Diffusing-wave spectroscopy of a flowing foam
Diffusing-wave spectroscopy has been applied to a model foam (shaving cream) subjected to shear stress. The observed data are consistent with the hypothesis [D. J. Durian et al., Phys. Rev. A 44, R7902 (1991)] that the dynamic process reflected in the light scattering involves local rearrangement events in the foam. The rate of such events is increased in flowing foam subject to shear stress. In this situation a second, slower process appears in the dynamic light scattering data, the origin of which remains conjectural.