Mechanics of Interfaces
Contact: Jörg Weissmüller
High-school curricula and everyday experience teach us that the surface of a fluid exerts forces, measured by the "surface tension", on the underlying bulk phase. As early as 1800, Young and Laplace have quantified the resulting pressure in small droplets in the capillary equation that bears their name. Two hundred years later, amazingly, the transfer of this simple phenomenon from the fluid to a solid remains subject of discussion. Open issues relate to the definition of and distinction between the two relevant capillary parameters for solids, surface stress and surface tension. Furthermore, the empirical data base for surface stress in materials is slim. The mechanical balance equations that link the surface stress to the compensating stresses in the bulk are only partly understood, real microstructures with nontrivial geometry continuing to be a challenge. Fascinating issues, with practical relevance in micromechanical systems and energy storage materials, concern the coupling of surface-induced stress and chemistry.
| Capillary equations for solids. | |
Experimental data for surface stress, f, and surface tension, γ, versus the superficial charge density, q, for a 111-textured gold electrode in dilute perchloric acid. Measurement using substrate bending technique with laser detection. |
