Liquid pistons, which could lead to new devices like micro displacement pumps and liquid switches, to adaptive lenses and advanced drug delivery systems, have been developed by engineering researchers at Rensselaer Polytechnic Institute.
The oscillating droplets of ferrofluid precisely displace a surrounding liquid and the pulsating motion of the ferrofluid droplets, which are saturated with metal nanoparticles, can be used to pump small volumes of liquid. The entire device is situated in a chamber filled with water.
These liquid pistons are highly tunable, scalable, and - because they lack any solid moving parts - suffer no wear and tear.
"It is possible to make mechanical pumps that are small enough for use in lab-on-a-chip applications, but it's a very complex, expensive proposition," said Professor Amir H. Hirsa.
"Our electromagnetic liquid pistons present a new strategy for tackling the challenge of microscale liquid pumping. Additionally, we have shown how these pistons are well-suited for chip-level, fast-acting adaptive liquid lenses," he added.
Pulses from an electromagnet provoke one of the ferrofluid droplets, the driver, to vibrate, which prompts a combination of magnetic, capillary, and inertial forces that cause the second droplet to vibrate in an inverted pattern.
The two droplets create a piston, resonating back and forth with great speed and a spring-like force.
Researchers can finely control the strength and speed of these vibrations by exposing the driver ferrofluid to different magnetic fields. In this way, the droplets become a liquid resonator, capable of moving the surrounding liquid back and forth from one chamber to another.
"There's really a lot we can do with these liquid pistons. It's an exciting new technology with great potential, and we're looking forward to moving the project even further along," said Hirsa.
Results of the study are published online by the journal Lab on a Chip.