CN114538422B

CN114538422B - Graphene alternating film with porous-micro air bag structure, preparation method and application

Info

Publication number: CN114538422B
Application number: CN202210073452.7A
Authority: CN
Inventors: 孟凡彬; 张礼奎; 陈耀; 刘倩; 徐正康
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2022-01-21
Filing date: 2022-01-21
Publication date: 2022-12-27
Anticipated expiration: 2042-01-21
Also published as: CN114538422A

Abstract

The invention discloses a graphene alternating film with a porous-micro air bag structure, a preparation method and application thereof, and the method comprises the following steps: step 1: dissolving alkaline-treated polyacrylonitrile nano-fiber aPAN in an aqueous solution, and performing ultrasonic dispersion to obtain a uniform fiber solution; adding the graphene oxide solution into the fiber solution, and fully stirring and uniformly mixing to obtain GO-aPAN; step 2: placing a layer of polyvinyl alcohol (PVA) aerogel film on a substrate, and then coating a GO-aPAN solution on the PVA film in a scraping manner; preparing a multilayer alternate membrane by adopting the method to obtain a GO/aPAN-PVA-n membrane, wherein the uppermost layer and the lowermost layer are both GO/aPAN membranes; wherein n is the total number of layers of the film, and n is more than or equal to 3; and step 3: pre-oxidizing the GO/aPAN-PVA-n film obtained in the step (2), carbonizing at a high temperature, and cooling to obtain the required graphene alternative film GC/C-n; according to the invention, a continuous conductive network is constructed in the graphene sheet layer through the carbon nanofiber, so that the obtained graphene sheet has good mechanical property, conductivity and electromagnetic shielding property.

Description

Graphene alternating film with porous-micro air bag structure, preparation method and application

Technical Field

The invention relates to the technical field of electromagnetic shielding, in particular to a graphene alternating film with a porous-micro air bag structure, a preparation method and application.

Background

In recent years, with the rapid development of modern electronic equipment, the daily living standard of people is greatly improved, but new pollution-electromagnetic interference is brought. Electromagnetic contamination can not only cause energy loss, but also signal interference and data loss and even crash of delicate systems. Conventional electromagnetic shielding materials, such as metal materials of Cu and Cr, have problems of high density and corrosion, etc., thereby limiting their wide use in this field. For conductive polymers, doping is usually required to achieve a good shielding effect, but this is usually the reason for poor thermal stability of the material. It is important to develop a shielding material that simultaneously combines excellent shielding properties with ultra-thin layers, high mechanical strength and good reliability to meet the requirements of emerging multifunctional devices and electronic systems.

Novel carbon materials such as graphene, carbon nanotubes, MXene, etc. have been widely developed. Among them, graphene has many excellent properties as a 2D carbon material. For example, the characteristics of good conductivity, mechanical strength, chemical stability, easy functionalization and large-scale preparation, and the extremely high specific surface area make it an ideal platform for energy application. Can be widely applied to the fields of electromagnetic wave absorption and electromagnetic shielding, polluted water treatment and the like. However, the existing materials often have the problems of low conductivity and electromagnetic shielding performance or poor mechanical property. Graphene has the potential for excellent properties by itself, but greatly affects the shielding properties of the material due to its own structural characteristics. Although the dense multilayer graphene thin film has good conductivity, high-performance electromagnetic shielding cannot be achieved only by improving the conductivity. On one hand, the preparation process of the graphene material is relatively complex, and a plurality of defects are often caused in the preparation process, so that the conductivity is reduced; on the other hand, it is difficult to achieve multi-level reflection loss of electromagnetic waves by a dense thin film.

Disclosure of Invention

Aiming at the problems existing in the prior art, the invention obtains the graphene alternative film with the porous-micro air bag structure and good mechanical property, conductivity and electromagnetic shielding property by constructing a continuous conductive network in the graphene lamellar through the carbon nanofiber, and the preparation method and the application thereof.

