Shish-kebab crystallites initiated by shear fracture in bulk polymers: 2. Crystallization on shearing

Abstract

Shish-kebab crystallites are initiated by the oriented precursors of the ordered structures in the flow processing of polymer materials. In our previous work, we have proposed that the sporadic local events of shear fracture and their memory are responsible for the heterogeneous initiation of shish-kebab crystallites in the shear flow of bulk polymers. Upon the cessation of the Poiseuille-flow-like force field in the binary polymer blends of two chain lengths, our dynamic Monte Carlo simulations demonstrated the formation of precursor and shish-kebab crystal structure at a low temperature. In the present work, we further investigated the boundary conditions of precursor formation at low temperatures while maintaining the force gradients reflecting the global shear rates. The phase diagram of morphological features upon the variations of temperatures and force gradients reveals that steady shish precursors survive at higher temperatures and larger force gradients than the region for shish-kebab crystallites, appearing as responsible for the subsequent shish-kebab formation upon cooling with or without shear cessation. The results are consistent with the related experimental observations and evidence the pre-ordering structure existing before shear-induced polymer crystallization.