Water is known for its exceptional dielectric properties and its ability to separate charges. Thanks to this ability, most materials acquire electric charge at the interface with water upon immersion. A particular example of such charging is presented by air-water interface. The phenomenon of charging can be probed by bubble electrophoresis: motion of gas bubbles in an electric field.
In this talk, I discuss the special properties of water and present a numerical study of electrophoresis of a gas bubbles using computer simulation. The model assumes that the bubble charging, which is responsible for its motion in an external ﬁeld, results from a preferential adsorption of solution anions at the gas-water interface. While in simple electrolytes motion of a bubble resembles that of solid particles, in solutions of multivalent salt we can observe an anomalous electrophoresis: motion of the bubble opposite the direction prescribed by the surface charge. I show that the electric double layer around the bubble also acquires an anomalous dipole moment directed against the external ﬁeld in contrast with the charged solid particle picture.