Dynamic Instability of a Sol−Gel-Derived Thin Film

Multidirectional Wrinkle Patterns Programmed by Sequential Uniaxial Strain with Conformal yet Nontraceable Masks

Surface wrinkling is a promising route to control the mechanical, electrical, and optical properties of materials in a wide range of applications. However, previous artificial wrinkles are restricted to single or random orientation and lacks selectivity. To address this challenge, this study presents multidirectional wrinkle patterns with high selectivity and orientation through sequential uniaxial strain with conformal polymeric shadow masks. The conformal but nontraceable polymeric stencil with microapertures are adhered to a flat substrate prior to oxidation, which forms discrete and parallel wrinkles in confined domains without any contamination. By fully investigating the process, this study displays compound topography of wrinkles consisting of wrinkle islands and surrounding secondary wrinkles on the same surface. With this topography, various diffusion properties are presented: from semi-transparent yet diffusive films to multidirectional diffusive films, which will be available for new types of optical diffuser applications.

Recent advances in wrinkle-based dry adhesion

Surface wrinkles driven by elastic instabilities have attracted significant interest in the field of materials science and engineering. They are simple and readily fabricated with various patterns of tunable size, morphology and surface topography from a wide range of material systems. Recently, they have been investigated as a new type of dry adhesives. In this review, after a brief introduction of different methods to prepare wrinkle surfaces, we focus on the investigation of dry adhesion mechanisms in different material systems. By exploiting wrinkle dimension, morphology, modulus, curvature, and different contacting surfaces (flat, hemispherical, spherical) and their complementarity, we show adhesion enhancement, reduction and selectivity. By comparing experimental results with theoretical predictions, we aim to provide a guideline to design and engineer wrinkle-based dry adhesives. Several examples of applications of engineered wrinkles are also demonstrated, including pick, release and transfer of nanoparticles and bulk materials, and gecko-like hybrid adhesives. The review is concluded with perspectives on the wrinkling technology for smart dry adhesives.