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, ${\mu }_s+\kappa$, and Gibbs elasticity $ϵ$), 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 $ϵ=32\pm 8\mathrm{mN}/\mathrm{m}$ and ${\mu }_s+\kappa =1.3\pm 0.7\mathrm{mPa}·\mathrm{m}·\mathrm{s}$ for sodium dodecyl sulfate, and $ϵ=65\pm 12\mathrm{mN}/\mathrm{m}$ and ${\mu }_s+\kappa =31\pm 12\mathrm{mPa}·\mathrm{m}·\mathrm{s}$ for bovine serum albumin, in good agreement with literature values.

• Received 18 August 2006

DOI:https://doi.org/10.1103/PhysRevLett.97.226101