Role of Thickness Confinement on Relaxations of the Fast Component in a Miscible A/B Blend

Peter Green, Ravi Sharma, Ban Dong

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Spatial compositional heterogeneity strongly influences the dynamics of the A and B components of bulk miscible blends. Its effects are especially apparent in mixtures, such as poly(vinyl methyl ether) (PVME)/polystyrene (PS), where there exist significant disparities between the component glass transition temperatures (Tgs) and relaxation times. The relaxation processes characterized by distinct temperature dependencies and relaxation rates manifest different local compositional environments for temperatures above and below the glass transition temperature of the miscible blend. This same behavior is shown to exist in miscible PS/PVME films as thin as 100 nm. Moreover, in thin films, the characteristic segmental relaxation times of the PVME component of miscible PVME/PS blends confined between aluminum (Al) substrates decrease with increasing molecular weight M of the PS component. These relaxation rates are film thickness dependent, in films up to a few hundred nanometers in thickness. This is in remarkable contrast to homopolymer films, where thickness confinement effects are apparent only on length scales on the order of nanometers. These surprisingly large length scales and M dependence are associated with the preferential interfacial enrichment - wetting layer formation - of the PVME component at the external Al interfaces, which alters the local spatial blend composition within the interior of the film. The implications are that the dynamics of miscible thin film blends are dictated in part by component Tg differences, disparities in component relaxation rates, component-substrate interactions, and chain lengths (entropy of mixing).

    Original languageAmerican English
    Pages (from-to)1215-1223
    Number of pages9
    JournalMacromolecules
    Volume51
    Issue number3
    DOIs
    StatePublished - 2018

    Bibliographical note

    Publisher Copyright:
    © 2018 American Chemical Society.

    NREL Publication Number

    • NREL/JA-5A00-71115

    Keywords

    • aluminum
    • glass
    • glass transition
    • interfaces
    • relaxation time
    • substrates
    • temperature

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