On the Dynamic Contact Angle of Capillary-Driven Microflows in Open Channels.

Area of Science:

• Fluid Dynamics
• Materials Science
• Physical Chemistry

Background:

• The Lucas-Washburn-Rideal (LWR) law is fundamental for understanding capillary-driven fluid penetration.
• The law traditionally assumes a constant contact angle, which contradicts experimental findings of lower liquid velocities.
• These discrepancies are often attributed to a velocity-dependent dynamic contact angle.

Purpose of the Study:

• To investigate the role of dynamic contact angles in open-channel fluid penetration.
• To determine the necessity of incorporating dynamic contact angles in microfluidic models.
• To evaluate theoretical models for predicting dynamic contact angle effects.

Main Methods:

• Experimental investigation of fluid penetration in open channels.
• Utilized a range of aqueous and organic liquids with a PMMA substrate.
• Analysis of fluid velocities and comparison with theoretical predictions.

Main Results:

• A dynamic contact angle is crucial for accurately modeling the early stages of fluid penetration, particularly in the viscous regime.
• Open-channel configurations amplify the significance of dynamic contact angles due to the free surface.
• The molecular-kinetic theory demonstrated the highest accuracy in predicting the dynamic contact angle's influence.

Conclusions:

• Dynamic contact angles are essential for accurate microfluidic simulations, especially under high-velocity conditions.
• The open-channel geometry necessitates explicit consideration of dynamic contact angles.
• Molecular-kinetic theory provides a reliable framework for understanding dynamic contact angle phenomena in open channels.