Protrusion formation during the collisional process of ethanol and water droplets: Capillary wave propagation on the water droplet

- Collision processes of liquid droplets were observed.
- Water-water and ethanol-water droplets were employed as the collision droplets.
- A protrusion was formed during the collision of ethanol and water droplets.
- A capillary wave propagates on the water droplet from the contact point to the counter pole.
- The protrusion formation is described by a surface-tension release deformation model.