Interfacial Tension Measurements in Microfluidic Quasi-Static Extensional Flows

Area of Science:

• Fluid dynamics
• Microfluidics
• Interfacial science

Background:

• Conventional methods for measuring interfacial tension are often slow and cumbersome.
• Droplet microfluidics offers advantages like speed, high throughput, portability, and ease of fluid manipulation.
• Achieving purely homogeneous extension in microfluidic devices is crucial for accurate interfacial tension measurements.

Purpose of the Study:

• To design and utilize a microfluidic device for measuring interfacial tension of immiscible fluids.
• To investigate droplet deformation under extensional flow in both confined and unconfined channel geometries.
• To develop and validate quasi-static 2D and 3D models for interfacial tension calculation.

Main Methods:

• A microfluidic device was designed with a flow-focusing droplet production region and a cross-junction for droplet stretching.
• Droplets were subjected to extensional flow at a stagnation point, leading to deformation.
• Quasi-static 2D Darcy approximation and 3D small deformation models were employed to calculate interfacial tension.

Main Results:

• Droplet deformation varied based on whether they were confined or unconfined by channel walls.
• An effective viscosity model accurately captured deformation for confined droplets under extensional flow.
• The 3D model provided more robust interfacial tension estimates for unconfined droplets compared to the 2D model.

Conclusions:

• Both 2D and 3D models provide accurate interfacial tension measurements under quasi-static extensional flows.
• The developed microfluidic method offers a viable alternative to conventional techniques like the pendant drop method.
• The study highlights the importance of considering droplet confinement in microfluidic interfacial tension measurements.