【Frontiers in HaiChuan Chemical Technology】Researchers from the University of Science and Technology of China have developed ultra-strong two-dimensional polyamide film materials

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In the field of materials science, strength and elasticity have long been regarded as mutually exclusive properties. Inorganic 2D materials (such as graphene and molybdenum disulfide), despite having extremely high Young’s moduli, suffer from issues such as poor structural tunability ； Although organic 2D polymers (such as conventional polyamides and COFs) possess good elasticity and structural tunability, their Young’s modulus is generally limited to 1–10 GPa, making them unsuitable for applications that require high strength. This performance contradiction severely limits the practical application of two-dimensional materials in fields such as flexible electronics and high-performance protection. Recently, the team led by Professor Liu Bo from the University of Science and Technology of China has successfully developed a series of two-dimensional polyamide materials through precise design of molecular structures and regulation of interlayer interactions. The Young’s modulus of the GH-TMC film reaches 35.6 GPa, its hardness is 2.0 GPa, and its elastic recovery rate is as high as 60% – thereby overcoming the technical limitation that traditional two-dimensional materials struggle to balance strength and elasticity. Its comprehensive mechanical properties far exceed those of most polymer and metal materials, as well as those of mainstream MOF and COF materials, offering new solutions for material upgrades in fields such as flexible electronics, high-performance protective coatings, and energy devices. The relevant findings were published in the journal Nature Communications under the title “Manipulating mechanical strength of isoreticular two-dimensional polyamide materials via multiple interactions”. Specifically, the research team proposed an innovative strategy of \"miniaturization of rigid units and synergy of multiple weak interactions\": on one hand, by reducing the size of the structural units in two-dimensional polyamides, the density of covalent bonds and the rigidity of the covalent network are increased. The smaller the structural units, the higher the Young’s modulus of the material. For example, GH-TMC uses small hexagonal ring structural units, resulting in a modulus that is significantly higher than that of materials such as GH-BTCA and Melem-TPC, which employ larger ring units (Figure 1) ； On the other hand, a triple interaction network composed of hydrogen bonds, π-π stacking, and misaligned electrostatic interactions is cleverly introduced; the high-density hydrogen bonds in the plane enhance molecular rigidity, while the reversible breaking and reformation of edge hydrogen bonds endow the material with elastic recovery capability. The misaligned electrostatic interactions between guanidinium cations and chloride ions, along with interlayer π-π stacking, stabilize the stack structure of the nanosheets, preventing performance losses due to interlayer slippage. To verify the reliability of the material properties, the team employed dual characterization methods: atomic force microscopy (AFM) peak force quantitative nano-mechanical imaging (PF-QNM) and in-situ scanning electron microscopy (SEM) nano-indentation. The results showed that the mechanical properties of the GH-TMC film exhibited excellent uniformity. The Young’s modulus and hardness show minimal variations across different testing areas; even in six consecutive indentation tests at a depth of 700 nm, the stress-displacement curves remained stable with no significant residual plasticity, demonstrating their structural stability at high strengths. What is even more noteworthy is that the H³/E⟡ value of this material is significantly higher than that of traditional polymers and metals, indicating a longer service life in high-frequency friction applications. Meanwhile, its 60% elastic recovery rate enables it to meet the requirements of repeated bending on flexible substrates, thus bridging the gap between the rigidity of inorganic materials and the strength of organic materials. The core value of this research lies not only in the development of a high-performance two-dimensional material, but also in establishing a regulatory paradigm for \"molecular structure-interlayer interactions-mechanical properties\". By designing a synergistic mechanism between the size of rigid units and multiple weak interactions, a general strategy is provided to address the \"strength-elasticity\" problem in two-dimensional materials. This strategy can be extended to other two-dimensional polymer systems. In the future, by further regulating the molecular structure and types of interactions, special two-dimensional materials suitable for various applications can be developed – such as low-modulus, highly elastic versions for flexible bioelectronics, or ultra-high-hardness versions for protective coatings. This will help move two-dimensional materials from the stage of basic research to practical applications, thereby injecting new momentum into the innovative development of advanced materials. This research was funded by the **Key Research and Development Program**, the General Project of the National Natural Science Foundation, the Special Fund for Basic Scientific Research in Central Universities, and the Anhui Provincial Natural Science Foundation. Liu Bo is the corresponding author of this paper, while Hu Qing, a doctoral student, is the first author.