Two-dimensional shear modulus of a Langmuir foam

S. Courty (1) , Benjamin Dollet (1) , F. Elias (2) , P. Heinig (3) , F. Graner (1)

1 LSP - Laboratoire de Spectrométrie Physique
2 LMDH - Laboratoire des Milieux Désordonnés et Hétérogènes
3 Max Planck Institute of Colloids and Interfaces

We deform a two-dimensional (2D) foam, created in a Langmuir monolayer, by applying a mechanical perturbation, and simultaneouslyimage it by Brewster angle microscopy. We determine the foam stress tensor (through a determination of the 2D gas-liquid line tension, 2.35 $\pm$ 0.4 pJ$\cdot$m$^{-1}$)and the statistical strain tensor, by analyzing the images of the deformed structure. We deduce the 2D shear modulus of the foam, $\mu= 38 \pm 3\; \mathrm{nN}\cdot \mathrm{m}^{-1}$. The foam effective rigidity is predicted to be $ 35 \pm 3\; \mathrm {nN}\cdot \mathrm {m}^{-1}$, which agrees with the value $37.5 \pm 0.8\; \mathrm {nN}\cdot \mathrm {m}^{-1}$ obtained in an independent mechanical measurement.

Mots clés: foam; Langmuir monolayer; 2D elasticity; Brewster angle microscopy

Domaines: Matière Molle [cond-mat.soft]

S. Courty, Benjamin Dollet, F. Elias, P. Heinig, F. Graner. Two-dimensional shear modulus of a Langmuir foam. 2003. ⟨hal-00000366v2⟩