No abstract

The heat capacity (C p ) of confined polystyrene in particles is investigated in the case of close-packed structure using differential scanning calorimetry (DSC). This confined geometry allows the highest possible free surface area (3/R) in a dense macroscopic sample. We show that C p of polystyrene increases above that of bulk below bulk glass transition (T g ) T > T g − 30 °C. Such deviation depends mainly on the fraction of free surface area, which is interpreted by the existence of zone of higher degrees of freedom on the free surface and comfort the previous results of the depression of a volumetric glass transition T g vol and the higher surface mobility by the photobleaching technique. On the other hand, the main discontinuity of C p coincides with the bulk glass transition zone T g , which comforts the finding of the existence of a core with a bulk behavior. The C p curves exhibit both behaviors observed in confined system: (i) a growth of C p in the glassy regime which is in agreement with the negative shift of the thermal expansion kink and (ii) a discontinuity of C p at the T g bulk which suggests an invariant segmental dynamics. Finally, the α-dynamic probed via the void closure in the area where C p increases was found to exhibit a bulk behavior. This suggests that the mobility or excessive expansion of the free surface does not affect the overall segmental dynamics of the particles which is most likely dominated by the core dynamics.