Drops Hover Indefinitely Above Vibrating Solid Surface
Like a miniature trampoline, a vertically oscillating surface can cause a liquid drop to bounce repeatedly for long times without splashing down. In the past, only liquid surfaces have performed this trick (see Video: Juggling Water Drops). Now Lebo Molefe, Tomas Fullana, and their colleagues at the Swiss Federal Institute of Technology in Lausanne (EPFL) have continuously bounced an oil drop using an atomically smooth mica surface [1]. They explain that an air “cushion” between the drop and the surface enables a soft rebound. The drop periodically deforms in shape as it approaches the surface, but it does not spray out in all directions.
At high frequencies (above about 100 Hz), the team observed a different behavior: The drop barely moves vertically but simply hovers in place as it deforms periodically in sync with the vibrating surface below. The team thinks that both this “bound” mode and the bouncing mode could potentially be useful for moving tiny drops on a surface where small-scale chemical reactions or biological tests could be performed. Such an open-air setup could be an alternative to the microscopic pipes currently used in microfluidic labs-on-a-chip.
–David Ehrenstein
David Ehrenstein is a Senior Editor for Physics Magazine.
References
- L. Molefe et al., “Drops can perpetually bounce over a vibrating wettable solid,” Phys. Rev. Lett. 135, 144001 (2025).