"Influence of Confinement and Substrate Interaction on the Crystallization Kinetics of PET Ultrathin Films"

The cold crystallization kinetics of ultra-thin polymeric films (thickness: 10 nm divided by 0.250 mm) of poly(ethylene terephthalate) (PET) have been investigated by dielectric spectroscopy, X-ray diffraction, infrared spectroscopy (FTIR, ATR, RAIR) and Atomic Force Microscopy (AFM) imaging. The crystallization kinetics, as well as the structural dynamics, departed form the bulk behavior in a region below 100 nm, with a stronger slowing down associated to films deposited on strongly interacting substrates. By means of AFM technique, the crystallization kinetics located at the free surface (air/polymer) were monitored: for thick samples, the kinetics at the free surface were found much faster than within the bulk. Reducing the thickness, as the free surface approached the substrate, the crystallization kinetics probed by AFM technique became slower. This effect was more relevant for strongly interacting substrates, up to prevent crystallization in very thin films.