Relaxation time of the topological T1 process in a two-dimensional foam

The elementary topological T1 process in a two-dimensional foam corresponds to the flip of one film with respect to the geometrical constraints, and is a process by which the structure of an out-of-equilibrium foam evolves. We study both experimentally and theoretically the T1 dynamics in a dry two-dimensional foam. The dynamics is controlled by the surface viscoelastic properties of the films (surface shear plus dilatational viscosity, μs+κ, and Gibbs elasticity, and is independent of the shear viscosity of the bulk liquid. Moreover, the dynamics of the T1 process provides a tool for measuring the surface rheological properties: we obtained =32±8mN/m and μs+κ=1.3±0.7mPa•m•s for sodium dodecyl sulfate, and =65±12mN/m and μs+κ=31±12mPa•m•s for bovine serum albumin, in good agreement with literature values.