Is the "Bricks-and-Mortar" Mesophase Bicontinuous?: Dynamic Simulations of Miktoarm Block Copolymer/Homopolymer Blends

ORAL

Abstract

A mesophase in binary blends of A-b-(BA')3 miktoarm star block copolymers and A homopolymers has been reported to consist of aperiodic discrete domains of A embedded in a continuous matrix of B, up to very high concentrations of A. Because of the material's potential as a thermoplastic elastomer, an understanding of its structural and mechanical properties, including its domain connectivity, rheological behavior, response to shear and to uniaxial tension, is warranted.  These properties are explored here using dissipative particle dynamics in three dimensions.  These simulations establish that the "bricks-and-mortar" phase while appearing discrete in two dimensions is bicontinuous. The simulations focusing on dynamics establish that the role of molecular bridging dominates the mechanical behavior, outweighing the influence of microphase segregation even at the highest homopolymer concentrations we study. Additionally, the phase is sensitive to the application of high shear, leading to anisotropic mechanical responses, which has ramifications for processability.   We find that upon application of shear the phase becomes closer to its speculated discrete nature. Molecular simulations on our longest accessible timescales show that the material is unable to relax back to its original structure, suggesting that the morphology depends heavily on the processing pathway.

*This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE's National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the U.S. DOE or the United States Government.

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Presenters

  • Cody T Bezik

    • University of Chicago ; Sandia National Laboratories

Authors

  • Cody T Bezik

    • University of Chicago ; Sandia National Laboratories

  • Joshua A Mysona

    • Argonne National Laboratory
    • University of Chicago

  • Ludwig Schneider

    • Pritzker School of Molecular Engineering, University of Chicago
    • University of Chicago, Pritzker School of Molecular Engineering
    • University of Chicago, PME
    • University of Chicago

  • Abelardo Ramirez-Hernandez

    • The University of Texas at San Antonio

  • Marcus Mueller

    • Georg-August University, Göttingen, Germany
    • University of Gottingen

  • Juan De Pablo

    • University of Chicago
    • Pritzker School of Molecular Engineering, University of Chicago