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SMAIS: a universal platform for the on-water surface synthesis of two-dimensional polymer crystals

Nature Protocols (2026) Cite this article

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Abstract

Two-dimensional polymers (2DPs) are covalent polymeric networks with intrinsic long-range order in two orthogonal directions. Their unique physicochemical properties include tunable opto-electronic properties, mechanical stability and precisely defined nanopores that enable ion and molecular sieving. Here we describe a universal approach for the precise synthesis of 2DPs through the surfactant-monolayer-assisted interfacial synthesis method. The surfactant-monolayer-assisted interfacial synthesis combines the on-water surface reactivity and the role of surfactant (for example, sodium oleyl sulfate and sodium dodecyl benzenesulfonate) to guide the monomer-programmed assembly, two-dimensional (2D) polymerization and crystallization processes on the water surface, yielding large-area and highly crystalline 2DPs. This versatile Protocol has been used to synthesize many 2DP crystals, including 2D polyamide, 2D polyimide, 2D polyimine, 2D poly(boronate ester), 2D poly(pyridinium salt), 2D polyphenylenevinylene, 2D polybenzimidazole and 2D polyaniline, with a large lateral size of ~28 cm2. The crystals have precisely tunable thicknesses ranging from ~1 to 200 nm by adjusting the reaction time and/or reactant concentration and large crystal domain (that is, the lateral size of a single crystalline region) up to ~160 μm2, which helps minimize grain boundaries and preserve the intrinsic properties of 2DPs. Synthesis typically takes 2–14 days, depending on the reaction type. Film collection via a horizontal dipping method and a simple washing procedure, yield the target 2DPs. The resulting 2DP crystals have been integrated into electronics, optoelectronics, membranes and energy conversion/storage devices, exhibiting excellent performance. This Protocol can be performed easily by researchers with intermediate expertise in framework materials and interfacial chemistry.

Key points

  • Two-dimensional (2D) polymers with customizable structures and physicochemical properties are promising materials for electronics, optoelectronics and membrane technologies. This Protocol describes the synthesis of large-area, highly crystalline 2D polymers with tunable thicknesses and large crystal domains by surfactant-monolayer-assisted interfacial synthesis.

  • In surfactant-monolayer-assisted interfacial synthesis, 2D polymerization occurs underneath a surfactant monolayer on the water surface. It can be applied to prepare various 2DP crystals, such as 2D polyimide, 2D polyimine and 2D polyaniline.

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Fig. 1: Device applications of 2DPs.
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Fig. 2: Synthetic procedure and design principles of the SMAIS method.
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Fig. 3: A reaction scheme illustrating the synthesis of 2PDA and v2DPA via amidation reaction.
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Fig. 4: Synthesis of 2D polyimide.
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Fig. 5: Synthesis of 2D polyimine.
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Fig. 6: Synthesis of 2D poly(boronate ester).
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Fig. 7: Synthesis of 2D polyphenylenevinylene.
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Fig. 8: Synthesis of 2D poly(pyridinium salt).
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Fig. 9: Synthesis of 2D polybenzimidazole.
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Fig. 10: Synthesis of quasi-2D polyaniline.
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Fig. 11: Synthesis of 2D polyaniline.
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Fig. 12: Langmuir trough setup for monitoring surface pressure.
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Fig. 13: Structural characterization of the SOS surfactant monolayer at the air–water interface.
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Fig. 14: Monitoring of the interfacial assembly process on the water surface.
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Fig. 15: Morphology and optical images of the 2D polymer films.
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Fig. 16: Crystallographic characterization of PI-2DP DhTPA films.
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Fig. 17: GIWAXS characterization of C2DP-Por and comparison with calculated stacking models.
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Data availability

The main data discussed in this Protocol are available within the figures and procedures. Additional data that supports the findings of this study can be obtained from the corresponding author on request.

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Acknowledgements

Funding: the research on which this Protocol was based was financially supported by the ERC Synergy Grant (2DPolyMembrane, grant no. 101167472), ERC Consolidator Grant (grant no. T2DCP), GRK2861 (grant no. 491865171), CRC 1415 (Chemistry of Synthetic Two-Dimensional Materials, grant no. 417590517) and the German Science Council and the Center of Advancing Electronics Dresden.

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Author notes

  1. These authors contributed equally: Chen Hu, Dongxu Wang, Zhiyong Wang.

Authors and Affiliations

  1. Center for Advancing Electronics Dresden and Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Dresden, Germany

    Chen Hu, Zhiyong Wang & Xinliang Feng

  2. Max Planck Institute of Microstructure Physics, Halle (Saale), Germany

    Dongxu Wang, Zhiyong Wang & Xinliang Feng

Authors
  1. Chen Hu
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  2. Dongxu Wang
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Contributions

Z.W. and X.F. conceived and initiated the project. Z.W., C.H. and D.W. wrote the protocol. Z.W. and X.F. supervised the study and the manuscript preparation. All authors read and approved the final manuscript.

Corresponding authors

Correspondence to Zhiyong Wang or Xinliang Feng.

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Nature Protocols thanks Jianzhuang Jiang, Chenfeng Ke, Yuya Oaki, Bien Tan and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Key references

Liu, K. et al. Nat. Chem. 11, 994–1000 (2019): https://doi.org/10.1038/s41557-019-0327-5

Wang, Z. et al. Nat. Synth. 1, 69–76 (2022): https://doi.org/10.1038/s44160-021-00001-4

Prasoon, A. et al. Nat. Commun. 14, 8313 (2023): https://doi.org/10.1038/s41467-023-44129-7

Yang, Y. et al. Angew. Chem. Int. Ed. 63, e202316299 (2024): https://doi.org/10.1002/anie.202316299

Zhang, T. et al. Nature. 638, 411–417 (2025): https://doi.org/10.1038/s41586-024-08387-9

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Hu, C., Wang, D., Wang, Z. et al. SMAIS: a universal platform for the on-water surface synthesis of two-dimensional polymer crystals. Nat Protoc (2026). https://doi.org/10.1038/s41596-026-01368-4

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