Nucleation and Crystallization of Polymer Melts under Cyclic Stretching: Entanglement Effect
Chunhua Zhu, Junhua Zhao
Abstract
It is well known that the local orientation order plays a key role in stretch-induced nucleation and crystal growth of polymer melts, where a competition between chain orientation and dynamics of entangled polymer chains must exist. However, it remains unclear how much the topological entanglements affect the crystallization of polymer melts when the local order remains approximately unchanged. In this study, the influence mechanism of entanglements on the crystallization of polymer melts under cyclic stretching is revealed using molecular dynamics simulations and primitive path analysis. Polymer systems with different entanglement densities and similar local order are constructed by cyclic stretching, which can be used to figure out the contribution of the entanglement effect to the polymer nucleation and crystal growth. The current results show that the polymer melts prefer to nucleate in the less-entangled regions. The polymer nucleation rate and crystal growth rate decrease exponentially and linearly with increasing entanglement density, respectively. The lower entanglement density holds the shorter nucleation time and eventually leads to the smaller average size of crystalline clusters and more crystalline regions. This study provides a physical insight to understand the cyclic-stretch-induced nucleation and crystal growth that involves the topological restriction of entanglements.