TY - JOUR A1 - Yin, Huajie A1 - Madkour, Sherif Aly Hassan Aly A1 - Schönhals, Andreas T1 - Unambiguous evidence for a highly mobile surface layer in ultrathin polymer films by specific heat spectroscopy on blends JF - Macromolecules N2 - Despite the decade long controversial discussion on the effect of nanometer confinement on the glass transition temperature (Tg) of ultrathin polymer films, there is still no consistent picture. Here, the dynamic calorimetric glass transition of ultrathin films of a blend, which is miscible in the bulk, is directly investigated by specific heat spectroscopy. By a self-assembling process, a nanometer thick surface layer with a higher molecular mobility is formed at the polymer/air interface. By measuring the dynamic calorimetric Tg in dependence on the film thickness, it was shown that the Tg of the whole film was strongly influenced by that nanometer thick surface layer, with a lower Tg. Since the observed thickness dependence of the dynamic Tg is similar to the thickness dependence of the Tg for thin films of homopolymers, it is concluded that also for homopolymer a highly mobile surface layer is relevant for the widely observed Tg depression. PY - 2015 DO - https://doi.org/10.1021/acs.macromol.5b01259 SN - 0024-9297 SN - 1520-5835 VL - 48 IS - 14 SP - 4936 EP - 4941 PB - American Chemical Society CY - Washington, DC AN - OPUS4-33841 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -