The dynamics of droplet impact on loose particles is essential for understanding a wide variety of processes, including raindrop-driven erosion and pollen dissemination. While advances have been made toward elucidating drop impact on smooth surfaces, relatively little is still known about the effects of drop impacts on monolayers of particles.
Esmaili et al. characterized the dynamics and splashing pattern of droplet impact on a solid surface covered with a granular monolayer of particles. Through systematic droplet falling experiments, the group found the presence of mobile particles lowers the critical impact velocity at which the droplet exhibits crown-shaped corona splashing, as the particle area fraction increased.
“There are a lot of work on a drop impact on a smooth surface,” said author Sunghwan Jung. “However, no work has been done on a drop impact on a mono layer of particles with complete theoretical predictions to our best knowledge.”
A transparent glass surface substrate allowed the group to visualize the spreading of a drop and particle movement. They visualized the side view by using a half-glass surface.
The two views showed a spreading drop is resisted by a layer of particles, producing a repeatable and clear transition between an initial horizontal spreading stage followed by corona splashing.
Although the researchers opted for a monolayer to facilitate making measurements, their results can be qualitatively generalized to multilayers of particles like a higher impact velocity or denser particles likely create the corona splash.
Jung said he hopes the group next looks to user their work to further investigate how raindrops help liberate spores and pollens from surfaces.
Source: “Corona splashing triggered by a loose monolayer of particles,” by Ehsan Esmaili, Zih-Yin Chen, Anupam Pandey, Seungho Kim, Sungyon Lee, and Sunghwan Jung, Applied Physics Letters (2021). The article can be accessed at https://doi.org/10.1063/5.0059466.