The technical scheme adopted by the invention is as follows:

a preparation method of a graphene alternating film with a porous-micro air bag structure comprises the following steps:

step 1: dissolving alkaline-treated polyacrylonitrile nano-fiber aPAN in an aqueous solution, and performing ultrasonic dispersion to obtain a uniform fiber solution; adding the graphene oxide solution into the fiber solution, and fully stirring and uniformly mixing to obtain GO-aPAN;

step 2: placing a layer of polyvinyl alcohol PVA aerogel film on a substrate, and then coating a GO-aPAN solution on the PVA film in a blade mode; preparing a multilayer alternate membrane by adopting the method to obtain a GO/aPAN-PVA-n membrane, wherein the uppermost layer and the lowermost layer are both GO/aPAN membranes; wherein n is the total number of layers of the film, and n is more than or equal to 3;

and step 3: and (3) pre-oxidizing the GO/aPAN-PVA-n film obtained in the step (2), carbonizing at a high temperature, and cooling to obtain the required graphene alternative film GC/C-n.

Further, in the step 1, the mass ratio of the aPAN nanofibers to the graphene oxide is 5-20.

Further, the pre-oxidation treatment temperature in the step 3 is 180-250 ℃, and the treatment time is 30-60 min.

Further, the high-temperature carbonization treatment temperature in the step 3 is 1800-2000 ℃, and the treatment time is 1-2 h.

Further, after the pre-oxidation treatment in the step 3, the temperature is increased to 1200 ℃ at the speed of 10 ℃/min, and then the temperature is increased to the temperature required by the high-temperature carbonization treatment at the speed of 10 ℃/min.

Further, the preparation method of the alkali-treated polyacrylonitrile nanofiber aPAN in the step 1 is as follows:

mixing polyacrylonitrile PAN powder with a solvent, heating to 60 ℃, and keeping the temperature for 3 hours; naturally cooling to room temperature to obtain a PAN solution with the mass concentration of 10 wt.%; electrospinning to obtain nano-fibers, and standing the obtained nano-fibers at 60 ℃ for 24 hours; soaking the nano-fibers in NaOH solution, and preserving heat for 2 hours at 40 ℃; and (4) carrying out emulsification treatment after cleaning, carrying out suction filtration to remove water, and drying to obtain the alkali-treated polyacrylonitrile nano-fiber aPAN.

Further, the preparation method of the PVA aerogel film in the step 2 is as follows:

dissolving PVA in water, stirring for 4h at 60 ℃, and cooling to room temperature; pouring the solution into a culture dish, and freeze-drying to obtain the product.

Further, the surface of the graphene alternative film is provided with an air bag porous structure, and carbon nanofibers in the graphene alternative film are mutually lapped to form a conductive network; the GO/aPAN and PVA interfaces exhibit a random stacked morphology.

An application of a graphene alternative film with a porous-micro air bag structure is disclosed, wherein the graphene alternative film is used as an electromagnetic shielding material.

The invention has the beneficial effects that:

(1) According to the invention, a continuous conductive network is constructed in the graphene sheet layer through the carbon nanofibers, so that the overall mechanical property, conductivity and electromagnetic shielding property of the film are improved;

(2) The graphene/carbon nanofiber micro-airbag structure formed by the film in the high-temperature thermal reduction process can improve the mechanical properties of the film, including tensile strength and reciprocating bending properties, and promote multiple reflection loss of electromagnetic wave energy in the film.

Drawings

FIG. 1 is SEM images of alternating films, GO/aPAN films and PVA aerogels obtained in examples 1-3 of the invention and comparative example 1; and EDS plot of the alternating films obtained in example 3.

FIG. 2 is a cross-sectional profile of the alternating thin films obtained in examples 1 to 3 of the present invention and comparative example 1.

FIG. 3 shows an infrared spectrum (a) and a Raman spectrum (b) of the alternating thin films obtained in examples 1 to 3 of the present invention and comparative example 1.

