  It was previously observed that colliding liquid droplets in a gaseous medium
tend to bounce off at elevated gas pressure up to about 12 atm. In this letter,
we extended the droplet collision experiment to up to 41 atm for the first time
and reported a noticeable discovery that the tendency is flattened off at
higher pressures. The colliding droplets stop bouncing but start to coalesce
beyond a critical Weber number, which increases with pressure but tends to a
limit value at 21 atm and above. A scaling analysis taking into account the
gas-film dynamics, the rarefied gas effects, and van der Waals force well
correlates with the experimental discovery.
