Influence of Freezing Layer on the Crystallization Kinetics of PCL on Oriented PE Film

Abstract

The effect of freezing layer on the crystallization kinetics of poly(ε-caprolactone) (PCL) thin and ultrathin films was investigated by monitor the growth process of it on oriented polyethylene (PE) and CaF2 with and without freezing layer, respectively. It was found that the PCL films with similar thicknesses crystallize much faster on oriented PE than on CaF2 substrate. For example, the crystallization rate constant of a 102 nm thick PCL film decreases tremendously by 3 orders of magnitude from 1.1×10−1 on PE substrate at 50 °C to 7×10−4 on CaF2 surface at 40 °C. Moreover, the crystallization of PCL accelerates on CaF2 surface while slows down at PE surface with increasing film thickness. The ultrathin films of PCL with thickness less than 14 nm exhibits the fastest crystallization rate on oriented PE with a rate constant of about 3.5×10−1, which is 3 times higher than that of a ca. 50 nm thick film. This illustrates the great influence of freezing layer on the crystallization process of PCL. The freezing layer thickness of PCL on PE is estimated to be in the range of 14–17 nm. Taking the radius of gyration (R g ∼ 15.6 nm) of the used PCL material into account, the obtained results may imply the existence of a correlation between the R g of PCL and its freezing layer thickness at PE substrate.