Deformation and failure of glassy polymer-polymer interfaces compatibilized by linear multiblock copolymers

Using coarse-grained molecular dynamics simulations, we study the mechanical properties and stress transfer mechanisms of weakly entangled, glassy polymer blends compatibilized by diblock, triblock, or pentablock copolymers. For a given number of copolymer junctions per unit area, copolymer architecture is found to play a minimal role, whereas block degree of polymerization and copolymer loading qualitatively impact the interfacial mechanics. Explicitly, the stress-strain and density-strain curves reveal distinctly different deformation mechanisms at low and high compatibilizer loading related to cavitation and fibril formation near the A/B interface. Furthermore, the competition between interfacial cavitation and chain pullout from the bulk leads to nonmonotonic dependencies of the toughness and strain-at-break on copolymer loading. For sufficiently long copolymers, the simulations predict an optimum loading that produces mechanical properties that nearly match those of the homopolymer glass. These results imply that moderate loading of long block copolymers is ideal for effective compatibilization and stress transfer across the interface.