A method for preparing graphene based on interlayer stress resonance

Abstract

The application discloses a graphene preparation method based on interlayer stress resonance. Macroscopic mechanical rotation energy is converted into high-frequency and directional stress energy which can precisely act on the van der Waals force between graphite layers through a series of carefully designed physical processes. Under specific rotation conditions, unstable vortex structures (such as Taylor vortex flow) are generated in the confined fluid. When the stress wave formed by the vortex in the viscoelastic fluid is coupled with the intrinsic vibration frequency between the graphite layers, resonance phenomenon is triggered. The resonance can amplify the strain energy between the graphite layers, so that the interlayer van der Waals force is efficiently and selectively overcome under the condition of energy input far lower than the in-plane fracture threshold of carbon-carbon bond, and the graphene is exfoliated to obtain large and few-layer graphene.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of graphene material preparation, and particularly relates to a graphene preparation method based on interlayer stress resonance. BACKGROUND

[0002] Preparation of high-quality graphene with both few-layer and large-size characteristics is crucial for promoting its practical application in high-end technology fields. Few-layer (especially single-layer or double-layer) graphene can maximize the exhibition of its excellent electrical, thermal and mechanical properties, such as extremely high carrier mobility and thermal conductivity; while continuous thin films with large size (centimeter level or even larger) can meet the stringent requirements of microelectronic devices, optoelectronic devices (such as transparent conductive electrodes, high-speed transistors) and composite materials for material uniformity, integrity and processability. Avoiding the grain boundary defects between small flake-shaped graphenes is the key to realizing high performance and high reliability. Existing physical exfoliation methods (such as ultrasonic and ball milling) are essentially based on random and high-energy impact or friction, which is rough and uncontrollable, and is prone to introduce lattice defects and result in small flake size. SUMMARY

[0003] In view of the difficulty in balancing size and layer number in the preparation of graphene in the prior art, the application provides a graphene preparation method based on interlayer stress resonance. Macroscopic mechanical rotation energy is converted into high-frequency and directional stress energy capable of precisely acting on the interlayer van der Waals force of graphite through a series of carefully designed physical processes. Under specific rotation conditions, unstable vortex structures (such as Taylor vortex) are generated in the confined fluid. When the stress wave formed by the vortex in the viscoelastic fluid is coupled with the intrinsic vibration frequency of the interlayer of graphite, resonance phenomenon is induced. Resonance can amplify the strain energy between the graphite layers, so that the interlayer van der Waals force is overcome efficiently and selectively under the condition of energy input far lower than the in-plane fracture threshold of carbon-carbon bond, so that the graphene is exfoliated to obtain large-size and few-layer graphene.

[0004] Specifically, a non-Newtonian fluid with viscoelasticity is used as a dispersant to obtain large-size few-layer graphene from graphite in a coaxial rotating microcavity reactor;

[0005] The non-Newtonian fluid with viscoelasticity has a Deborah number De>1; wherein De= λω, λ is the relaxation time of the fluid, and ω is the angular velocity of the inner rotating body;

[0006] The coaxial rotating microcavity reactor comprises an inner rotating body and an outer static shell, and a ring-shaped microcavity is formed between the inner rotating body and the outer static shell, and the diameter-width ratio Γ of the ring-shaped microcavity satisfies: Γ ≤ 0.1,

[0007] ;

[0008] wherein Ri R is the radius of the inner rotating body o R is the radius of the inner rotating body

[0009] Further, the non-Newtonian fluid with viscoelasticity is a shear-thinning fluid. It is one of polyvinylpyrrolidone, xanthan gum, polyethylene oxide and sodium alginate. The non-Newtonian fluid with viscoelasticity can store and release deformation energy, convert the continuous pulsation generated by the vortex into more intense instantaneous stress pulse, and enhance the peeling driving force; its shear-thinning property is conducive to reducing the viscosity in the high shear zone, reducing energy consumption, and maintaining high viscosity in the low shear zone to ensure uniform suspension of graphite particles. The viscous fluid itself can also effectively wet the graphite surface and penetrate the interlayer, to some extent, play a role in lubrication and wedging, and further reduce the peeling energy barrier.

