Effect of Free Chain Conformation on Flow-Induced Shish Nucleation in Lightly Cross-Linked Polyethylene

We investigate the effect of the free chain conformation on the flow-induced shish nucleation in lightly cross-linked high-density polyethylene melts by comparing nucleation processes under the quasi-static extension (QSE) and the fast extension (FE). Under the QSE, free chains maintain their equilibrium conformations, leading to the nucleation process being governed by the free energy change of crystallization. In this case, the shish is formed through the chain-folding pathway, and its length is determined by the critical nuclei (∼0.1 μm). By contrast, the FE remarkably orients the long free chains, which preferentially crystallize and allow the shish length to reach one micron. Moreover, the free chain conformation also influences the shish radius through the combined effects of the full stretch of cross-linked chains and the orientation of free chains. These results reveal the fundamental role of the free chain conformation in determining the nucleation path and the morphology of shish.