(180f) Decoupling Between Equilibrium and Out-of-Equilibrium Dynamics in Thin Polystyrene Films

The way the dynamics of glass forming systems is modified by confinement, i.e. in systems with large interface, has been the subject of intense research in recent years. This contribution aims to present a detailed investigation on the glassy dynamics of thin polystyrene (PS) films. The segmental dynamics is probed by broadband dielectric spectroscopy (BDS) and AC-calorimetry, which are able to probe the spontaneous fluctuations at equilibrium. The temperature marking the equilibrium to out-of equilibrium transition of the glass former, namely the glass transition temperature (T_g), and the physical aging, namely the slow evolution of disordered glassy material towards thermodynamic equilibrium occurring below T_g, are probed by differential scanning calorimetry (DSC) and capacitive dilatometry (CD). As a general important conclusion, we show that the out-of-equilibrium dynamics, in terms of T_g and physical aging, is decoupled from the equilibrium dynamics. This result contrasts with the general view that the out-of-equilibrium dynamics is exclusively related to the molecular mobility of the glass former. This means that, apart from the intrinsic molecular mobility, geometrical factors are also important in determining the T_g and physical aging behavior of thin polymer films. Possible explanations to these results are discussed.