Measurements of line tension for solid-liquid-vapor systems using drop size dependence of contact angles and its correlation with solid-liquid interfacial tension

According to the modified Young equation, one of the direct ways of measuri ng line tension for solid-liquid-vapor systems takes advantage of the depen dence of the contact angle on the radius of curvature of the three-phase li ne. This approach was used to determine line tension measurements for six o rganic liquids on two different self-assembled monolayer (SAM) surfaces (mi xed monolayers of methyl and carboxylic acid terminated alkanethiol on gold at two different composition levels). Low-rate advancing contact; angles w ere measured using Axisymmetric Drop Shape Analysis-Profile (ADSA-P). The g eneral trend observed for each system was that the contact angle decreases as the radius of the three-phase line for the sessile drop increases from a pproximately 1 to 5 mm. It was found that the drop size dependence of conta ct angles can be interpreted as being due to a positive line tension. The l ine tension values are all in the order of 10(-6) J/m. Also a correlation w as observed between the line tension and the solid-liquid interfacial tensi on for a series of liquids on each of the two surfaces. This observation co nforms to the predictions from a phase rule discussion for capillary system s.