Ion crater healing and variable temperature ellipsometry as complementary probes for the glass transition in thin polymer films
Laboratoire Polymères et Procédés, Université de Bretagne Sud, rue St Maudé, BP 92116, 56325 Lorient Cedex, France
2 Faculty of Physics, Catholic University of Rio Grande do Sul, Av. Ipiranga 6681, C.P. 1429, 90619-900 Porto Alegre, RS, Brazil
3 IUT d’Evry, Département SGM, Batiment des Sciences, rue du Père Jarland, 91025 Evry Cedex, France
Published online: 5 November 2003
Poly(methyl methacrylate) (PMMA) thin films of various tacticity and thickness were bombarded at grazing angles by 20 MeV Au ions at different temperatures. The shape of the tracks was investigated by scanning force microscopy (SFM) after annealing for various time at different temperatures and constant quenching rate. The thickness dependent glass transition temperature, T g (h), was estimated from the temperature of relaxation of ion-caused nanodeformations in the films. T g (h) obtained from the thermal healing of the holes and hillocks is found in good agreement with the one determined by variable temperature ellipsometry for PMMA film thickness of 80 nm and corresponds to the T g of each bulk PMMA stereoisomer. Below this thickness, some significant divergences are observed between the T g measured by the two techniques. We propose that the healing of ion crater hillock and the kink in the thermal expansion arise from the different nature of chains motions which are perturbed to different extents according to the main polymer chain preferential orientation in the thin film. This can be tentatively interpreted by a so-called “anisotropic” character of the glass transition.
PACS: codes. – 05.70.Np - Interface and surface thermodynamics / codes. – 34.50.Dy - Interactions of atoms and molecules with surfaces; photon and electron emission; neutralization of ions
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2003