Self-wrinkling coating for impact resistance and mechanical enhancement

Self-damping photonic crystals with differentiated reversible crosslinking domains for biomimetic delayed visual perception of underwater impact stress

Structural color-based impact sensors output light or electrical signals through entropic elasticity storing and releasing of the polymer network, inspiring the design of armors for underwater equipment. Designing self-damping units at the molecular and nanostructural levels will contribute to capturing and analyzing relevant impact and mechanical signals by the naked eye. Herein, inspired by the octopus' sucker, we proposed self-damping photonic crystals (SDPCs) with differentiated reversible crosslinking domains, which can delayed-release entropic elasticity in water and visually perceive stress field evolution via structural color. These domains are generated by weak and strong hydrogen bonds (H-bonds) assigned by differentiated copolymerization, corresponding to weak and strong crosslinking domains, respectively. The compressed network stores entropic elasticity, showing size-effect-induced blueshift structural colors. During entropic elasticity release, the weak/strong crosslinking domains are disrupted successively, resulting in temporary macropore asymmetry and forming transient Laplacian pressure difference (ΔP). The self-damping effect based on the continuous recombination of domains and the equilibrium iteration of ΔP achieves a delayed visual perception of entropy elasticity release. Given this, impact stress sensing and structural color self-erasing techniques have been developed.

Self-Wrinkling-Induced Mechanically Adaptive Patterned Surface of Photocuring Coating for Abrasion Resistance

Providing mechanically adaptive performance to surfaces is significant in preserving materials from damage in variable environments, however, it has rarely been studied. Inspired by the mechanically adaptive behaviors of the surface microstructure on the carapace of desert scorpions and bark of desert tamarisks, a self-wrinkled mechanically adaptive patterned surface (SWMAPS) using one-step UV-curing and self-wrinkling technique is reported. Because of the fluorinated polyurethane photo-initiator formed by self-assembly at the top surface, UV-induced photo-crosslinking can spontaneously generate a gradient-crosslinked structure and wrinkled patterns with different morphology. With mechanically adaptive behavior originating from self-assembled fluorinated polyurethane photo-initiators, gradient-crosslinked structures, and self-wrinkled patterns, the SWMAPS remains intact under 600 cycles of reciprocating friction with little variation in the coefficient of friction and water contact angle. The SWMAPS prepared by programmable UV irradiation maintains integral under 1800 cycles of reciprocating friction with a stable friction coefficient. Furthermore, the SWMAPS is fabricated with high efficiency, regulated morphology, good surface mechanical properties, and self-recovery performance. This strategy establishes a new field of mechanically adaptive patterned surfaces, which significantly improves durability and prolongs the service life of materials in variable environments.

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.

Preparation of a self-matting, anti-fingerprint and skin-tactile wood coating via biomimetic self-wrinkling patterns

Inspired by natural wrinkled surfaces, artificial surfaces with biomimetic wrinkled structures have been widely used to improve optical properties, wettability, and antibacterial properties. However, the preparation of wrinkled structures has the disadvantages of long-time consumption and complex processes. Herein, we prepared a self-wrinkling polyurethane-acrylate (PUA) wood coating via biomimetic self-wrinkling patterns by using a light-emitting diode (LED)/excimer/mercury lamp curing system, which was capable of self-matting, anti-fingerprint and skin-tactile performance. By adjusting the irradiation intensity in the curing system, the wavelength (λ) and amplitude (A) of wrinkles on the coating surface were controlled to enhance the coating performance. After curing by the LED, excimer, and mercury lamps at energy intensities of 500, 30, and 300 mW/cm2 respectively, the self-wrinkling coating showed excellent surface performance. The self-wrinkling coating represented low gloss of 4.1 GU at 85°, high hardness of 4H. Interestingly, the coating surface had a high hydrophobicity (104.5°) and low surface energy (29-30 mN/m) and low coefficient (COF) of friction (0.1-0.2), which were consistent with those of the human skin surface. Besides, the wrinkled structure also improved the thermal stability of the coating samples. This study provided a promising technique for the mass production of self-wrinkling coatings that could be used in wood-based panels, furniture, and leather.

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.