A high modulus high resilience lightweight material and method of making same

Abstract

This invention proposes for the first time a high-modulus, high-resilience lightweight material. It introduces a dissipative cavity with nanoscale wall thickness within a high-density graphene honeycomb framework prepared by freeze-drying using solvent plasticizing foaming technology. This nanoscale wall thickness provides strong resistance to deformation and allows for reversible elastic buckling deformation along the direction perpendicular to the load under load, thus exhibiting high strain recoverability at high modulus. The prepared lightweight graphene bulk material shows great potential for multiple protections against electromagnetic radiation, high temperatures, and noise pollution, and can be used as a multifunctional structural material in engineering applications.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, specifically relating to a high-modulus, high-resilience lightweight material and its preparation method. Background Technology

[0002] Lightweight honeycomb materials possess abundant porosity and high specific stiffness, leading to their wide application in structural engineering, energy absorption, thermal insulation, and catalyst loading. In practical applications, high stiffness is a prerequisite for engineering materials, while elastic recoverability determines the structural reliability and long-term stability of the material. However, due to the strong correlation between stiffness and wall thickness, thick support walls of high-stiffness materials are prone to structural failure due to a sharp increase in internal tension during deformation, especially for brittle inorganic materials. Therefore, high-stiffness monolithic structures inevitably experience abrupt failure deformation under overload, and the structural deformation limit is very small.

[0003] The geometric design of structural units has become a major strategy for improving the mechanical properties of lightweight materials. In traditional honeycomb structures, a small wall thickness to size ratio is a typical feature that ensures high recoverability through out-of-plane elastic buckling under large deformations. Furthermore, arched layered structures can easily transform into many small arches under large deformations, generating more elastic buckling units and thus exhibiting excellent elasticity. However, this design concept is only applicable to low-density porous structures and cannot meet the application requirements of high elastic modulus. For high-stiffness materials, researchers have prepared various high-modulus micro / nano lattices by precisely controlling lattice topology and assembling complex hierarchical structures from micro to macro scales. Octahedral trusses, as a classic tensile-dominated structural lattice unit, have superior specific stiffness compared to other lightweight materials. However, this strategy comes at the cost of recoverable strain below 20%. To date, the conflict between high stiffness and structural recoverability remains unresolved in existing structural paradigms. Summary of the Invention

[0004] To overcome the aforementioned technical deficiencies, this invention provides a high-modulus, high-resilience lightweight material and its preparation method, thereby resolving the conflict between high stiffness and structural recoverability in the prior art. It can achieve a 200% increase in Young's modulus, reaching over 10 MPa, with a maximum recoverable strain of 90%, and a deformation recovery rate of over 50% after 1000 cycles of compression with 60% strain.

[0005] On one hand, the high-modulus, high-resilience lightweight material described in this application includes a graphene honeycomb aerogel framework with a pore size of 100 μm or more. The pore walls of the honeycomb aerogel framework are composed of multiple graphene layers, and continuous dissipative cavities are formed between the graphene layers and oriented along the pore walls. The two walls of the dissipative cavities are arched outwards, with a cavity diameter of less than 30 μm and a cavity wall thickness of less than 100 nm. The graphene aerogel honeycomb framework, as a high-mechanical-efficiency structure for microporous assembly, provides high mechanical stiffness; the dissipative cavities with nanometer-thickness in the pore walls allow for large elastic buckling deformation along the perpendicular load direction, exhibiting strong resistance to deformation, thus enabling the material to possess both high modulus and high resilience. In this invention, the dissipative cavity is quasi-ellipsoidal in shape, and its orientation direction is the major axis direction of the ellipsoid. The orientation of the dissipative cavity along the pore walls means that the major axis direction of the dissipative cavity is substantially along the pore wall direction of the aerogel framework in which it is located. Figure 8 As shown in the figure. This orientation structure further provides continuous support and a rapid stress diffusion channel for multiple connected dissipation cavities, improving the modulus and avoiding stress concentration.

[0006] The multi-scale structure from the aforementioned cellular network to the continuous dissipative cavity nanowall further exhibits high electromagnetic shielding effect, good noise absorption and low thermal conductivity, which is conducive to realizing multiple protection potential in a wide range of engineering applications such as energy-saving buildings, precision instruments and advanced equipment.

