Georgia Tech Ph.D. candidate Alexandros Fragkopoulos adjusts equipment used to create unstable toroidal droplets in silicone oil.
By John Toon
For most people, the drip, drip, drip of a leaking faucet is an annoyance. But for Ph.D. candidate Alexandros Fragkopoulos, the droplets are the sound of serious research.
The research has implications for the life sciences, where biological materials, including cells, undergo shape changes reminiscent of the droplet behavior. The findings could also improve industrial processes such as fuel injection that depend on droplet formation.
“Surface tension drives the evolution of the droplets,” Fragkopoulos said. “Fluids tend to minimize their surface area for a given volume because that minimizes the energy required to have an interface between different fluids. Spherical shapes minimize that energy, and as a result, toroidal droplets want to evolve to become spherical. We’re studying how that transition occurs.”
Using a sheet of laser light to observe the scattering from polystyrene particles in water droplets formed within thick silicone oil, the researchers have observed how droplets change shape and identified the factors that set the droplets on the path to either collapse or break up. The research, which was supported by the National Science Foundation, was reported in the journal Proceedings of the National Academy of Sciences.
The researchers also studied how charge affects the toroidal-droplet evolution and addressed the role of mechanical non-linearities in the surrounding fluid. Though fundamental, the research findings could aid in manipulating fluid streams and drops in microfluidics and other areas.