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Self-assembly and properties of diblock copolymers by coarse-grain molecular dynamics

Nature Materials volume 3, pages 638–644 (2004)Cite this article

Abstract

Block-copolymer amphiphiles have been observed to assemble into vesicles and other morphologies long known for lipids but with remarkably different properties. Coarse-grain molecular dynamics (CG-MD) is used herein to elaborate the structures and properties of diblock copolymer assemblies in water. By varying the hydrophilic/hydrophobic ratio of the copolymer in line with experiment, bilayer, cylindrical and spherical micelle morphologies spontaneously assemble. Varying the molecular weight (MW) with hydrophilic/hydrophobic ratio appropriate to a bilayer yields a hydrophobic core thickness that scales for large MW as a random coil polymer, in agreement with experiment. The extent of hydrophobic-segment overlap in the core increases nonlinearly with MW, indicative of chain entanglements and consistent with the dramatic decrease reported for lateral mobility in polymer vesicles. Calculated trends with MW as well as hydrophilic/hydrophobic ratio thus agree with experiment, demonstrating that CG-MD simulations provide a rational design tool for diblock copolymer assemblies.

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Figure 1: Snap-shots taken from coarse-grain molecular dynamics simulations of diblock copolymers in water.
Figure 2: Coarse-graining scheme used to model a PEO-PEE diblock copolymer.
Figure 3: Membrane core dimensions versus MWphob.
Figure 4: Master plot of membrane tension versus dilation curves for a wide range of diblock copolymer systems.
Figure 5: Density profiles revealing the chain entanglement and interdigitation.
Figure 6: Chain overlap, experimental diffusivity, and chain entanglements.

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Acknowledgements

We would like to thank John C. Shelley, Carlos Lopez, Steve Nielsen, Ivaylo Ivanov and Preston B. Moore. This work has been supported by the National Science Foundation (Pennsylvania University's Materials Research Science and Engineering Centre) and the National Institutes of Health.

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Authors and Affiliations

  1. Department of Chemistry, Center for Molecular Modeling, University of Pennsylvania, 19104-6323, Philadelphia, USA

    Goundla Srinivas & Michael L. Klein

  2. Department of Chemical & Biomolecular Engineering, University of Pennsylvania, 19104-6315, Philadelphia, USA

    Dennis E. Discher

  3. Laboratory for Research on the Structure of Matter, University of Pennsylvania, 19104-6202, Philadelphia, USA

    Goundla Srinivas, Dennis E. Discher & Michael L. Klein

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Correspondence to Michael L. Klein.

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Srinivas, G., Discher, D. & Klein, M. Self-assembly and properties of diblock copolymers by coarse-grain molecular dynamics. Nature Mater 3, 638–644 (2004). https://doi.org/10.1038/nmat1185

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