On the contribution of the chain ends to the surface tension of a polymer melt.

We propose a physical picture describing the mechanisms by which chain ends affect the surface tension of a mono-dispersed polymer melt with chain length N. The driving effect is the adsorption equilibrium of chain ends within a bulk slice adjoining the surface and acting as a confined end reservoir. The thickness of that limited space is a characteristic length of the melt. This picture conforms to a previous approach proposed years ago by de Gennes. However, the characteristic length [Formula: see text] that we consider is different from the one [Formula: see text] that he considered. Our choice is carefully argued. The resulting model correctly reflects the transition between the two N regimes reported in experimental studies, with the correct exponents. Stretching contributions are also considered, and appear small compared to the above-mentioned adsorption equilibrium effects. We think that the usefulness of the newly introduced characteristic length might exceed the specific problem addressed in the present paper. The equilibrium state of a lamellar diblock copolymer is briefly discussed for illustration.