The influence of vapor pressure on droplet contact dynamics on smooth surfaces.

Droplet impact experiments were performed with different fluids using Total Internal Reflection Microscopy (TIRM) on a smooth surface to gain insight into the mechanism for the air film failure of volatile liquids. Several parameters were varied including the impact velocity and droplet volatilities to understand the relationship between the fluid properties and the air film rupture. It was observed that while increasing the Weber number of the impacting droplets generally lead to sooner air film failure, there was significant variance in the magnitude of the contact times at the same Weber numbers for different fluids. It is hypothesized that the vapor output from the droplets themselves, in the immediate area surrounding the droplet, impacts the air film dynamics, as this vapor is constituted by the fluid and thus a different composition compared with the bulk gas in the environment.