Path Instabilities of Clean and Surfactant Coated Bubbles Rising in Water

Abstract

My experiment examined the shape and path of air bubbles (diameter range .1cm -.3cm) rising through water. Comparing the shape and trajectories of clean bubbles to those of bubbles generated using water contaminated with a surfactant (Triton-100), I found that for sufficient concentrations of the surfactant, (cTriton > 5 x 10-3 mol/m3) the bubbles assumed a spherical shape whereas clean bubbles adopted ellipsoidal geometries. Monitoring the trajectories of these two distinct forms of bubbles, I found that the spherical bubbles had significantly lower terminal velocities. Also, I found that the spherical and ellipsoidal bubbles had distinct trajectory-state transitions. As the diameters of the respective bubbles were increased, the paths of the spherical bubbles transitioned from rectilinear to angled to zigzag while the paths of the ellipsoidal bubbles transitioned from rectilinear to angled to spiral to processing spiral to zigzag.