A Novel Microfluidic Pressure Sensor for the Study of Capillary Pressure and Multiphase Flow in Porous Media

Pressure quantification and control at the microscale is crucial to numerous applications involving fluid mechanics problems. Despite recent advancement of technologies, microscale pressure measurement such as in microfluidic devices and multiphase flow is still not trivial. In particular, capillary pressure is a defining variable porous medium flows and plays a key role in flow modeling and prediction. It, however, has rarely been directly measured at the pore level, primarily due to its small length scale and the high spatial and temporal resolutions it would require. To that end, we design and fabricate an on-chip sensor using soft lithography with a thin polydimethylsiloxane (PDMS) membrane that deflects subject to pressure changes in the fluid flow, which is in turn quantified optically using astigmatic particle tracking. Combined with a microscope and a high-speed camera, the microfluidic pressure allows us to perform in-situ measurements of capillary pressure within individual pore spaces, providing valuable insight into the pore scale mechanisms. Furthermore, the sensor also enables a detailed quantification of the well-known Haines jumps from a pressure perspective, which is previously not possible.