Negative Excess Interfacial Entropy between Free and End-Grafted Chemically Identical Polymers

We measured the temperature dependence of the interfacial tension between free melt and end-grafted chemically identical polymers. The excess interfacial entropy (ΔS_MB) was found to be extremely small and negative. This is in sharp contrast to the case of liquid surfaces and interfaces between different liquids, where ΔS_MB is usually much larger and positive, i.e., molecules at such surfaces and interfaces have a higher degree of freedom than in the bulk. A quantitative comparison with theoretical predictions revealed large differences which we attribute to the finite compressibility of the polymer melt, not yet taken into account by theory.