By shining laser beams on the water surface, engineers at the University of Houston have succesfully created an upward water fountain in deep water. This phenomenon is known as the Marangoni effect, first described in 1860.
The Marangoni effect causes convection and explains the behavior of water when differences in surface tension exist.
Jiming Bao, professor of electrical and computer engineering at UH, said, “It is well known that an outward Marangoni convection from a low surface tension region will make the free surface of a liquid depressed. We report that this established perception is only valid for thin liquid films. Using surface laser heating, we show that in deep liquids, a laser beam pulls up the fluid above the free surface generating fountains with different shapes.”
This Marangoni effect‘s laser-induced liquid fountains can potentially impact applications involving liquids or soft matters such as lithography and 3D printing, heat transfer and mass transport, crystal growth and alloy welding, dynamic grating, spatial light modulation, and microfluidics and adaptive optics.
Motivated by his past work, the fruitful simulation of inward surface depression in a shallow liquid, engineers, expanded the profundity of ferrofluid in this study. Ferrofluid is best known for its astonishing surface spikes generated by a magnet.
Using a low-power continuous-wave laser beam, they created a non-uniform surface temperature field for triggering the Marangoni effect. Varying the liquid layer thickness help engineers understand the distinct deformations between deep and shallow liquids.
Bao said, “Understanding the distinct surface deformation in liquids with different depths helps unravel the dynamics of the surface deformation process.”
This is the first time engineers have reported laser fountains and the depth-dependent transition from surface indentation to laser fountain.
Bao said, “We emphasize that there have been numerous attempts to understand the Marangoni flow-driven surface deformation, but no existing theory can predict the deformation patterns of a liquid with an arbitrary depth in a straightforward manner.”
- Feng Lin et al. Marangoni convection-driven laser fountains on free surfaces of liquids. DOI: 10.1016/j.mtphys.2021.100558