Graphene / resin composite material of biomimetic hierarchical cross structure and preparation method thereof

Abstract

The application discloses a graphene / resin composite material with a bionic hierarchical cross structure and a preparation method thereof, relates to the technical field of resin-based composite materials, and discloses the graphene / resin composite material with the bionic hierarchical cross structure, which comprises a resin matrix and a framework in the resin matrix. The framework comprises an upper-layer framework, a middle-layer framework and a lower-layer framework. The upper-layer framework, the middle-layer framework and the lower-layer framework each independently comprises a plurality of parallelly-stacked reduced graphene oxide layers. The reduced graphene oxide layers in the upper-layer framework are parallel to the reduced graphene oxide layers in the lower-layer framework, and the included angle between the reduced graphene oxide layers in the middle-layer framework and the reduced graphene oxide layers in the upper-layer framework is 45 degrees. The graphene / resin composite material with the bionic hierarchical cross structure in the application imitates the cross-layer structure of a snail shell and the "brick mud" structure of a pearl layer, and has high strength and high toughness.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resin-based composite materials, and particularly relates to a graphene / resin composite material with a bionic hierarchical cross structure and a preparation method thereof. BACKGROUND

[0002] Resin-based composite materials have excellent properties such as high specific modulus, high specific strength, corrosion resistance, and the like, and are widely used in fields such as construction engineering, aerospace, rail transportation, and national defense industry. However, due to the high crosslinking density and brittleness of the resin matrix after curing, the resin-based composite material has problems such as high internal stress, low fracture toughness, and sensitivity to microcracks, which limit its further application. Graphene has high strength and toughness and excellent electrical and thermal properties. The introduction of graphene nanofillers into the resin can improve the toughness of the resin matrix, and is an effective way to improve the comprehensive performance of the resin-based composite material.

[0003] The graphene surface has a large number of active groups that can be stably connected to the resin through covalent bonds, improving the interfacial properties between the reinforcement and the matrix and the toughness of the resin matrix. Meanwhile, graphene has excellent thermal and electrical properties, and the addition of an appropriate amount of graphene to the resin can improve the comprehensive performance of the graphene-reinforced resin-based composite material and broaden its application field. Most existing researches modify and functionalize graphene or epoxy resin to improve the dispersion of graphene in the resin and the interfacial properties between the two. However, due to the rich oxygen-containing groups in the resin molecules, graphene is prone to react with them, making it difficult to achieve uniform dispersion of graphene and effectively solve the compatibility problem between the two. Meanwhile, the surface functionalization of graphene is uncontrollable, and the interfacial properties between graphene and the resin matrix are difficult to control, making it impossible to achieve the strength and toughness synergy of the graphene-reinforced resin-based composite material.

[0004] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0005] Based on the deficiencies of the prior art described above, the purpose of the present application is to provide a graphene / resin composite material with a bionic hierarchical cross structure and a preparation method thereof, aiming to solve the problem that graphene-reinforced resin-based composite materials are difficult to have high strength and high toughness.

[0006] The technical scheme of the present application is as follows:

[0007] In a first aspect of the present application, a graphene / resin composite material with a bionic hierarchical cross structure is provided, wherein the graphene / resin composite material with a bionic hierarchical cross structure comprises a resin matrix and a skeleton in the resin matrix.

[0008] The skeleton comprises an upper skeleton, a middle skeleton, and a lower skeleton.

[0009] The upper skeleton, the middle skeleton and the lower skeleton each independently comprise a plurality of parallelly-stacked reduced graphene oxide layers, the reduced graphene oxide layers in the upper skeleton are parallel to the reduced graphene oxide layers in the lower skeleton, and the included angle between the reduced graphene oxide layers in the middle skeleton and the reduced graphene oxide layers in the upper skeleton is 45°.

[0010] Optionally, the plurality of parallelly-stacked reduced graphene oxide layers in the upper skeleton, the middle skeleton and the lower skeleton are connected by mineral bridges, and the mineral bridges comprise reduced graphene oxide.

[0011] Optionally, the mineral bridges further comprise nanomaterials, the nanomaterials are loaded on the reduced graphene oxide, and the nanomaterials comprise nanoparticles and nanofibers.

