ABSTRACT
From the diagram presented in Fig. 1, it is quite straightforward to imagine how such a large scatter in the experimental values of the contact line tension may come about. Since every surface is, as far as its surface energy is concerned, inhomogeneous at least at a very small scale, the contact line is expected to exhibit a corrugation as shown in the figure, which is not accessible with optical imaging techniques. As a consequence, the total free energy of the contact line which is measured using a coarse-graining experimental technique (such as optical microscopy) consists not only of the genuine contact line tension or its sum over the corrugations as proposed by Neumann and co-workers [13], but also of the excess free energy connected to the increased total surface near this line. Since the typical length scale at which the wettability of the substrate varies is likely to exceed the above-mentioned critical length /, the measured line tension may well exceed its
genuine (unperturbed) value. This may at least explain large positive apparent line tensions.