[0010] Further, the diameter-width ratio Γ satisfies: 0.01 ≤ Γ ≤ 0.1.

[0011] Further, the coaxial rotating microcavity reactor further comprises an online optical monitoring device for monitoring the absorbance of the dispersion system in the microcavity in real time. By monitoring the absorbance change rate dA / dt of the graphite-fluid dispersion system at a specific wavelength, the rotation parameters of the inner rotating body are dynamically adjusted based on the change rate to realize closed-loop control of the peeling process.

[0012] The average particle size of the prepared graphene is not less than 10 μm, the graphene sheet layer is less than 10 layers, and the Raman D / G peak ratio is less than 0.10.

[0013] The present application has the advantages that: by regulating the rotation speed, medium viscosity, cavity gap and other rotation conditions in a special reactor, the gravitational waves formed in rotation are used to open the graphite layer without damaging the carbon ring structure, thereby reducing the generation of defects from the root. The prepared graphene sheet has less than 10 layers of graphene sheet, most of which is 1-5 layers, the lateral size is 10-20 μm, and the average value of the Raman spectrum D / G peak intensity ratio is at least 0.05. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 SEM image of the graphene sheet prepared in Example 1.

[0015] Figure 2 SEM image of the graphene sheet prepared in Example 2. DETAILED DESCRIPTION

[0016] The traditional shear peeling mainly relies on the steady shear force generated by the fluid interlayer velocity gradient, which has a direct action mode, but the peeling efficiency is low, and it is difficult to avoid damage to the graphene lattice structure. The present method is different, which aims to excite the resonance effect between the graphite layers to realize efficient and low-damage peeling.

[0017] The basic principle is as follows: under certain rotational conditions, when the rotation speed, fluid viscosity and cavity gap are matched, an unstable vortex structure (such as Taylor vortex) is formed in the restricted fluid, and the generation, shedding and evolution process of the vortex structure induces strong periodic pressure pulsation. In viscoelastic fluid, the pulsation field is significantly amplified and modulated, forming a wide-band dynamic stress wave. When the main frequency component of the stress wave is coupled with the intrinsic vibration frequency determined by the shear modulus and interlayer spacing of the graphite layer, the resonance effect is triggered.

[0018] Resonance causes the interlayer strain energy to be amplified sharply, thereby selectively overcoming the van der Waals force between the layers at an input energy much lower than the threshold for breaking the carbon-carbon bond, and achieving efficient exfoliation. In this process, the energy is precisely directed to "dissociate" the graphite layers, rather than being wasted in destroying the carbon ring structure in the fracture surface, thereby fundamentally inhibiting the generation of defects.

[0019] In addition, the resonance exfoliation is essentially a fatigue cumulative "cleavage" process, which is different from the violent "tearing" mechanism in traditional methods, and is therefore more conducive to maintaining the structural integrity and ultra-large size of the graphene sheet.

[0020] To realize the above-mentioned resonance exfoliation mechanism, the present application performs multi-physical field collaborative design on the reaction system. First, in terms of flow field regulation, by limiting the diameter-width ratio (Γ ≤ 0.1) of the rotating micro-cavity, strong geometric constraints are introduced to make the fluid unstable when reaching a certain critical rotation speed, and to change from stable Couette flow to non-steady vortex structure containing Taylor vortex. Second, in terms of medium selection, a non-Newtonian fluid with significant viscoelasticity is used. Such medium exhibits obvious elastic response when the Deborah number is greater than 1 (De>1), can store and periodically release deformation energy, and can convert the pressure pulsation induced by vortex flow into stronger transient stress wave, thereby enhancing the dynamic excitation of the graphite interlayer. At the same time, its shear thinning property makes the fluid viscosity decrease in the high shear zone, reducing energy loss, and keeps a relatively high viscosity in the low shear zone, which is helpful for the uniform dispersion and stable suspension of graphite particles. In addition, in terms of interface, the viscoelastic fluid can effectively wet the graphite surface and partially penetrate into the interlayer, playing a lubricating and wedging role, weakening the interlayer interaction force, and further reducing the exfoliation energy barrier. There is a significant coupling between the flow field, the medium and the interface: the vortex structure excites the elastic response of the medium, the viscoelastic medium amplifies and modulates the pressure pulsation, and the good interface wettability ensures the effective transmission of stress. The synergistic effect of the three makes the system energy more efficiently focused on the interlayer dissociation process.