[0007] In embodiments of the present invention, the density of the lightweight material is 60-200 mg·cm³. -3 .

[0008] On the other hand, this application also provides a method for preparing the above-mentioned high modulus and high resilience lightweight material, including:

[0009] (1) A water dispersion of graphene oxide with a concentration of 60-200 mg / g was freeze-dried at -18℃ for more than 8 hours to obtain a honeycomb aerogel framework. The high concentration of graphene oxide dispersion ensured the number of graphene oxide assembly units in the pore wall. The freezing environment at -18℃ formed large ice crystal size, which ultimately ensured the micron-sized pore wall and the hundred-micron-sized honeycomb pore diameter of the aerogel.

[0010] (2) The obtained aerogel is placed in a foaming agent solution for foaming. The foaming agent solution is a hydrazine hydrate solution with a mass fraction of less than 30%. The foaming conditions are room temperature, and the foaming time is generally 4-12 hours. The solvent provides plasticity to effectively form a continuous dissipation cavity while avoiding the destruction of the honeycomb pore framework. After foaming, the aerogel is replaced with ethanol solvent and dried at normal pressure to finally obtain a high modulus and high resilience bulk material. The effective foaming method ensures the double-arch structure of the dissipation cavity, and the dissipation cavity is continuous, providing continuous support and a fast stress diffusion channel.

[0011] Furthermore, the graphene oxide can be prepared using the Hummers method, a modified Hummers method, or electrochemical methods. The graphene oxide sheet size suitable for this invention is 10–80 μm.

[0012] Furthermore, after foaming, chemical or thermal reduction is performed. The reducing agent for chemical reduction is one of commonly used reducing agents such as hydroiodic acid, hydrazine hydrate, vitamin C, and ethylenediamine, with the hydroiodic acid / acetic acid reduction system being preferred.

[0013] The beneficial effects of this invention are as follows:

[0014] (1) By embedding the graphene dissipation cavity structure into the freeze-dried skeleton, the Young's modulus can be increased by 200%, reaching more than 10 MPa, and the maximum recoverable strain can reach 90%. After 1000 cycles of compression with 60% strain, the deformation recovery rate can reach more than 50%.

[0015] (2) Due to the maturity of freeze-drying technology, it is conducive to the large-scale use of this high-modulus and high-resilience nanomaterial.

[0016] (3) The solvent plasticizing foaming process used is relatively simple and does not require special drying process, which is conducive to large-scale preparation.

[0017] (4) The lightweight material prepared has multiple functions. Its shielding effectiveness can reach 99dB in the 2-18GHz frequency band, its average sound absorption coefficient can reach 0.66 in the 450-6000kHz band, and its thermal conductivity at room temperature can reach as low as 26mW. Therefore, it can be used in a variety of functional protection places, such as electromagnetic shielding, sound absorption and heat insulation. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope (SEM) diagram of the lightweight material prepared in Example 1, showing its dissipation cavity morphology and structure. Figure 8 The indications are consistent.

[0019] Figure 2 The curve of the lightweight material prepared in Example 1 after 1000 cycles at 60% compressive strain is shown.

[0020] Figure 3 This is an in-situ electron microscope image showing the structural changes of the dissipation cavity during compression.

[0021] Figure 4 The image shows the physical sample of the lightweight material prepared for Comparative Example 1.

[0022] Figure 5 This is a schematic diagram of an electron microscope scan of the lightweight honeycomb material prepared for Comparative Example 2.

[0023] Figure 6The curve of the lightweight honeycomb material prepared in Comparative Example 2 after 1000 cycles at 60% compressive strain is shown.

[0024] Figure 7 This is an in-situ electron microscope image showing the structural changes of the honeycomb pore wall under compression without a dissipation cavity.

[0025] Figure 8 This diagram illustrates the formation of dissipation cavities in the pore walls of a honeycomb aerogel framework. The left image shows the pore wall before foaming, and the right image shows the pore wall after foaming. The diagram shows that the long axis of the dissipation cavity is along the pore wall direction of the aerogel framework in which it is located. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments. However, the scope of protection of the present invention is not limited thereto.

