Suspending solid particles in pendant liquid drops

The interaction of a solid particle with a fluid interface has important applications in nature and industry. Aphids and water-walking insects make use of surface tension at a particle-fluid interface. Industrial applications of this relationship include the production of stable foams, printing of complex materials, capillary gripping uses, water treatment technologies, and the removal of particles or contaminants from the atmosphere or hydrophobic surfaces.

Thoraval et al. explored the limiting conditions under which a particle would fall rather than remain attached to a pendant drop of water.

Using high-speed imaging, the snap-in dynamics and behavior of a spherical particle were observed throughout its interaction with a drop of water. Various types of particles were evaluated, including glass, aluminum, silicon nitride, zirconia, and steel.

The maximum particle size supported by the liquid was found to depend on particle density, nozzle diameter, drop diameter, and the surface tension and density of the liquid.

“Our study provides a simple physical explanation of the dominant mechanisms that can influence the stability of a particle at a fluid interface,” said co-author Marie-Jean Thoraval. “However, it also raises important unanswered questions on the influence of several parameters, such as the inertia of the particle or the fluid, and the geometry or wetting properties of the solid surfaces.”

Future studies will focus on the fundamental physics affecting the release of the particle after its attachment to the liquid drop.

Source: “Attachment of a particle to a pendant drop: how large can we go?,” by Yumeng Feng, Weiwei Zhao, Yangyu Duan, Siqi Zhu, Xurui Zhang, and Marie-Jean Thoraval, Physics of Fluids (2022). The article can be accessed at https://doi.org/10.1063/5.0074604 .