Gas layer dynamics when drop bounces off a liquid surface
Gas layer dynamics when drop bounces off a liquid surface lead image
The micron-scale morphology and dynamics of the thin gas layer between a liquid drop and a surface, known as the interfacial gas layer, is a controlling factor on whether the drop bounces or merges with the surface after impact. However, most research on gas layer dynamics to date has focused on either drops impacting on solid surfaces or merging with liquid surfaces.
Tang et al. of Princeton University and the University of Twente report their analysis of the gas layer dynamics for a drop bouncing off of a liquid surface. Using color interferometry and high-speed imaging, they studied the dynamics for thin liquid surfaces, including one with a thickness approximately equal to the drop’s radius. This situation is technologically critical in applications such as spray coating and 3D printing—those in which a drop impinges on a thin liquid layer created by preceding drops.
“Our research shows that the presence of the deformable impacted surface drastically modifies the shape and evolution of the thin gas layer as observed previously during drop impact on solid surfaces,” Tang said.
The researchers measured significant differences in gas layer dynamics in both the drop approaching and rebounding stages. Unlike impact on a solid surface, the liquid surface absorbs part of the impact inertia by deforming itself, and the rebound stage is highly influenced by interacting capillary oscillations and substrate interactions.
The result, they report, is the observation of a new class of gas layer profiles, including a rim-dimple morphology and a reversed bell shape, the latter reflecting interaction between the drop and film surface. The authors anticipate that “these complex dynamics will stimulate further theoretical and computational studies to explore such behavior.”
Source: “Bouncing drop on liquid film: Dynamics of interfacial gas layer,” by Xiaoyu Tang, Abhishek Saha, Chung K. Law, and Chao Sun, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5063257 .
