From Micro to Macro: Predicting Polymer Blend Toughness*

While computational techniques have recently made strides, substantial work remains in translating microscopic simulation insights into macroscopic predictive tools. In this case study, we develop a micromechanical model and show how to parameterize it with self-consistent field theory to predict macroscopic glassy polymer blend toughness. These mixtures frequently exhibit phase separation, resulting in brittleness. Though compatibilizers can toughen these blends, optimizing compatibilizer architecture is challenging due to their extensive design space. Our microscopic theory reveals that compatibilizers increase blend toughness by increasing the number and length of molecular bridges that stitch the interface together. Self-consistent field theory then predicts the microscopic variables in this theory from experimentally accessible parameters. We validate both theories by comparing their predictions to extant experiments and extensive molecular dynamics simulations in which we vary polymer incompatibility, chain stiffness, compatibilizer areal density, and blockiness of copolymer compatibilizers. These results allow for the quick optimization of compatibilizer design in silico and suggest a possible avenue for more general bridging of the gap between micro- and macroscales.