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Observing polymerization in 2D dynamic covalent polymers

Nature volume 603, pages 835–840 (2022)Cite this article

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Abstract

The quality of crystalline two-dimensional (2D) polymers1,2,3,4,5,6 is intimately related to the elusive polymerization and crystallization processes. Understanding the mechanism of such processes at the (sub)molecular level is crucial to improve predictive synthesis and to tailor material properties for applications in catalysis7,8,9,10 and (opto)electronics11,12, among others13,14,15,16,17,18. We characterize a model boroxine 2D dynamic covalent polymer, by using in situ scanning tunnelling microscopy, to unveil both qualitative and quantitative details of the nucleation–elongation processes in real time and under ambient conditions. Sequential data analysis enables observation of the amorphous-to-crystalline transition, the time-dependent evolution of nuclei, the existence of ‘non-classical’ crystallization pathways and, importantly, the experimental determination of essential crystallization parameters with excellent accuracy, including critical nucleus size, nucleation rate and growth rate. The experimental data have been further rationalized by atomistic computer models, which, taken together, provide a detailed picture of the dynamic on-surface polymerization process. Furthermore, we show how 2D crystal growth can be affected by abnormal grain growth. This finding provides support for the use of abnormal grain growth (a typical phenomenon in metallic and ceramic systems) to convert a polycrystalline structure into a single crystal in organic and 2D material systems.

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Fig. 1: Disorder-to-order transition.
Fig. 2: Nucleation–elongation processes.
Fig. 3: Normal and abnormal 2D grain growth routes.
Fig. 4: Identification of grain boundaries and their kinetic movement.

Data availability

The main data supporting the findings of this study are available within the paper and its Supplementary Information. Additional data are available from the corresponding authors upon reasonable request.

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Acknowledgements

We thank L. Verstraete and N. Bilbao for helpful discussions. We thank Y. Liao for helping with the preparation of the manuscript. We thank Y. Zhang for helping with data analysis. This work was supported by the Research Foundation - Flanders (FWO), in part by FWO under EOS 30489208, the Marie Sklodowska Curie ETN project ULTIMATE (GA-813036), and KU Leuven Internal Grant 3E180504, China Scholarship Council (201908350094), the Basque Foundation for Science (Ikerbasque), POLYMAT, the University of the Basque Country (Grupo de Investigación GIU17/054), Diputación Foral de Guipuzkoa, Gobierno Vasco (PIBA and BERC programmes), Gobierno de España (Ministerio de Economía y Competitividad CTQ2016-77970-R). Technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF) is acknowledged. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 722951). This project has received funding from the European Union´s Horizon 2020 research and innovation programme under grant agreement no. 664878 and no. 899895. In addition, support through the project IF/00894/2015, the advanced computing CPCA/A2/2524/2020 granting access to the Navigator cluster at LCA-UC and within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020 funded by national funds through the Portuguese Foundation for Science and Technology I.P./MCTES is gratefully acknowledged.

Author information

Author notes

  1. Gaolei Zhan

    Present address: Department of Chemistry, National University of Singapore, Singapore, Singapore

  2. Zhen-Feng Cai

    Present address: Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland

  3. These authors contributed equally: Gaolei Zhan, Zhen-Feng Cai

Authors and Affiliations

  1. Department of Chemistry, Division of Molecular Imaging and Photonics, KU Leuven, Leuven, Belgium

    Gaolei Zhan, Zhen-Feng Cai, Lihua Yu, Niklas Herrmann & Steven De Feyter

  2. CICECO−Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, Aveiro, Portugal

    Karol Strutyński & Manuel Melle-Franco

  3. POLYMAT, University of the Basque Country UPV/EHU, Donostia-San Sebastian, Spain

    Marta Martínez-Abadía & Aurelio Mateo-Alonso

  4. Ikerbasque, Basque Foundation for Science, Bilbao, Spain

    Aurelio Mateo-Alonso

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Contributions

G.Z., Z.-F.C. and S.D.F. conceived the idea and designed the experiments. G.Z., Z.-F.C., L.Y. and N.H. carried out the in situ STM experiments and analysed the data. K.S. and M.M.-F carried out the DFT and tight-binding calculation. M.M.-A. carried out the synthesis of the monomer. The text was initially composed by G.Z., Z.-F.C., A.M.-A. and S.D.F., and all authors further contributed to the discussion of the experimental work and the final version of the manuscript.

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Correspondence to Zhen-Feng Cai or Steven De Feyter.

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Supplementary information

Supplementary Information

Supplementary Text 1–4 and Figs. 1–30.

Supplementary Data 1

Statistical analysis of critical nucleation size for Fig. 2e.

41586_2022_4409_MOESM3_ESM.mp4

Supplementary Video 1 In situ STM showing the dynamic nucleation process at liquid–solid interface with a scan rate of 1.5 min per frame. The video shows the emergence and elongation of some 2DPs nuclei within the disordered area. The video also demonstrates the disappearance of on-surface generated 2DPs nuclei, implying the reversible boroxine chemistry on the HOPG surface. The video is played at ×180 speed. Image size: 80 nm × 80 nm.

Supplementary Video 2 In situ STM showing the nucleation–elongation processes. The video is played at ×180 speed. Image size: 150 nm × 150 nm.

Supplementary Video 3 In situ STM showing the restricted motion of 2DPs nuclei, with the presence of surface defect. The video is played at ×180 speed. Image size: 60 nm × 60 nm.

Supplementary Video 4 In situ STM showing the slow kinetics during normal grain growth. The video is played at ×180 speed. Image size: 60 nm × 60 nm.

41586_2022_4409_MOESM7_ESM.mp4

Supplementary Video 5 In situ STM showing the preferential growth of some nuclei (S2). During abnormal grain growth (AGG), S2 grows at the expense of R1 and S1. The video is played at ×180 speed. Image size: 100 nm × 100 nm.

Supplementary Video 6 In situ STM showing the formation of a unidirectional domain (S2) by taking advantage of abnormal grain growth. The video is played at ×180 speed. Image size: 80 nm × 80 nm.

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Zhan, G., Cai, ZF., Strutyński, K. et al. Observing polymerization in 2D dynamic covalent polymers. Nature 603, 835–840 (2022). https://doi.org/10.1038/s41586-022-04409-6

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