Two Simultaneous Mechanisms Causing Glass Transition Temperature Reductions in High Molecular Weight Freestanding Polymer Films as Measured by Transmission Ellipsometry

Justin E. Pye and Connie B. Roth
Phys. Rev. Lett. 107, 235701 – Published 28 November 2011
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Abstract

We study the glass transition in confined polymer films and present the first experimental evidence indicating that two separate mechanisms can act simultaneously on the film to propagate enhanced mobility from the free surface into the material. Using transmission ellipsometry, we have measured the thermal expansion of ultrathin, high molecular-weight (MW), freestanding polystyrene films over an extended temperature range. For two different MWs, we observed two distinct reduced glass transition temperatures (Tg’s), separated by up to 60 K, within single films with thicknesses h less than 70 nm. The lower transition follows the expected MW dependent, linear Tg(h) behavior previously seen in high MW freestanding films. We also observe a much stronger upper transition with no MW dependence that exhibits the same Tg(h) dependence as supported and low MW freestanding polymer films.

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  • Received 5 January 2011

DOI:https://doi.org/10.1103/PhysRevLett.107.235701

© 2011 American Physical Society

Authors & Affiliations

Justin E. Pye and Connie B. Roth*

  • Department of Physics, Emory University, Atlanta, Georgia 30322, USA

  • *To whom correspondence should be addressed. cbroth@emory.edu

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Issue

Vol. 107, Iss. 23 — 2 December 2011

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