INDUCED CRYSTALLIZATION THROUGH STRETCHED NETWORK

摘要

@@Flow-induced crystallization of crystallization of polymer is not only a fundamental non-equilibrium thermodynamic problem, but also of importance for polymer processing. During polymer processing, such extrusion, injection molding and fiber spinning, polymer materials are subjected to various flow fields. After more than 60 years effort in polymer community, no satisfactory molecular theory has been achieved yet. The idea of flow-induced disentanglement, orientation and stretch has been the basic idea dominated in the community dated back to Keller and de Gennes, which suggest that the long chains plays the crucial role at the flow-induced nucleation or shish. Recent work from Rastogi group further supports the nucleation role of long chains. However, a contrary picture has been presented by Kitama et al, who suggest that the short chains instead of the long chains are the major contributor of shish. Some other discoveries also suggest the initially shish-kebab picture may not be proper. Hsiao group reported multiple shish rather than a single shish induce crystallization of single lamella. Han and co-authors reported shish can be produced with a small shear rate and suggested disentanglement may not be a necessary condition for the formation of shish. Without disentanglement at small shear rate, the sheared material resembles a stretched network. This picture may be more consistent with Hu and Frenkel's simulation, which shows single stretched molecular chain can induce the formation of shish-kebab structure. The complex of experimental system and condition may be the origin for such discrepancies from different groups, which block further pursuing the molecular mechanism of flow-induced crystallization of polymer.