Thin liquid films and capillary bridges can effectively enhance the connectivity of a porous medium, making it possible for the drainage of apparently trapped liquid clusters. This drainage due to film flow was recently characterized in a paper published in Phys. Rev. Fluids by PoreLab researcher Marcel Moura and collaborators. The experimental work has shown the existence of an active zone behind the main fluid-fluid interface, where the film flow drainage is more likely to occur. The authors have also directly imaged the network of capillary bridges in the medium (secondary network), which acts as the pathway for fluid transport due to film flow.
M. Moura, E. G. Flekkøy, K.
J. Måløy, G. Schäfer and R. Toussaint, “Connectivity enhancement due to film
flow in porous media,” Phys. Rev. Fluids
4, 094102 (2019).