Method for making graphene meta-aerogels with superelasticity

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Multifunctional graphene meta-aerogels have shown great promise for future domestic and military applications. In a study published in Nature Communicationa laser-etching approach to produce graphene meta-aerogels with unique properties has been demonstrated.

Study: Metamaterials based on superelastic graphene airgel. Image Credit: ktsdesign/Shutterstock.com

What are graphene meta-aerogels?

Three-dimensional graphene meta-aerogels derived from their allotropic monoliths, such as sponges and foams, have become very attractive carbon-based metamaterials. They possess remarkable qualities such as superior compressibility, ultralight weight and excellent electrical conductance and thermal insulation.

Main challenges for graphene meta-aerogels

There are significant difficulties in obtaining new functionalities in graphene meta-aerogels. For example, the lack of multi-scale morphological control from tunable macro-structures to well-arranged micro-structures limits the use of graphene meta-aerogels in applications such as portable electronic devices, soft robotics, and sensitive systems. to stimuli.

Figure 1. Traditional etching and laser etching for graphene (AG) aerogels with arbitrary geometries. a Schematic illustration of traditional engraving for tools and works of art, such as a pair of chopsticks, a bowl and a carving of a courier. b Schematic illustration of GA laser engraving with arbitrary shapes. vs GA’s peony flower pattern with fine structures as small as a fifty cent coin after laser engraving. D GA pieces with elaborate shapes and rabbets can be assembled reversibly into a stereoscopic eagle. e GAs with serpentine structure, reversibly stretched with a tensile stress of 1200%. F GAs with re-entrant structure, presenting reversible deformations of 133%. g The spiral GAs stretched reversibly with a tensile stress of 900% and even up to 5400%. © Wu, M., Geng, H. et al. (2022).

Synthesis methods of graphene meta-aerogels

Lyophilization is a commonly used process to define the macrostructure of graphene meta-aerogels. This method can help to obtain graphene meta-aerogels with the natural appearance of molds, which can to some extent organize the configurations of graphene layers, resulting in porous, cellular and hyperbolic frameworks.

With this approach, however, it is difficult to achieve exact and particular shapes with superior performance.

3D printing is another interesting extrusion approach to produce lattice and periodic graphene meta-aerogels with configurable architectures. Nevertheless, the requirement to use a high graphene oxide (GO) distribution to achieve adequate viscosity poses a constraint in reducing the size of the printed structures.

Achieve high stiffness and elasticity in graphene aerogels

The macro-mechanical characteristics of graphene meta-aerogels are strongly influenced by their internal microstructure. The deformation of graphene meta-aerogel involves three operations in the order of linear elasticity, collapse and densification during the compression phase, according to the open-cell model.

When the walls of graphene reach their maximum bending moment and eventually collapse, micro-scale hinges are formed.

The bending stiffness of graphene walls (GW) has a direct impact on the modulus of elasticity of a graphene meta-aerogel. Therefore, attempts have been made to increase the bending stiffness of GWs using hydrothermal treatment, molecular crosslinks and polymer reinforcement to achieve higher stiffness and elastic modulus in graphene meta-aerogels.

Unfortunately, the specific bending stiffness of a film-like structure is fundamentally lower than that of a fibrillar or tubular material.

Fabrication and structure of graphene meta-aerogels (GmAs).

Figure 2. Fabrication and structure of graphene meta-aerogels (GmAs). a Schematic illustrations of GmAs manufacturing procedures and a sheet with the optical photograph of the sheet skeleton. b TEM image of graphene oxide (GO) sheets covering polyimide (PI) nanofibers. vse Cross-sectional SEM images of GmAs at different scales. F Three GmAs support more than 6000 times their weight without any macroscopic deformation. g A GmA (2 cm × 2 cm × 1.8 cm) stands on Setaria viridis. © Wu, M., Geng, H. et al. (2022).

