Ionogels are compelling materials for technological devices due to their excellent ionic conductivity, thermal and electrochemical stability, and non-volatility. However, most existing ionogels suffer from low strength and toughness. Here, we report a simple one-step method to achieve ultra-tough and stretchable ionogels by randomly copolymerizing two common monomers with distinct solubility of the corresponding polymers in an ionic liquid. Copolymerization of acrylamide and acrylic acid in 1-ethyl-3-methylimidazolium ethyl sulfate results in a macroscopically homogeneous covalent network with in situ phase separation: a polymer-rich phase with hydrogen bonds that dissipate energy and toughen the ionogel; and an elastic solvent-rich phase that enables for large strain. These ionogels have high fracture strength (12.6 MPa), fracture energy (~24 kJ m−2) and Young’s modulus (46.5 MPa), while being highly stretchable (~600% strain) and having self-healing and shape-memory properties. This concept can be applied to other monomers and ionic liquids, offering a promising way to tune ionogel microstructure and properties in situ during one-step polymerization.
Your institute does not have access to this article
Subscription info for Chinese customers
We have a dedicated website for our Chinese customers. Please go to naturechina.com to subscribe to this journal.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Lodge, T. P. & Ueki, T. Mechanically tunable, readily processable ion gels by self-assembly of block copolymers in ionic liquids. Acc. Chem. Res. 49, 2107–2114 (2016).
Ding, Y. et al. Preparation of high‐performance ionogels with excellent transparency, good mechanical strength, and high conductivity. Adv. Mater. 29, 1704253 (2017).
Zhou, B. et al. Flexible, self-healing, and fire-resistant polymer electrolytes fabricated via photopolymerization for all-solid-state lithium metal batteries. ACS Macro Lett. 9, 525–532 (2020).
Shi, L. et al. Highly stretchable and transparent ionic conductor with novel hydrophobicity and extreme-temperature tolerance. Research 2020, 2505619 (2020).
Tamate, R. et al. Self‐healing micellar ion gels based on multiple hydrogen bonding. Adv. Mater. 30, 1802792 (2018).
Kim, Y. M. & Moon, H. C. Ionoskins: nonvolatile, highly transparent, ultrastretchable ionic sensory platforms for wearable electronics. Adv. Funct. Mater. 30, 1907290 (2020).
Ren, Y. et al. Ionic liquid–based click-ionogels. Sci. Adv. 5, eaax0648 (2019).
Lu, B. et al. Pure PEDOT: PSS hydrogels. Nat. Commun. 10, 1043 (2019).
Xu, J. et al. Multi-scale ordering in highly stretchable polymer semiconducting films. Nat. Mater. 18, 594–601 (2019).
Liu, Y. et al. Soft and elastic hydrogel-based microelectronics for localized low-voltage neuromodulation. Nat. Biomed. Eng. 3, 58–68 (2019).
Ma, Y. et al. Flexible hybrid electronics for digital healthcare. Adv. Mater. 32, 1902062 (2020).
Kim, H. J., Chen, B., Suo, Z. & Hayward, R. C. Ionoelastomer junctions between polymer networks of fixed anions and cations. Science 367, 773–776 (2020).
Osada, I., de Vries, H., Scrosati, B. & Passerini, S. Ionic‐liquid‐based polymer electrolytes for battery applications. Angew. Chem. Int. Ed. Engl. 55, 500–513 (2016).
Chen, N., Zhang, H., Li, L., Chen, R. & Guo, S. Ionogel electrolytes for high‐performance lithium batteries: a review. Adv. Energy Mater. 8, 1702675 (2018).
Chen, N. et al. Biomimetic ant-nest ionogel electrolyte boosts the performance of dendrite-free lithium batteries. Energy Environ. Sci. 10, 1660–1667 (2017).
Hyun, W. J., Thomas, C. M. & Hersam, M. C. Nanocomposite ionogel electrolytes for solid‐state rechargeable batteries. Adv. Energy Mater. 10, 2002135 (2020).
