Rheology and microstructure of a particle-laden soap film

Particle-stabilized foams have proven to be materials with promising mechanical properties for the construction industry: individual particle-covered bubbles in the form of gas marbles are able to undergo large over- and under-pressure. However, their rheology has yet to be formally described. We study experimentally the rheological behavior of a particle-laden soap film as a macroscopic 2D model suspension: a tetradecyl trimethyl ammonium bromide (TTAB) solution in a water-glycerol mixture is made to form the liquid soap film in which we trap slightly polydisperse polystyrene beads. The solid particles' diameter (Ø 80 µm) is larger than the typical thickness of the film, the surface tension then gives rise to attractive forces. We perform the study at controlled shear-rate in an original simple shear geometry and highlight, at high-particulate fraction, a visco-plastic behavior. We then compare these results to local measurements of the shear-rate obtained through image correlation, thus revealing the inhomogeneity of the shear. An extended kinetic law captures it well, as well as providing us with a theoretical origin for a boundary-dependent diffusion length of the rearrangements, associated with a transition in the orientational order in the microstructure.