FIG. 4 shows the conductivity of the alternating thin films obtained in examples 1 to 3 of the present invention and comparative example 1.

Fig. 5 is a stress-strain curve of the alternating thin films obtained in examples 1 to 3 of the present invention and comparative example 1.

FIG. 6 is an optical photograph of the alternating films obtained in examples 1 to 3 of the present invention and comparative example 1.

Fig. 7 shows the results of the conductivity test of the alternate films obtained in examples 1 to 3 of the present invention and comparative example 1 after the alternate films were continuously bent 250 times.

Fig. 8 is a stress-strain curve of the alternate films obtained in examples 1 to 3 of the present invention and comparative example 1 after they were continuously bent 250 times.

FIG. 9 is an optical photograph of the alternating film obtained in example 3 of the present invention after it was continuously bent 250 times.

FIG. 10 shows the electromagnetic properties of the alternating thin films obtained in examples 1 to 3 of the present invention and comparative example 1.

Detailed Description

The invention is further described with reference to the following figures and specific examples.

step 1: dissolving alkaline-treated polyacrylonitrile nano-fiber aPAN in an aqueous solution, and performing ultrasonic dispersion to obtain a uniform fiber solution; adding the graphene oxide solution into the fiber solution, and fully stirring and uniformly mixing to obtain GO-aPAN; the mass ratio of the aPAN nano-fiber to the graphene oxide is 5-20.

And 2, step: placing a layer of polyvinyl alcohol PVA aerogel film on a substrate, and then coating a GO-aPAN solution on the PVA film in a blade mode; preparing a multilayer alternate membrane by adopting the method to obtain a GO/aPAN-PVA-n membrane, wherein the uppermost layer and the lowermost layer are both GO/aPAN membranes; wherein n is the total number of layers of the film, and n is more than or equal to 3.

And 3, step 3: and (3) pre-oxidizing the GO/aPAN-PVA-n film obtained in the step (2), carbonizing at a high temperature, and cooling to obtain the required graphene alternative film GC/C-n. The pre-oxidation treatment temperature is 180-250 ℃, and the treatment time is 30-60 min. The high-temperature carbonization treatment temperature is 1800-2000 ℃, and the treatment time is 1-2 h. After the pre-oxidation treatment in the step 3, the temperature is raised to 1200 ℃ at the speed of 10 ℃/min, and then the temperature is raised to the temperature required by high-temperature carbonization treatment at the speed of 10 ℃/min.

The preparation method of the alkali-treated polyacrylonitrile nano-fiber aPAN in the step 1 comprises the following steps:

mixing polyacrylonitrile PAN powder with a solvent, heating to 60 ℃, and keeping the temperature for 3 hours; naturally cooling to room temperature to obtain a PAN solution with the mass concentration of 10 wt.%; obtaining nano-fibers through electrospinning, and placing the obtained nano-fibers for 24 hours at the temperature of 60 ℃; soaking the nano-fiber in NaOH solution, and preserving heat for 2 hours at 40 ℃; and (3) carrying out emulsification treatment after cleaning, carrying out suction filtration to remove water, and drying to obtain the alkaline-treated polyacrylonitrile nano-fiber aPAN.

The preparation method of the PVA aerogel film comprises the following steps:

Example 1

step 1: dissolving alkaline-treated polyacrylonitrile nano-fiber aPAN in 2.5mL of aqueous solution, and performing ultrasonic dispersion to obtain uniform fiber solution; adding 10g of graphene oxide solution (with the concentration of 10 mg/g) into the fiber solution, and fully stirring and uniformly mixing to obtain GO-aPAN; the mass ratio of the aPAN nanofibers to graphene oxide was 10.

And 2, step: placing a layer of polyvinyl alcohol PVA aerogel film on a substrate, and then coating a GO-aPAN solution on the PVA film in a blade mode to obtain a GO/aPAN film; and after the PVA film is naturally air-dried, the other side of the PVA film is subjected to blade coating of a GO/aPAN film to obtain the GO/aPAN-PVA-n film, wherein n =3.

