Profiling a soft solid layer to passively control the conduit shape in a compliant microchannel during flow.

Area of Science:

• Microfluidics
• Soft Matter Physics
• Fluid Dynamics

Background:

• Microchannel shape is critical for fluid dynamics, rheology, and particle/cell separation.
• Current methods for controlling microchannel shape (fabrication, active actuation) have limitations.
• A need exists for passive, adaptable methods to control microchannel geometry.

Purpose of the Study:

• To propose and validate a passive approach for tuning microchannel geometry.
• To leverage elastohydrodynamics for achieving predetermined flow shapes.
• To explore the use of soft coatings for adaptable microchannel design.

Main Methods:

• Developed a theoretical framework based on nonlinear differential equations for soft coating-fluid interface dynamics.
• Investigated microchannels with a soft top wall and a rigid bottom wall.
• Demonstrated shape control by analyzing the interaction between viscous flow and the soft layer.

Main Results:

• Successfully demonstrated the tuning of four distinct microchannel geometries using the proposed passive method.
• Validated the theoretical model through proof-of-concept experiments.
• Found that slip length patterning on the rigid wall offers limited additional control over channel shape compared to the soft coating.

Conclusions:

• The passive elastohydrodynamic approach offers a viable alternative for controlling microchannel shapes.
• This method allows for the a priori tuning of microfluidic geometries without complex fabrication or active systems.
• The findings open new avenues for designing adaptable microfluidic devices for various applications.