Researchers use acoustic levitation to study charged liquid droplets splitting
Researchers use acoustic levitation to study charged liquid droplets splitting lead image
Field-induced drop ionization (FIDI) experiments investigate the splitting of charged liquid droplets, a phenomenon that occurs naturally in thunderstorms, sea spray aerosols, and waterfalls. In FIDI, uncharged droplets fall downstream through the electric field of a parallel plate capacitor to create charged progeny droplets.
Reporting in Review of Scientific Instruments, two chemists from the BAM Federal Institute for Materials Research and Testing in Germany developed an FIDI method that employs acoustic levitation to study an individual droplet for an extended period of time. This approach has the advantages of contactless sample handling, as well as greater control of droplet size and timing.
Coauthors Casten Warschat and Jens Riedel set up their experiment with a home-built acoustic levitator and electrodes spanning up an axially symmetric electric field perpendicular to the axis of sound propagation. They used high-speed photography to record the droplet rupture, and laser-induced fluorescence to highlight the progeny droplet ejection. Lastly, they performed mass spectrometry to chemically analyze the progenies.
In FIDI experiments, the observable time window is restricted by the droplet falling through the electric field. Acoustic levitation, however, keeps the droplet steady for longer study. Also, prior studies were limited to droplets in the micrometer regime. The technique by Warschat and Riedel allows for droplets of any size, from micrometers to millimeters.
The researchers demonstrated this advanced flexibility by using millimeter drops with fluid dynamics on the millisecond timescale — previously inaccessible with the FIDI method. The experimental results matched well with theoretical predictions.
According to Riedel, the next step in this line of research is to further investigate the influence of droplet size, charge state of pre-charged droplets, and droplet pH on the fission dynamics.
Source: “Studying the field induced breakup of acoustically levitated drops,” by C. Warschat and J. Riedel, Review of Scientific Instruments (2017). The article can be accessed at https://doi.org/10.1063/1.5004046 .