And step 3: and (3) putting the GO/aPAN-PVA-n membrane obtained in the step (2) into a muffle furnace, heating to 200 ℃, and preserving heat for 40min for pre-oxidation treatment. Then the film is placed in a graphite furnace, the temperature is raised to 1200 ℃ from room temperature at the speed of 10 ℃/min, then the temperature is raised to 1900 ℃ at the speed of 10 ℃/min, and the temperature is kept for 1.5h. And naturally cooling the film to room temperature after the procedure is finished, and carrying out the whole process under a vacuum condition to finally obtain the required graphene alternating film GC/C-n. Wherein G is graphene, the first C is carbon nanofiber, and the second C is carbon aerogel.

mixing 10g of polyacrylonitrile PAN powder with 90g of DMF solvent, heating to 60 ℃, and keeping the temperature for 3h; naturally cooling to room temperature to obtain a PAN solution with the mass concentration of 10 wt.%; and obtaining the nano-fiber by electrospinning. The electrospinning parameters were as follows: 20G of needle head, flow rate of 2 mul/min, voltage of 15kV and receiving distance of 15cm.

Placing the obtained nano-fiber at 60 ℃ for 24h; soaking the nano-fibers in a 1M NaOH solution, and preserving heat for 2 hours at 40 ℃; cooling to room temperature, washing with deionized water to neutral state (color changes from yellow to white), treating with emulsifier (rotation speed of 1000rpm/min, treatment time of 5 min) to obtain solution, and vacuum filtering to remove water. And finally, placing the obtained product in a vacuum oven at 80 ℃ for 24h for drying to obtain the alkali-treated polyacrylonitrile nano-fiber aPAN.

The preparation method of the PVA aerogel film comprises the following steps:

dissolving 5g of PVA in 95g of water, stirring for 4 hours at the temperature of 60 ℃, and cooling to room temperature; the solution was poured into a petri dish, frozen with liquid nitrogen and freeze-dried for 48h to prepare multiple samples for use.

Example 2

The other steps were the same as in example 1

Step 2: placing a layer of polyvinyl alcohol PVA aerogel film on a substrate, and then coating a GO-aPAN solution on the PVA film in a blade mode to obtain a GO/aPAN film; after it had dried naturally, a GO/aPAN film was knife coated on the other side of the PVA film. And then placing a layer of polyvinyl alcohol PVA aerogel film, then coating the GO-aPAN solution on the PVA film in a scraping way, and naturally air-drying the PVA film to obtain the required GO/aPAN-PVA-n film, wherein n =5.

Example 3

The other steps are the same as in example 1

Step 2: placing a layer of polyvinyl alcohol PVA aerogel film on a substrate, and then coating a GO-aPAN solution on the PVA film in a blade mode to obtain a GO/aPAN film; after it had dried naturally, a GO/aPAN film was knife coated on the other side of the PVA film. Then, a layer of polyvinyl alcohol PVA aerogel film is placed, then GO-aPAN solution is coated on the PVA film in a scraping mode, and the PVA film is naturally air-dried; and then placing a layer of polyvinyl alcohol PVA aerogel film, then coating a GO-aPAN solution on the PVA film in a blade mode, and naturally air-drying the PVA film to obtain the required GO/aPAN-PVA-n film, wherein n =7.

Example 4

The specific operation steps are as in example 3, and the differences are as follows:

in step 1, the mass ratio of the aPAN nanofibers to the graphene oxide is 5.

In the step 3, the pre-oxidation treatment temperature is 180 ℃, and the heat preservation time is 60min; when the high-temperature carbonization treatment is carried out, firstly the temperature is increased from room temperature to 1200 ℃ at the heating rate of 10 ℃/min, then the temperature is increased to 1800 ℃ at the heating rate of 5 ℃, and the heat preservation time is 2h.

