Abstract
Polymers that extend covalently in two dimensions have attracted recent attention1,2 as a means of combining the mechanical strength and in-plane energy conduction of conventional two-dimensional (2D) materials3,4 with the low densities, synthetic processability and organic composition of their one-dimensional counterparts. Efforts so far have proven successful in forms that do not allow full realization of these properties, such as polymerization at flat interfaces5,6 or fixation of monomers in immobilized lattices7,8,9. Another frequently employed synthetic approach is to introduce microscopic reversibility, at the cost of bond stability, to achieve 2D crystals after extensive error correction10,11. Here we demonstrate a homogenous 2D irreversible polycondensation that results in a covalently bonded 2D polymeric material that is chemically stable and highly processable. Further processing yields highly oriented, free-standing films that have a 2D elastic modulus and yield strength of 12.7 ± 3.8 gigapascals and 488 ± 57 megapascals, respectively. This synthetic route provides opportunities for 2D materials in applications ranging from composite structures to barrier coating materials.
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A self-standing three-dimensional covalent organic framework film
Nature Communications Open Access 14 January 2023
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Data availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Acknowledgements
Membraackackackne fabrication, permeability testing and transport analysis of 2DPA-1 was supported by the Center for Enhanced Nanofluidic Transport (CENT), an Energy Frontier Research Center sponsored by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences under award #DE-SC0019112. The synthetic chemistry and mechanical testing aspects of this work were funded by the Army Research Laboratory under cooperative agreement W911NF-18-2-0055. H.J.K. holds a Career Award at the Scientific Interface from the Burroughs Wellcome Fund, which supported the molecular modelling aspects of this work. We acknowledge fabrication support from the Center for Nanoscale Systems at Harvard, a member of the National Nanotechnology Coordinated Infrastructure Network (NNCI), which is supported by the National Science Foundation under NSF award no. 1541959. This research used beamline 11-BM Complex Materials Scattering (CMS) of the National Synchrotron Light Source II (NSLS-II) and the Center for Functional Nanomaterials (CFN), both of which are US DOE Office of Science User Facilities operated for the DOE Office of Science by Brookhaven National Laboratory under contract no. DE-SC0012704. We thank E. Tsai for her assistance in performing experiments at the beamline, R. Verduzco for beamline access, A. Penn and E. Brignole for MIT.Nano assistance for STEM and Cryo EM, and S. Xin Li for discussions on 2D membrane properties. We acknowledge MIT.Nano facilities and the Cypher VRS DURIP award (N000142012203) for the support on AFM characterizations. M.K. acknowledges support by the German Research Foundation (DFG) Research Fellowship KU 3952/1-1.
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Authors and Affiliations
Contributions
Y.Z. and M.S.S. conceived and designed the reaction system, with initial laboratory synthesis and characterization of 2DPA-1 performed by Y.Z. Characterization using HR-AFM measurement and other imaging tools, and subsequent data analysis, was performed by Y.Z., P.G., X.G. and J.T. P.L., A.T.L., and J.F.Y. offered substrates for AFM characterization. Post-synthesis modification for molecular imaging and intermediate characterization was performed by Y.Z.; M.Q. and D.J.L. contributed to data analysis. Y.Z. and M.S.S. designed and developed the NMR characterization technique for defect quantification. Y.Z., M.Q. and G.Z. performed budge tests. Z. Yuan, G.Z., G.H. and M.Q. calculated permeabilities for 2DPA-1 from bulge test results. Y.Z. performed nanoindentation tests at MIT with complementary measurements from E.D.W. and E.S.-R. at ARL. Substrates for nanoindentation tests are designed and fabricated by M.K. Y.Z. designed and T.I. conducted polarized photoluminescence measurements. Y.Z. measured mechanical properties of scrolled fibres. G.Z., D.K., J. Yang, M.S.S. and H.J.K. contributed theory and material simulation. Z. Yang and H.J.K. performed molecular structure calculations for 2DPA-1. Y.Z. and M.S.S. co-wrote the manuscript with input from all other authors.
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Extended data figures and tables
Extended Data Fig. 1 Schematic illustration of rotation suppression and auto-catalysis.
a, Linkage-core conjugations inhibit out-of-plane rotation. b, Auto-catalytic self-templating. Computational method: gas-phase geometry optimizations with Q-Chem v4.2 to compute 298 K conjugation enthalpies using the ωB97-XD/6-311 + G(d, p) DFT functional and basis set combination.
Extended Data Fig. 2 Characterization of 2DPA-1.
a, Fourier-transform infrared (FTIR) spectrum of as-synthesized 2DPA-1 powder. b, Atomic force microscopy (AFM) image of bilayer nanoclusters and its height histogram along the white line (inset). c, AFM image of stacked nanosheets; inset shows its height histogram along the white line. d, AFM surface topology of a spin-coated film. e, AFM image from amplitude channel at its second eigenmode, obtained from a film surface. f, The size distribution obtained from e.
Extended Data Fig. 3 Silylation of 2DPA-1.
a, Synthetic scheme of the silylation reaction. b, FTIR spectra of reaction mixture and its starting material. rt, room temperature; TMSOTf, trimethylsilyl trifluoromethanesulfonate; TEA, triethylamine.
Extended Data Fig. 4 Bulge test of 2DPA-1 films for air permeability.
a, Cross-sectional view of a clean holey substrate. b, Bubble height versus time. Film thickness is 12.8 nm.
Extended Data Fig. 5 Scrolled fibre tensile test of 2DPA-1 composites.
a, Schematic illustration of an Archimedean scroll fibre. b, Optical micrograph of a hair (left) and a scrolled fibre (right). Scale bar, 100 mm. c, Representative true stress–strain curves from a 2D composite scrolled fibre, its polycarbonate (PC) control fibre, and a graphene/PC composite fibre (data reproduced from ref. 31). The volume fraction for 2DPA-1/PC is 6.9% and for graphene/PC it is 0.19%. d, Plot of modulus enhancement ((E − EPC)/EPC) versus different volume fractions of 2DPA-1.
Extended Data Fig. 6 True stress–strain plots of composite scrolled fibres and their PC controls.
a, Volume fraction (V2DP) = 0.9%. b, V2DP = 2.3%. c, V2DP = 6.9%. d, V2DP = 7.7%. e, V2DP = 13.3%.
Extended Data Fig.7 Optical set-up for photoluminescence measurements.
Excitation wavelength 532 nm, excitation power 500 μW for photoluminescence measurements, and 2 μW for excitation polarization. EMCCD, electron-multiplying charge-coupled device.
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Zeng, Y., Gordiichuk, P., Ichihara, T. et al. Irreversible synthesis of an ultrastrong two-dimensional polymeric material. Nature 602, 91–95 (2022). https://doi.org/10.1038/s41586-021-04296-3
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DOI: https://doi.org/10.1038/s41586-021-04296-3
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