[0027] In the following examples, the low-concentration hydrazine hydrate solution was obtained by diluting an 80% hydrazine hydrate solution by proportion.

[0028] Example 1

[0029] A 90 mg / ml aqueous graphene oxide dispersion was frozen at -18°C for 8 hours, followed by vacuum drying. The dried aerogel framework was then foamed in 30 wt% hydrazine hydrate for 5 hours, and finally air-dried to obtain a high-performance lightweight material with the following microstructure: Figure 1 As shown, the lightweight material has a honeycomb aerogel framework. The pore walls of the honeycomb aerogel framework are composed of multiple layers of graphene. The multiple layers of graphene in the pore walls form continuous cavities (dissipation cavities) due to foaming. The cavity of the dissipation cavity is quasi-ellipsoidal in shape along the orientation of the framework wall, and the two walls of the dissipation cavity are arched outward.

[0030] Testing revealed that the graphene honeycomb aerogel framework has pore sizes exceeding 100 μm, with the dissipative cavity structure having a diameter of approximately 15 μm and a wall thickness of approximately 40 nm. The resulting aerogel has a density of 85 mg / cm³. 3 The Young's modulus of the obtained aerogel is 0.95 MPa.

[0031] After 1000 compression recovery cycles at 60% strain, it can recover 75% of its deformation. Its compression cycle curve is shown below. Figure 2 As shown, the microstructure changes of the honeycomb pores and layered dissipation cavity walls during compression are as follows: Figure 3As shown in the figure, within a single wall of a honeycomb cell, there are numerous continuous arched dissipation cavities with nanoscale wall thicknesses serving as load units. Compression exerts pressure on these dissipation cavities. On one hand, each arched cell deforms into several smaller arched structures to dissipate stress, and can immediately spring back to its original shape after the load is released. On the other hand, the continuous layered arched cells can promptly disperse the load, preventing stress concentration and subsequent fracture, and the continuous cells support each other to improve the overall structural stiffness.

[0032] Example 2

[0033] A 60 mg / ml aqueous graphene oxide dispersion was frozen at -10°C for 12 h, followed by vacuum drying. The dried aerogel skeleton was then foamed in 20 wt% hydrazine hydrate for 6 h and naturally dried to obtain a high-performance lightweight material. Characterization showed that the lightweight material has a honeycomb aerogel skeleton, the pore walls of which are composed of multiple graphene layers. The multiple graphene layers in the pore walls form continuous cavities (dissipative cavities) due to the foaming effect. The dissipative cavities are quasi-ellipsoidal in shape and oriented along the skeleton wall, and the two walls of the dissipative cavities are arched outward.

[0034] Testing revealed that the graphene honeycomb aerogel framework has a pore size exceeding 100 μm, while the dissipation cavity structure has a diameter of approximately 20 μm and a wall thickness of 32 nm. This lightweight material has a density of 57 mg / cm³. 3 It has a Young's modulus of 0.48 MPa and can recover 85% of its deformation after 1000 compression recovery cycles at 60% strain.

[0035] Example 3

[0036] A 200 mg / ml aqueous graphene oxide dispersion was frozen at -30°C for 8 hours, followed by vacuum drying. The dried aerogel skeleton was then foamed in 10 wt% hydrazine hydrate for 6 hours and naturally dried to obtain a high-performance lightweight material. Characterization showed that the lightweight material has a honeycomb aerogel skeleton, the pore walls of which are composed of multiple graphene layers. The multiple graphene layers in the pore walls form continuous cavities (dissipative cavities) due to the foaming effect. The dissipative cavities are quasi-ellipsoidal in shape and oriented along the skeleton wall, and the two walls of the dissipative cavities are arched outward.

[0037] Testing revealed that the graphene honeycomb aerogel framework has a pore size exceeding 100 μm, while the dissipation cavity structure has a diameter of approximately 30 μm and a wall thickness of 58 nm. This lightweight material has a density of 190 mg / cm³. 3 It has a Young's modulus of 12 MPa and can recover 60% of its deformation after 1000 compression recovery cycles at 60% strain.

