The Entropic Contribution to the Surface Tension of Polymer Melts

Many Cahn-Hilliard surface theories of polymer melts predict an entropic contribution to the surface tension of polymer melts. The size of this contribution is predicted to be on the order of 10-15By using a homologous series of polyethylenes, where the molecular weight varies from those of short chain alkanes to polymer molecules, we can scale out the enthalpic contribution and expose the entropic contribution which manifests itself at higher molecular weights. In order for the calculation to work a strong corresponding states principle must exist for the enthalpic contribution to the surface tension and we must be able to scale the surface tension data with the cohesive energy density for the bulk liquid. A method of obtaining a true measure of the cohesive energy density of polymer melts is described.