TY - JOUR A1 - Boucher, V.M. A1 - Cangialosi, D. A1 - Yin, Huajie A1 - Schönhals, Andreas A1 - Alegría, A. A1 - Colmenero, J. T1 - Tg depression and invariant segmental dynamics in polystyrene thin films N2 - We investigate the segmental dynamics and glass transition temperature (Tg) of polystyrene (PS) thin films. The former is investigated by alternating current (AC) calorimetry and dielectric spectroscopy (BDS). The Tg, underlying the equilibrium to out-of-equilibrium crossover from the supercooled liquid to the glass, is obtained by differential scanning calorimetry (DSC) and capacitive dilatometry (CD). We show that the intrinsic molecular dynamics of PS are independent of the film thickness both for the freestanding and supported films, whereas Tg decreases with film thickness from several microns down to 15 nm. This result is found for complementary methods and in a simultaneous measurement in BDS and CD. This questions the widespread notion that segmental mobility and the equilibrium to out-of-equilibrium transition are, under any experimental conditions, fully interrelated. For thin films, it appears that the molecular mobility and Tg are affected differently by geometrical factors. PY - 2012 DO - https://doi.org/10.1039/c2sm25419k SN - 1744-683X VL - 8 IS - 19 SP - 5119 EP - 5122 PB - RSC Publ. CY - Cambridge AN - OPUS4-25805 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yin, Huajie A1 - Cangialosi, D. A1 - Schönhals, Andreas T1 - Glass transition and segmental dynamics in thin supported polystyrene films: The role of molecular weight and annealing N2 - Broadband dielectric spectroscopy (BDS), specific heat spectroscopy (HCS) and capacitive scanning dilatometry (CSD) are used to study the glass transition and segmental dynamics in thin supported polystyrene (PS) films. Different molecular weights (Mw = 50 kg/mol, Mw = 260 kg/mol, Mw = 1408 kg/mol) and annealing protocols are employed in the study. The segmental dynamics is independent of the film thickness for each Mw in the temperature window of the dielectric measurement. The thermal glass transition temperature, Tg, measured by CSD depends on the film thickness and shows also a dependence on Mw. These observations are explained in terms of the formation of irreversibly adsorbed layer due to chain adsorption on the Al substrates during annealing. KW - Thin polystyrene films KW - Glass transition KW - Segmental dynamics PY - 2013 DO - https://doi.org/10.1016/j.tca.2013.05.034 SN - 0040-6031 SN - 1872-762X VL - 566 SP - 186 EP - 192 PB - Elsevier CY - Amsterdam AN - OPUS4-28736 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -