Wetting Tension Due to Coulombic Interaction in Charge-Related Wetting Phenomena

The influence of Coulombic interaction on wetting is elucidated within the framework of electromechanics. The Maxwell stress and osmotic pressure acting on a meniscus are integrated to obtain a concise analytical expression for the Coulombic contribution to wetting tension. The results are verified alternatively by using a thermodynamic approach. The method is applied to three important charge-related wetting configurations in which droplets are placed on a solid substrate. First, when the constant-potential boundary condition is applied at the substrate surface, only the electrocapillary term which represents the electrostatic free energy of the electrical double layer contributes to the wetting tension. Second, in the case of the constant-charge condition, the wetting tension includes an additional edge-effect term. It is found that the wetting tension in this case is dependent on the interface profile near the three-phase contact line. Third, in the case of electrowetting on dielectrics, the wetting tension also includes the edge-effect term. The wetting-tension term appearing in the Lippmann−Young equation is recovered as a special case of the third case.