Free Surface Relaxations of Star-Shaped Polymer Films

Peter Green, Emmanouil Glynos, Kyle Johnson, Bradley Frieberg, Alexandros Chremos, Suresh Narayanan, Georgios Sakellariou

    Research output: Contribution to journalArticlepeer-review

    28 Scopus Citations

    Abstract

    The surface relaxation dynamics of supported star-shaped polymer thin films are shown to be slower than the bulk, persisting up to temperatures at least 50 K above the bulk glass transition temperature Tgbulk. This behavior, exhibited by star-shaped polystyrenes with functionality f=8 arms and molecular weights per arm Marm<Me (Me is the entanglement molecular weight), is shown by molecular dynamics simulations to be associated with a preferential localization of these macromolecules at the free surface. This new phenomenon is in notable contrast to that of linear-chain polymer thin film systems, where the surface relaxations are enhanced in relation to the bulk; this enhancement persists only for a limited temperature range above the bulk Tgbulk. Evidence of the slow surface dynamics, compared to the bulk, for temperatures well above Tg and at length and time scales not associated with the glass transition has not previously been reported for polymers.

    Original languageAmerican English
    Article numberArticle No. 227801
    Number of pages5
    JournalPhysical Review Letters
    Volume119
    Issue number22
    DOIs
    StatePublished - 28 Nov 2017

    Bibliographical note

    Publisher Copyright:
    © 2017 American Physical Society.

    NREL Publication Number

    • NREL/JA-5A00-70685

    Keywords

    • polymer films
    • surface dynamics

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