Stepwise Crystallization Kinetics of poly (ethylene terephthalate) Ultrathin Film studied by Fast Scanning Calorimetry

Under confinement, unique features of crystallization arise substantial investigations, among which the slowing down and accelerating crystallization are both reported. In order to characterize the crystallization kinetics of thin films of poly (ethylene terephthalate) (PET). We utilize fast scanning calorimetry (Flash DSC1™) to study the isothermal crystallization in a wide range of film thicknesses and temperatures. Nucleation at the free surface, which account for the stepwise crystallization behavior, dominate the overall crystallization at large undercooling. This is due to the fast transformation of disordered chains into crystals caused by the highly mobile surface layer. When crystallized at low undercooling, heterogeneous nucleation at the interface enhanced crystallization. Additional heterogeneities, which are introduced by the interface, considerably increase the amount of supercritical nuclei. These findings can be interpreted in terms of the undercooling vs half-crystallization time by a phase diagram, by which one can manipulate the crystallization under confinement through controlling the interface or temperature.