Head-On and Offset Impact of Droplets: Surface Tension Contrast Driven Coalescence Events

The study investigates dynamics of the bi-droplet impact and the spreading behavior in head-on and offset collisions with a focus on a parameter called the surface tension contrast κ. The aims of the study is to understand how varying surface tensions between impacting and sessile droplets affect coalescence and spreading dynamics. Using water and aqueous Sodium Dodecyl Sulfate (SDS) solutions across a range of concentrations to reduce the surface tension of the fluids as compared to water, experiments were conducted to observe the spreading lengths post-impact. High-speed photography captured the impact events, and the data were analyzed to quantify the influence of surface tension contrasts on the spreading behavior. The findings highlight the critical role of the surface tension contrast in determining the maximum spreading lengths during droplet coalescence. It is seen that, as the surface contrast increases, a decrease in maximum spreading lengths is observed. This study provides valuable insights into applications such as inkjet printing, microfabrication, and spray coating, where precise droplet deposition is crucial.