Images 1 and 2 were taken with two cameras operating at up to 25,000 frames a second. The images show what was happening from underneath the droplets and to the side. The sequence starts on the left, immediately after one droplet spreads into the other. A surface jet forms with one droplet appearing to move across the other (after around 12 milliseconds) and to mix in the process. But the droplets are not mixing. The camera to the side reveals that one of the droplet is just sitting on the other. They have not mixed because of their respective surface tensions.