[0012] Optionally, the plurality of parallelly-stacked reduced graphene oxide layers in the upper skeleton, the middle skeleton and the lower skeleton each comprise a reduced graphene oxide sheet, and the reduced graphene oxide sheet is provided with nanomaterials; the nanomaterials comprise nanoparticles and nanofibers.

[0013] Optionally, the particle size of the nanoparticles is 5-35 nm.

[0014] The diameter of the nanofibers is 10-30 nm, and the length of the nanofibers is 2-8 μm.

[0015] Optionally, the nanoparticles comprise at least one of silicon-based nanoparticles, metal nanoparticles and metal oxide nanoparticles.

[0016] The nanofibers comprise at least one of carbon nanotubes, carbon nanofibers and polymer nanofibers.

[0017] Optionally, the resin matrix comprises at least one of thermoplastic resin and thermosetting resin.

[0018] In a second aspect, the application provides a preparation method of the biomimetic hierarchical cross-structure graphene / resin composite material as described above, and the preparation method comprises the following steps:

[0019] A skeleton and a resin glue solution are provided.

[0020] The resin glue solution is poured on and immersed into the skeleton, and after curing, the biomimetic hierarchical cross-structure graphene / resin composite material is obtained.

[0021] Optionally, the preparation method of the skeleton comprises the following steps:

[0022] A reduced graphene oxide dispersion solution is provided.

[0023] The reduced graphene oxide dispersion liquid is assembled into an upper-layer framework comprising a plurality of reduced graphene oxide layers arranged in parallel and stacked, a middle-layer framework comprising a plurality of reduced graphene oxide layers arranged in parallel and stacked, and a lower-layer framework comprising a plurality of reduced graphene oxide layers arranged in parallel and stacked by using a method of two-way freeze casting combined with freeze drying.

[0024] The reduced graphene oxide layers in the lower-layer framework are arranged at an angle of 0° with the bottom of the mold, the reduced graphene oxide layers in the middle-layer framework are arranged at an angle of 45° with the bottom of the mold, and the reduced graphene oxide layers in the upper-layer framework are arranged at an angle of 0° with the bottom of the mold.

[0025] Optionally, the method for preparing the reduced graphene oxide dispersion liquid comprises the following steps:

[0026] Providing graphene oxide;

[0027] Loading a nanomaterial on the surface of the graphene oxide by using one of a chemical grafting method, a self-growth method, and a solution blending method to obtain graphene oxide loaded with the nanomaterial on the surface;

[0028] Reducing the graphene oxide loaded with the nanomaterial on the surface to obtain reduced graphene oxide loaded with the nanomaterial on the surface;

[0029] Adding a binder, a dispersant, and a rheological agent into water, and then adding the reduced graphene oxide loaded with the nanomaterial on the surface to mix, and removing bubbles by ultrasonic treatment to obtain a reduced graphene oxide dispersion liquid.

[0030] Beneficial effects: The graphene / resin composite material with a biomimetic hierarchical cross structure in the application mimics the cross-layer structure of a snail shell and the “brick mud” structure of a pearl layer. The framework in the graphene / resin composite material with a biomimetic hierarchical cross structure mimics the cross-layer structure of a snail shell, and provides multiple toughening mechanisms, and the cross-layer structure brings stable micro-crack deflection and significantly increased macro-crack propagation path. The reduced graphene oxide layers in the framework and the resin matrix mimic the “brick mud” structure of a pearl layer, and the arrangement of the “brick mud” structure avoids local damage caused by stress concentration due to end cracking. The two aspects work together to significantly improve the toughness and washout resistance of the graphene / resin composite material with a biomimetic hierarchical cross structure, so that the graphene / resin composite material with a biomimetic hierarchical cross structure has high strength and high toughness. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 FIG. 1 is a structural schematic diagram of a graphene / resin composite material with a biomimetic hierarchical cross structure.

[0032] Figure 2A schematic diagram of the structure of the skeleton in the graphene / resin composite material of the bionic hierarchical cross structure.

[0033] Figure 3 (a) is an isometric schematic diagram of the upper skeleton, and (b) is a front view of the upper skeleton.

[0034] Figure 4 A schematic diagram of the graphene / resin composite material of the bionic hierarchical cross structure. Figure 3 (b) is an enlarged view of the A area in (b).

