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Tough and stretchable ionogels by in situ phase separation

Nature Materials volume 21, pages 359–365 (2022)Cite this article

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Abstract

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.

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Fig. 1: Schematics of three types of ionogels.
Fig. 2: Photographs, mechanical demonstration and SEM images of various ionogels.
Fig. 3: Mechanical characterization of various gels.
Fig. 4: Self-recovery, self-healing and shape-memory properties of P(AAm0.8125-co-AA0.1875) ionogel.

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Data generated or analysed during this study are provided as Source Data or included in the Supplementary Information. Further data are available from the corresponding authors on request. Further details on the methods are available in the Supplementary Information.

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Acknowledgements

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.

Author information

Authors and Affiliations

  1. State Key Laboratory for Strength and Vibration of Mechanical Structures, International Center for Applied Mechanics, Department of Engineering Mechanics, Xi’an Jiaotong University, Xi’an, China

    Meixiang Wang, Pengyao Zhang & Jian Hu

  2. Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA

    Meixiang Wang, Mohammad Shamsi, Jacob L. Thelen, Vi Khanh Truong, Jinwoo Ma & Michael D. Dickey

  3. Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, USA

    Wen Qian

  4. School of Science, STEM College, RMIT University, Melbourne, Victoria, Australia

    Vi Khanh Truong

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  1. Meixiang Wang
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Contributions

M.W., J.H. and M.D.D. conceived the idea. J.H. and M.D.D. supervised the project. M.W. carried out most of the experiments. P.Z. participated in the fracture energy measurements. M.S. and V.K.T. participated in the SEM measurements. M.S. participated in the SAXS measurements. J.L.T. contributed to the SAXS data processing and analysis. W.Q. conducted the nano-IR measurements. J.M. contributed to the demonstration of the falling metal ball. M.W., J.H., and M.D.D. wrote the paper, and all authors reviewed the manuscript.

Corresponding authors

Correspondence to Jian Hu or Michael D. Dickey.

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Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Materials thanks Xuanhe Zhao and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–17, Notes 1–4, Tables 1 and 2, Videos 1–5 and refs. 1–7.

Supplementary Video 1

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%.

Supplementary Video 2

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%.

Supplementary Video 3

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%.

Supplementary Video 4

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%.

Supplementary Video 5

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%.

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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

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