Research Methodology

The team demonstrated a laser-etching approach to produce graphene meta-aerogels with multifunctional macro-scale architectures and highly organized micro-scale frameworks in this study.

Graphene meta-aerogels could be rapidly formed into various shapes, such as linear, planar and three-dimensional lattice structures and masses of holes.

Graphene meta-aerogels have microscopic structures consisting of interwoven submicron fibers and graphene films. The one-dimensional nanofiber-reinforced 2D film structure significantly increases the bending stiffness of the GWs.

The easy fabrication method allowed for the insertion of various functional elements into the structure, allowing items to be fabricated with predetermined geometries and functionality.

The team developed magnetically responsive aerogels and ceramic aerogels as prototypes, demonstrating strong potential for multifunctional use.

Important Study Findings

In this research, the team presented a laser-etching approach to fabricate graphene meta-aerogels with distinct properties and multiple functionalities. They achieved this by using a one-dimensional, nanofiber-enhanced 2D film structure.

This research has uncovered an easy method to fine-tune graphene meta-aerogel structures from an optimizable macro-scale to well-arranged micro-scale configurations.

Laser engineering of GmA meta-structures with interesting properties.

Picture 3. Laser engineering of GmA meta-structures with interesting properties. a Specific weight distributions of GmA after laser etching. The images give specific weights and shapes of different GmA. b a GmA (3.3 cm × 2.7 cm × 1 cm) with an ultralight specific weight of 0.1 mg cm−3 can overcome gravity by relying on electrostatic force. vs Photographs of the GmA (3.3 cm × 2.7 cm × 1 cm) with a specific gravity of 0.1 mg cm−3 before and after 50 compression cycles at 80% strain. D Snapshots of GmAs (0.8 cm × 0.5 cm × 0.8 cm) with different configurations during uniaxial compression, Snapshots of GmAs (0.8 cm × 0.5 cm × 0.8 cm) with different configurations during uniaxial compression, concave shape configuration (GmA−1.2) (top row), blank configuration (GmA) (middle row) and convex shape configuration (GmA+6) (bottom row). e The finite element calculation shows the process of compressing concave shaped samples (GmA−1.2) and convex (GmA+6) configurations, and the color reflects the displacement amplitude distribution. F Variations of the Poisson’s ratio of GmA±n during uniaxial compression. ± represents the positive or negative Poisson’s ratio behavior of GmA. n means the n mm of the major axis of the ellipses in the GmA, representing the changing size of the hole. g The snapshots of the GmA sectional views (0.8 cm × 0.5 cm × 0.8 cm) of the left and right asymmetry configuration and the finite element simulation process during the compression process. h Snapshots of GmA cross-sectional views (0.8 cm × 0.5 cm × 0.8 cm) of upper and lower asymmetry configuration and finite element simulation process during compression process. Source data is provided in the form of a source data file. © Wu, M., Geng, H. et al. (2022).

The 2D frames reinforced with internal one-dimensional nanofibers guaranteed a stable bulk deformation mechanism, leading to a considerable increase in flexibility, durability and rigidity.

The laser-etching approach produced arbitrary graphene meta-aerogel architectures with exceptional properties, including high elasticity, dramatically low specific gravity, and a wide Poisson’s ratio range.

In the compression phase, the interior deformation mechanism of graphene meta-aerogels was constant massive deformation instead of the micro-scale buckling seen in soft graphene aerogels. Therefore, graphene meta-aerogels have outperformed the majority of carbon aerogels due to their excellent durability, stiffness and strength, and complete shape recovery after arbitrary compression.

The proposed technique can introduce polymers and particles into the frame, producing articles with predetermined shapes and functions.

With the development of graphene meta-aerogels with exceptional capabilities, this study paves the way for the future development of versatile aerogels with customizable meta-structures.

Reference

Wu, M., Geng, H. et al. (2022). Superelastic metamaterials based on graphene airgel. Communication Nature, 13. Available at: https://www.nature.com/articles/s41467-022-32200-8

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