The infiltration of a fluid into a porous medium has been the focus of extensive research across multiple domains ranging from soil science, reservoir engineering and metallurgy.
Particularly it finds wide application of Metal Matrix Composites (MMCs) due to its simple and versatile nature, giving rise to materials with desirable properties, namely heat dissipation, low thermal expansion and wear resistance. MMCs are formed by a continuous metal phase (the matrix) infiltrating dispersed ceremic fibers (reinforcment).
Existing models, however, used to characterize such phenomena seem to take semi-empirical forms and are unsatisfactory as they lack correct theoretical limits, are sensitive to the most critical regions (50% infiltration) and incorrectly predict spontaneous infiltration at high contact angles.
An alternative explanation is proposed which attributes the irreversible energy losses to the nature of the experiment and to Haines jumps, due to the presence of "pinning points".
According to this model, the position of the triple line jumps back and front, forming concave and convex mensiscuses as the liquid infiltrates the pore. There is a maximum pressure associated with filling a particular pore (determined solely by its size and "pinning points"), which once surpassed, the rest of the pore (and potentially other connected pores) is otherwise able to fill at a much lower pressure. However due to the nature of infiltration, pressure is monotonically increasing in the experiment and thus there is an energy loss associated with the additional pressure (as shown in the image above).
The physics of capillarity behind infiltration were investigated on two and three dimensional lattices considering microstructures of “packed pores” which were abstracted as directed graphs. Critical exponents were extracted under a percolation model, using statistical size scaling and verified against literature values. The two videos below show the resulting simulations.