High-strength and high-toughness amorphous graphene film and preparation method thereof

Abstract

The application provides a high-strength and high-toughness amorphous graphene film and a preparation method thereof. By breaking and converting traditional large-size liquid crystal crystal regions in a slurry into small-size micro-crystal regions with uniform sizes and different orientations, uniform microstructure helps uniform transmission and dispersion of external load in the film, avoiding early failure caused by local stress concentration. In addition, disorderly arranged graphene oxide layers can significantly disturb the crack propagation path, force the crack to deflect and branch during the propagation process, and then dissipate the crack tip energy, thereby inhibiting further crack propagation. The structure significantly improves the tensile strength of the film while greatly improving the toughness of the film.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of nanomaterial preparation, and particularly relates to a high-strength and high-toughness amorphous graphene film and a preparation method thereof. BACKGROUND

[0002] The graphene film is a macroscopic two-dimensional material assembled by graphene nanosheet layers, and perfectly inherits the excellent intrinsic properties of graphene, such as extremely high electrical conductivity and thermal conductivity and excellent mechanical strength. These properties make it show great application potential in multiple frontier technology fields, such as being used as a transparent electrode of high-performance flexible electronic devices, a high-efficiency heat dissipation film, a new generation of sensing element and a lightweight high-strength composite material, etc. Therefore, the graphene film is regarded as one of the important basic materials for promoting the development of flexible electronics, energy devices and intelligent systems, and the preparation technology and structure performance regulation thereof have always been the research focus in the field of nanomaterials. However, the current graphene composite film has the defects of large brittleness, weak strength, easy folding and easy breaking, which seriously limits its wide application.

[0003] At present, the mainstream strategy for strengthening the graphene film is to induce the high orientation and ordered arrangement of graphene sheets in the film to obtain a high-crystallinity structure. Although this kind of structure can significantly improve the strength of the film, it is often accompanied by obvious brittleness, which makes it difficult to simultaneously realize high strength and high toughness. SUMMARY

[0004] In view of the problem that the existing graphene film is difficult to simultaneously improve the strength and toughness, the present application provides a preparation method of a high-strength and high-toughness amorphous graphene film. By breaking the traditional large-size liquid crystal domains in the slurry and converting them into small-size microcrystalline domains with uniform size and different orientations, the shrinkage generated in the drying process of the graphene film is controlled, and then the stacking of the sheet layers is inhibited to form an amorphous structure. The amorphous structure can effectively reduce the formation of local defects (such as large-size cavities, agglomerates, etc.), so that the graphene oxide sheet layers are more uniformly distributed in the film. The uniform microstructure is helpful for the uniform transmission and dispersion of external load in the film, avoiding the early failure caused by local stress concentration. In addition, the disordered arrangement of the graphene oxide sheet layers can significantly disturb the crack propagation path, forcing the crack to deflect and branch during the propagation process, thereby dissipating the crack tip energy and inhibiting the further propagation of the crack. Based on the above synergistic effect, the structure can significantly improve the toughness of the film while significantly improving the tensile strength of the film.

[0005] Specifically, the preparation method provided in the present application comprises the following steps: (1) adding an aqueous solution of monovalent cation salt into an aqueous dispersion of graphene oxide, stirring and mixing at room temperature to obtain ion-modified graphene oxide slurry; the average size of the liquid crystal domains in the ion-modified graphene oxide slurry is 15-50 μm; (2) Defoaming the ion-modified graphene oxide slurry obtained in step (1), and then placing the slurry on a substrate with a gap of 1-5 mm between the doctor blade and the substrate, and then uniformly coating and drying the slurry with the doctor blade; (3) Reducing the substrate in step (2) together with the unexfoliated graphene oxide film to obtain a graphene film; (4) Repeatedly immersing and washing the graphene film obtained in step (3) in deionized water and ethanol, and then peeling the graphene film from the substrate after drying to obtain a high-strength and high-toughness amorphous graphene film.

[0006] Further, the concentration of the graphene oxide aqueous dispersion in step (1) is 2 mg / ml to 18 mg / ml, and the concentration of monovalent cations in the ion-modified graphene oxide slurry is 0.005 mol / L-0.04 mol / L.

[0007] Further, the monovalent cation salt in step (1) is one or more of potassium chloride, sodium chloride, ammonium chloride, potassium sulfate, sodium sulfate, ammonium sulfate, and potassium nitrate.

