Abstract
Glassy polymers are generally stiff and strong yet have limited extensibility1. By swelling with solvent, glassy polymers can become gels that are soft and weak yet have enhanced extensibility1,2,3. The marked changes in properties arise from the solvent increasing free volume between chains while weakening polymer–polymer interactions. Here we show that solvating polar polymers with ionic liquids (that is, ionogels4,5) at appropriate concentrations can produce a unique class of materials called glassy gels with desirable properties of both glasses and gels. The ionic liquid increases free volume and therefore extensibility despite the absence of conventional solvent (for example, water). Yet, the ionic liquid forms strong and abundant non-covalent crosslinks between polymer chains to render a stiff, tough, glassy, and homogeneous network (that is, no phase separation)6, at room temperature. Despite being more than 54 wt% liquid, the glassy gels exhibit enormous fracture strength (42 MPa), toughness (110 MJ m−3), yield strength (73 MPa) and Young’s modulus (1 GPa). These values are similar to those of thermoplastics such as polyethylene, yet unlike thermoplastics, the glassy gels can be deformed up to 670% strain with full and rapid recovery on heating. These transparent materials form by a one-step polymerization and have impressive adhesive, self-healing and shape-memory properties.
This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 51 print issues and online access
$199.00 per year
only $3.90 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
Data availability
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 author on request. More details on the methods are available in the Supplementary Information. Source data are provided with this paper.
References
Young, R. J. & Lovell, P. A. Introduction to Polymers (CRC Press, 2011).
Sun, J.-Y. et al. Highly stretchable and tough hydrogels. Nature 489, 133–136 (2012).
Sun, T. L. et al. Physical hydrogels composed of polyampholytes demonstrate high toughness and viscoelasticity. Nat. Mater. 12, 932–937 (2013).
Wang, M., Hu, J. & Dickey, M. D. Tough ionogels: synthesis, toughening mechanisms, and mechanical properties─a perspective. JACS Au 2, 2645–2657 (2022).
Wang, M., Hu, J. & Dickey, M. D. Emerging applications of tough ionogels. NPG Asia Mater. 15, 66 (2023).
Wang, M. et al. Tough and stretchable ionogels by in situ phase separation. Nat. Mater. 21, 359–365 (2022).
Geyer, R., Jambeck, J. R. & Law, K. L. Production, use, and fate of all plastics ever made. Sci. Adv. 3, e1700782 (2017).
Fan, H. & Gong, J. P. Fabrication of bioinspired hydrogels: challenges and opportunities. Macromolecules 53, 2769–2782 (2020).
Ueki, T. & Watanabe, M. Polymers in ionic liquids: dawn of neoteric solvents and innovative materials. Bull. Chem. Soc. Jpn 85, 33–50 (2012).
Liu, X., Liu, J., Lin, S. & Zhao, X. Hydrogel machines. Mater. Today 36, 102–124 (2020).
Gong, J. P., Katsuyama, Y., Kurokawa, T. & Osada, Y. Double‐network hydrogels with extremely high mechanical strength. Adv. Mater. 15, 1155–1158 (2003).
Zhao, X. Multi-scale multi-mechanism design of tough hydrogels: building dissipation into stretchy networks. Soft Matter 10, 672–687 (2014).
Kim, J., Zhang, G., Shi, M. & Suo, Z. Fracture, fatigue, and friction of polymers in which entanglements greatly outnumber cross-links. Science 374, 212–216 (2021).
Kamiyama, Y. et al. Highly stretchable and self-healable polymer gels from physical entanglements of ultrahigh–molecular weight polymers. Sci. Adv. 8, eadd0226 (2022).
Gong, J. P. Why are double network hydrogels so tough? Soft Matter 6, 2583–2590 (2010).
Corkhill, P. H., Trevett, A. S. & Tighe, B. J. The potential of hydrogels as synthetic articular cartilage. Proc. Inst. Mech. Eng. H 204, 147–155 (1990).
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).
Yu, L. et al. Highly tough, Li‐metal compatible organic–inorganic double‐network solvate ionogel. Adv. Energy Mater. 9, 1900257 (2019).
Ren, Y. et al. Ionic liquid–based click-ionogels. Sci. Adv. 5, eaax0648 (2019).
Gallagher, A. J. et al. Dynamic tensile properties of human skin. In 2012 IRCOBI Conference Proc. 494–502 (International Research Council on the Biomechanics of Injury, 2012).
Sato, K. et al. Phase‐separation‐induced anomalous stiffening, toughening, and self‐healing of polyacrylamide gels. Adv. Mater. 27, 6990–6998 (2015).
Zhang, H. J. et al. Tough physical double‐network hydrogels based on amphiphilic triblock copolymers. Adv. Mater. 28, 4884–4890 (2016).
