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Cavitation is a common damage mechanism in soft solids. Here, we study this using a phaseseparation technique in stretched, elastic solids to controllably nucleate and grow small cavities by several orders of magnitude. The ability to make stable cavities of different sizes, as well as the huge range of accessible strains, allows us to systematically study the early stages of cavity expansion. Cavities grow in a scale-free manner, accompanied by irreversible bond breakage that is distributed around the growing cavity, rather than being localized to a crack tip. Furthermore, cavities appear to grow at constant driving pressure. This has strong analogies with the plasticity that occurs surrounding a growing void in ductile metals. In particular we find that, although elastomers are normally considered as brittle materials, small-scale cavity expansion is more like a ductile process. Our results have broad implications for understanding and controlling failure in soft solids. arXiv:1811.00841v2 [cond-mat.soft]

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We show that a structure with a fibrillar surface terminated by a continuous film can be switched between two metastable states. The first state, in which the film is stretched between fibrils, has previously been shown to have strongly enhanced adhesion compared to an unstructured flat control. In the second state, the film collapses onto the substrate between fibrils and is held up away from the substrate at the fibrils, resulting in a surface with a periodic array of bumps with much reduced adhesion. The interface can be switched mechanically between these two states repeatedly, thus providing a means for active control of surface mechanical properties. We develop a simple model that shows what combination of parameters, such as film thickness, dimensions, and spacing between fibrils, is required for such an architecture to be metastable in each of these two states.