[0035] Figure 5 A schematic diagram of the reduced graphene oxide sheet with nanoparticles and nanofibers loaded on the surface. DETAILED DESCRIPTION

[0036] The present application provides a graphene / resin composite material of a bionic hierarchical cross structure and a preparation method thereof. In order to make the purpose, technical scheme and effect of the present application more clear and definite, the present application is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein is only for the purpose of describing the specific embodiments and is not intended to limit the present application.

[0038] The present application provides a graphene / resin composite material of a bionic hierarchical cross structure, wherein, as shown in Figure 1 and 2 The graphene / resin composite material of the bionic hierarchical cross structure (which is also a graphene reinforced resin-based composite material) comprises a resin matrix 20 and a skeleton 10 in the resin matrix 20.

[0039] The skeleton 10 comprises an upper skeleton 11, a middle skeleton 12 and a lower skeleton 13.

[0040] The upper skeleton 11, the middle skeleton 12 and the lower skeleton 13 each independently comprise a plurality of parallel and stacked reduced graphene oxide layers, the reduced graphene oxide layers 110 in the upper skeleton 11 are parallel to the reduced graphene oxide layers 130 in the lower skeleton 13, and the included angle α between the reduced graphene oxide layers 120 in the middle skeleton 12 and the reduced graphene oxide layers 110 in the upper skeleton 11 is 45°.

[0041] The interlayer spacing between the reduced graphene oxide layers 110, 120, 130 in the upper skeleton 11, the middle skeleton 12 and the lower skeleton 13 can be set according to actual needs, and the size range of the interlayer spacing is 20-200 μm, for example, can be 20 μm, 50 μm, 100 μm, 150 μm or 200 μm, etc.

[0042] In the embodiment, the reduced graphene oxide layers 110, 120, 130 each include a reduced graphene oxide sheet, which can be a single-layer reduced graphene oxide sheet (i.e., single-layer reduced graphene oxide), a few-layer reduced graphene oxide sheet (i.e., few-layer reduced graphene oxide), or a multi-layer reduced graphene oxide sheet (i.e., multi-layer reduced graphene oxide).

[0043] Nature is imitated, and organisms have undergone evolution for millions of years to combine multiple interfaces in a unique way to solve the problem of synergistic strength and toughness by combining multiple levels of structure. The cross-laminated structure of the conch shell brings an external toughening mechanism that acts on multiple size ranges. When subjected to load, the propagation of microcracks, the arrest and deflection of microcracks at rotating interfaces all lead to more energy dissipation. The "brick and mud" structure of the nacre layer is a typical biological structure with multiple interface characteristics and performs excellently in terms of synergistic strength and toughness. The high-strength and high-toughness design of the skeleton composed of reduced graphene oxide in the present application is inspired by the conch shell and the nacre layer.

[0044] Inspired by the conch shell, the overall structure of the skeleton is a cross-laminated structure. The cross-laminated structure of the skeleton brings an external toughening mechanism that acts on multiple size ranges. When subjected to load, the propagation of microcracks, the arrest and deflection of microcracks at rotating interfaces all lead to more energy dissipation. The cross-laminated structure of the skeleton can inhibit unstable catastrophic fracture in the macroscopic dimension, cause crack deflection when subjected to impact, obtain a tortuous crack propagation path, increase load energy dissipation, and thus improve the toughness and impact resistance of the material.

[0045] Inspired by the nacre layer, the resin matrix and the reduced graphene oxide layers in the upper skeleton, the middle skeleton and the lower skeleton constitute a "brick and mud" structure, the reduced graphene oxide layers (or reduced graphene oxide sheets) are "bricks", and the resin matrix is "mud". The "brick and mud" structure avoids local damage due to stress concentration caused by end cracking and performs excellently in terms of synergistic strength and toughness.

[0046] In the present embodiment, the cross-laminated structure of the conch shell and the "brick and mud" structure of the nacre layer are imitated, which can effectively reduce stress concentration and rely on multiple external toughening mechanisms such as crack deflection and crack bridging to enhance the toughness of the material, achieving the synergistic strength and toughness of the graphene / resin composite material with a biomimetic hierarchical cross-structure, which has good application prospects in the field of aerospace.

[0047] Specifically, the reduced graphene oxide layers 110 in the upper layer framework 11 are parallel to the horizontal plane.