Joodaki, H. & Panzer, M. B. Skin mechanical properties and modeling: a review. Proc. Inst. Mech. Eng. H 232, 323–343 (2018).
Wang, Y. J. et al. Ultrastiff and tough supramolecular hydrogels with a dense and robust hydrogen bond network. Chem. Mater. 31, 1430–1440 (2019).
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).
Zhang, X., Du, C., Du, M., Zheng, Q. & Wu, Z. L. Kinetic insights into glassy hydrogels with hydrogen bond complexes as the cross-links. Mater. Today Phys. 15, 100230 (2020).
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).
Yarger, J. L., Cherry, B. R. & van Der Vaart, A. Uncovering the structure–function relationship in spider silk. Nat. Rev. Mater. 3, 18008 (2018).
Guo, Y. et al. Enhancing impact resistance of polymer blends via self-assembled nanoscale interfacial structures. Macromolecules 51, 3897–3910 (2018).
Liu, J. et al. Polystyrene glasses under compression: ductile and brittle responses. ACS Macro Lett. 4, 1072–1076 (2015).
Zhu, H. et al. Biobased plasticizers from tartaric acid: synthesis and effect of alkyl chain length on the properties of poly(vinyl chloride). ACS Omega 6, 13161–13169 (2021).
Pita, V. J. R. R., Sampaio, E. E. M. & Monteiro, E. E. C. Mechanical properties evaluation of PVC/plasticizers and PVC/thermoplastic polyurethane blends from extrusion processing. Polym. Test. 21, 545–550 (2002).
Huang, Q., Wan, C., Loveridge, M. & Bhagat, R. Partially neutralized polyacrylic acid/poly(vinyl alcohol) blends as effective binders for high-performance silicon anodes in lithium-ion batteries. ACS Appl. Energy Mater. 1, 6890–6898 (2018).
Eisenberg, A., Yokoyama, T. & Sambalido, E. Dehydration kinetics and glass transition of poly(acrylic acid). J. Polym. Sci. 7, 1717–1728 (1969).
Song, P. A., Yu, Y., Wu, Q. & Fu, S. Facile fabrication of HDPE-g-MA/nanodiamond nanocomposites via one-step reactive blending. Nanoscale Res. Lett. 7, 355 (2012).
Max, J.-J. & Chapados, C. Infrared spectroscopy of aqueous carboxylic acids: comparison between different acids and their salts. J. Phys. Chem. A 108, 3324–3337 (2004).
Parikh, S. J., Mukome, F. N. D. & Zhang, X. ATR–FTIR spectroscopic evidence for biomolecular phosphorus and carboxyl groups facilitating bacterial adhesion to iron oxides. Colloids Surf. B Biointerfaces 119, 38–46 (2014).
Rungrodnimitchai, S. Rapid preparation of biosorbents with high ion exchange capacity from rice straw and bagasse for removal of heavy metals. Sci. World J. 2014, 634837 (2014).
Qu, J. et al. Synergistic effects between phosphonium‐alkylphosphate ionic liquids and zinc dialkyldithiophosphate (ZDDP) as lubricant additives. Adv. Mater. 27, 4767–4774 (2015).
Swatloski, R. P., Spear, S. K., Holbrey, J. D. & Rogers, R. D. Dissolution of cellose with ionic liquids. J. Am. Chem. Soc. 124, 4974–4975 (2002).
Acknowledgements
M.D.D. acknowledges support from the Coastal Studies Institute. We thank G. McKenna, Z. Bao, M. Balik and C. Bowman for their helpful discussions. S.S. and B.T.O. acknowledge support from NSF award no. 2324190. W.Q. is partially supported by Nebraska Research Initiative. All NMR measurements were made in the Molecular Education, Technology and Research Innovation Center (METRIC) at NC State University.
Author information
Authors and Affiliations
Contributions
M.W., X.X. and M.D.D. conceived the idea. M.D.D. supervised the project. M.W. carried out most of the experiments. X.X. contributed to the SEM, transmittance test, adhesive demonstration and three-arm gripper design. X.X. and W.B. contributed to the FTIR measurement. S.S. and B.T.O. contributed to the dynamic mechanical analysis test. M.S. participated in the SEM measurement. E.F. participated in the Joule heating measurement. W.Q. contributed to the FTIR analysis. M.W., X.X. and M.D.D. wrote the paper, and all authors reviewed the paper.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Peer review
Peer review information
Nature thanks Jinhwan Yoon and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
Extended Data Fig. 1 Comparison of three classes of polymeric materials.
