Particle attraction to walls by diffusion induced stratified flows: experimentation*

We present experiments for a new phenomena in which particulate suspended in stable stratification are attracted to vertical walls. The mechanism originates from a broken symmetry in the diffusion induced stratified flow exterior to a sphere near a vertical wall which creates an effective force of attraction arising through the viscous stress tensor. This boundary layer behavior drives particles initially within one radius of the wall to collapse in finite time. Details of the experimental observations will be discussed and further contrasted with prior self-assembly phenomena which documented two spheres collapsing in finite time in a stratified water column (https://www.nature.com/articles/s41467-019-13643-y).