[0048] The nacre layer is composed of aragonite layers and organic layers. The nano protrusions on the surface of the aragonite layers, the mineral bridges between the aragonite layers, and the deformability of the organic fiber are all toughening mechanisms for tensile and shear deformation. When the nacre layer is subjected to tensile and shear stress, the aragonite layers slide relative to each other, the nano protrusions on the surface produce an obstacle effect, and the deformation sliding resistance of the material is increased; the mineral bridges strengthen the interface, and when they cannot bear the stress, the mineral bridges break, and the broken bridges will re-contact after the aragonite layers slide a distance, thereby providing sliding resistance; the organic fiber between the aragonite layers has strong adhesion and deformability, which can ensure the adhesion between the aragonite layers under strong stress and avoid stress concentration. Therefore, the nacre layer can simultaneously achieve high strength and high toughness. Based on this, in some embodiments of the present application, the reduced graphene oxide layers in the upper layer framework, the middle layer framework, and the lower layer framework are connected by mineral bridges, and the mineral bridges comprise reduced graphene oxide. That is, the reduced graphene oxide layers in the upper layer framework are connected by mineral bridges, the reduced graphene oxide layers in the middle layer framework are connected by mineral bridges, and the reduced graphene oxide layers in the lower layer framework are connected by mineral bridges.

[0049] As shown in Figure 3 and 4 , the reduced graphene oxide layers 110 in the upper layer framework are connected by mineral bridges 111.

[0050] In the present embodiment, the reduced graphene oxide layers in the upper layer framework, the middle layer framework, and the lower layer framework are connected by mineral bridges (composed of reduced graphene oxide, specifically composed of reduced graphene oxide with nano materials loaded on the surface, and the nano materials include nanoparticles and nanofibers), which can provide sliding resistance when subjected to tensile and shear stress, and after the mineral bridges break, the reduced graphene oxide layers slide, the bridges re-contact and provide an obstacle effect, thereby strengthening the interface.

[0051] In the present application, the interface of the reduced graphene oxide simulates the two interface characteristics of the nacre layer, namely the "nano protrusions" and the "organic fiber". Specifically, the reduced graphene oxide sheets in the reduced graphene oxide layers 110, the reduced graphene oxide layers 120, and the reduced graphene oxide layers 130 are provided with nano materials on the surface; the nano materials include nanoparticles and nanofibers. Specifically as shown in Figure 5As shown, the reduced graphene oxide sheets 114 are provided with nanoparticles 112 and nanofibers 113.

[0052] The nanoparticles serve as "nano-protrusions" interface features, and the nanofibers serve as "organic fiber" interface features. The nanoparticles increase the roughness of the surface of the reduced graphene oxide sheets, and provide a certain sliding resistance when the reduced graphene oxide sheets are subjected to tensile and shear stress. The nanofibers bond the reduced graphene oxide sheets together, and can be unfolded under the action of tensile stress, maintain the bonding between the reduced graphene oxide sheets, disperse the internal stress of the material, and thus improve the toughness of the material.

[0053] In the present application, the "brick clay" structure of the nacre is imitated, and three interface features of the nacre (mineral bridge, nanoparticles imitating "nano-protrusions", and nanofibers imitating "organic fiber") are combined, so that the graphene / resin composite material with the biomimetic hierarchical cross structure has toughening mechanisms such as crack deflection, sheet layer pull-out, and fiber bridging, and thus has high toughness and impact resistance.

[0054] In some embodiments, the nanoparticles have a particle size of 5-35 nm (for example, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, or 35 nm, etc.), which imitates the "nano-protrusions" of the nacre. The nanoparticles increase the roughness of the surface of the reduced graphene oxide sheets, and provide a certain sliding resistance when the reduced graphene oxide sheets are subjected to tensile and shear stress. The nanofibers have a diameter of 10-30 nm (for example, 10 nm, 15 nm, 20 nm, 25 nm, or 30 nm, etc.), and a length of 2-8 μm (for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or 8 μm, etc.), which imitates the "organic fiber". The nanofibers bond the reduced graphene oxide sheets together, and can be unfolded under the action of tensile stress, maintain the bonding between the reduced graphene oxide sheets, disperse the internal stress of the material, and thus improve the toughness of the material.

[0055] In some embodiments, the nanoparticles include at least one of silicon-based nanoparticles, metal nanoparticles, and metal oxide nanoparticles, but are not limited thereto.

