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Anisotropic self-assembly of spherical polymer-grafted nanoparticles

Nature Materials volume 8, pages 354–359 (2009)Cite this article

Abstract

It is easy to understand the self-assembly of particles with anisotropic shapes or interactions (for example, cobalt nanoparticles or proteins) into highly extended structures. However, there is no experimentally established strategy for creating a range of anisotropic structures from common spherical nanoparticles. We demonstrate that spherical nanoparticles uniformly grafted with macromolecules (‘nanoparticle amphiphiles’) robustly self-assemble into a variety of anisotropic superstructures when they are dispersed in the corresponding homopolymer matrix. Theory and simulations suggest that this self-assembly reflects a balance between the energy gain when particle cores approach and the entropy of distorting the grafted polymers. The effectively directional nature of the particle interactions is thus a many-body emergent property. Our experiments demonstrate that this approach to nanoparticle self-assembly enables considerable control for the creation of polymer nanocomposites with enhanced mechanical properties. Grafted nanoparticles are thus versatile building blocks for creating tunable and functional particle superstructures with significant practical applications.

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Figure 1: Theoretical predictions and comparison of theory to experiments.
Figure 2: Experimental study of particle self-assembly.
Figure 3: Shear-stress response to steady-shear application at 180 ∘C at a shear rate of 0.1 s−1 for composites with matrix M=42 kg mol−1 (black) and 142 kg mol−1 (red) and of pure homopolymers.

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Acknowledgements

The authors acknowledge financial support from the National Science Foundation (through the Division of Materials Research, DMR-0804647 (S.K.K.), a Nanoscale Science and Engineering Center, NSF Award Number DMR-0642573 (P.A., S.K.K., Y.L., B.C.B., L.S.S.) and a Materials Research Science and Engineering at Princeton (A.Z.P.)). D.A. is a member of the New York Structural Biology Center, which is a STAR Center supported by the New York State Office of Science, Technology, and Academic Research. Work benefited from the use of the Advanced Photon Source supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. V.G. and V.P. acknowledge partial support from the Welch Foundation, the US Army Research Office under Grant No. W911NF-07-1-0268 and funds made available through the CONTACT program from AFOSR. S.K.K. thanks M. Olvera (Northwestern), T. Russell (U Mass), R. Krishnamoorti (Houston) and S. Sen (Kolkota) for useful discussions and for critical comments on this paper.

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Authors and Affiliations

  1. Department of Chemical Engineering, Columbia University, New York, New York 10027, USA

    Pinar Akcora, Hongjun Liu & Sanat K. Kumar

  2. Department of Chemistry, Columbia University, New York, New York 10027, USA

    Joseph Moll

  3. Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, USA

    Yu Li & Brian C. Benicewicz

  4. Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA

    Linda S. Schadler

  5. Skirball Institute for Biomolecular Medicine, New York University School of Medicine, New York 10016, USA

    Devrim Acehan

  6. Department of Chemical Engineering and PRISM, Princeton University, Princeton, New Jersey 08544, USA

    Athanassios Z. Panagiotopoulos

  7. Department of Chemical Engineering, University of Texas, Austin, Texas 8712, USA

    Victor Pryamitsyn & Venkat Ganesan

  8. Advanced Photon Source Division, Argonne National Laboratory, Argonne, Illinois 60439, USA

    Jan Ilavsky & Pappanan Thiyagarajan

  9. Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA

    Ralph H. Colby

  10. Polymers Division, National Institutes of Standards and Technology, Gaithersburg, Maryland 20899, USA

    Jack F. Douglas

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  1. Pinar Akcora
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Contributions

P.A. conducted most of the experiments in the research; S.K.K. planned the research and supervised it along with L.S.S. The paper was written by S.K.K. and J.F.D. Y.L. and B.C.B. made the functionalized particles. H.L., S.K.K., A.Z.P., V.G. and V.P. conducted the theoretical calculations reported. J.M. carried out the rheology experiments in collaboration with R.H.C. and S.K.K. D.A. helped with the TEM measurements, and J.I. and P.T. carried out the USAXS experiments and analysis.

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Correspondence to Sanat K. Kumar.

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Akcora, P., Liu, H., Kumar, S. et al. Anisotropic self-assembly of spherical polymer-grafted nanoparticles. Nature Mater 8, 354–359 (2009). https://doi.org/10.1038/nmat2404

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