The significant influence of internal stresses on the dynamics of bubbles in a yield stress fluid

The shape and trajectory of bubbles in Carbopol gels were accurately observed over long periods. As the concentration increases, the trajectories are observed to evolve from vertical and rectilinear to three-dimensional shapes. Local strain and velocity fields have been determined. Bubble injection is quasistatic in order to obtain a separation governed by the equilibrium among surface tension, buoyancy and stresses applied to the bubble. Internal stresses in the fluid, of structural origin and induced by the mechanical history in the fluid volume, remain in the fluid for at least several months. They play a major role in bubble formation and propagation. (C) 2012 Elsevier B.V. All rights reserved.