Droplet penetration into porous networks: Role of pore morphology

The mechanisms of droplet penetration into porous media are investigated in etched porous networks. In particular, we investigate the role of pore morphology on the rate of penetration, surface and sub-surface spreading rates, observed contact angle, and resultant spatial distribution of fluid within the porous network. Experiments on a range of pore networks illustrate the critical role played by morphology and fluid properties in determining the physics of fluid penetration. A description of different local penetration events, the calculation of the associated displacement pressures and the time scale associated with different events is given. This description is in good agreement with the experimental observations of fluid penetration at the pore scale. From an understanding of the physical mechanisms observed at the local pore scale one can build a general, but realistic, macroscopic model for fluid penetration into realistic complex porous substrates. We discuss the development of comprehensive tools for understanding penetration into large disordered networks of capillaries.