Wetting, disorder, and pattern formation

Displacement of a more viscous fluid by a less viscous one in a homogeneous medium leads to an interfacial instability. This description, however, neglects the inherent heterogeneity observed in most real systems, as well as the non-hydrodynamic interactions between the fluids with the solid surfaces. Here, we revisit the Saffman-Taylor instability using a roughened Hele-Shaw cell as an analogue disordered porous medium and show that the interplay between disorder and wettability of the medium can fundamentally alter the pattern formation dynamics. Our observations show the critical role of the contact-line dynamics in the macroscopic pattern formation, and point to new directions for controlling flows with applications ranging from microfluidics to CO2 sequestration.