Elastic materials with a large reversible deformation function have a wide range of requirements in various engineering applications. However, at present, the elasticity and other mechanical properties of almost all highly elastic materials are affected by temperature, and no material can achieve high elasticity in deep and low temperature environments such as outer space.
This problem has long plagued researchers in the field of international material research and development and application. After years of continuous research, Professor Chen Yongsheng's team at the School of Chemistry of Nankai University has developed a new three-dimensional graphene material that can maintain good stability and high temperature in the low temperature range from 4K (about -269 ℃) to 1273K (about 1000 ℃) elasticity. This new type of "space sponge" has good application prospects in the fields of production and experiment under extreme conditions, and aerospace equipment manufacturing.
Elastic materials are a class of materials with large reversible deformation capabilities, such as common rubber and polymer foam materials, which have been widely used in human production and life. The new highly elastic materials have great application prospects in high-end research and technology fields such as wearable devices, artificial muscles, and sensors. However, the elasticity and other mechanical properties of almost all currently highly elastic materials are affected by temperature. For example, silicone rubber softens or decomposes under high temperature conditions; on the contrary, it gradually loses its elasticity as the temperature decreases, and undergoes glass transition to become hard and brittle. The same problem also exists with foam or sponge materials of highly elastic polymers.
In fact, the toughness and elasticity of materials usually decrease significantly in low temperature environments. The elastic strain range of ordinary inorganic metal and ceramic materials is extremely limited. The methods to improve such defects include constructing porous, multi-level material structures, such as metal microlattices, nano-ceramic microlattices, and so on. However, these materials are based on the secondary processing of traditional materials, so without exception, their mechanical properties are still affected by temperature. Although the preparation of super-elastic alloys and ceramics with shape memory function based on reversible phase change can increase the elastic strain range or toughness of the material to a certain extent and extend the temperature range of the material application, it cannot fundamentally change the effect of temperature on elasticity. .
Carbon nanomaterials, such as carbon nanotubes and graphene, have extremely high mechanical strength, flexibility, and excellent thermal stability, and are considered to be very suitable as building units to prepare elastic materials that are not affected by temperature. In graphene and the entire field of nanomaterials research, it is one of the important and difficult issues to obtain a macroscopic bulk material constructed from nanomaterial monomers, such as three-dimensional graphene, and enable it to maintain the intrinsic properties of nanometer monomers. .
Previous studies have shown that three-dimensional graphene materials with compressive elasticity not only have a large deformation variable recoverable elastic deformation ability at room temperature, but also this mechanical behavior is also manifested when the material is immersed in liquid helium (77K, about -196 ℃ ) Or 900 ° C in an inert atmosphere. In view of the unique microstructure of three-dimensional cross-linked graphene sponge (three-dimensional graphene material) and the intrinsic properties of monolithic graphene, Chen Yongsheng's team focused his research on elucidating the super compression of graphene and its macroscopic three-dimensional cross-linked phase materials. Whether elasticity and other mechanical properties can be maintained under extremely low temperature conditions.
The three-dimensional graphene material developed by the team is composed of randomly arranged single-layer graphene sheets through covalent bond chemical cross-linking, and has the same mechanical properties as room temperature under extremely low temperature conditions as low as the temperature of liquid helium. , Including highly recoverable super elasticity, constant Young's modulus (physical quantity describing the solid material's resistance to deformation), nearly zero Poisson's ratio (an elastic constant reflecting the lateral deformation of the material), and excellent fatigue resistance. The team researchers pointed out that at present, no other materials have such low-temperature superelastic properties and no temperature-dependent elastic and mechanical properties in the temperature range of 4K to 1273K.
Through the self-built mechanical property test system, Chen Yongsheng's team accurately and systematically tested the mechanical properties of the three-dimensional graphene material in the temperature range of 4-1273K (about -269 ℃ to 1000 ℃); the scanning electron microscope transformed by the team was used And in-situ temperature-varying sample stage, the microstructure deformation characteristics of the three-dimensional graphene material during the compression-rebound process under extremely low and high temperature conditions were obtained; the verification of theoretical model calculations clarified that the temperature invariance of this new material originates Graphene's unique sp2 hybrid two-dimensional carbon atom planar crystal structure.
The research team pointed out that under deep low temperature conditions, the remarkable mechanical stability of graphene and three-dimensional graphene materials makes them the best research objects for applications in outer space and other extreme low temperature or harsh environments. For other two-dimensional nanomaterials, if they have a structure similar to graphene, such as graphyne, silene, planar germanium, and two-dimensional Bi1-xSbx flakes, and assemble them as structural units in a manner similar to three-dimensional graphene, It is also possible that the obtained macroscopic materials fully retain the unique properties of the two-dimensional structural unit and exhibit macroscopic specific energy.
It is reported that the research was completed by the team of Professor Chen Yongsheng of Nankai University and the team of Professor Pulickel Ajayan of Rice University in the United States, and was supported by the Ministry of Science and Technology and the National Natural Science Foundation of China.