The capillary race: Optimal surface tensions for fastest penetration

The minimization of the penetration time into a capillary with respect to the solid and liquid surface tensions was studied for the cases of equilibrium contact angles (ECAs) and dynamic contact angles (DCAs). Two correlations for the ECA and two correlations for the DCA were used as case studies. For all cases, a global minimum in the penetration time with respect to both surface tensions does not exist. If one of the surface tensions is predetermined, a correlation between the solid and liquid surface tensions that gives the minimum penetration time is presented. This correlation strongly depends on the model used for the ECA and the DCA.