[0021] The following examples are intended to further illustrate the present application and are not intended to be limiting to the scope of the present application. Unless otherwise indicated, parts by weight and percentages by weight are used in the following examples.

[0022] 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.

[0023] The embodiments of the present application are further described in the following multiple examples.

[0024] It should be clear that the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0025] The terms used in the embodiments of the present application are only for the purpose of describing the 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.

[0026] Embodiment 1

[0027] The natural flake graphite with an average particle size of 20 μm was exfoliated in a coaxial rotating microcavity reactor with a diameter-width ratio Γ = (b-a) / a = 0.08, and the reaction medium was a 15 wt% polyvinylpyrrolidone (PVP) aqueous solution with De ≈ 2.0. In the process, the inner shell speed was set to 12000 rpm, and CFD simulation verified that the Taylor vortex shedding frequency (f-vortex) generated at this speed was closest to the theoretical calculation of the graphite interlayer intrinsic frequency (f-intrinsic), so as to realize resonance enhanced exfoliation, and the processing time was 60 minutes. When the dominant frequency f-vortex of the stress wave and the graphite interlayer intrinsic frequency f-intrinsic satisfy the following conditions, resonance exfoliation can be realized:

[0028]

[0029] The results show that more than 80% of the products are 1-5 layer few-layer graphene; the average value of the Raman spectrum D / G peak intensity ratio is as low as 0.07, indicating that the graphene crystal structure is complete and has few defects.

[0030] As Figure 1As shown, the average lateral dimension of the product reaches approximately 15 μm, maintaining the large size characteristics of the raw material. Simultaneously, the high exfoliation yield measured by UV-Vis spectroscopy confirms the significant advantages of this resonance-assisted exfoliation process in terms of efficiency, quality, and size preservation. When the rotational speed is precisely controlled to the theoretically predicted "resonance range," the dominant frequency (f-vortex) generated by the flow field effectively couples with the interlayer vibrational mode (f-intrinsic) of graphite, inducing an interlayer resonance effect. This resonance allows the input mechanical energy to be used efficiently and selectively to overcome interlayer van der Waals forces, rather than to damage in-plane sp... 2 Carbon bonds were used to obtain high-quality graphene with low defects and large size while ensuring high exfoliation efficiency and high yield.

[0031] Example 2

[0032] A coaxial rotating microcavity reactor with an aspect ratio Γ = (ba) / a = 0.08 was used to exfoliate natural flake graphite with an average particle size of 20 μm. The reaction medium was a 0.5 wt% xanthan gum aqueous solution with De>1. The inner shell rotation speed was set to 12000 rpm, and the processing time was 60 minutes.

[0033] like Figure 2 The average size of the product shown is about 12 μm, the number of layers is less than 5, and the average Raman D / G peak ratio is 0.09.

[0034] This embodiment uses a different viscoelastic medium (xanthan gum) than Example 1, and at the same resonant rotation speed, it also obtains high-quality graphene. This proves that the key to the success of this invention lies in the viscoelasticity (non-Newtonian fluid properties) of the medium itself, rather than specific chemical substances. The viscoelastic medium can effectively store the energy of the eddy current field and release it in the form of stress pulses, greatly enhancing the resonant exfoliation effect.

