In situ atomic force microscopy of the melting of melt-crystallized polyethylene

Abstract

High temperature AFM is used to observe the melting of polyethylene lamellae crystallized from the melt in situ in real-time. Both oriented and un-oriented samples are observed. The melting of shish–kebab structures, including revealing the bare oriented shish, is achieved. Lamellae are observed to melt from their edges, and this is proposed to be due to the inherent higher mobility at the crystal edges rather than differences in stability within the crystal due to different levels of post crystallization perfecting. Observation of the melting of structures that have been observed during growth confirms that material crystallized at lower temperatures melts first, followed by material crystallized in confined geometries, and finally the rest of the isothermally crystallized lamellae that melt back from the edges with an apparently random morphology that is not the reverse of the growth process. In situ observation during melting is confirmed as an alternative and complementary technique to etching to reveal behaviour during crystallization when crystallization is too rapid for in situ observation.