Buckling instabilities in moving chains of bubbles

When slender structures are subjected to a compressive force, they will buckle and bend as mediated by the bending modulus of the solid material or the viscosity of the liquid. Here, we explore a slender structure with no internal bending modulus by producing a chain of microscopic monodisperse bubbles in an aqueous bath. The chain rises due to the buoyancy of the bubbles. There is an attractive interaction between the bubbles and if the bubbles are produced quickly such that one bubble is produced and contacts the next, they adhere. Producing many bubbles in this fashion allows us to create a chain of sticky bubbles that are frictionless and have no bending cost. Tuning the rate of bubble production results in buckling instabilities in the rising chain as it moves through the aqueous bath due to the hydrodynamic drag. We predict the buckling onset, buckling amplitude, and speed of the chain using scaling arguments to balance buoyancy and viscous drag.