In 1882, Lord Rayleigh predicted that a droplet would emit jets when zapped with enough charge. Rayleigh was right, and today the jets are the basis for a Nobel Prize-winning technique called electrospray ionization, which is widely used to study the structure of large biomolecules. Yet no one had ever seen Rayleigh jets. Until now.
In the 9 January issue of Nature, researchers present the first photographs of charged droplets ejecting two thin jets from either end. Thomas Leisner of the Technical University at Ilmenau, Germany, and colleagues levitated charged 60-micrometer droplets of ethylene glycol in an electric field. As the particles evaporated, the electrical charge began to overwhelm the surface tension that keeps the particles together. By studying how the droplets quivered, the researchers were able to trigger a snapshot at the exact moment the jets appeared.
Although the pictures are satisfying in that they fulfill a century-old prediction, much mystery remains. For instance, the team found that the jets occur at lower charges than predicted by Rayleigh. "Nobody knows how these jets are formed, nor what makes them so fine," says Leisner.