Thickness dependence of the dynamics in thin films of isotactic poly (methylmethacrylate)
Department of Physics and Guelph-Waterloo Physics Institute, University of Waterloo, 200 University Avenue West,
Waterloo, Ontario, N2L 3G1, Canada
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Published online: 5 November 2003
The film thickness dependence of both the glass transition temperature (T g ) and the 1 kHz alpha relaxation were studied for thin films of isotactic Poly (methylmethacrylate) (i-PMMA) supported on aluminium substrates. Films in the thickness range 7-200 nm were studied. The ellipsometrically determined T g was found to show reductions for films thinner than 60 nm, with the largest observed reduction being 12 K for a 7 nm thick film. Measurements of the T g were also performed on i-PMMA films supported on silicon substrates. Dielectric studies of the temperature dependent 1 kHz alpha relaxation peak, showed that the position (T α ) and shape of the peak have no film thickness dependence. This was shown to hold for films with one free surface and films with a 30 nm thermally evaporated capping layer. Capping the films was shown to have no effect on the thickness dependence of either T g or T α . The implications of these results are discussed further and the different film thickness dependencies of T g and T α are discussed. This is done within the framework of the Vogel-Fulcher-Tamann (VFT) theory of glass forming materials and also in the context of the existence of a dynamic correlation length ξ.
PACS: codes. – 61.41.+e - Polymers, elastomers, and plastics / codes. – 61.43.Fs - Glasses / codes. – 64.70.Pf - Glass transitions / codes. – 65.60.+a - Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc. / codes. – 68.15.+e - Liquid thin films / codes. – 68.35.Ja - Surface and interface dynamics and vibrations
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2003