Interplay of entropic and enthalpic contributions to the surface tension of polymer melts

The most common observation is that the surface tension of molten polymer l iquids is an increasing function of the molecular weight of the chains. How ever, when chain ends have been chemically modified, the opposite trend is found. In this article, we discuss theoretically, the interplay between seg regation effects of chain ends to the surface tension which are enthalpic d ominated (that contribution originated from the small chemical shift betwee n end-groups and monomers from the backbone), and an entropic contribution originated from the self-organisation of the chains in the immediate vicini ty of the interface (formation of loops), We find that enthalpic contributi ons are knot able to account for the decrease of surface tension with molec ular weight, and plausibly enough, the entropic contribution that we have c onsidered is responsible for this feature. (C) 2001 Elsevier Science B.V. A ll rights reserved.