Coupling of elasticity to capillarity in soft aerated materials.

We study the elastic properties of soft solids containing air bubbles. Contrary to standard porous materials, the softness of the matrix allows for a coupling of the matrix elasticity to surface tension forces acting on the bubble surface. Thanks to appropriate experiments on model systems, we demonstrate how the elastic response of the soft porous solid is governed by two dimensionless parameters: the gas volume fraction and a capillary number comparing the elasticity of the matrix with the stiffness of the bubbles. Furthermore, we show that our experimental results are accurately predicted by computations of the shear modulus through a micro-mechanical approach.