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High-resolution cryo-electron microscopy structure of block copolymer nanofibres with a crystalline core

Abstract

Seeded growth of crystallizable block copolymers and π-stacking molecular amphiphiles in solution using living crystallization-driven self-assembly is an emerging route to fabricate uniform one-dimensional and two-dimensional core–shell micellar nanoparticles of controlled size with a range of potential applications. Although experimental evidence indicates that the crystalline core of these nanomaterials is highly ordered, a direct observation of their crystal lattice has not been successful. Here we report the high-resolution cryo-transmission electron microscopy studies of vitrified solutions of nanofibres made from a crystalline core of poly(ferrocenyldimethylsilane) (PFS) and a corona of polysiloxane grafted with 4-vinylpyridine groups. These studies show that poly(ferrocenyldimethylsilane) chains pack in an 8-nm-diameter core lattice with two-dimensional pseudo-hexagonal symmetry that is coated by a 27 nm 4-vinylpyridine corona with a 3.5 nm distance between each 4-vinylpyridine strand. We combine this structural information with a molecular modelling analysis to propose a detailed molecular model for solvated poly(ferrocenyldimethylsilane)-b-4-vinylpyridine nanofibres.

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Fig. 1: Preparation and characterization of self-assembled nanofibres.
Fig. 2: High-resolution cryo-TEM analysis of corona and core of the nanofibres.
Fig. 3: Molecular modelling and high-resolution cryo-TEM analysis of the core domain of PFS24-b-P4VP192 nanofibres.
Fig. 4: Molecular modelling showing the core chain folding present in the nanofibres.

Data availability

All data generated or analysed during this study are included in the Article and Supplementary Information, and available from the corresponding author upon reasonable request.

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Acknowledgements

This work was funded by a Canada 150 Research Chair and an NSERC Discovery Grant (I.M.). J.T. acknowledges the award of a Marie Skłodowska-Curie Fellowship from the EU and funding support from the Shanghai Institute of Organic Chemistry, the Shanghai Branch, CAS; Shanghai Rising-Star Program (22QA1411200); and the National Natural Science Foundation of China (22271306). We thank the Chemical Imaging Facility at the University of Bristol for use of their bright-field TEM, and the Centre for Advanced Materials and Related Technology (CAMTEC) at the University of Victoria for the related characterization. U.B. acknowledges access and support of the GW4 Facility for High-Resolution Electron Cryo-Microscopy, funded by the Wellcome Trust (202904/Z/16/Z and 206181/Z/17/Z) and BBSRC (BB/R000484/1).

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Contributions

J.T and I.M. conceived the project. J.T. and S.L. synthesized the materials. J.T. performed the experiments with assistance from the other authors. J.T., S.-H.X. and U.B. performed the cryo-TEM studies and data analysis. J.T. performed the atomic force microscopy analysis. J.T., Y.Z. and S.L. performed the XRD experiments. All authors contributed to the data discussions. J.T. and I.M. analysed the data and wrote the manuscript with input from the other authors.

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Correspondence to Ian Manners.

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Nature Materials thanks Dganit Danino, Subi George and Darrin Pochan for their contribution to the peer review of this work.

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Supplementary Figs. 1–18, materials and methods, polymer synthesis and characterization, block copolymer self-assembly and references.

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Tian, J., Xie, SH., Borucu, U. et al. High-resolution cryo-electron microscopy structure of block copolymer nanofibres with a crystalline core. Nat. Mater. 22, 786–792 (2023). https://doi.org/10.1038/s41563-023-01559-4

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