Aqueous solutions and liquid metals in contact with other phases or components experience strong Coulomb forces at their interfaces. The interfacial energy of such liquids facing solid walls is given by the sum of the free surface energy of the liquid and the electrostatic energy of the diffusive electric double layer due to the wall surface charge density. As a consequence, the interfacial stress of the liquid at the wall appears to be an anisotropic stress tensor, which has a stress component of opposite sign normal to the surface, compared with its two components parallel to the surface. This alternative description of the interfacial energy makes it possible to predict static contact angles, once the wall surface charge density is known. This paper investigates the relationship between the long-range Coulomb effects in the ionic solution and the interfacial energy, and concentrates on experiments in which other surface effects are minimized and in which chemical reactions at the surface are absent or frozen. Data for water and mercury, as an example, fit well if the same surface charge density of the wall is assumed in both cases. As an application to micro fluid dynamics, the electroosmotic mobility, the streaming current, or the pressure drop of a flow through a microchannel can be predicted only from contact angle measurements done. (C) 2003 Elsevier Science (USA). All rights reserved.