Hugues Vandeparre

In situ tuning the optical properties of a cavity by wrinkling

In this letter we propose an original, in situ, approach to tune the optical properties of an optical cavity, based on the wrinkling of compressed metal/polymer multilayer thin films. This phenomenon is conceptually described, simulated, and experimentally confirmed. The main idea is to use wrinkling to modulate the effective refractive index of the upper interface. This modulation induces a spectral shift of the cavity modes. The work presented here constitutes a first step to the development of stretchable and curved photonics.

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.

Hierarchical wrinkling patterns

This paper reports a simple and flexible method for generating hierarchical patterns from wrinkling instability. Complex features with gradually changing topographies are generated by using the spontaneous wrinkling of a rigid membrane (titanium) on a soft foundation (polystyrene) compressed via the diffusion of a solvent. We show that the morphology of these unreported wrinkled patterns is directly related to the rheological properties of the polymer layer and the geometry of the diffusion front. Based on these ingredients, we rationalize the mechanism for the formation of hierarchical wrinkling patterns and quantify our experimental findings with a simple scaling theory. Finally, we illustrate the relevance of our structuration method by studying the mechanosensitivity of fibroblasts.

Confined wrinkling: impact on pattern morphology and periodicity

Wrinkling instabilities are observed in compressed multilayers made of materials with contrasted properties. Here, we study the influence of confinement, i.e. using foundations with dimensions smaller than 50 nm, on the wrinkled patterns. We show that confinement generates a change in morphology from labyrinths to a dotted pattern with hexagonal symmetry. This transition occurs when the amplitude of the wrinkles becomes comparable to the thickness of the upper membrane, i.e. A ≃ h. For very thin foundations (h < 100 nm), a drastic deviation from the usual evolution of the wavelength with the foundation thickness is observed. This new regime was explained by considering the van der Waals interactions between the metal layer and the substrate. The VDW energy term was involved in a new scaling law model that agrees with the experimental data.