Molecular dynamics study of slip at the interface between immiscible polymers

Nonequilibrium molecular dynamics simulations were used to study the structural properties and viscous response of interfaces in binary blends of symmetric polymers. The polymers were made immiscible by increasing the repulsion between unlike species. As the repulsion increased, the interface narrowed, and the fraction of chain ends in the interfacial region increased. The viscosity in the interfacial region η_I was lower than the bulk viscosity, leading to an effective slip boundary condition at the interface. As the degree of immiscibility increased, the interfacial viscosity decreased, and the slip length increased. When the radius of gyration of the chains was much larger than the interfacial width, η_I was independent of chain length. As predicted by de Gennes and co-workers, η_I corresponds to the bulk viscosity of chains whose radius of gyration is proportional to the width of the interfacial region.