Synopsis: Saturn-Shaped Drops

An electric field can pull apart a millimeter-sized oil drop, causing it to shed thin rings from its equator that then break up into tiny droplets.
Synopsis figure
Q. Brosseau and P. M. Vlahovska, Phys. Rev. Lett. (2017)

Place a drop of liquid in an electric field and it will stretch out along the field direction, forming jets that spray tiny liquid beads out of each end. Now Quentin Brosseau and Petia Vlahovska from Brown University, Rhode Island, have uncovered a new behavior where, instead of jets, the drop extrudes rings of liquid from its equator, resembling the planet Saturn.

Jet spraying occurs when the drop is filled with liquid that is more conducting than the fluid in which it is suspended. When an electric field is applied, the liquid at the surface of the drop flows from the equator to the poles. As a result, the drop stretches along the polar axis, so that it resembles an American football with two pointy cones at each end. The pointy interfaces are unstable and tiny beads of liquid spray out. This behavior occurs in thunderclouds and ink-jet printers, in which droplets are surrounded by poorly conducting air.

In their experiments, Brosseau (now at New York University) and Vlahovska (now at Northwestern University) flipped the system around—using a silicon oil drop that was less conducting than the surrounding fluid of castor oil. This time, the liquid at the surface flowed to the drop’s equator rather than its poles, causing the millimeter-sized drop to flatten into the shape of a lens. Again the drop’s interface was unstable, and it shed thin rings of liquid that subsequently broke up into beads about 10 micrometers in size. This shedding continued for a few tens of seconds until the original drop was transformed into thousands of uniformly sized beads. Although not fully understood, the process could be used to precisely dose out pharmaceuticals in tiny liquid particles or to create thousands of microreactors for high-throughput chemistry experiments.

This research is published in Physical Review Letters.

–Katherine Wright

Katherine Wright is a Contributing Editor for Physics.


More Features »


More Announcements »

Subject Areas

Fluid Dynamics

Previous Synopsis

Biological Physics

Explaining Grid-Cell Firing

Read More »

Next Synopsis

Related Articles

Synopsis: Sorting Blood Cells via Their Stiffness
Biological Physics

Synopsis: Sorting Blood Cells via Their Stiffness

A proposed modification to a microfluidic cell-sorting device could separate cells by their deformability, an important marker for several diseases. Read More »

Synopsis: Antispiral Formation at a Liquid Surface
Fluid Dynamics

Synopsis: Antispiral Formation at a Liquid Surface

Liquid falling from a horizontal film displays an intriguing pattern of inwardly rotating spirals. Read More »

Synopsis: Turning Round Drops Square
Soft Matter

Synopsis: Turning Round Drops Square

Researchers can change the shape of a liquid drop by placing it between two stretched elastic films, allowing the drop to be used as a tiny adjustable lens. Read More »

More Articles