[0056] In some embodiments, the silicon-based nanoparticles include, but are not limited to, at least one of silicon dioxide (SiO2) nanoparticles and silicon carbide (SiC) nanoparticles.

[0057] In some embodiments, the metal nanoparticles include, but are not limited to, at least one of silver (Ag) nanoparticles, copper (Cu) nanoparticles, and the metal oxide nanoparticles include, but are not limited to, at least one of ferriferrous oxide (Fe3O4), maghemite colloid (γ-Fe2O3). When these nanoparticles are loaded on the reduced graphene oxide layer, the electromagnetic shielding performance of the graphene / resin composite of the biomimetic hierarchical cross-structure can be improved while being toughened.

[0058] In some embodiments, the metal oxide can further include at least one of zinc oxide (ZnO) nanoparticles, barium titanate (PbTiO3) nanoparticles, lead titanate (PbTiO3) nanoparticles, and thus the graphene / resin composite of the biomimetic hierarchical cross-structure can be endowed with certain piezoelectric effect.

[0059] In some embodiments, the nanofiber includes, but is not limited to, at least one of carbon nanotubes, carbon nanofibers, and polymer nanofibers.

[0060] In some embodiments, the resin matrix includes at least one of thermoplastic resin and thermosetting resin.

[0061] In some embodiments, the thermoplastic resin includes, but is not limited to, at least one of epoxy resin, polyester resin, vinyl resin, and bismaleimide resin.

[0062] In some embodiments, the thermosetting resin includes, but is not limited to, polyimide.

[0063] The embodiment of the present application further provides a preparation method of the graphene / resin composite of the biomimetic hierarchical cross-structure as described above, and the preparation method includes the following steps:

[0064] S1, providing a skeleton and a resin glue solution;

[0065] S2, pouring the resin glue solution on the skeleton and immersing the resin glue solution into the skeleton, and obtaining the graphene / resin composite of the biomimetic hierarchical cross-structure after curing.

[0066] In step S1, in some embodiments, the preparation method of the skeleton includes the following steps:

[0067] S11, providing a reduced graphene oxide dispersion solution;

[0068] S12, assembling the reduced graphene oxide dispersion solution into an upper skeleton including a plurality of parallel layers of stacked reduced graphene oxide layers, a middle skeleton including a plurality of parallel layers of stacked reduced graphene oxide layers, and a lower skeleton including a plurality of parallel layers of stacked reduced graphene oxide layers by using a two-way freeze casting method combined with freeze drying.

[0069] S13, according to the reduced graphene oxide layer in the lower skeleton and the mold bottom is 0 ° angle, the reduced graphene oxide layer in the middle skeleton and the mold bottom is 45 ° angle, the reduced graphene oxide layer in the upper skeleton and the mold bottom is 0 ° angle, the lower skeleton, the middle skeleton and the upper skeleton are stacked in the mold in turn, and the skeleton is obtained.

[0070] The application adopts bidirectional freeze casting technology to assemble reduced graphene oxide into a three-dimensional structure skeleton, and then pours resin matrix into the skeleton (or the resin matrix is immersed in the skeleton while the resin matrix is wrapped outside the skeleton), effectively solving the problem of uneven dispersion of traditional graphene and the problem of difficult control of the interface performance between graphene and resin matrix, which leads to the problem that graphene reinforced resin matrix composite is difficult to have high strength and high toughness.

[0071] In step S11, in some embodiments, the preparation method of the reduced graphene oxide dispersion liquid comprises the following steps:

[0072] S111, providing graphene oxide (which can be single-layer graphene oxide, few-layer graphene oxide or multi-layer graphene oxide, corresponding to single-layer reduced graphene oxide, few-layer reduced graphene oxide or multi-layer reduced graphene oxide);

[0073] S112, loading nanomaterials on the surface of the graphene oxide by using one of chemical grafting method, self-growth method and solution blending method (for specific selection, see the above description), to obtain graphene oxide loaded with nanomaterials on the surface;

[0074] S113, reducing the graphene oxide loaded with nanomaterials on the surface to obtain reduced graphene oxide loaded with nanomaterials on the surface;

[0075] S114, adding a binder, a dispersant and a rheological agent into water, and then adding the reduced graphene oxide loaded with nanomaterials on the surface to mix, and removing bubbles by ultrasonic, to obtain a reduced graphene oxide dispersion liquid.

