Metamaterials and origamic metal-organic structures

Origami is a process of folding paper usually associated with child’s play, primarily to form a paper-folded crane, but has recently become a fascinating research topic. Origami-inspired materials can achieve mechanical properties that are difficult to achieve with conventional materials, and materials scientists are still exploring such constructions based on origami tessellation at the molecular level.

In a new report now published in Natural communicationsEunji Jin and a particle chemistry and acceleration research team from the National Institute of Science and Technology in Ulsan, Republic of Korea, described the development of a two-dimensional porphyrin metal-organic structure self-assembled from nodes zinc and porphyrin linkers based on origami tiling.

The team combined theory and experimental results to demonstrate the origami mechanisms underlying the 2D porphyrin metal-organic framework with the flexible linker as the pivot point. The 2D tiling hidden within the 2D metal-organic framework revealed origami molecules at the molecular level.

Mathematics and the Science of Paper Folding

The art of paper folding, also known as origami, is now expanding beyond this niche and into science, engineering, architecture and other industries. The list of applications for origami is expanding, as evidenced by solar cells, electronics and biomedical devices. The length scales used for origami have also evolved from the meter to the nanoscale, with close relationships to origami tilings such as Miura-ori, double undulation surfaces, Yoshimura and square patterns to n name just a few. Each origami tiling contains similar or repeating patterns, although tilings are highly deployable blueprints for constructing mechanical metamaterials with negative Poisson’s ratio; an exotic mechanical property.

Despite the advent of a variety of origami-inspired materials, constructing molecular materials based on origami tilings remains a challenge. Materials scientists have shown how it is possible to develop origami-inspired materials using metal-organic structures that serve as an ideal platform with virtually unlimited and highly customizable unique functionalities. Researchers are exploring geometries involving tessellation to uncover the hidden dynamics of metal-organic structures.

In this new work, Jin and colleagues described metal-organic structures based on double-undulation origami tessellation surfaces that they assembled from a flexible porphyrin linker and a secondary building unit to zinc impeller. Thermal motion revealed in metal-organic structures depended on origami mechanics to exhibit unusual folding behaviors. Such metal-organic frameworks based on origami tessellation may soon be incorporated as an emerging and active class of mechanical metamaterials.

Unveiling crystal structures

The research team grew the PPF 301 crystals with a zinc porphyrin component through a solvothermal reaction. These crystals displayed a pale purple color and had a rectangular plate shape. During the experiments, the porphyrin core underwent metalation to develop a five-coordinate zinc ion. The self-assembled 2D layer of PPF-301 exhibited a wavy structure with flexible aryloxy groups, where the 2D square structures were constructed from a tetratopic porphyrin linker. The team observed the synchrotron X-ray powder diffraction pattern of the “as-synthesized” origami-based crystal sample PPF301, which matched well with the simulated pattern. Since the double undulation surfaces were highly deployable, the PPF301 construct showed origami movement based on flexible nodal points.

The thermal response and origami tiling of PPF301 crystal

Jin and his team tested a possible structural change in the PPF301 crystals by performing temperature-dependent synchrotron single-crystal X-ray diffraction in an accelerator laboratory. During the experiments, they prepared a crystal in a sealed capillary with a small amount of solvent added to prevent loss of crystallinity. The expansion of the crystalline interlayers contributed to an increase in cell volume and, although changes in interlayer spacing were present in the 2D metal-organic structures, the coefficient of thermal expansion of the material was significantly higher than that of many metal-organic structures. 2D.

Additionally, the material’s double-ripple surfaces deviated, and the team compared the experiment and the mechanical model based on origami tessellation. They then identified the origin of the origami movement in the metamaterial through the dihedral angle and bond angles of the aryloxy group, which contributed to the 2D origami framework of PPF-301.

Mechanical properties of origami metamaterial

The research team studied the mechanical properties of PPF-301 based on origami motion and performed quantum mechanical calculations to construct an optimized structure, then calculated the total electronic energies of the construct. Using maximum and minimum values ​​of elastic stresses, they verified the directional contribution of the material. When the team applied mechanical stress, the movement accompanied changes in the dihedral angles and bond angles in the aryloxy group.

Previously, materials scientists had examined several flexible metal-organic structures exhibiting anomalous properties, including negative linear compressibility and negative Poisson’s ratio. However, it is difficult to generate 2D flexible metal-organic structures, although the characteristics and properties of the material developed in this study are suitable for its behavior in the form of an origami metamaterial.

Outlook

In this way, Eunji Jin and his team discovered dynamic crystals that completely changed the general idea that solids were non-dynamic concrete entities. Flexible metal-organic structures showed remarkable transformation based on abundant molecular building blocks, organic linkers, and metal knots. Scientists achieved local movements of these building blocks, including bending, twisting, and rotation behaviors using topology.

They revealed the hidden dynamic behaviors of metal-organic structures with flexible geometries. The research team retained the intrinsically wrinkled pattern of the 2D layer to open a distinct category of metal-organic structured metamaterials with mechanical properties. By regulating the distance between metal nodes based on external stimuli, they developed advanced molecular quantum computing processes suitable for future applications of origami’s metal organic frameworks.

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