Mesler entrainment-like microbubble entrainment underneath drop impact on immiscible thin liquid films*

The impact of a water droplet on an oil film substrate causes microbubble entrainment consistent across multiple drop sizes and velocities. The experiment was conducted by studying the impact of a water droplet on a glass slide oriented at 45 degrees and coated with a thin film of silicone oil. In order to further understand how the microbubble entrainment forms under different conditions, the height at which the drop was released was changed as well as the size of the drop. Using backlighting and high speed camera techniques, the impact trend was observed similar to the Mesler entrainment. However, an unexpected trend was also observed, in which the number of bubbles as well as the area of the entrainment did not follow a steady decline with an increase in drop size and in velocity, but rather, the number of bubbles and the area increased and peaked in the lower ends of the drop velocity experiments before decreasing. This trend was consistent across all drop sizes and velocities.