[0076] In step S114, in some embodiments, the binder comprises at least one of polyvinyl alcohol (PVA) and polyethylene glycol (PEG), but is not limited thereto.

[0077] In some embodiments, the dispersant comprises at least one of an anionic dispersant, a non-ionic dispersant and a high molecular dispersant, but is not limited thereto.

[0078] In some embodiments, the rheological agent comprises at least one of an organic rheological agent, but is not limited thereto.

[0079] In step S12, in some embodiments, the step of preparing the upper layer framework specifically comprises:

[0080] A square tube-shaped mold is adhered to the surface of a copper sheet, a polydimethylsiloxane (PDMS) wedge with an inclined angle is prepared at the bottom of the mold, so that the included angle between the upper surface of the PDMS wedge and the copper sheet is 20°, the reduced graphene oxide dispersion liquid is placed in the square tube-shaped mold containing the PDMS wedge, and then placed on the surface of a cold source at a temperature of -90°C to -30°C for bidirectional freeze casting, and then placed in a freeze dryer for drying for 72 hours to obtain the upper layer framework (during bidirectional freeze casting, mineral bridges are formed between the several reduced graphene oxide layers constituting the upper layer framework). Then the same method is used to obtain the middle layer framework and the lower layer framework.

[0081] In step S13, the mold is a silica gel mold, and specifically, the bottom of the silica gel mold is parallel to the horizontal plane. The middle layer framework is cut so that the reduced graphene oxide layer therein forms an angle of 45° with the bottom of the silica gel mold.

[0082] The application is further described below through specific examples.

[0083] Example 1

[0084] The embodiment provides a preparation method of a graphene / resin composite material with a biomimetic hierarchical cross structure, comprising the following steps:

[0085] The few-layer graphene oxide is modified by using 3-aminopropyltriethoxysilane (APTES), 0.2 g of graphene oxide powder and 3 wt% (3% of the mass of the mixture liquid composed of graphene oxide powder, APTES and ethanol) of APTES are dispersed in 100 mL of ethanol, stirred for 3 h, washed and centrifuged with deionized water and ethanol, and then dried at 60°C to obtain the modified graphene oxide powder.

[0086] The 0.15 g of modified graphene oxide powder is dispersed in 25 mL of a 2 mol / L citric acid solution for protonation treatment, 40 mL of a 3 wt% sodium silicate solution is slowly added dropwise at 80°C, and then aged for 24 hours, centrifuged, washed with deionized water and ethanol, and dried at 60°C to obtain the graphene oxide loaded with silica nanoparticles (with an average particle size of 7.3 nm).

[0087] The surface of the graphene oxide loaded with silica nanoparticles and the commercial amino-functionalized multi-walled carbon nanotubes is dispersed in 300 mL of deionized water at a mass ratio of 2:1, the solution system is adjusted to pH 2.5 with hydrochloric acid, and then the solution is acidified and left to stand for 6 hours. After centrifugation, the solution is washed with deionized water and ethanol, and then dried at 60°C to obtain graphene oxide loaded with silica nanoparticles and amino-functionalized carbon nanotubes (diameter 10-20 nm, length 2-8 μm).

[0088] The graphene oxide loaded with silica nanoparticles and amino-functionalized carbon nanotubes is reduced by the unsaturated water vapor method. Specifically, 0.25 g of graphene oxide loaded with silica nanoparticles and amino-functionalized carbon nanotubes and 25 μL of water are added to the inner liner of a reaction kettle, and the reaction kettle is placed in a 150°C oven for 10 hours. After natural cooling to room temperature, reduced graphene oxide loaded with silica nanoparticles and amino-functionalized carbon nanotubes (which is a few-layer reduced graphene oxide) is obtained.

[0089] A square copper sheet is used as a cold source surface, and a square tubular mold of a certain height is adhered to the copper sheet. The square tubular mold and the copper sheet are tilted as a whole at an angle of 20° (the angle between the copper sheet and the bottom horizontal plane is 20°), and the PDMS solution is poured into the mold so as to just cover the surface of the copper sheet. Then, the mold is placed in an 80°C oven for 2 hours to obtain a mold with a PDMS wedge (the angle between the upper surface of the PDMS wedge and the copper sheet is 20°).

