Characterization of In-Situ Capillary Pressure in Porous Media Using Multiplex Microfluidic Pressure Sensors

Understanding and quantifying pressure at the microscale is critical for a wide range of applications in fluid dynamics, particularly in microfluidic systems and multiphase flow environments. For instance, measuring capillary pressure in porous media remains a longstanding challenge, primarily due to its small length scale and the high spatial and temporal resolutions. In this work, we present the development of an on-chip pressure sensor designed specifically for microfluidic environments by incorporating a thin polydimethylsiloxane (PDMS) membrane that undergoes deflection in response to fluid pressure changes. These membrane deformations are measured optically using astigmatic particle tracking techniques, in combination with a high-speed camera and optical microscopy. This configuration enables high-resolution, in-situ measurement of capillary pressures within individual pore spaces. By mapping out real-time pressure data across a two-dimensional field, our method provides valuable insight into microscale flow behavior, interfacial dynamics, and pore-scale transport phenomena. This approach opens new avenues for validating theoretical models of complex flow in porous media and enhances the predictive capability of numerical simulations. Our technique represents a significant step forward in addressing the need for spatially resolved pressure measurements in microfluidic research.