Do Small Bubbles Follow Stokes Law?

The motion of gas bubbles in a liquid medium is known to be affected by the presence of surface active molecules which modify the hydrodynamic conditions prevailing at the gas-liquid interface. In the past, gas bubbles rising in aqueous solutions have been said to follow Stokes law (rigid interface). In this work, we present some theoretical calculations and experimental data on the influence of surfactants for the motion of air bubbles rising in non-Newtonian solutions. It is shown that the rheology of the system introduces a complex balance of forces acting on the bubble.