Two-dimensional shear modulus of a Langmuir foam

We deform a two-dimensional (2D) foam, created in a Langmuir monolayer, by applying a mechanical perturbation, and simultaneously image it by Brewster-angle microscopy. We determine the foam stress tensor (through a determination of the 2D gas-liquid line tension, 2.35 ± 0.4 pJ · m ^-1) and the statistical strain tensor, by analyzing the images of the deformed structure. We deduce the 2D shear modulus of the foam. μ = 38 ± 3 nN · m ^-1. The foam effective rigidity is predicted to be 35 ± 3 nN · m ^-1, which agrees with the value 37. 5 ± O.8 nN · m ^-1 obtained in an independent mechanical measurement.