Shi, L. et al. Dielectric gels with ultra-high dielectric constant, low elastic modulus, and excellent transparency. NPG Asia Mater. 10, 821–826 (2018).
Liu, Y., He, K., Chen, G., Leow, W. R. & Chen, X. Nature-inspired structural materials for flexible electronic devices. Chem. Rev. 117, 12893–12941 (2017).
Shi, L. et al. Highly stretchable and transparent ionic conducting elastomers. Nat. Commun. 9, 2630 (2018).
Lei, Z. & Wu, P. A highly transparent and ultra-stretchable conductor with stable conductivity during large deformation. Nat. Commun. 10, 3429 (2019).
Cao, Z., Liu, H. & Jiang, L. Transparent, mechanically robust, and ultrastable ionogels enabled by hydrogen bonding between elastomers and ionic liquids. Mater. Horiz. 7, 912–918 (2020).
Zhang, L. M. et al. Self‐healing, adhesive, and highly stretchable ionogel as a strain sensor for extremely large deformation. Small 15, 1804651 (2019).
Li, T., Wang, Y., Li, S., Liu, X. & Sun, J. Mechanically robust, elastic, and healable ionogels for highly sensitive ultra‐durable ionic skins. Adv. Mater. 32, 2002706 (2020).
Correia, D. M. et al. Ionic liquid–polymer composites: a new platform for multifunctional applications. Adv. Funct. Mater. 30, 1909736 (2020).
Le Bideau, J., Viau, L. & Vioux, A. Ionogels, ionic liquid based hybrid materials. Chem. Soc. Rev. 40, 907–925 (2011).
Yu, L. et al. Highly tough, Li‐metal compatible organic–inorganic double‐network solvate ionogel. Adv. Energy Mater. 9, 1900257 (2019).
Zhao, X. Multi-scale multi-mechanism design of tough hydrogels: building dissipation into stretchy networks. Soft Matter 10, 672–687 (2014).
Gong, J. P., Katsuyama, Y., Kurokawa, T. & Osada, Y. Double‐network hydrogels with extremely high mechanical strength. Adv. Mater. 15, 1155–1158 (2003).
Sun, J.-Y. et al. Highly stretchable and tough hydrogels. Nature 489, 133–136 (2012).
Zhang, H. J. et al. Tough physical double‐network hydrogels based on amphiphilic triblock copolymers. Adv. Mater. 28, 4884–4890 (2016).
Sato, K. et al. Phase‐separation‐induced anomalous stiffening, toughening, and self‐healing of polyacrylamide gels. Adv. Mater. 27, 6990–6998 (2015).
Gong, J. P. Why are double network hydrogels so tough? Soft Matter 6, 2583–2590 (2010).
Corkhill, P., Trevett, A. & Tighe, B. The potential of hydrogels as synthetic articular cartilage. Proc. Inst. Mech. Eng. H 204, 147–155 (1990).
Zhang, H. et al. Polyelectrolyte microcapsules as ionic liquid reservoirs within ionomer membrane to confer high anhydrous proton conductivity. J. Power Sources 279, 667–677 (2015).
Ueki, T. & Watanabe, M. Polymers in ionic liquids: dawn of neoteric solvents and innovative materials. Bull. Chem. Soc. Jpn 85, 33–50 (2012).
Ueki, T., Watanabe, M. & Lodge, T. P. Doubly thermosensitive self-assembly of diblock copolymers in ionic liquids. Macromolecules 42, 1315–1320 (2009).
Weng, D. et al. Polymeric complex-based transparent and healable ionogels with high mechanical strength and ionic conductivity as reliable strain sensors. ACS Appl. Mater. Interfaces 12, 57477–57485 (2020).
Sun, T. L. et al. Physical hydrogels composed of polyampholytes demonstrate high toughness and viscoelasticity. Nat. Mater. 12, 932–937 (2013).
