Dynamic Surface Wrinkles for In Situ Light-Driven Dynamic Gratings

Phase-transition-induced dynamic surface wrinkle pattern on gradient photo-crosslinking liquid crystal elastomer

Liquid crystal elastomers (LCEs) with various deformation properties based on phase transition were widely used as actuators and provided potential to fabricate functional surfaces with tunable microstructure. Herein, we demonstrate a strategy to fabricate dynamic micro wrinkles on LCE surfaces based on LC phase transition. Stable micron-sized surface wrinkles on the anthracene-containing LCE film (AnLCE) are fabricated by ultraviolet exposure induced gradient cross-linking and subsequently stretching-releasing (UV-SR). The surface wrinkle is stabilized by the orientation of liquid crystal mesogens in the crosslinked top layer, while it can be erased by heating due to the isotropic phase-transition and recovered by stretching-releasing again. The dynamic natures cooperated with multi display modes under natural light, UV light and polarized light enable wrinkled AnLCE as a dynamic and multi-mode display platform. This strategy provide a path for modifying LCEs and regulating surface polarized images via wrinkling, which may be potential in soft sensors and optics, smart windows and anti-counterfeiting.

Smart Wrinkled Interfaces: Patterning, Morphing, and Coding of Polymer Surfaces by Dynamic Anisotropic Wrinkling

In contrast to traditional static surfaces, smart patterned surfaces with periodical and reversible morphologies offer limitless opportunities for encoding surface functions and properties on demand, facilitating their widespread application as functional building blocks in various devices. Advances in intelligently controlling the macroscopic properties of these smart surfaces have been accomplished through various techniques (such as three-dimensional printing, imprint lithography and femtosecond laser) and responsive materials. In contrast to the sophisticated techniques above, dynamic anisotropic wrinkling, taking advantage of dynamic programmable manipulation of surface wrinkling and its orientation, offers a powerful alternative for fabricating dynamic periodical patterns due to its spontaneous formation, versatility, convenient scale-up fabrication, and sensitivity to various stimuli. This review comprehensively summarizes recent advances in smart patterned surfaces with dynamic oriented wrinkles, covering design principles, fabrication techniques, representative types of physical and chemical stimuli, as well as fine-tuning of wrinkle dimensions and orientation. Finally, advanced applications of these smart patterned surfaces are presented, along with a discussion of current challenges and future prospects in this rapidly evolving field. This review would offer some insights and guidelines for designing and engineering novel stimuli-responsive smart wrinkled surfaces, thereby facilitating their sustainable development and progressing toward commercialization.

Photochemical Design for Diverse Controllable Patterns in Self-Wrinkling Films

Harnessing the spontaneous surface instability of pliable substances to create intricate, well-ordered, and on-demand controlled surface patterns holds great potential for advancing applications in optical, electrical, and biological processes. However, the current limitations stem from challenges in modulating multidirectional stress fields and diverse boundary environments. Herein, this work proposes a universal strategy to achieve arbitrarily controllable wrinkle patterns via the spatiotemporal photochemical boundaries. Utilizing constraints and inductive effects of the photochemical boundaries, the multiple coupling relationship is accomplished among the light fields, stress fields, and morphology of wrinkles in photosensitive polyurethane (PSPU) film. Moreover, employing sequential light-irradiation with photomask enables the attainment of a diverse array of controllable patterns, ranging from highly ordered 2D patterns to periodic or intricate designs. The fundamental mechanics of underlying buckling and the formation of surface features are comprehensively elucidated through theoretical stimulation and finite element analysis. The results reveal the evolution laws of wrinkles under photochemical boundaries and represent a new effective toolkit for fabricating intricate and captivating patterns in single-layer films.

Functional PDMS Elastomers: Bulk Composites, Surface Engineering, and Precision Fabrication

Polydimethylsiloxane (PDMS)-the simplest and most common silicone compound-exemplifies the central characteristics of its class and has attracted tremendous research attention. The development of PDMS-based materials is a vivid reflection of the modern industry. In recent years, PDMS has stood out as the material of choice for various emerging technologies. The rapid improvement in bulk modification strategies and multifunctional surfaces has enabled a whole new generation of PDMS-based materials and devices, facilitating, and even transforming enormous applications, including flexible electronics, superwetting surfaces, soft actuators, wearable and implantable sensors, biomedicals, and autonomous robotics. This paper reviews the latest advances in the field of PDMS-based functional materials, with a focus on the added functionality and their use as programmable materials for smart devices. Recent breakthroughs regarding instant crosslinking and additive manufacturing are featured, and exciting opportunities for future research are highlighted. This review provides a quick entrance to this rapidly evolving field and will help guide the rational design of next-generation soft materials and devices.

Adaptive 2D and Pseudo-2D Systems: Molecular, Polymeric, and Colloidal Building Blocks for Tailored Complexity

Two-dimensional and pseudo-2D systems come in various forms. Membranes separating protocells from the environment were necessary for life to occur. Later, compartmentalization allowed for the development of more complex cellular structures. Nowadays, 2D materials (e.g., graphene, molybdenum disulfide) are revolutionizing the smart materials industry. Surface engineering allows for novel functionalities, as only a limited number of bulk materials have the desired surface properties. This is realized via physical treatment (e.g., plasma treatment, rubbing), chemical modifications, thin film deposition (using both chemical and physical methods), doping and formulation of composites, or coating. However, artificial systems are usually static. Nature creates dynamic and responsive structures, which facilitates the formation of complex systems. The challenge of nanotechnology, physical chemistry, and materials science is to develop artificial adaptive systems. Dynamic 2D and pseudo-2D designs are needed for future developments of life-like materials and networked chemical systems in which the sequences of the stimuli would control the consecutive stages of the given process. This is crucial to achieving versatility, improved performance, energy efficiency, and sustainability. Here, we review the advancements in studies on adaptive, responsive, dynamic, and out-of-equilibrium 2D and pseudo-2D systems composed of molecules, polymers, and nano/microparticles.

Controllable Buckle Delaminations in Polymer-Supported Periodic Gradient Films by Mechanical Compression

Surface instabilities including wrinkles and buckle-delaminations are widespread in nature and can be found in a wide range of practical applications. Compared with the homogeneous wrinkle mode, the buckle-delaminations are spontaneously stress-localized, and their initiation positions and geometrical parameters are hardly precisely controlled by a simple method. Here, we report on the controllable buckle-delaminations in periodic thickness-gradient metal films on polydimethylsiloxane (PDMS) substrates by uniaxial mechanical compression. It is found that a periodic thickness-gradient film is spontaneously formed by masking a copper grid during deposition. The released mechanical strain tends to concentrate in thinner film regions, resulting in the restricted growth of buckle-delaminations. The geometrical features, evolutional behaviors, and underlying physical mechanisms of such buckle-delaminations are analyzed and discussed in detail based on the buckling model and finite element simulations. This work would provide a better understanding of the restricted buckle-delaminations in heterogeneous film-substrate systems and controllable fabrication of ordered structural arrays by copper grid masking and mechanical loading.