Manipulation of droplet rebounding and separation using surfactant
Journal
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition
Date Issued
2012
Author(s)
Abstract
The transition boundaries of various regimes characterizing the impact outcomes between two identical droplets made of water mixed with surfactant were investigated experimentally. In particular, the regime of bouncing, which was generally not observable for water in near head-on collision at atmospheric condition, was found to be created by the addition of surfactant. This regime can be easily expanded using various surfactants of little amount. Furthermore, while the transition boundary between coalescence and separation that were generated at higher Weber numbers, which is defined as the ratio of impact inertia to surface force and is the key factor for identification of the regimes, was concluded by previous studies to follow a curve that was derived based on energy conservation, this boundary was found to deviate significantly when surfactant was added. These differences were likely caused by the dynamic distribution of surfactant and hence the gradients of surface tension due to nonuniform concentration near the droplet surface, known as Marangoni effect. This could substantially affect the fluid motions by varying such critical mechanisms as the interfacial deformation of liquid droplets and draining dynamics of the gas between the approaching interfaces. The results thus yield a prospect of using little surfactant to manipulate the collision outcome when two droplets or interfaces impact.
Type
conference paper