Line tension is defined in thermodynamics as the work of formation of a unit length of three-phase line.  Its measurement is controversial, with widely varying values reported in the literature.  At the millimetre scale, line tension of order 10^-6 J/m has been measured in a variety of low-energy systems from the drop size dependence of contact angles.  These values are not in accord with theory and have been criticized (but only qualitatively) as arising from solid surface imperfections.

Recent studies of contact angles on polymer films have uncovered subtle, specific liquid-solid interactions in most systems, even those normally considered to be purely dispersive.  These interactions are absent only in certain systems with nonpolar, bulky liquid molecules and inert solids.  The drop size dependence of contact angles has not been studied before in such systems.

We will report new measurements of the drop size dependence of contact angles in systems with and without specific interactions.  Results to date for a number of liquids on one inert solid reveal a somewhat smaller, positive line tension of order 10^-7 J/m.