Surface tension of an ideal solid: What does it mean?

The surface tension (ST) of an ideal (rigid, smooth, and inert) solid surface is usually calculated from a set of two equations: the Young equation and an additional equation that expresses the correlation between the individual STs of two phases and their interfacial tension. The present discussion suggests that this calculated ST may not be an appropriate characteristic of wettability of a solid surface. The reasons include the nonmeasurability of this ST and theoretical aspects related to the rigidity and inertness of an ideal solid. Instead, it is suggested to measure the contact angles of a set of a few standard liquids, from which a 'wettability index' can be calculated by properly averaging the wettability indices calculated for each of standard liquid. The optimal identity of these liquids and the optimal weights of the averages should be found by experimentation.

Automated summary

When calculating the surface tension of an ideal solid surface, it is suggested to measure the contact angles of standard liquids instead of directly using the calculated surface tension values. This approach provides a more accurate assessment of wettability of the solid surface, and the optimal choice of liquids and weights can be determined through experimentation.