Rayleigh-Taylor instability in soft viscoelastic gels

Abstract

One common instability in fluids and other soft materials is Rayleigh-Taylor instability. Rayleigh-Taylor instability, which is defined by dimples and wrinkles of a characteristic wavelength, arises from the competition between gravitational, capillary, and other forces at the interface between two fluids or the surface of a soft solid. Over the last several decades, researchers have incorporated additional forces into the calculation of Rayleigh-Taylor instability to represent a greater variety of systems. In this thesis, we experimentally produce Rayleigh-Taylor instability in soft elastic hydrogels and soft viscoelastic oleogels. By studying Rayleigh-Taylor instability in gels with various thicknesses and material properties, we are able to characterize the effects of a gel's rigidity and thickness on the onset, geometric properties, and---in the viscoelastic case---time evolution of Rayleigh-Taylor instability-driven pattern formation. The viscoelastic oleogels exhibited a wide range of geometries, including competing wavenumbers within a single gel surface and fractal-like buckling in the thickest regions of the gel. The oleogels deformed over the course of several minutes to an hour, and in some cases, their deformations were dependent on multiple characteristic timescales. To the best of our knowledge, this is the first experimental study of Rayleigh-Taylor instability in viscoelastic solids, and our experimental results have good agreement with recent theoretical models of viscoelastic Rayleigh-Taylor instability in soft solids.