Surface and Interfacial Tension of Graft Polymer Melts*

Understanding surface properties of polymer melts is crucial for designing new polymeric coatings, adhesives, and composites. Here, we study the effect of molecular architecture on surface and interfacial tension of graft and linear polymer melts by molecular dynamics simulations. In particular, we elucidate the effect of the degree of polymerization of the side chains n_sc and their grafting density 1/n_g on the surface tension of the graft polymer/vacuum interface, and the interfacial tension of the interface between graft and linear polymer melts. For the case of the graft polymer/vacuum interface, our simulations confirm that the surface tension is a linear function of the fraction of the backbone ends f_be and side-chain ends f_se. This dependence of the surface tension highlights the entropic origin of the surface tension corrections associated with the redistribution of the grafting points and ends at the interface. However, the interfacial tension between graft and linear polymer melts does not show any significant dependence on the molecular structure of the graft polymers, thus pointing out the dominance of the enthalpic contribution to the interfacial tension.