Nucleation and Crystallization of Polymer Melts under Cyclic Stretching: Entanglement Effect

It is well known that the local orientation order playsa key rolein stretch-induced nucleation and crystal growth of polymer melts,where a competition between chain orientation and dynamics of entangledpolymer chains must exist. However, it remains unclear how much thetopological entanglements affect the crystallization of polymer meltswhen the local order remains approximately unchanged. In this study,the influence mechanism of entanglements on the crystallization ofpolymer melts under cyclic stretching is revealed using moleculardynamics simulations and primitive path analysis. Polymer systemswith different entanglement densities and similar local order areconstructed by cyclic stretching, which can be used to figure outthe contribution of the entanglement effect to the polymer nucleationand crystal growth. The current results show that the polymer meltsprefer to nucleate in the less-entangled regions. The polymer nucleationrate and crystal growth rate decrease exponentially and linearly withincreasing entanglement density, respectively. The lower entanglementdensity holds the shorter nucleation time and eventually leads tothe smaller average size of crystalline clusters and more crystallineregions. This study provides a physical insight to understand thecyclic-stretch-induced nucleation and crystal growth that involvesthe topological restriction of entanglements.