Berlin 2001 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 19: Poster: New Methods, Thin Polymer Films, Monolayers
CPP 19.17: Poster
Thursday, April 5, 2001, 12:30–15:00, AT1
Shift of the glass transition in (ultra)-thin films of isotactic polymethyl-methacrylate (i-PMMA). — •Jörg Hauwede, Lutz Hartmann, Wladimir Gorbatschow, and Friedrich Kremer — University of Leipzig, Department of Physics and Geosciences, Linnestrasse 5, 04103 Leipzig
The shift of the glass transition temperature - with respect to the bulk value - in ultra-thin films (20 nm - 100 nm) of spincasted isotactic polymethyl-methacrylate (i-PMMA), Mn = 37.000 is measured by ellipsometry and broadband dielectric spectroscopy. While the former is essentially a (macroscopic) dilatometric method, the latter senses molecular fluctuations.
In the ellipsometric studies (were the sample is spincasted on a 111-Si/SiOx-surface) a pronounced increase of Tg is observed with decreasing thickness (ΔTg = 30 K for d = 20 nm). In contrast in the dielectric measurements (where the sample has to be electrically contacted by Al-electrodes) a decrease of Tg takes place (ΔTg = -10 K for d = 20 nm). This can be interpreted as a confining effect as similarly observed in low-molecular- weight systems. The discrepancy is presumably caused by the different interactions of the polymer with the underlying substrate.
F. Kremer, A. Huwe, M. Arndt, P. Behrens and W. Schwieger J. Phys. Condens Matter, 11 , A175 - A188 (1999)
A. Huwe, F. Kremer, P. Behrens and W. Schwieger Phys. Rev. Lett., 82 , 11, p. 2338-2341 (1999)