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Soft Matter and Biological Physics
Eur. Phys. J. E 10, 223-230 (2003)
DOI: 10.1140/epje/i2002-10111-4

Effect of physical ageing in thin glassy polymer films

S. Kawana1 and R.A.L. Jones2

1  Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, United Kingdom
2  Department of Physics and Astronomy, University of Sheffield, The Hicks Building, Hounsfield Road, Sheffield S3 7RH, United Kingdom

kawana@rc.m-kagaku.co.jp

(Received 28 October 2002 / Published online: 1 April 2003)

Abstract
We have studied the effect of physical ageing in thin supported glassy polystyrene films by using ellipsometry to detect overshooting in the expansivity-temperature curve upon heating of aged samples. Films with thickness 10-200 nm have been aged at $70\un{^\circ C}$ and $80\un{^\circ C}$ (below the bulk glass transition temperature). We observe clear relaxation peaks in the expansivity-temperature curve for films thicker than 18 nm but not for the 10 nm film. The intensity of the relaxation peak is inversely proportional to the film thickness, while the temperatures characteristic to the relaxation peak are almost independent of the film thickness. These observations are successfully interpreted by the idea that the surface layer of the order of 10 nm has liquid-like thermal properties.

PACS
64.70.Pf - Glass transitions.
68.60.-p - Physical properties of thin films, nonelectronic.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2003