[0008] Further, the stirring speed in step (1) is 100-700 rpm.

[0009] Further, the substrate in step (2) is one of polyethylene terephthalate, polytetrafluoroethylene, polypropylene, and glass.

[0010] The reduction in step (3) can be one or more of hydrazine hydrate vapor reduction, hydrogen iodide solution reduction, vitamin C solution reduction, and thermal reduction.

[0011] The present application also provides a high-strength and high-toughness amorphous graphene film prepared by the above method. The thickness of the film is 5-100 μm.

[0012] As a conventional choice for dispersion and impurity removal, when preparing a graphene oxide (GO) dispersion solution, the present application first dissolves graphene oxide raw material in a solvent, performs ultrasonic dispersion treatment to prepare a graphene oxide solution, and then removes impurities by high-speed centrifugal concentration of the dilute graphene oxide solution to obtain a graphene oxide dispersion solution.

[0013] The present application has the following advantages: 1. Unique amorphous structure graphene film: Through the "ion-induced liquid crystal refinement" strategy, the graphene film with an amorphous structure different from the traditional crystalline structure is obtained by drying and assembling the GO dispersion solution broken by liquid crystals, which provides a new structural design idea for graphene films.

[0014] 2. Synergistic improvement of strength and toughness: The graphene film prepared by the method exhibits significantly enhanced tensile strength and toughness, and the tensile strength of the film can reach 784 MPa, and the toughness can reach 23.0 MJ / m 3. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Surface morphology of the thin film of Example 1; Figure 2 Surface morphology of the thin film of Comparative Example 1; Figure 3 XRD images of the amorphous thin film of Example 1 and the crystalline thin film of Comparative Example 1; Figure 4 Mechanical curves of the amorphous thin film of Example 1 and the crystalline thin film of Comparative Example 1, wherein the red line represents the amorphous thin film and the black line represents the crystalline thin film. DETAILED DESCRIPTION

[0016] The following examples are given to further illustrate the present application and are not intended to limit the scope of the present application. Unless otherwise indicated, parts and percentages in the following examples are by weight.

[0017] The raw materials used in the present application are all conventional commercially available products unless otherwise specified; the methods used in the present application are all conventional methods in the art unless otherwise specified.

[0018] The following examples are given to further illustrate the present application and are not intended to limit the scope of the present application. Unless otherwise indicated, parts and percentages in the following examples are by weight.

[0019] It should be apparent that the described embodiments are only some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative effort shall fall within the scope of the present application.

[0020] The terms used in the embodiments of the present application are merely for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0021] Example 1 (1) Preparation of 12.5 mg / ml graphene oxide (GO) aqueous dispersion (2) Preparation of 0.1 mol / L potassium chloride aqueous solution (3) The graphene oxide dispersion obtained in step 1 and the potassium chloride aqueous solution obtained in step 2 were mixed in a volume ratio of 4:1 to obtain an ion-modified GO dispersion. The concentration of graphene oxide in the spinning solution was 10 mg / ml, and the concentration of potassium chloride was 0.02 mol / L. Polarized light microscopy observation showed that the average size of the liquid crystal domains in the ion-modified spinning solution was reduced to 15-50 μm.

[0022] (4) Prepare graphene oxide film by coating and drying the ion-modified GO dispersion prepared in step 3: After mixing and degassing the GO dispersion, place it on a polyethylene terephthalate (PET) substrate, keep the gap between the scraper and the substrate 1 mm, coat the composite solution evenly with the scraper, and dry it in an environment of 25°C and 30% humidity.

[0023] (5) The substrate, together with the unpeeled graphene oxide film, was placed in a reducing atmosphere and reduced at 85°C to obtain a graphene film. The reducing atmosphere was hydrazine hydrate vapor.

[0024] (6) After reduction, the film is repeatedly soaked and cleaned with deionized water and ethanol. After drying, it is slowly peeled off from the substrate to obtain the graphene film.

[0025] like Figure 1 As shown, the surface of the prepared graphene film has relatively fine wrinkles, which disrupts the orderly stacking of GO. The prepared film is as follows: Figure 3 As shown, it is amorphous, with a tensile strength of 784 MPa, an elongation at break of 5.88%, and a toughness of 23.0 MJ / m. 3 .