[0035] Example 3

[0036] A coaxial rotating microcavity reactor with a conical rotor and stator, maintaining an extremely small aspect ratio (Γ = (ba) / a = 0.03) in the reaction zone, was used to exfoliate natural flake graphite with an average particle size of 20 μm. The reaction medium was a 15 wt% PVP aqueous solution. The inner shell rotation speed was set to 12,000 rpm, and the processing time was 60 minutes.

[0037] It was found that the proportion of 1-3 layers of graphene was significantly increased, and the Raman D / G peak ratio was further reduced to 0.05, which was the best among all examples. CFD simulation showed that a very stable and regular Taylor vortex array was formed under strong constraint of Γ = (b-a) / a = 0.03. The strong constraint made the Taylor vortex generation more uniform and stronger, thus generating a more pure and powerful periodic stress field, making the resonance effect more significant. Therefore, the exfoliation effect (especially the layer number and defect control) was optimal.

[0038] Example 4

[0039] The coaxial rotating microcavity reactor with a diameter-width ratio Γ = (b-a) / a = 0.08 was used to exfoliate natural flake graphite with an average particle size of 20 μm, and the reaction medium was 15 wt% PVP aqueous solution. In the process, the inner shell speed was set to 12000 rpm, and the treatment time was 15 minutes.

[0040] It was found that the number of layers of the product increased, and most of the product was within 10 layers, with 1-5 layers accounting for about 50%, and the Raman D / G peak ratio being about 0.10. This shows that even with a significant reduction in treatment time, the present application can still effectively exfoliate a considerable amount of few-layer graphene. This proves that the resonance exfoliation mechanism has very high energy efficiency and acts quickly. Traditional physical exfoliation methods are difficult to achieve significant results within 15 minutes.

[0041] Comparative Example 1

[0042] The difference from Example 1 is that the inner shell speed is set to 6000 rpm.

[0043] It was found that most of the product was more than 10 layers thick, and the proportion of 1-5 layers was less than 20%. The average Raman D / G peak intensity ratio was 0.18, and the defects were significantly increased. The average lateral size of the product was about 8 μm, and the sheet size was small.

[0044] When the speed deviates from the theoretical resonance interval, the flow field pulsation frequency cannot be effectively coupled with the interlayer vibration of the graphite, and the interlayer resonance effect is weak. The exfoliation power mainly comes from ordinary viscous shear force, which is a direct but inefficient force and can easily cause damage to the graphene lattice during the exfoliation process, resulting in an increase in defects, a decrease in size, and a significant decrease in yield. This comparative example proves that accurate control of the speed to the resonance interval is a prerequisite for efficient and low-damage exfoliation, rather than simply high speed.

[0045] Comparative Example 2

[0046] The difference from Example 1 is that the medium used is a 65 wt% glycerol aqueous solution with Deborah number De<<1. The 65 wt% glycerol aqueous solution is a Newtonian fluid, and its viscosity value is similar to that of the PVP solution in Example 1 at the operating shear rate. It is found that the product has a wide layer distribution, with an average of about 10 layers, and the average Raman D / G peak ratio is 0.16, indicating that the lattice defects are significantly increased, and the damage received during exfoliation is greater.

[0047] This shows that although the viscosities are similar, the Newtonian fluid lacks the mechanism of elastic energy storage and release. In the vortex field, it cannot produce enhanced stress pulses like viscoelastic fluids. Therefore, the periodic pulsating energy of the flow field cannot be effectively amplified and transmitted, and the resonance effect is greatly weakened. The exfoliation process degenerates into a steady-state shear-based process, and the efficiency and quality are significantly reduced. This comparative example proves that the viscoelasticity (non-Newtonian property) of the medium is an indispensable factor for producing a strengthened resonance effect and achieving efficient energy transfer.

[0048] Comparative Example 3

[0049] The difference from Example 1 is that a commercial high-speed shear emulsifier is used for exfoliation. The commercial high-speed shear emulsifier is similar to the coaxial rotating microcavity reactor rotor-stator structure of the present application, but has a larger gap and a diameter-width ratio Γ>1, without strong geometric constraints.

