TY - JOUR A1 - Labahn, Diana A1 - Mix, Renate A1 - Schönhals, Andreas T1 - Dielectric relaxation of ultrathin films of supported polysulfone JF - Physical review E N2 - 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. KW - Adsorbed layers KW - Aluminium KW - Annealing KW - Contact angle KW - Dielectric relaxation KW - Electrodes KW - Glass transition KW - Polymer films KW - Thin films PY - 2009 DO - https://doi.org/10.1103/PhysRevE.79.011801 SN - 1539-3755 SN - 1063-651X VL - 79 IS - 1 SP - 011801-1 - 011801-9 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-19050 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -