Illuminating the No-Man's Land of Waters' Surface: Strong Electric Charge Observed at the Interface Between Oil and Water Is Not Due to Impurities
ScienceDaily (Nov. 27, 2012)
Here's an amusing kitchen-table experiment to illustrate waters unusual properties: put a drop of pure insulating oil in a glass of pure, non-conducting water, and create an electric field using two wires hooked up to a battery. You'll see the oil move from the negative to the positive pole of the little circuit you've created. You have created charge in a mixture that was neutral, and a huge amount of it too, judging from the speed at which the droplets move. The same thing happens for gas bubbles in water; the phenomenon of charging applies to all hydrophobic/water interfaces.
A century of debates
It's not a new discovery; scientists have observed the phenomenon in the middle of the 19th century. But despite more than a century of research, the reason why such a huge electric charge exists is still the subject of heated debate.
In an article published this week in Angewandte Chemie -- a journal of reference in the field -- EPFL scientist Sylvie Roke challenges a hypothesis put forward last spring in the same journal. With experimental proof to back her up, the holder of the Julia Jacobi chair in photomedicine makes her case: the phenomenon is not caused by the inevitable "impurities" present in oils, as her colleagues claim, but rather by certain intrinsic properties of the water molecules involved.