Impact of dispersity on the welding of polymer interfaces: Structure, dynamics, and interfacial entanglements from...

Understanding how molecular-weight dispersity influences welding at polymer-polymer interfaces is essential for many technological applications. Here, we use molecular dynamics simulations to model thermal welding in entangled polymer melts following Schulz-Zimm molecular weight distribution, allowing us to elucidate the mechanisms driving interfacial entanglement formation. Owing to the enhanced constraint-release pathway provided by short, mobile chains in disperse melts, we find that, at fixed welding time and weight-average molecular weight Mw, the interfacial diffusion of long entangled chains accelerates with increasing dispersity. At early times, chain ends dominate interfacial diffusion, with dispersity regulating the subsequent involvement of interior segments as welding proceeds. Dispersity dictates interfacial entanglement formation, leading to an earlier onset of saturation with increasing dispersity and controlling the contribution of mechanically effective topological constraints at the interface. We further correlate the growth of interfacial entanglements with the interpenetration depth of monomers and show that dispersity modulates the minimum interpenetration distance required for entanglement development. Collectively, these results provide molecular-level insight into adhesion in industrially relevant polymer systems and highlight how dispersity can be leveraged to optimize polymer performance.