Zhejiang University team creates new substances, and the results are published in Nature

Ceramics and rubber are two materials that we often use in our daily lives. In our impression, ceramics are hard and brittle, and once they slip and fall to the ground, they will break with a "bang". Rubber, on the other hand, feels soft and bouncy. If you squeeze it hard, it will dent and then return to its original shape.

Hardness and elasticity are a pair of "contradictions" in nature. It seems to be a fantasy to want a substance to have both properties at the same time.

Recently, a collaborative team of Professor Tang Ruikang and Researcher Liu Zhaoming from the Department of Chemistry at Zhejiang University invented a new substance that combines organic compounds and inorganic ionic compounds at the molecular scale, perfectly achieving the "compatibility" of hardness and elasticity in the same substance, while also having plasticity like plastic.

Previously, the scientific community mainly tried to compromise the properties of organic and inorganic substances by mixing them together. At the microscopic scale, organic and inorganic substances still existed relatively independently. This time, the Zhejiang University team achieved the combination of organic compounds and inorganic ionic compounds at the molecular level for the first time, and obtained a new substance with properties completely different from previous materials.

The team named this new material "elastic ceramic plastic". On June 8, Beijing time, this achievement was published online in the top international journal Nature. The first author of the paper is Fang Weifeng, a doctoral student in the Department of Chemistry, and the co-corresponding authors are Tang Ruikang and Liu Zhaoming. The research work was supported by Dr. Mu Zhao, doctoral students He Yan and Kong Kangren from Zhejiang University, and Associate Researcher Jiang Kai from East China Normal University.

Team Photos

The Ordinary "Yellow Button"

The reporter saw at the scene that the new substance was a small yellow block shaped like a button, which looked ordinary on the surface. Even the research team did not realize that it was a new substance at first.

Of course, such new substances do not appear out of thin air; they undergo a rather long “gestation” process.

In traditional cognition, the preparation methods of materials in the fields of inorganic chemistry and polymer chemistry are completely different, but in 2019, Tang Ruikang's team proposed a new concept of "inorganic ion oligomers and their polymerization reactions", breaking the boundaries between the two.

Since calcium carbonate can be prepared like plastic, can inorganic substances be made using organic chemistry? The research team conducted a large number of experiments.

"Organic matter is connected by covalent bonds, and inorganic ionic compounds are combined by ionic bonds. To achieve the unity of organic and inorganic matter in one molecule, this medium is very important," said Tang Ruikang.

The research team integrated the synthetic concept of "functionalization reaction" in organic chemistry into inorganic synthetic chemistry, designed a functionalization reaction of inorganic ion oligomers, introduced organic functional molecules into "inorganic ion molecules", and realized the synthesis of hybrid molecules with organic fragments and inorganic ion fragments.

"After screening many chemical reactions, we finally chose the classic acid-base reaction in inorganic chemistry. This method can simply and quickly connect alkaline ion salts with acidic organic molecules to form hybrid molecules. Taking calcium carbonate oligomers and lipoic acid molecules as examples, through the polymerization of ionic fragments and the polymerization reaction of disulfide bonds in lipoic acid, we can form macroscopic materials from hybrid molecules 'from the bottom up'." Liu Zhaoming said.

The macroscopic material formed by the polymerization of this hybrid molecule is the "little yellow button" we finally see.

A new structure with a hidden meaning

The material structure formed by this hybrid molecule is not as simple as the realization of inorganic and organic matter "hand in hand". Through three-dimensional imaging by cryo-electron microscopy experiments, the research team discovered that this is a new structure.

In this molecule, the inorganic ionic bond network and the organic covalent bond network are interwoven and intertwined, "you have me, I have you". This interwoven network is like a retractable skeleton, which has both the properties of inorganic matter and the characteristics of organic matter, so it has a certain hardness and elasticity. When a certain external force is applied, the inorganic skeleton can provide hardness and strength. When the external force is large and elastic deformation occurs, the entire skeleton deforms to produce a buffering effect. After the external force is removed, the organic skeleton plays a rebound role, allowing the entire network to return to its original state.

Cryo-EM 3D reconstruction, 2D reconstruction and EM images of the ion-covalent double network

"This structure of interlaced organic covalent bond networks and inorganic ionic bond networks is unprecedented," said Tang Ruikang. In the past, the fusion of organic and inorganic substances was a simple superposition of the two, like pouring inorganic powder into the framework of organic matter and stirring it evenly. If you break it down layer by layer, at the molecular level, it is still "you are yours, I am mine", so to be more precise, it is just a mixture of the two. "Our experiment this time produced brand-new molecules that did not exist before, so we obtained a brand-new structure, breaking the barriers between traditional organic compounds and inorganic ionic compounds at the molecular scale."

The all-powerful "pentagonal warrior"

Chemistry is the study of creating new substances.

In short, this achievement of Zhejiang University is that researchers have created a new molecule by splicing molecular units containing organic and inorganic substances, thus forming a new material world.

This new substance that breaks through our cognition is, at the molecular level, an intertwined network of organic covalent and inorganic ions, in which the chemical ratio of organic and inorganic substances is approximately half each. At the macroscopic material level, it is a composite plastic that has the properties of both rubber and ceramics.

Scientists at Zhejiang University compared the performance of this new material with representative ceramics, rubber, plastics, and metals, and found that it achieved high scores in several indicators such as hardness, rebound, strength, deformation, and processability. It has the hardness of marble, the elasticity of rubber, and the plasticity of plastic. In addition, it has a feature that traditional plastics do not have: it will not soften after heating. It is so powerful that it can be called a "pentagonal" warrior.

Comparison of five properties of elastic ceramic plastics with other materials

Tang Ruikang said: "From new molecules to new structures to new materials, we have opened up a new world."

The results were highly praised by the reviewers and editors of the paper: "This article reports a completely new material that has the strength and hardness of ceramics and the deformability, flexibility and elasticity of polymers. This will not only attract the attention of the materials science community, but also the interest of the entire scientific community, because new materials always open up new possibilities." At the same time, "Nature" also came with a special research brief.

Talking about the next step of work, Tang Ruikang said that new molecules, new structures and new materials are expected to be applied in many research fields from basic chemistry to materials science, while also leaving more room for imagination for future scientific research.

The project was funded by the National Natural Science Foundation of China (22022511, 22275161), the National Key R&D Program (2020YFA0710400), and the Basic Research Business Expenses for the Central Universities (226-2022-00022, 2021FZZX001-04).

Conceptual image of elastic ceramic plastic with bicontinuous network