The butterfly effect of tiny density difference in microfluidic channel

Microfluidic technology plays a vital role in modern industry and advanced scientific research due to its exceptional features. Owing to the small scales and minor density differences between multiphase fluids, the impact of microgravity on the droplet behavior has been largely overlooked. However, this work reveals that even subtle density differences can have a butterfly effect on the behavior of microdroplet. Droplets within microchannels exhibit three distinct motion regimes: (i) contacting mode: the droplet gradually descends during its movement along the channel and finally contacts the wall; (ii) floating mode: the droplet descends first but floats out maintaining a stable distance from the wall; (iii) bouncing mode: the droplet bounces off the wall at the moment of contacting it. This study uncovers the physical mechanisms of how the working parameters influence droplet behavior and establishes a phase diagram depicting the droplet behavior.