Hu, X., Vatankhah‐Varnoosfaderani, M., Zhou, J., Li, Q. & Sheiko, S. S. Weak hydrogen bonding enables hard, strong, tough, and elastic hydrogels. Adv. Mater. 27, 6899–6905 (2015).
Kong, W. et al. Muscle‐inspired highly anisotropic, strong, ion‐conductive hydrogels. Adv. Mater. 30, 1801934 (2018).
Mredha, M. T. I. et al. A facile method to fabricate anisotropic hydrogels with perfectly aligned hierarchical fibrous structures. Adv. Mater. 30, 1704937 (2018).
Asaletha, R., Kumaran, M. & Thomas, S. Thermoplastic elastomers from blends of polystyrene and natural rubber: morphology and mechanical properties. Eur. Polym. J. 35, 253–271 (1999).
Bai, R., Yang, J. & Suo, Z. Fatigue of hydrogels. Eur. J. Mech. A 74, 337–370 (2019).
M.D. acknowledges support from the Coastal Studies Institute. J.H. acknowledges the support of the National Natural Science Foundation of China (11702207). We thank Prof. L. Cai for helpful discussion. We thank Mr M. Yang and Mr X. Chen for help with 3D printing. Nano-IR analysis was performed by W.Q. at the NanoEngineering Research Core Facility (NERCF), which is partially funded by the Nebraska Research Initiative.
The authors declare no competing interests.
Peer review information
Nature Materials thanks Xuanhe Zhao and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Figs. 1–17, Notes 1–4, Tables 1 and 2, Videos 1–5 and refs. 1–7.
This movie shows that the P(AAm0.8125-co-AA0.1875) ionogel is strong enough to lift a 1 kg weight, while the pure PAA and PAAm ionogel and P(AAm0.8125-co-AA0.1875) hydrogel break. Cm = 6 M, CMBAA = 0.1 mol%.
This movie demonstrates the ultra-tough properties of the gel when a metal ball drops on a membrane of P(AAm0.8125-co-AA0.1875) ionogel stretched across a rigid frame. The membrane (thickness = 0.5 mm) was glued to two polyacrylate clamps with a circular opening (diameter = 7 cm). A stainless steel ball with a diameter of 2.54 cm and mass of 64 g was dropped from a height of 2 m. Upon hitting the membrane, the ball bounced back and the membrane remained intact with small deformation, while the P(AAm0.8125-co-AA0.1875) hydrogel was stretched to rupture after large deformation. Cm = 6 M, CMBAA = 0.1 mol%.
This movie shows the excellent self-healing property of the P(AAm0.8125-co-AA0.1875) ionogel. The dog-bone samples were cut into half pieces and then the pieces from two different samples were put together to heal. After storing the sample at 80 °C for 1 h, the self-healed sample could lift the 1 kg weight. The copolymer ionogel samples were stained with methylene blue and rhodamine B. Cm = 6 M, CMBAA = 0.1 mol%.
This movie shows the excellent shape-memory properties of P(AAm0.8125-co-AA0.1875) ionogel by demonstrating the fast programming and recovery process. The ionogel sample was stained with rhodamine B for visualization. Cm = 6 M, CMBAA = 0.1 mol%.
This movie exhibits superb shape-memory behaviour of P(AAm0.8125-co-AA0.1875) ionogel using a more complicated six-layer structure of a ‘blooming flower’. Six layers of the copolymer ionogel samples were glued together to mimic the flower bud blooming process and the ionogels could fully recover within 25 s. The ionogel samples were stained with methylene blue. Cm = 6 M, CMBAA = 0.1 mol%.
About this article
Cite this article
Wang, M., Zhang, P., Shamsi, M. et al. Tough and stretchable ionogels by in situ phase separation. Nat. Mater. 21, 359–365 (2022). https://doi.org/10.1038/s41563-022-01195-4