Geometric Control of Pressure-Driven Infiltration in Microfluidic Channels

Pressure-driven infiltration in capillary-opposed microchannels is commonly controlled through surface chemistry, while the role of channel geometry remains less understood. Here, we show that sinusoidal channel profiles can regulate liquid advancement by creating periodic capillary barriers that produce stepped meniscus motion under an applied pressure. We develop an analytical force-balance model that incorporates applied pressure, capillary forces, and viscous dissipation to predict conditions for interface advancement and arrest. High-speed synchrotron X-ray radiography of enclosed three-dimensional (3D)-printed microchannels confirms the predicted qualitative behavior, including successive arrest and release events during filling. Because the native printed material is near-neutral in wettability and does not sustain capillary-opposed flow, a conformal iCVD fluoropolymer coating was used to increase the contact angle to about 106°. Together, the model and experiments show that channel geometry can be used to tune pressure-driven infiltration independently of surface chemistry, establishing a geometric strategy for passive flow regulation in microfluidic systems.