📝 SummarXiv

Abstract

When a less viscous Newtonian fluid displaces an aging aqueous clay suspension in a confined space, a rich array of interfacial patterns emerges due to a predominantly viscous instability. In the present work, we controlled the mechanical properties of clay suspensions by incorporating additives and studied the interfacial instabilities that resulted when these suspensions were radially displaced by water in a Hele-Shaw cell. When the elasticity of clay was low, the interfacial dynamics exhibited features of nonlinear viscous fingering in heterogeneous media. By tuning the nature and content of additives that delay clay aging, we uncovered two novel propagation mechanisms: pattern growth via skewering and zig-zag finger propagation. These patterns have hitherto never been observed in experiments with colloidal systems. For moderate clay elasticities, we demonstrate here that shear-thinning-induced flow anisotropy leads to the formation of dendrites with dominant side branches. As clay elasticity increases due to the incorporation of salts, the energy required to create fractures becomes smaller than that for system-wide yielding. This scenario is characterized by the emergence of viscoelastic fractures. Our work demonstrates that incorporating additives is an effective strategy to manipulate the onset and growth of interfacial instabilities during the confined displacement of clay by miscible Newtonian fluids.