Example 5

in step 1, the mass ratio of the aPAN nanofibers to the graphene oxide is 20.

In the step 3, the pre-oxidation treatment temperature is 250 ℃, and the heat preservation time is 30min; when the high-temperature carbonization treatment is carried out, firstly the temperature is increased from room temperature to 1200 ℃ at the heating rate of 10 ℃/min, then the temperature is increased to 2000 ℃ at the heating rate of 5 ℃, and the heat preservation time is 1h.

For explaining the beneficial effect setting of the invention

Comparative example

The other steps of this comparative example were as in example 1 except that in step 2 the film was a GO/aPAN (i.e., GO/aPAN-PVA-1) film.

FIGS. 1 (a-f) are SEM images of thin films obtained in step 2 of examples of the present invention and comparative examples. FIG. 1a is a schematic of the surface topography of a GO/aPAN film obtained in a comparative example. FIG. 1b is a schematic view of the surface topography of PVA aerogel. FIG. 1c is a cross-sectional topography of a GO/aPAN film obtained from a comparative example. FIG. 1d is a cross-sectional topography of the GO/aPAN-PVA-3 film obtained in step 2 of example 1. FIG. 1e is the cross-sectional topography of the GO/aPAN-PVA-5 film obtained in example 2. FIG. 1f is a cross-sectional topography of the GO/aPAN-PVA-7 film obtained in example 3. From fig. 1a it can be seen that the aPAN nanofibers can be uniformly distributed on the surface of GO, illustrating that steps like alkaline treatment and ultrasonic dispersion can disperse the entangled long-size PAN nanofibers and can promote their uniform distribution in GO solution, which is beneficial for the construction of high temperature reduction treatment conductive network. From FIG. 1b, it can be seen that the PVA aerogel prepared by freeze drying presents a relatively regular three-dimensional structure, which is beneficial to the construction of a porous structure in an alternate film. From FIG. 1c it can be seen that the GO/aPAN film exhibits a dense structure.

As can be seen from fig. 1 d-1 f, in the interfaces between the PVA and the GO/aPAN film, the PVA and GO/aPAN solutions can be fused with each other, and form an anchor bolt structure through interaction such as hydrogen bonds, which can promote mutual adhesion between the interfaces, thereby improving the interface strength. The intermediate layer of the alternating film has a porous structure, so that the interface between GO/aPAN and PVA can be obviously distinguished, and the successful preparation of the GO/aPAN-PVA-n alternating film is illustrated.

FIGS. 1 g-1 i are EDS diagrams of the alternating thin films obtained in examples 1 to 3. It can be seen from the figure that the C and O elements mainly derived from GO and PVA are distributed at the cross section of the entire film. And as can be seen from the main distribution of the N element, which is mainly derived from the aPAN nanofibers, the success of the preparation of the alternating films was demonstrated.

FIGS. 2 a-2 d are cross-sectional topographical views of the alternating films obtained in comparative example (a), example 1 (b), example 2 (c), and example 3 (d). FIG. 2e is a surface topography of the alternating film obtained in example 3, and FIG. 2f is an inner layer topography of the alternating film obtained in example 3. It can be seen from the figure that the carbon nanofiber reinforced graphene film (GC/C-1) exhibits a loose layered structure as can be seen from fig. 2a after pre-oxidation and heat treatment. The structure is completely different from a compact GO/aPAN membrane before reduction, even forms a micro-airbag porous structure, and is mainly caused by gases released by GO and aPAN in the defect repair process of graphene and carbon nanofiber. This structure will improve the electromagnetic shielding effect to a large extent by increasing the number of reflections. And the above multilayer structure becomes more and more apparent with the introduction of PVA (fig. 2 (b-d)).

