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- Dielectric relaxation (2)
- Glass transition (2)
- Adsorbed layers (1)
- Aluminium (1)
- Annealing (1)
- Contact angle (1)
- Electrodes (1)
- Polymer films (1)
- Polysulfone (1)
- Thin films (1)
Molecular dynamics of ultrathin supported polysulfone films studied by dielectric spectroscopy
(2008)
Ultra-thin films of polysulfone are prepared by spin coating down to thicknesses below 10 nm on an aluminum support and investigated by broadband dielectric spectroscopy. As a main result is was found that the glass transition temperature Tg does not depend on the film thickness for thicknesses larger than 10 nm. Secondly from the analysis of the dielectric strength it is concluded that the polysulfone segments form an adsorbed layer with a reduced mobility at the Al support having a thickness of ca. 5 nm.
The dynamic glass transition (α relaxation, structural relaxation) of ultrathin polysulfone films prepared between aluminum electrodes is investigated by dielectric relaxation spectroscopy. As a main result, it is found that the glass transition temperature Tg does not depend on the thickness of the polymeric layer down to a thickness of 10 nm. For thicknesses lower than 10 nm, an increase of Tg is observed. A more detailed analysis of the temperature dependence of the relaxation rates reveals that the Vogel temperature increases and the fragility decreases systematically with decreasing film thickness d. Further, the dielectric strength Δε decreases with decreasing d. This is discussed by the formation of a surface layer of adsorbed polysulfone segments having a reduced molecular mobility with regard to the time scale characteristic of the glassy dynamics of bulk polysulfone. Plotted versus inverse film thickness Δε decreases linearly with 1/d and becomes zero for an extrapolated length scale of 10 nm. From that it is concluded that the thickness of the adsorbed boundary layer is about 5 nm. Contact-angle measurements were carried out to confirm the strong interaction between aluminum and polysulfone. It is also shown that preparation details like annealing conditions strongly influence the glass transition of supported ultrathin films.