Smart Patterned Surface with Dynamic Wrinkles

Patterned surfaces are fundamentally important to physics, chemistry, materials, and biology science, endowing significant functions and thus bearing broad and fantastic applications whether in natural or man-made events. Among the various methods for patterning surfaces, wrinkling or buckling offers a powerful alternative to prepare surface patterns because of its spontaneous nature, versatility, easy preparation in large-scale, and capability to be responsive to various stimuli. In particular, patterned surfaces with dynamic wrinkles can tailor the encoded surface properties on demand and can provide a promising alternative for smart surfaces, which has potential for wide applications in enhanced and tunable optical or photoelectric devices, responsive microstructures, switchable wettability, smart adhesion and friction, and so on. The concept of smart patterned surfaces based on dynamic wrinkles is fundamental and versatile, and it is expected that there will be extensive future work based on this concept in generalizing this work to other smart materials and systems, and in using dynamic pattern systems to tune not only morphology but also functional properties encoded in the system's topography. In this Account, we present recent progress on smart surfaces with dynamic wrinkle patterns, including their design, preparation, and potential applications. First, we provide a brief introduction of a basic concept for mechanical instability induced wrinkle patterns and outline the general strategies and mechanics for dynamic wrinkles. Then, we discuss how the wrinkling and dewrinkling processes of a rigid skin bound to a soft substrate in bilayers or gradient layer systems occur by controlling the mechanical properties and geometric characteristics of the top and bulk layers, thereby paving the way for a smart patterned surface using chemical and physical approaches. Next, we discuss various chemical and physical stimuli, including light, temperature, pH, and chemicals, which can be harnessed into an extensive library of complex dynamic wrinkles. We highlight recent advances in preparing multiresponsive dynamic wrinkling patterns by adjusting the intrinsic properties of the skin layers (i.e., Young's modulus and cross-linking density) via dynamic chemistry, such as the Diels-Alder reaction, photodimerization, and supramolecular chemistry. Then, we outline how functional inclusions, such as photothermic or photoelectric additives and magnetic nanoparticles, can enable the composite elastic substrate as a dynamic platform for various functional top-layers to fabricate a smart surface for a desired function. In particular, photothermally reconfigurable wrinkle systems were investigated, where the carbon nanotube (CNT) served to efficiently convert its absorbed light energy into heat, hence actuating a real-time response of a near-infrared light (NIR)-sensitive wrinkle pattern and providing access to the development of advanced optoelectronic devices. In addition, based on their unique characteristics, applications of dynamic wrinkle patterns for smart displays, memory, flexible electronics, dynamic gratings, tunable adhesion, friction, and wettability are presented. Finally, we conclude by offering our perspective on future developments of this rapidly evolving field.