Using colloidal deposition to mobilize immiscible fluids from porous media

Colloidal particles hold promise for mobilizing trapped immiscible fluids from porous media, with implications for key water applications. Most studies focus on accomplishing this goal using particles that localize at immiscible fluid interfaces. Researchers typically seek to optimize the surface activity of particles while minimizing their deposition onto the surrounding solid matrix. Here, we demonstrate that deposition can, surprisingly, promote mobilization of a trapped fluid from a porous medium. Using confocal microscopy, we directly visualize colloidal particles and trapped immiscible fluid within a transparent, 3D porous medium. As particles deposit on the solid matrix, more trapped fluid become mobilized. We unravel the underlying physics by analyzing the extent of deposition and the geometry of trapped fluid droplets at the pore scale: deposition increases viscous stresses on droplets, overcoming the influence of capillarity that keeps them trapped. This analysis enables us to predict the extent of fluid mobilized through colloidal deposition and reveals a new way by which colloids can be harnessed to mobilize trapped fluid from a porous medium.