Contact dynamics of an emulsion droplet impacting a solid surface

Liquid suspensions and emulsion droplets are common in agriculture and chemical processing. When impacting drops get close to the surface, the air deforms the drop resulting in a ring of contact with a thin disk of air trapped. Here, we used high-speed interferometry to study the initial dynamics of an emulsion drop impacting an ultra-smooth solid surface with a surface roughness of 0.5 nm. We mixed water with oil and used a probe sonicator to produce an oil-water emulsion. The air layer is unaffected for lighter oil-water emulsions (ρ_oil<ρ_w). However, when heavier oil is used (ρ_oil>ρ_w), oil nano-lenses form on the water-air interface affecting contact dynamics. The present work gives insight into how emulsion droplets interact with the surface and make their first contact, which would apply to biological and chemical systems.