[0090] The reduced graphene oxide loaded with silica nanoparticles and amino-functionalized carbon nanotubes, PVA, KYC9366 dispersant (Kewin Chemicals), and KYC426 rheological agent (Kewin Chemicals) are dissolved in deionized water, wherein the concentration of the reduced graphene oxide loaded with silica nanoparticles and amino-functionalized carbon nanotubes is 5 mg / mL, the concentration of PVA is 5 mg / mL, the concentration of the KYC9366 dispersant is 5 mg / mL, and the concentration of the KYC426 rheological agent is 0.075 mg / mL. The solution is stirred uniformly, and ultrasonic treatment is performed for 10 minutes to remove air bubbles, thereby obtaining a reduced graphene oxide dispersion (in which the surface of the reduced graphene oxide sheets is loaded with silica nanoparticles and amino-functionalized carbon nanotubes).

[0091] The low-temperature reaction bath is cooled to -90°C in advance, the reduced graphene oxide dispersion is placed in the mold with the PDMS wedge inside, and then the mold is placed on the cold source surface at a temperature of -90°C for bidirectional freeze casting. After the reduced graphene oxide dispersion is completely frozen, the mold is removed by placing the mold in a refrigerator at -20°C. Then, the mold is dried in a freeze dryer for 72 hours to obtain an upper-layer skeleton. In the same way, a middle-layer skeleton and a lower-layer skeleton are obtained.

[0092] A silica gel mold (bottom is horizontal) is provided, and the reduced graphene oxide layer in the lower skeleton is at 0° to the bottom of the silica gel mold, the reduced graphene oxide layer in the middle skeleton is at 45° to the bottom of the silica gel mold (the middle skeleton is cut in advance so that the reduced graphene oxide layer therein is at 45° to the bottom of the silica gel mold), the reduced graphene oxide layer in the upper skeleton is at 0° to the bottom of the silica gel mold, and the lower skeleton, the middle skeleton and the upper skeleton are sequentially stacked in the mold to obtain a skeleton.

[0093] The epoxy resin (specifically, epoxy resin 862), methylhexahydrophthalic anhydride (MHHPA) and 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30) are mixed in a mass ratio of 100:100:1 to prepare an epoxy resin precursor glue solution, the prepared skeleton is poured with the epoxy resin glue solution under vacuum and at 80°C, and the skeleton is soaked in the epoxy resin glue solution for 1 hour, then cured at 100°C for 2 hours, and then cured at 150°C for 2 hours to obtain a biomimetic hierarchical cross-structure graphene / resin composite material.

[0094] In summary, the present application simulates the cross-layer structure of the shell of a snail and the "brick mud" structure of a pearl layer to provide a high-strength and high-toughness biomimetic hierarchical cross-structure graphene / resin composite material and a preparation method thereof. The high-strength and high-toughness biomimetic hierarchical cross-structure graphene / resin composite material is mainly composed of a skeleton composed of reduced graphene oxide and a resin matrix, wherein the skeleton composed of reduced graphene oxide as a whole simulates the cross-layer structure of the shell of a snail to provide various external toughening mechanisms such as crack deflection and expansion, inhibit unstable catastrophic fracture from the microscale to the macroscale, and improve the toughness and impact resistance. Mineral bridges composed of reduced graphene oxide exist between the reduced graphene oxide layers in the upper skeleton, the middle skeleton and the lower skeleton, and the layered structure causes the crack to expand along the reduced graphene oxide layer and the resin layer, resulting in interface debonding and crack deflection at the interface, greatly extending the crack propagation path and consuming more fracture energy; the mineral bridges strengthen the interface and can provide sliding resistance when subjected to tensile and shear stress. The reduced graphene oxide layer has a more fine "brick mud" structure, and the reduced graphene oxide sheet is loaded with nanomaterials to provide various interface toughening mechanisms, hinder the sliding between the reduced graphene oxide layers, maintain the adhesion between the layers, and further improve the toughening effect and strength. The biomimetic hierarchical cross-structure graphene / resin composite material provided by the present application has high strength and high toughness, improves the impact resistance of traditional resin-based composite materials, and can realize the multifunctionality of the material, thereby providing a new idea for the synergistic design of a new structure-function integrated composite material.

[0095] It is to be understood that the application is not limited to the examples described above, which can be modified or adapted in several ways by those skilled in the art without departing from the scope of the present application, as defined by the appended claims.

