ABSTRACT
We can regard the interfacial tension represented in Eq. (1) as the free energy per unit area of the interface [4]. This may be readily understood by imagining a soap film surrounded by a square wire with one movable side. The liquid-vapor interfacial tension is equal to the work necessary to spread the film surface by a unit area, opposing the tension acting on the movable side [5]. Hence we can regard Eq. (1) as the relation between three kinds of energies, i.e., we can calculate the reversible energy change (σSV−σSL) using σLV cos αY without knowledge of σSV or σSL themselves when a unit area of the solid surface is wetted by liquid. It is usually not easy to directly measure the interfacial tensions on the left-hand side of Eq. (1), and the wetting behavior is often discussed using σLV and αY.