[0026] Example 2 The procedure was the same as in Example 1, except that the monovalent cationic salt was replaced with ammonium sulfate. The resulting film exhibited a tensile strength of 666 MPa, an elongation at break of 5.48%, and a toughness of 18.2 MJ / m. 3 .

[0027] Example 3 The procedure was the same as in Example 1, except that the concentration of the monovalent cation salt in the ion-modified GO dispersion was increased to 0.04 mol / L. The resulting film exhibited a tensile strength of 656 MPa, an elongation at break of 5.68%, and a toughness of 18.6 MJ / m. 3 .

[0028] Example 4 The procedure was the same as in Example 1, except that the concentration of graphene oxide in the dispersion was increased to 15 mg / ml. The resulting film exhibited a tensile strength of 632 MPa, an elongation at break of 5.28%, and a toughness of 16.7 MJ / m. 3 .

[0029] Example 5 The procedure was the same as in Example 1, except that the distance between the doctor blade and the substrate was adjusted to 2 mm. The resulting film exhibited a tensile strength of 606 MPa, an elongation at break of 5.16%, and a toughness of 15.6 MJ / m. 3 .

[0030] Comparative Example 1 Directly use 10 mg / ml of the aqueous dispersion of graphene oxide to film with the same blade coating conditions as in Example 1, as Figure 2 The obtained film has obvious convex folds on the surface and the stacking condition is obviously increased compared with Example 1.

[0031] The tensile strength of the obtained film is 226 MPa, the elongation at break is 3.76%, and the toughness is 4.2 MJ / m 3 .

[0032] Comparative Example 2 The same operation as in Example 1, only the concentration of monovalent cation salt is increased to 0.06 mol / L, at this time the electrostatic repulsion between graphene oxide layers is too weak to maintain the stability of the system, and the graphene oxide is obviously aggregated into many small pieces, which cannot be formed into a uniform and dense graphene film.

[0033] Comparative Example 3 The same operation as in Example 1, only the concentration of monovalent cation salt is reduced to 0.005 mol / L, at this time the electrostatic repulsion between graphene oxide layers is still strong, and the graphene oxide liquid crystal has no obvious change, and the mechanical properties of the obtained film have no obvious change, the tensile strength is 253 MPa, the elongation at break is 3.88%, and the toughness is 4.9 MJ / m 3 .

[0034] The above examples illustrate the structure, features and effects of the present application, and the above description is only the preferred embodiment of the present application. Any changes made in accordance with the concept of the present application, or equivalent embodiments with equivalent changes, shall be within the scope of the present application.

Claims

1. A method for preparing a high-strength, high-toughness amorphous graphene film, characterized in that, Includes the following steps: (1) Add an aqueous solution of a monovalent cation salt to an aqueous dispersion of graphene oxide and stir at room temperature to obtain an ion-modified graphene oxide slurry; the average size of the liquid crystal region in the ion-modified graphene oxide slurry is 15-50 μm. (2) After degassing the ion-modified graphene oxide slurry obtained in step (1), place it on the substrate, keep the gap between the scraper and the substrate 1-5 mm, spread it evenly with the scraper, and dry it. (3) Reduce the substrate from step (2) together with the unpeeled graphene oxide film to obtain a graphene film; (4) The graphene film obtained in step (3) is repeatedly soaked and cleaned with deionized water and ethanol, dried and peeled off from the substrate to obtain a high-strength and high-toughness amorphous graphene film.

2. The method according to claim 1, characterized in that, The concentration of the aqueous dispersion of graphene oxide in step (1) is 2 mg / ml to 18 mg / ml, and the concentration of monovalent cations in the ion-modified graphene oxide slurry is 0.005 mol / L to 0.04 mol / L.

3. The method according to claim 1, characterized in that, The monovalent cation salt mentioned in step (1) is one or more of potassium chloride, sodium chloride, ammonium chloride, potassium sulfate, sodium sulfate, ammonium sulfate, and potassium nitrate.

4. The method according to claim 1, characterized in that, The stirring speed in step (1) is 100 to 700 rpm.

5. The method according to claim 1, characterized in that, The substrate in step (2) is one of polyethylene terephthalate, polytetrafluoroethylene, polypropylene, and glass.

6. A high-strength, high-toughness amorphous graphene film prepared by the method as described in claim 1.

7. The high-strength, high-toughness amorphous graphene film according to claim 6, characterized in that, Thickness ranges from 5 to 100 μm.

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