Exploiting interfacial gel formation and buckling instability to control viscous fingering pattern morphology

Developing strategies to control the viscous fingering pattern morphology spurs investigations into systems involving complex fluids. The case when a gel forms at the interface between the displacing and displaced fluid is especially interesting as reactions have previously been shown to both stabilize and destabilize patterns. However, little attention has been paid to sodium alginate-calcium chloride systems, despite the rich dynamics of hydrogel formation. We investigate the impact of the gelation reaction on pattern formation by varying Hele-Shaw cell thicknesses, displacement rates, and calcium chloride concentrations. Results reveal a rich regime map where calcium concentration dictates the dominant growth mode. Each regime is described through microscopic observation, macroscopic observation, and supporting theory. Further, we show that the syneresis of the alginate hydrogel leads to the development of a secondary wrinkling instability, which can be predicted from solid mechanics theory. The collective results present a new avenue to study and manipulate viscous fingering morphologies in systems with a cross-linking reaction with application to manufacturing, environmental, and biological processes.