Flow focusing geometry generates droplets through a plug and squeeze mechanism

Area of Science:

• Fluid dynamics
• Microfluidics
• Droplet generation

Background:

• Microdroplets are commonly produced using T-junction and flow focusing microfluidic devices.
• The underlying mechanisms of droplet formation in these two geometries are often considered distinct.

Purpose of the Study:

• To investigate and compare the droplet formation mechanisms in T-junction and flow focusing microfluidic devices.
• To determine if the pressure dynamics in flow focusing devices are similar to those in T-junctions.

Main Methods:

• Direct measurement of pressures within the microfluidic drop maker.
• Analysis of pressure fluctuations during droplet formation.
• Comparison of pressure data between T-junction and flow focusing geometries at low-to-moderate capillary numbers.

Main Results:

• Flow focusing devices exhibit pressure fluctuations that are nearly identical to those observed in T-junctions.
• The observed pressure dynamics suggest a shared underlying mechanism for droplet formation in both geometries.
• The process is dominated by interfacial stresses and a plugging-squeezing mechanism.

Conclusions:

• The mechanisms of droplet formation in T-junction and flow focusing microfluidic devices are fundamentally similar, particularly at low-to-moderate capillary numbers.
• Droplet generation in both geometries is governed by interfacial stresses and a plugging-squeezing process.
• Direct pressure measurements provide key insights into the physics of microdroplet formation.