Effects of phase separation and interfaces on incompatible polymer crystallization

We apply molecular dynamics (MD) simulations to investigate the roles of phase separation and interfaces in the crystallization of incompatible polymer blends. We use binary blends of polyethylene (PE) and isotactic polypropylene (iPP) oligomers with pre-constructed planar interfaces as the model systems. By varying the simulation temperatures, we adjust the incompatibility and the interface-induced orientational and conformational order of polymer segments. However, PE and iPP oligomers are mildly incompatible so that the interface-induced order is nevertheless weak. To access a broader range of interface-induced order, we also simulate iPP with "artificial" PE oligomers. We weaken the intra-species attraction between the "artificial" PE and iPP to enhance the incompatibility. We also modify the dihedral potential to increase the stiffness of the "artificial" PE. The enhanced incompatibility and stiffness give rise to the increased and longer-ranged interface-induced order in the phase-separated blends. By simulating crystal nucleation and tracking the distributions of crystal nuclei in the natural and "artificial" blends of PE and iPP, we demonstrate the effects of phase separation and interfaces on the crystallization of incompatible polymers.