Fig. 2e is a surface topography of the alternating thin film obtained in example 3, and it can be seen from the figure that, besides the clearly visible micro-balloon structure on the surface, there is also a conductive network formed by carbon nanofibers, and the mutual overlapping of the fibers can promote the improvement of conductivity and is beneficial to electromagnetic shielding. FIG. 2f is a chart of the inner layer topography of the alternating thin films obtained in example 3. PVA presents a disordered stacking morphology at the interface after carbonization, which is a completely different structure from graphene. Because the porous carbon at the interface can form a certain layering phenomenon, and the carbon layer which can be formed after high-temperature carbonization has certain overlap joint, the loss of electromagnetic waves at the interface can be promoted, and the integral shielding performance is improved.

FIG. 3 shows FTIR spectra (a) and Raman spectra (b) of the GC/C-n graphene alternating films obtained in examples 1 to 3 and comparative example 1. As can be seen from the figure. The diffraction peak of all GC/C films exhibited a narrow and sharp feature at 26.1 deg., as shown in fig. 3 a. This corresponds to a perfect structure of the graphite (002) crystal planes, which means that the graphene layers are more regularly accumulated and have a more regular order after high temperature annealing. This demonstrates that stable alternating graphene films can be prepared by pre-oxidizing and heat treating GO/aPAN-PVA-n. As the number of cross layers increases, the 2 θ value shows a tendency to increase, indicating that the alternating structure favors the reduction of GO. But the half-peak width also exhibited an increasing trend, indicating that the interlayer spacing was also increasing, which exhibited similar results to SEM characterization.

As can be seen from fig. 3b, there are distinct D and G peaks as with graphene, and the intensity of the G peak is significantly higher than the D peak. This demonstrates the successful preparation of graphene, presenting lower defects, which is consistent with XRD results.

FIG. 4 is a schematic graph of the conductivities of the graphene alternating thin films GC/C-n obtained in examples 1 to 3 and a comparative example. In general, the conductivity of the material has a critical influence on the electromagnetic shielding performance, and thus, the conductivity of the GC/C film is tested. As can be seen from the figure, GC/C-1 exhibits excellent conductivity, which can reach values of 1000S/cm. As the number of alternating layers increases, the conductivity of the film tends to decrease, mainly due to the increase in resistance caused by the increase in porosity in the alternating layers of porous carbon. Nevertheless, the conductivity of GC/C-7 can still reach 117S/cm.

FIG. 5 is a graph showing the stress-strain curves of GC/C-n graphene alternating films obtained in examples 1 to 3 and a comparative example. It can be seen from fig. 5 that the mechanical properties thereof show a similar trend. The maximum tensile strength of GC/C-1 can reach 16MPa. The introduction of the porous carbon material may reduce the interfacial bonding between graphene/carbon nanofiber sheets after high temperature reduction, thereby resulting in a decrease in strength. But the graphene and the carbon nano-fiber still have excellent mechanical properties due to the strength of the graphene and the carbon nano-fiber and the mutual combination of the graphene and the carbon nano-fiber. As the number of layers increases, the strain tends to increase gradually although the strength decreases.

FIG. 6 is an optical photograph of the graphene alternative thin films GC/C-n obtained in examples 1 to 3 and a comparative example. All GC/C films were able to recover to the original state after bending 180 ° and maintain good structural stability.

FIG. 7 is a schematic graph of the conductivity of the graphene alternative thin film obtained in examples 1 to 3 and the comparative example after GC/C-n is continuously bent 250 times. It can be seen that there is no significant decrease in conductivity from before bending.

Fig. 8 is a stress-strain curve of the graphene alternative thin film GC/C-n obtained in examples 1 to 3 of the present invention and the comparative example after being continuously bent 250 times. As can be seen from the figure, the mechanical properties are not significantly reduced compared to before cyclic bending. FIG. 9 is an optical photograph of the graphene alternative thin film GC/C-7 obtained in example 3 after being continuously bent 250 times. The steel plate still has good bending performance after being bent, and can be restored to an initial state after stress is released.

