# Velocity Profiles in Slowly Sheared Bubble Rafts

This study looks at the jamming of a flow of bubble rafts in a Couette viscometer. The experiment consists of first forming a single layer of bubbles at a fluid-air interface by flowing nitrogen through a solution of 44% glycerine, 28% each of water and "miracle bubble" (presumable containing some surfactant). The single layer of bubbles permits the authors to speak of a bubble "raft" and treat this as a two dimensional problem. In the paper, the units of stress are appropriatly modified for 2D (ie. $[ \sigma ] = [ N/m ]$). The bubble rafts are located between the concentric cylinders that define the Couette cylinder. The outer cylinder is driven at a constant rotation rate, while the torque on the inner cylinder is measured via a torsion wire (this cylinder is passive - not driven).