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 (Delta S(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 Delta S(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.