Claims

1. Graphene / resin composite of biomimetic hierarchical cross structure, characterized in that, The graphene / resin composite material of the biomimetic hierarchical cross structure comprises a resin matrix and a skeleton in the resin matrix; The skeleton comprises an upper skeleton, a middle skeleton and a lower skeleton; Each of the upper skeleton, the middle skeleton and the lower skeleton independently comprises a plurality of parallelly stacked reduced graphene oxide layers, the reduced graphene oxide layers in the upper skeleton are parallel to the reduced graphene oxide layers in the lower skeleton, and the angle between the reduced graphene oxide layers in the middle skeleton and the reduced graphene oxide layers in the upper skeleton is 45°; The plurality of parallelly stacked reduced graphene oxide layers in the upper skeleton, the middle skeleton and the lower skeleton are connected by mineral bridges, and the mineral bridges comprise reduced graphene oxide.

2. The graphene / resin composite of the biomimetic hierarchical cross-structure according to claim 1, characterized in that, The mineral bridges further comprise nanomaterials, the nanomaterials are loaded on the reduced graphene oxide, and the nanomaterials comprise nanoparticles and nanofibers.

3. The graphene / resin composite of the biomimetic hierarchical cross- structure according to claim 1, characterized in that, The plurality of parallelly stacked reduced graphene oxide layers in the upper skeleton, the middle skeleton and the lower skeleton each comprise a reduced graphene oxide sheet, and the reduced graphene oxide sheet is provided with nanomaterials; The nanomaterials comprise nanoparticles and nanofibers.

4. The graphene / resin composite of the biomimetic hierarchical cross-structure according to claim 2 or 3, characterized in that, The particle size of the nanoparticles is 5-35 nm; The diameter of the nanofibers is 10-30 nm, and the length of the nanofibers is 2-8 μm.

5. The graphene / resin composite of the biomimetic hierarchical cross- structure according to claim 3, wherein The nanoparticles comprise at least one of silicon-based nanoparticles, metal nanoparticles and metal oxide nanoparticles; The nanofibers comprise at least one of carbon nanotubes, carbon nanofibers and polymer nanofibers.

6. The graphene / resin composite of the biomimetic hierarchical cross-structure according to claim 1, wherein, The resin matrix comprises at least one of thermoplastic resin and thermosetting resin.

7. A method of preparing a graphene / resin composite of the biomimetic hierarchical cross-structure according to claim 1, characterized by, The method comprises the following steps: providing a skeleton and a resin glue solution; pouring the resin glue solution on and immersing the resin glue solution into the skeleton, and obtaining the graphene / resin composite material of the biomimetic hierarchical cross structure after curing.

8. The production method according to claim 7, characterized by, The method for preparing the skeleton comprises the following steps: providing a reduced graphene oxide dispersion liquid; adopting a method of two-way freeze casting combined with freeze drying to assemble the reduced graphene oxide dispersion liquid into an upper skeleton comprising a plurality of parallelly stacked reduced graphene oxide layers, a middle skeleton comprising a plurality of parallelly stacked reduced graphene oxide layers and a lower skeleton comprising a plurality of parallelly stacked reduced graphene oxide layers; stacking the lower skeleton, the middle skeleton and the upper skeleton in the mold in sequence according to that the reduced graphene oxide layers in the lower skeleton form a 0° angle with the bottom of the mold, the reduced graphene oxide layers in the middle skeleton form a 45° angle with the bottom of the mold, and the reduced graphene oxide layers in the upper skeleton form a 0° angle with the bottom of the mold, to obtain the skeleton.

9. The production method according to claim 8, characterized by, The method for preparing the reduced graphene oxide dispersion liquid comprises the following steps: providing graphene oxide; adopting one of a chemical grafting method, a self-growth method and a solution blending method to load nanomaterials on the surface of the graphene oxide, to obtain graphene oxide with nanomaterials loaded on the surface; reducing the graphene oxide with nanomaterials loaded on the surface to obtain reduced graphene oxide with nanomaterials loaded on the surface; and The binder, dispersant and rheological agent are added into water, and then the reduced graphene oxide on which the nanomaterial is surface-loaded is added for mixing, and air bubbles are removed by ultrasonic treatment to obtain a reduced graphene oxide dispersion liquid.

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