Dissipative self-assembly is common in biological systems, where it serves to maintain a far-from-equilibrium functional state through fuel consumption. Synthetic dissipative systems have been prepared that can mimic some of the properties of biological systems, but they often show poor mechanical performance. Here, we report a shear-induced transient hydrogel that is highly stretchable. The system is constructed by adding Cu(ii) into the aqueous solution of a pseudopolyrotaxane, which is itself formed by threading molecular tubes on polyethylene glycol chains. Vigorous shaking transforms the solution into a gel, which gradually relaxes back to the sol state over time. This cycle can be repeated at least five times. A mechanism is proposed that relies on a shear-induced transition from intrachain to interchain coordination and subsequent thermal relaxation. The far-from-equilibrium hydrogel is highly stretchable, which is probably due to ‘frictional’ sliding of the molecular tubes on the polyethylene glycol chains. On shaking, the hydrogel undergoes fast self-healing.
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Crystallographic data for the structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre under deposition no. CCDC 1563693 (7@2b). Copies of the data can be obtained free of charge from www.ccdc.cam.ac.uk/structures/. All other data supporting the findings of this study are available within the Article and its Supplementary Information and/or from the corresponding author upon reasonable request.
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This research was financially supported by the National Natural Science Foundation of China (nos. 21772083 and 21822104), SZSTI (nos. JCYJ20170307105848463 and KQJSCX20170728162528382), the Shenzhen Nobel Prize Scientists Laboratory Project (C17213101) and the Open Project of the State Key Laboratory of Supramolecular Structure and Materials (sklssm201807, Jilin University). The authors thank SUSTech-MCPC for instrumental support and C.A. Schalley, Z.-T. Li, W. Lu and S. Craig for valuable suggestions and comments. This Article is dedicated to Y. Liu and J. Rebek.
W.J., H.K. and L.-P.Y. are listed as the inventors on a Chinese patent application from Southern University of Science and Technology (patent application no. CN201710569674.7). The patent, currently under substantive examination, comprises the following aspects of this study: binding of the PEGs with the endo-functionalized molecular tubes, the preparation of the hydrogels and the shear-thickening measurements.
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Titration data, 1H and 13C NMR spectra, mass spectra, crystallographic data, computational details, and details of control experiments.
CIF for compound 7@2b; CCDC reference: 1563693
structure-factor file for compound 7@2b; CCDC reference: 1563693
Demonstration of shear-induced transition from a sol to a gel
Demonstration of the high elasticity of the shear-induced transient hydrogel.
Demonstration of the breakage of the merged hydrogel without shaking
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Ke, H., Yang, LP., Xie, M. et al. Shear-induced assembly of a transient yet highly stretchable hydrogel based on pseudopolyrotaxanes. Nat. Chem. 11, 470–477 (2019). https://doi.org/10.1038/s41557-019-0235-8
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