[0038] Example 4

[0039] A 100 mg / ml aqueous graphene oxide dispersion was frozen at -20°C for 8 hours, followed by vacuum drying. The dried aerogel skeleton was then foamed in 10 wt% hydrazine hydrate for 8 hours and naturally dried to obtain a high-performance lightweight material. Characterization showed that the lightweight material has a honeycomb aerogel skeleton, the pore walls of which are composed of multiple graphene layers. The multiple graphene layers in the pore walls form continuous cavities (dissipative cavities) due to the foaming effect. The dissipative cavities are quasi-ellipsoidal in shape and oriented along the skeleton wall, and the two walls of the dissipative cavities are arched outward.

[0040] Tests showed that the graphene honeycomb aerogel skeleton has a pore size of over 100 μm, the dissipation cavity structure has a diameter of about 35 μm, and the wall thickness is 50 nm. The lightweight material has a density of 88 mg / cm3, a Young's modulus of 1.2 MPa, and can recover 70% of its deformation after 1000 compression recovery cycles at 60% strain.

[0041] Comparative Example 1

[0042] Similar to Example 1, but with the concentration of hydrazine hydrate foaming agent replaced at 85%, the resulting sample could not be molded; the violent foaming caused its structure to collapse. The macroscopic sample is shown below. Figure 4 As shown.

[0043] Comparative Example 2

[0044] Similar to Example 1, the freeze-dried graphene oxide aerogel was directly chemically reduced, wherein the honeycomb pore size was 210 μm and the wall thickness was 1.2 μm, and its microstructure was as follows. Figure 5 As shown, the Young's modulus is 0.5 MPa, and after 1000 compression recovery cycles at 60% strain, it can recover 15% of its original deformation. Its compression cycle curve is shown below. Figure 6 As shown, the changes in the microstructure of the honeycomb pores and pore walls during compression are as follows: Figure 7 As shown, the thick honeycomb pore walls cannot dissipate stress in time, and are prone to brittle fracture due to the sharp increase in internal tension during deformation. After the load is released, the structure cannot return to its original state.

[0045] Comparative Example 3

[0046] A 90 mg / ml aqueous graphene oxide dispersion was frozen at -180°C in liquid nitrogen, followed by vacuum drying. The freeze-dried graphene oxide aerogel was then directly chemically reduced. The honeycomb pore size was 60 μm, the wall thickness was 45 nm, the Young's modulus was 0.32 MPa, and it could recover 20% of its deformation after 1000 compression recovery cycles at 60% strain.

[0047] Comparative Example 4

[0048] A 60 mg / ml aqueous graphene oxide dispersion was frozen at -180°C in liquid nitrogen, followed by vacuum drying. The freeze-dried graphene oxide aerogel was then foamed in 30 wt% hydrazine hydrate for 5 h. After natural drying, its pore structure collapsed.

Claims

1. A high-modulus, high-resilience, lightweight material, characterized in that, The invention includes a graphene honeycomb aerogel framework with a pore size of 100 μm or more. The pore walls of the honeycomb aerogel framework are composed of multiple graphene layers, and continuous dissipation cavities are formed between the graphene layers and oriented along the pore walls. The two walls of the dissipation cavities are arched outwards, the cavity diameter is less than 30 μm, and the cavity wall thickness is less than 100 nm.

2. The high modulus, high resilience, lightweight material according to claim 1, characterized in that: Lightweight materials have a density of 60-200 mg·cm³ -3 .

3. The method for preparing a high-modulus, high-resilience lightweight material as described in claim 1, comprising the following steps: Aqueous dispersions of graphene oxide with a concentration of 60-200 mg / g were freeze-dried at -10℃ to -30℃ for more than 8 hours to obtain a honeycomb aerogel framework. The obtained aerogel was placed in a foaming agent solution for foaming, and then dried to obtain a bulk material with nanoscale dissipative cavity walls. The foaming agent solution was a hydrazine hydrate solution with a mass fraction of less than 30%, and the foaming condition was room temperature.

4. The preparation method according to claim 3, characterized in that: The graphene oxide was prepared using the Hummers method, a modified Hummers method, or an electrochemical method.

5. The preparation method according to claim 3, characterized in that: After foaming, it is reduced.

6. The preparation method according to claim 3, characterized in that: The foaming time is 4-12 hours.

7. The preparation method according to claim 3, characterized in that: The diameter of the graphene oxide sheets ranges from 10 to 80 μm.

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