On the motion of gas bubbles in a viscoelastic liquid

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Abstract
The discontinuity of terminal velocity versus bubble volume previously reported as taking place in viscoelastic liquids, was studied experimentally and theoretically. A comparison of terminal velocity data for gas bubbles and glass spheres in aqueous polymer (Separan‐AP30) solutions provides strong evidence that the discontinuity results from a change in interfacial conditions from “no‐slip” to free shear. A numerical solution of the creeping flow equations using an empirical curve fit for viscosity versus shear‐rate indicates that only a fraction of the experimentally observed velocity jump is due to the shear dependence of the viscosity alone (neglecting elastic effects). However, simple qualitative arguments seem to suggest that a relatively modest elastic contribution to the force balance on the bubble would be sufficient to account for the experimental observations.