J. Phys. IV France 10 (2000) Pr7-247-Pr7-250
Glass transition of ultrathin films probed by X-ray reflectivityE. Cecchetto, N.R. de Souza and B. Jérôme
Department of Chemical Engineering, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WWAmsterdam, The Netherlands
X-ray reflectometry was used to measure the temperature dependence of the thickness of ultrathin films of two low-molecular-weight glass formers. In bulk samples, this type of measurements reveals the presence of a glass transition by a sudden break of slope. We have observed a broadening of the glass transition in films thinner than roughly 150 nm, indicating an inhomogeneous distribution of relaxation times in these films. Our results are explained by confinement effect and interpreted in the frame of a theoretical model based on the concept of collective dynamics over a cooperative length.
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