Weld formation between polymer films subject to a thermal gradient -- insights from Molecular Dynamics simulations

The weld between adjoining polymer filaments is formed by polymers diffusing across the interface. This process has important scientific and technological applications. In the simplest, symmetric case the two filaments are constituted of identical polymers in the same thermodynamic state. However, in some cases asymmetric settings are of interest. For instance, in polymer extrusion additive manufacturing, a high-temperature liquid polymer melt is placed in contact with a room-temperature glassy substrate, which results in material and heat exchange across their interface. Here, we investigate whether and how this asymmetric interdiffusion differs from the symmetric setup. We present results of Molecular Dynamics simulations of polymer films that are first equilibrated at a given temperature and then placed in contact with each other. As the films are laid side-by-side, polymers begin interdiffusing. By comparing symmetric, isothermal films, and asymmetric pairs equilibrated at different temperatures, we explore how the thermal gradient influences the formation of the weld.