Capillary Flow Dynamics in Composite Rectangular Microchannels with Rough Walls.

Area of Science:

• Physics
• Materials Science
• Fluid Dynamics

Background:

• Capillary transport in microchannels is crucial for microfluidic devices.
• Microchannel geometry and surface properties, like roughness, influence fluid behavior.
• Understanding these factors is key to controlling fluid flow at the microscale.

Purpose of the Study:

• To develop a model for fluid capillary transport in rectangular microchannels with varying wall materials and roughness.
• To investigate the influence of microchannel aspect ratio on fluid motion during initial viscous regimes.
• To determine the effective static contact angle and friction coefficient for different aspect ratios and surface roughness.

Main Methods:

• Development of a fluid capillary transport model for horizontally positioned rectangular microchannels.
• Utilizing an effective static contact angle and an effective friction coefficient averaged over the cross-section.
• Conducting extensive experimental investigations with various microchannels to obtain coefficients for different aspect ratios.

Main Results:

• Lower aspect ratios result in smaller effective contact angles and larger effective friction coefficients.
• Surface roughness, particularly pinning-depinning events, significantly reduces the effective static contact angle, even at high aspect ratios.
• Effective friction coefficient values align well with existing literature for both rough and smooth surfaces.

Conclusions:

• A nondimensional time parameter was proposed to identify when contact angle effects dominate fluid dynamics.
• Contact angle effects become negligible for times exceeding approximately 1 second for the studied materials and fluid properties.
• The findings provide insights into optimizing microchannel design for controlled capillary-driven fluid transport.