Glass transition and segmental dynamics in thin supported polystyrene films: The role of molecular weight and annealing

• The segmental dynamics and the Tg for thin supported PS films were investigated.
• The segmental dynamics is independent of the film thickness for each Mw.
• The Tg depends on the film thickness and the Mw.
• These behaviours are due to PS chain adsorption onto the Al substrates.

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.