FIG. 10 shows the electromagnetic properties of the GC/C-n graphene alternating films obtained in examples 1 to 3 and comparative example. FIG. 10a is a graph showing the total EMI shielding performance SE in the frequency range of 8.0 to 12.0GHz _T . FIG. 10b is the EMI absorption loss value SE _A . FIG. 10c shows the EMI reflection loss value SE _R . Fig. 10d shows the shielding performance. Fig. 10e shows the effective absorption coefficient. Fig. 10f shows the electromagnetic shielding coefficients R, T, and a of the alternating graphene thin film obtained in example 3. It can be seen from the figure that the high conductivity of the thin film imparts excellent electromagnetic shielding performance to the GC/C film. As materials with higher conductivity generally exhibit higher reflection and loss capabilities. The porous structure of the micro-air bags and the alternate carbon materials of the graphene and carbon nanofiber composite film can promote multiple reflection loss and absorption of electromagnetic waves. Thus, the shielding performance of the film as a whole can be improved to a great extent.

The thickness of the film also shows a tendency to increase (3 to 160 μm) with increasing number of alternating layers, with electromagnetic shielding values increasing from 32dB to 80dB in the range of 8 to 12 GHz. SE can be seen from FIGS. b and c _A The value is significantly higher than SE _T This means that absorption is a main cause of the excellent EMI shielding effect. The higher SEA values mean that when the electromagnetic penetration is into the interior of the material, its main loss mechanism is conductanceElectrical losses and multiple reflection losses. As can be seen from fig. d, the alternating film obtained by the present invention has excellent shielding effectiveness, which is increased from 99.87% to 99.99999%, which means that the electromagnetic waves can be substantially lost by the thin film. In e it can be seen that the effective absorption coefficient of the alternating film obtained in example 3 can reach 0.999996, meaning that it can suppress more than 99.9996% of the electromagnetic energy. f is that example 3 is almost completely shielded by the pellicle at 8 to 12GHz electromagnetic energy.

The parameters in the invention are obtained through calculation or analysis and can not be obtained through simple experiments. For example, when the content of the aPAN nanofibers is too low, the voids between the GO sheets cannot be sufficiently filled, and thus a sufficient network structure cannot be formed after high temperature annealing, as compared to the mass ratio of the aPAN nanofibers to GO. Thus, the conductivity and the electromagnetic shielding performance cannot be effectively improved. Too much fiber content can lead to agglomeration of fibers between GO lamellae, increasing the interlayer spacing, and thus increasing the graphene nanoplatelet interlayer spacing after high temperature annealing. And during annealing, the aPAN nano-fiber releases a large amount of gas, so that the size of the pore is increased, and the mechanical property, the conductivity and the like of the final film are reduced. Thus, at a mass of 5% to 20%, on the one hand, the carbon nanofibers are able to form a continuous conductive network, and on the other hand, the high conductivity of the micro-balloon film is maintained without affecting the expansion of the interlayer spacing dimension, preferably 10%.

If the pre-oxidation temperature is 180-250 ℃, the PVA can be violently decomposed if the temperature is too high, so that the PVA layer can not form a porous structure finally. If the temperature is too low, pre-oxidation of the aPAN nanofibers cannot be guaranteed, and a stable structure of the fibers cannot be guaranteed during high-temperature annealing treatment, so that the fibers may be severely decomposed, and carbon fibers cannot be formed. The pre-oxidation treatment time is 30-60 min, and in an air atmosphere, if the time is too long, GO can be strongly oxidized and even decomposed, which is not favorable for preparing high-temperature annealing graphene. Too long a time also leads to severe decomposition of the PVA.

