Geometric criterion for capillary thread breakup in rectangular microchannels.

Breakup of fluid threads in rectangular microchannels occurs when equilibrium neck shapes cease to exist, with a critical volume depending solely on channel aspect ratio.

• Why it matters: Understanding how channel shape influences breakup is essential for optimizing droplet formation in microfluidic devices, oil recovery, and emulsion production, yet no unified geometric criterion exists.
• What they did: Using numerical simulations, stop-flow, and static equilibrium analyses, the study identifies the critical neck geometry and volume at breakup, revealing two distinct collapse modes based on a threshold aspect ratio.
• The result: This geometry-based criterion enables the design of microchannel features that control droplet size and production, facilitating advanced applications like densely packed emulsions and improved oil recovery.