Surfactant Effect on Binary Droplet Collision

The droplets collision dynamics with different surfactant and viscous fluids are investigated. The high speed camera and reliable measuring methods facilitate the experimental procedures. Depending on the two independent factors of Weber number and impact parameter, the consequences of droplets collision can be categorized into five distinct regimes: (Ⅰ) coalescence after minor deformation, (Ⅱ) bouncing, (Ⅲ) coalescence after substantial deformation, (Ⅳ) reflective separation and (Ⅴ) stretching separation, and it reveals that the viscosity, surfactant types and concentrations all have great influences on regime diagrams, especially the finding of the extensive bouncing regime and the retardant occurrence of separation regime.
It is because the Marangoni effect which is motivated by the surfactant gradient could manifestly affect droplet interfacial behaviors. However, these induced transformations will dominate over the microscopic situations such as droplet bouncing but become trivial in the macroscopic conditions such as droplet separation phenomena.