Interaction of liquid foams with porous substrates

Abstract

We review the most recent studies of drainage/imbibition of foams placed on porous substrates: the latest theoretical models, simulation studies and experimental observations. Foam products are ideal for imbibition and penetration into porous media, and they have gained substantial interests in both industrial and scientific areas. Foams are suitable products in cosmetics and pharmaceutical industry and have recently been used in drug delivery processes due to the improved wetting behaviour. A description of the features and parameters affecting foam drainage placed on porous substrates is presented; complexity and simultaneous actions occurring in the process are discussed. The difference between free foam drainage and the drainage of foam placed on a porous substrate is clarified, and a new phenomenon, which is a formation of a free liquid layer at the foam/porous substrate interface, was theoretically predicted and experimentally verified. Considering the effect of parameters on the rate of imbibition into thick or thin porous substrate revealed the existence of three different regimes of the process. Recent theoretical predictions and simulation of wetted area, foam height and possibility of free liquid layer formation in the course of drainage and imbibition into thin porous layer showed a good agreement with experimental observations.