UD) analogues.
How does the side-chain architecture (S-UD) outperform main-chain (M-UD) in terms of stretchability and self-healing, and what are the trade-offs?
S-UD consistently outperforms M-UD in stretchability (e.g., ~3257% vs ~2474% at −78 °C) and self-healing efficiency (~75.9% vs ~34.3%). However, M-UD exhibits higher fracture stress, indicating a trade-off between flexibility and strength. The side-chain design promotes chain mobility and H-bond reconfiguration, which is critical for cryogenic self-healing.
What is the significance of the DFT analysis in explaining the superior cryogenic self-healing of S-UD?
DFT analysis reveals that S-UD has lower (more thermodynamically favorable) energy values across most convergence angles except 30° and 180°, and a deeper potential well at 0°. This indicates a stronger gravitational effect on mutual chain convergence, enhancing the probability of successful bond reformation under cryogenic conditions.
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