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The distribution of glass-transition temperatures in nanoscopically confined glass formers

Nature Materials volume 2, pages 695–700 (2003)Cite this article

Abstract

Despite the decade-long study of the effect of nanoconfinement on the glass-transition temperature (Tg) of amorphous materials, the quest to probe the distribution of Tgs in nanoconfined glass formers has remained unfulfilled. Here the distribution of Tgs across polystyrene films has been obtained by a fluorescence/multilayer method, revealing that the enhancement of dynamics at a surface affects Tg several tens of nanometres into the film. The extent to which dynamics smoothly transition from enhanced to bulk states depends strongly on nanoconfinement. When polymer films are sufficiently thin that a reduction in thickness leads to a reduction in overall Tg, the surface-layer Tg actually increases with a reduction in overall thickness, whereas the substrate-layer Tg decreases. These results indicate that the gradient in Tg dynamics is not abrupt, and that the size of a cooperatively rearranging region is much smaller than the distance over which interfacial effects propagate.

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Figure 1: Tg of single-layer PS films identified by fluorescence using pyrene as dopant or label.
Figure 2
Figure 3: Tg identified by fluorescence for 14-nm-thick pyrene-labelled PS free-surface layers (diamonds) as a function of total film thickness where the underlayer thickness is varied.
Figure 4: Tg identified by fluorescence for a three-layer PS film (each layer 12-nm thick, only one pyrene-labelled layer).
Figure 5: Summary of Tg − Tg(bulk) for single pyrene-labelled PS layers inserted at specific locations in unlabelled PS films.

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Authors and Affiliations

  1. Department of Chemical Engineering, Northwestern University, Evanston, 60208-3120, Illinois, USA

    Christopher J. Ellison & John M. Torkelson

  2. Department of Materials Science and Engineering, Northwestern University, Evanston, 60208-3120, Illinois, USA

    John M. Torkelson

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Ellison, C., Torkelson, J. The distribution of glass-transition temperatures in nanoscopically confined glass formers. Nature Mater 2, 695–700 (2003). https://doi.org/10.1038/nmat980

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