Viscoelasticity enables access to a wider variety of surface patterns via gravity-driven instability

Studies of the Rayleigh-Taylor instability traditionally discussed fluids, but in recent decades, academic interest in a broader class of materials has risen. Despite numerous theoretical studies on Newtonian and viscoelastic liquids, experimental characterization of the Rayleigh-Taylor instability in viscoelastic solids has been missing. Here, we experimentally and theoretically study the gravity-driven emergence of various surface patterns on viscoelastic gels. First, we will briefly summarize how linear stability analysis on the deforming viscoelastic solids introduce dimensionless parameters that govern the instability. We identified the interplay between gravity, surface tension, and viscoelastic relaxation to produce surface patterns. Then, we present the effect of those parameters on the pattern selection, which is supported by the rheological characterization of the material. We show that the patterns that emerge on the free surface of viscoelastic solids differ from those of elastic solids. Finally, we present a tension-induced secondary instability that manifests fractal-like protrusions along the walls of highly deformed gels that are formed by the Rayleigh-Taylor instability.