Diffusiophoresis-Induced Rayleigh-Taylor Instability

Diffusiophoresis plays an important role in the transport of colloids in ionic solutions. Prior literature has demonstrated the utility of diffusiophoresis in membraneless water filtration, zeta-potential measurements, Turing patterns on vertebrate skin, and exclusion zone formation near ion exchange membranes. While preliminary results indicate that diffusiophoresis can induce Rayleigh-Taylor instabilities, a comprehensive analysis of such phenomena remains unexplored in the literature. Here, we conduct an integrated experimental and theoretical investigation to identify and isolate the mechanisms behind the formation of this instability. To this end, we build a vertical capillary device consisting of dissolved salt and a polystyrene suspension with an ion-exchange membrane. Due to concentration gradients, particles move diffusiophoretically, creating an exclusion zone and subsequently induce a Rayleigh-Taylor instability. We analyze images captured with a high-resolution camera and extract details of the exclusion zone as well as the instability. We also perform simulations using a classic Rayleigh-Taylor model where density variations arise due to banding induced by diffusiophoresis. Our work provides new insights into diffusiophoresis-induced instabilities, which might have been overlooked in systems with concentration gradients.