Point-source imbibition into dry aqueous foams

We use experiments, modeling and numerics to study the imbibition dynamics from a point source into a homogeneous dry aqueous foam. A distinctive feature of foams compared to solid porous material is that imbibition occurs in the liquid microchannels of the foam called Plateau borders, which have a volume varying in space and time. Dynamics is driven by the capillary pressure and resisted by the viscous and gravity forces in the liquid microchannels. Assuming a constant pressure in the imbibing liquid reservoir, we show that the imbibition front advances and flattens out in time due to gravity, the effect of which is quantified by introducing the Bond number B, which compares the gravitational effects to the capillary pressure using the mean bubble radius as the characteristic length. This evolution describes both miscible and immiscible imbibing liquids. For the latter, we introduce the idea of an effective interfacial tension $\gamma_{\textit{eff}}$ to take the oil-water interfacial energy into account. The details of the imbibition process are confirmed by experiments and numerics using foams with tangentially immobile interfaces in the channel-dominated model