(31e) Molecular Dynamics Simulations of Crystal Nucleation in Incompatible Polymer Blends

We apply molecular dynamics (MD) simulations to investigate crystal nucleation in incompatible polymer blends under deep supercooling conditions. We use binary blends of united-atom polyethylenes (PE) and isotactic polypropylenes (iPP) oligomers with pre-constructed planar interfaces as the model systems. To complement the weakly phase-separated oligomeric PE and iPP, we also construct strongly phase-separated blends of artificial PE and iPP with modified inter-species interactions. Simulations of isothermal nucleation are performed for phase-separated blends with different degrees of incompatibility. In weakly segregated blends, slow and incompatible iPP chains in crystallizable PE domains can significantly hinder the crystal nucleation and growth. When the crystallizable polymer is blended with a more mobile species in interfacial regions, enhanced molecular mobility leads to the fast growth of crystalline order. However, the incubation time remains the same as that in pure samples. By inducing anisotropic alignment near the interfaces of strongly segregated blends, phase separation also promotes crystalline order to grow near interfaces between different polymer domains.