a,b, Schematics (a) and tensile stress-strain curves (b) illustrating the role of identical solvent loading in gel and glassy gel. Adding solvent improves extensibility of glassy polymers, but usually weakens the mechanical properties (for example, hydrogel). In contrast, glassy gel is extensible like a gel, but stiff like the glassy polymer due to strong solvent-polymer interactions that non-covalently crosslink the polymer. Insets in b show individual tensile stress-strain curves. As an example, consider poly(acrylic acid) (PAA). In the absence of solvent, the polymer is glassy and stiff, yet brittle. Swelling in water produces a hydrogel (56 wt% water) that is many orders of magnitude softer, weaker, and extensible than the glassy polymer. In contrast, replacing water with an ionic liquid solvent (58 wt% ionic liquid) is nearly as stiff as a glass, while maintaining extensibility of a gel. c, A spider plot summary in terms of liquid content, toughness, recovery, fracture strength, and elongation. The experimental data is for PAA and the values in a are from tensile tests reported in b, c, and Supplementary Fig. 4.
Extended Data Fig. 2 Synthesis and properties of glassy gels.
a, Schematic illustration of the simple one-step approach to synthesize glassy gels from representative monomer (AA) and ionic liquid (PP). b,c, Transmission (b) and weight (c) changes of various gels. Inset in b shows photographs of various gels (thickness = 2 mm, diameter = 12 mm). Error bars on the data in c show standard deviation from three independent samples.
Extended Data Fig. 3 Glassy gels have multiple functions.
a, The ionic bonds give strong adhesion to surfaces despite being stiff and glassy (Middle: metal ball diameter from left to right: 0.25 inch, 0.5 inch and 1 inch). b, Heating-induced shape memory (width = 4 mm, length = 4.7 cm). The scale bar is 10 mm. c, Self-healing behavior. The gels merge together after healing at 80 °C for 60 s and are able to support a 500 g hanging weight. The diameter of the gel and the hole is 12 and 3 mm, respectively. In a-c, PAA-PP-6.0 M glass gel with a thickness of 1 mm is used.
Supplementary information
Supplementary Information
This file contains 20 Supplementary Figs. (chemical and mechanical characterizations, swelling, adhesion and conductivity tests, and application demonstrations), 3 Supplementary Notes (discussion of the toughening mechanism, multiple functions and application), 7 Supplementary Tables (composition and mechanical properties of various gels) and 10 Supplementary References.
Supplementary Video 1
The simple one-step synthesis of glassy gels. This video shows the simple one-step synthesis of the glassy gel. Note that as the glassy gel has excellent adhesive properties, a hydrophobic layer (ease release 200, Mann Release Technologies) was sprayed on the mould to remove the gel easily, making the glassy gel translucent.
Supplementary Video 2
Strong glassy gels. This video shows the high toughness of the PAA-PP-6.0 M glassy gel (0.156 g, cross-sectional area: 2 mm2) by lifting a 4 kg weight.
Supplementary Video 3
Recovery properties of the glassy gels. This video shows the excellent recovery of the glassy gel. Taking PAA-PP-6.0 M gel as an example, it was stretched to 350% strain and had a huge residual strain (324% strain). When elevating the temperature (that is, 80 °C), the residual strain can be fully recovered within 30 s.
Supplementary Video 4
Mixing of AA monomer and PP ionic liquid produces a strong exotherm. This video shows the exothermic behaviour of the AA and PP mix (Cm = 5.0 M, the volume of the mixture is 2 ml).
Supplementary Video 5
Adhesive properties of the glassy gels. This video shows the strong adhesion of the glassy gel. Taking PAA-PP-6.0 M gel as an example, it can hold stainless-steel metal balls (diameter: 0.25 inch, 0.5 inch and 1 inch) even when shaken vigorously, tilted vertically (shear) or flipped upside down (tension).
Supplementary Video 6
Shape memory properties of the glassy gels. This video shows the excellent shape-memory behaviour of the glassy gel. Taking PAA-PP-6.0 M gel as an example, it can be programmed fast and recovered rapidly. The glassy gel sample was stained red for visualization.
Supplementary Video 7
Self-healing properties of the glassy gels. This video shows the good self-healing property of the glassy gel. Taking PAA-PP-6.0 M gel as an example, the healed disc-shaped glassy gels (80 °C for 60 s) can hold a 500 g weight.
Supplementary Video 8
Glassy gel-based grippers by Joule heating. This video exhibits the performance of a heat-driven gripper composed of glassy gel (that is, PAA-PP-6.0 M) and liquid metals (LMs). The gripper can be easily softened by Joule heating by passing a current through the LMs. It can thereby grab and hold the object. Notably, a hydrophobic layer (ease release 200, Mann Release Technologies) was sprayed on the gel to eliminate strong adhesion so that the object could easily be released when cooled.
Rights and permissions
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
About this article
Cite this article
Wang, M., Xiao, X., Siddika, S. et al. Glassy gels toughened by solvent. Nature 631, 313–318 (2024). https://doi.org/10.1038/s41586-024-07564-0
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41586-024-07564-0
Comments
By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.
