Ionomer Interfacial Behavior from Molecular Dynamics Simulations: Impact of Ion Content on Interfacial Structure and Mixing

Ionomers are polymers with a modest fraction of charged groups; their thermomechanical properties make them attractive for use in many applications, including packaging and additive manufacturing, in which interfacial adhesion is a crucial factor. Here, molecular dynamics simulations are used to investigate how synthetically controllable parameters such as ion content impact the interfacial adhesion of these materials. Specifically, freestanding coarse-grained ionomer films are simulated, and their surfaces are subsequently brought into contact with each other. Composition profiles show a pronounced layering of neutral and charged groups near the interface, which is in agreement with prior experimental observations. We also track the mixing of ions and backbone monomers after contact of the two surfaces and find that increasing the ion content decreases the mixing of backbone monomers but increases the mixing of ions.