[0050] It is found that the product is a mixture of multi-layer graphite with more than 10 layers and tiny graphene fragments with less than 1 μm, and the effective large-size few-layer graphene yield is extremely low. And the Raman D / G peak ratio is as high as 0.30 or more, indicating that the crystal structure is severely damaged.

[0051] This is because the absence of strong geometric constraints prevents the formation of a stable and orderly Taylor vortex field inside the device, and instead produces chaotic and high-energy turbulent flow. This turbulent flow produces random and impact forces, rather than the periodic and directional shear force field required by the present application. It mainly plays a "crushing" role rather than a "cleavage" role, resulting in the graphite being crushed into small-size fragments and introducing a large number of defects. It is proved that the specific microcavity reactor structure (small diameter-width ratio Γ) of the present application is crucial for generating the required flow field pattern, and cannot be replaced by traditional high-speed shear devices.

[0052] The method realizes the unification of high quality and high yield. In the peeling process, graphene with low defect density (Raman D / G peak ratio less than 0.1) and micron size can be obtained at the same time, solving the problem of mutual restriction between quality and yield in the traditional peeling process. The whole process is physical peeling, without using strong acid or strong oxidant, without subsequent reduction or complex purification, with small environmental burden and high operation safety. Due to the fact that energy mainly acts on interlayer resonance dissociation rather than indiscriminate shearing, the system energy consumption is low, and it has good economy. The mechanism used is based on the frequency matching of fluid dynamics instability and material intrinsic vibration, and does not depend on a specific chemical environment, so it can be extended to the peeling of other layered materials, such as hexagonal boron nitride and molybdenum disulfide. The core of the application is not the improvement of the device structure, but a peeling idea oriented to frequency matching, which realizes the efficient accumulation of energy between layers by regulating the coupling relationship between the vortex frequency of the flow field and the interlayer response characteristics. This method improves the selectivity and controllability of peeling from the physical mechanism, and provides a quantifiable and scalable technical path for the large-scale preparation of two-dimensional materials.

[0053] The above embodiments illustrate the structure, features and effects of the present application in detail. The above description is only the preferred embodiment of the present application. Any change or modification made according to the idea of the present application, or equivalent embodiment with equivalent change, shall be within the scope of protection of the present application.

Claims

1. A method for preparing graphene based on interlayer stress resonance, characterized in that, Large-size few-layer graphene was obtained by processing graphite as a raw material in a coaxial rotating microcavity reactor using a viscoelastic non-Newtonian fluid as a dispersant. The coaxial rotating microcavity reactor includes an inner rotating body and an outer static shell, with an annular microcavity formed between the inner rotating body and the outer static shell. The aspect ratio Γ of the annular microcavity satisfies: Γ ≤ 0.

1. ； Where R i Let R be the radius of the internal body of revolution. o The radius of the inner wall of the outer static shell.

2. The method according to claim 1, characterized in that, The viscoelastic non-Newtonian fluid is a shear-thinning fluid.

3. The method according to claim 2, characterized in that, The viscoelastic non-Newtonian fluid is one of polyvinylpyrrolidone, xanthan gum, polyethylene oxide, and sodium alginate.

4. The method according to claim 1, characterized in that, The viscoelastic non-Newtonian fluid has a Deborah number De > 1; where De = λω, λ is the relaxation time of the fluid, and ω is the angular velocity of the internal rotating body.

5. The method according to claim 1, characterized in that, The aspect ratio Γ satisfies: 0.01 ≤ Γ ≤ 0.

1.

6. The method according to claim 1, characterized in that, The coaxial rotating microcavity reactor also includes an online optical monitoring device for real-time monitoring of the absorbance of the dispersion system within the microcavity.

7. A graphene prepared by the method according to claim 1, characterized in that, The average particle size of graphene is not less than 10 μm.

8. The graphene according to claim 7, characterized in that, The Raman D / G peak ratio of graphene is less than 0.

10.

9. The graphene according to claim 7, characterized in that, Graphene has fewer than 10 sheets.

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