Localization of folds and cracks in thin metal films coated on flexible elastomer foams.

Thin metal films coated on soft elastomeric foam substrates exhibit enhanced electromechanical performance. The open-cell foam structure conveys highly anisotropic mechanical properties within the top, thin capping elastomer at the surface of the foam. Upon stretching, large strain fields inducing cracks and folds localize above the foam cells, while the surrounding cell ligaments remain almost strain-free, enabling stable electrical conduction in the metallic coating.

Wrinkling hierarchy in constrained thin sheets from suspended graphene to curtains.

We show that thin sheets under boundary confinement spontaneously generate a universal self-similar hierarchy of wrinkles. From simple geometry arguments and energy scalings, we develop a formalism based on wrinklons, the localized transition zone in the merging of two wrinkles, as building blocks of the global pattern. Contrary to the case of crumpled paper where elastic energy is focused, this transition is described as smooth in agreement with a recent numerical work [R. D. Schroll, E. Katifori, and B. Davidovitch, Phys. Rev. Lett. 106, 074301 (2011)]. This formalism is validated from hundreds of nanometers for graphene sheets to meters for ordinary curtains, which shows the universality of our description. We finally describe the effect of an external tension to the distribution of the wrinkles.

Wrinkling of stimuloresponsive surfaces: mechanical instability coupled to diffusion.

In this Letter, we propose a new mechanism to generate wrinkled patterns, based on the coupling between molecular diffusion and the buckling instability of rigid membranes "glued" on a polymer layer. The geometry of the diffusion front and the minimization of wrinkling energy conspire to generate various patterns of folds (e.g., parallel or radial folds, herringbone) and various dynamics (continuous or discrete). The diffusion process gives us the opportunity to study the stability of the various wrinkled patterns and to follow the creation or annihilation of topological defects.

Slippery or sticky boundary conditions: control of wrinkling in metal-capped thin polymer films by selective adhesion to substrates.

Wrinkling patterns at the metallized surface of thin polymer films are shown to be sensitive to the sticky or slippery character of the polymer-substrate interface. Existing theoretical models were expanded to specific boundary conditions (adhesive versus slippery) in order to rationalize these observations. Based on this concept, we were able to propose a new and simple method to orient the wrinkles by chemically patterning the substrate with regions of high and low adhesion.