Spontaneous Imbibition in Paper-Based Microfluidic Devices: Experiments and Numerical Simulations

Area of Science:

• Fluid Dynamics
• Analytical Chemistry
• Materials Science

Background:

• Microfluidic paper-based analytical devices (μPADs) are vital for point-of-care diagnostics.
• Capillary force drives analyte transport in μPADs, but low imbibition rates can limit sensitivity.
• Accurate modeling of spontaneous capillary flow is essential for sensitive and precise μPADs.

Purpose of the Study:

• To quantitatively investigate spontaneous capillary flow in filter paper for μPAD applications.
• To develop an improved numerical model for predicting wetting dynamics in μPADs.

Main Methods:

• Experimental investigation using light-transmitting imaging to monitor wetting saturation.
• Numerical modeling employing the Richards equation with two-phase flow properties derived from pore-network modeling.
• Incorporation of a dynamic term in capillary pressure to account for strong wetting dynamics.

Main Results:

• Observed a transition from saturated to unsaturated wetting fronts during capillary imbibition.
• Found that the single-phase Darcy model significantly overestimates wetting penetration depths.
• Demonstrated that the improved model, incorporating two-phase flow and dynamic capillary pressure, significantly enhances prediction accuracy.

Conclusions:

• The study provides a more accurate understanding of spontaneous imbibition in filter paper.
• The developed quantitative model offers valuable insights for designing more sensitive and accurate μPADs.
• Improved modeling of capillary flow is key to advancing microfluidic diagnostic technologies.