Wrinkling membranes with compliant boundaries

Laser patterning captured in real-time: surface modifications of multilayer thin-films under nanosecond laser heating

Controlled wrinkle formation has attracted intensive research interest as a means to modify surface properties. However, most of the currently explored methods rely on mechanically stretching polymer substrates with hard surface coatings, and the application of these methods to different materials is limited. Here, for the first time, we demonstrate laser-assisted periodic wrinkle formation on silicon nitride (SiN) membranes that are coated with titanium (Ti)/nickel (Ni) multilayers. Corrugated surface formation mechanism, as well as grain nucleation and growth, are studied using ultrafast transmission electron microscopy (UTEM). Periodic wrinkling and patterning of multilayers on thin SiN membranes are induced by a nanosecond pulsed laser, and the deformation of the film is captured by single-shot imaging. The investigated structures revealed periodic wrinkling of the membrane and corrugated surface formation on both sides of the film. The findings of this work could allow laser-irradiation-based fast fabrication of corrugated films with tailored properties.

Macroscopic Geometry-Dominated Orientation of Symmetric Microwrinkle Patterns

Orientated wrinkle patterns with controlled microarchitectures are highly attractive because of their potential and broad application in technologies ranging from flexible electronic devices to smart windows. Here, we demonstrate a macroscopic, geometry-dominated strategy to fabricate symmetric microwrinkles with precisely controllable pattern dimensions and orientations through a dynamic interfacial release process. The release-induced approach is based on the release of multilayer elastomer composites from polymeric sacrificial layers in solutions combined with crosslinking-induced contraction of the elastomer substrates. Crosslinking-induced contraction provides the driving force for developing and stabilizing surface wrinkle formation, whereas the polymeric sacrificial layer provides a mild and simultaneous release process to form orientated wrinkles through kinetic control of local strain development. The macroscopic shape of the composite controls release kinetics, hence strain history, leading to the generation of photonic reflective surfaces. Moreover, stable wrinkles fabricated from various materials including metals, ceramics, and carbons can be achieved. This versatile, mold-free, and cost-effective platform technology demonstrates how global strain distributions can be harnessed through kinetics to drive local pattern development.

Mechano-responsive lateral buckling of miniaturized beams standing on flexible substrates

We fabricate an elastomeric beam standing on a flexible substrate using 3D printing and soft lithography and investigate lateral buckling generated in the part of the wall when this beam is under pure bending. We also observe changes in the morphology of wrinkling along the applied strain and geometry of the wall, and then analyze it with scaling concepts. Furthermore, the degree of lateral buckling is controlled through the tip design in the ratchet structure and it is verified with finite element simulation. Based on this, a millimeter scale device with a visual difference according to the curvature is manufactured.

Competitive concurrence of surface wrinkling and dewetting of liquid crystalline polymer films on non-wettable substrates

Polymeric thin films coated on non-wettable substrates undergo film-instabilities, which are usually manifested as surface deformation in the form of dewetting or wrinkling. The former takes place in fluidic films, whereas the latter occurs in solid films. Therefore, there have rarely been reports of systems involving simultaneous deformations of dewetting and wrinkling. In this study, we propose polymeric thin films of liquid crystalline (LC) mesogens prepared on a non-wettable Si substrate and apply a treatment of plasma irradiation to form a thin polymerized layer at the surface. The resulting compressive stress generated in the surface region drives the formation of wrinkles, while at the same time, dipolar attraction between LC molecules induces competitive cohesive dewetting. Intriguing surface structures were obtained whereby dewetting-like hole arrays are nested inside the randomly propagated wrinkles. The structural features are readily controlled by the degree of surface cross-linking, hydrophilicity of the substrates, and the LC film thickness. In particular, dewetting of LC mesogens is observed to be restricted to occur at the trough regions of wrinkles, exhibiting the typical behavior of geometrically confined dewetting. Finally, wrinkling-dewetting mixed structures are separated from the substrate in the form of free standing films to demonstrate the potential applicability as membranes.

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.

Wrinkling of structured thin films via contrasted materials

Regular surface patterns induced by the wrinkling of thin films have received intense attention in both science and engineering. We investigate the wrinkling of structured thin films that consist of two types of materials arranged in periodic patterns. A mechanical model is proposed to understand the physics of the wrinkling, and a set of scaling laws for the wrinkle wavelength are obtained. Periodic wrinkles are generated in the local regions of structured films via in-plane contrasted elastic modulus between heterogeneous materials. The wrinkle morphology and location can be tailored by designing structured thin films in a controllable way. Our findings provide the basis for understanding the wrinkling of structured thin films and for the manufacture of regular surface patterns via wrinkling.