The generalized theory of capillarity identifies line tension as a natural and necessary extension of analysis for the systems with multi-phase boundary curves. Theoretically, finding an estirnate for line tension is very complicated. Modeling of molecular interactions almost always requires significant simplifications which would cause considerable uncertalnty in the resulting values. Experimentally, line tension is typically small and hence much more difficult to measure than surface tension. A review of the literature shows that there is little consensus among researchers with respect to both sign and magnitude of line tension.

Our preferred method to detennine line tension for solid-liquid-vapor systems takes advantage of dependence of contact angles on the drop size according to the modified Young equation (Eq. 2.22). Using a sensitive and accurate contact angle and drop size rneasurement methodology, i.e., Axisymmetric Drop Shape Analysis (ADSA), a large number of contact angle data were pmduced Le., 27, solid-liquid-vapor systems were studied. Potential artifacts that may effect the observed drop size dependence of contact angles including contortions of the three-phase line, solid surface deformation, thin film effect, and heterogeneity of the solid surface, were considered. They all proved insignificant either by the use of models developed to descnie and analyze the effect of the particular feature, or by thermodynamic reasoning, or the use of available literature (see section 4.4). It was established that line tension was positive for all of the systems studied. The magnitude of line tension determined ranges from below from 10⁻⁷ J/m for systems with low contact angles to 10⁻⁴ J/m For the high energy system studied (the range reflects mainly the matenal properties such as intemolecular forces). Exploratory steps taken to examine line tension behavior near the wetting transition suggested that the he tension decreases as the contact angle decreases and perhaps vanishes at complete wetting. A high energy system, i.e., liquid tin on a silica surface, was also studied. The seemingly large iine tension value obtained, i.e., 10⁻⁴ J/m, should not be entirely surprising, as it was found that there exists a positive correlation between line tension and solid-liquid interfacial tension.