The annealing temperature is 1800-2000 ℃, the functional groups of GO can only be partially removed when the temperature is too low, and the lattice defects can not be completely repaired, so that the conductivity is lower, and the electromagnetic shielding performance and the mechanical performance are poorer; however, previous research work shows that the crystal defects of graphene oxide can be well repaired at 1900 ℃, and in actual operation, the higher the temperature is, the more energy is consumed, so that the operation is more difficult. The heat preservation time is 1-2 h, which indicates that the time is too short, GO cannot completely repair the defects, and PAN nanometer cannot be completely carbonized, so that the conductivity and the like of the final film are reduced. Too high a temperature makes the operation more difficult, requires more instrumentation and results in more energy.

According to the invention, a continuous conductive network is constructed in the graphene sheet layer through the carbon nanofibers, so that the overall mechanical property, conductivity and electromagnetic shielding property of the film are improved. And the formed graphene/carbon nanofiber micro-airbag structure can improve the mechanical properties (tensile strength, reciprocating bending property and the like) of the film in the high-temperature thermal reduction process, and promote the multiple reflection loss of electromagnetic wave energy in the film. In addition, the multilayer alternating structure constructed by the PVA and the GO/aPAN nano-fiber further increases multiple reflection and absorption of electromagnetic waves after high-temperature annealing and other treatments, and facilitates wide application of the multilayer alternating structure in the field of electromagnetic shielding, such as interface polarization at the interface of the multilayer alternating structure, conductive loss of the multilayer alternating structure and the GO/aPAN nano-fiber. The thin film obtained by the invention not only exerts the advantages of light weight and small thickness of the graphene film, but also realizes high conductivity, high mechanical strength and electromagnetic shielding performance.

Claims

1. A preparation method of a graphene alternating film with a porous-micro air bag structure is characterized by comprising the following steps:

step 1: dissolving alkaline-treated polyacrylonitrile nano-fiber aPAN in an aqueous solution, and performing ultrasonic dispersion to obtain a uniform fiber solution; adding the graphene oxide solution into the fiber solution, and fully stirring and uniformly mixing to obtain GO-aPAN; the mass ratio of the aPAN nano-fiber to the graphene oxide is 5-20;

and step 3: pre-oxidizing the GO/aPAN-PVA-n film obtained in the step (2), carbonizing at a high temperature, and cooling to obtain the required graphene alternative film GC/C-n; the pre-oxidation treatment temperature is 180-250 ℃, and the treatment time is 30-60 min; the high-temperature carbonization treatment temperature is 1800-2000 ℃, and the treatment time is 1-2 h; after the pre-oxidation treatment, the temperature is raised to 1200 ℃ at the speed of 10 ℃/min, and then the temperature is raised to the temperature required by the high-temperature carbonization treatment at the speed of 10 ℃/min.

2. The method for preparing the graphene alternating film with the porous-micro airbag structure according to claim 1, wherein the alkaline-treated polyacrylonitrile nanofiber aPAN in the step 1 is prepared by the following steps:

mixing polyacrylonitrile PAN powder with a solvent, heating to 60 ℃, and keeping the temperature for 3 hours; naturally cooling to room temperature to obtain a PAN solution with the mass concentration of 10 wt.%; obtaining nano-fibers through electrospinning, and placing the obtained nano-fibers for 24 hours at the temperature of 60 ℃; soaking the nano-fibers in NaOH solution, and preserving heat for 2 hours at 40 ℃; and (4) carrying out emulsification treatment after cleaning, carrying out suction filtration to remove water, and drying to obtain the alkali-treated polyacrylonitrile nano-fiber aPAN.

3. The method for preparing the graphene alternating film with the porous-micro air bag structure according to claim 1, wherein the preparation method of the PVA aerogel film in the step 2 is as follows:

4. The graphene alternating film with the porous-micro air bag structure obtained by any one of the preparation methods of claims 1-3, wherein the surface of the graphene alternating film has an air bag porous structure, and carbon nanofibers inside the graphene alternating film are mutually overlapped to form a conductive network; the GO/aPAN and PVA interfaces exhibit a random stacked morphology.

5. The use of the graphene alternating film with a porous-micro balloon structure according to claim 4, wherein the graphene alternating film is used as an electromagnetic shielding material.