Nanometer film for electromagnetic shielding and preparation method and application thereof

Abstract

The invention discloses a nano film for electromagnetic shielding and a preparation method and application thereof. The preparation method comprises the following steps: firstly, preparing an MXene suspension; then mixing the MXene suspension liquid with absolute ethyl alcohol to obtain an electric spraying liquid; mixing polyacrylonitrile and enzymatic hydrolysis lignin to prepare a spinning solution; an upper layer lignin / PAN nanofiber membrane is prepared by adopting an electric spraying solution and a spinning solution, and a middle layer MXene (at) lignin / PAN composite membrane and a lower layer lignin / PAN nanofiber membrane are assembled into a'spinning and spraying 'nano membrane with a sandwich layer-by-layer structure. The spinning and spraying nano film prepared by the method has the advantage of high electromagnetic shielding performance of the low-conductivity filler, can be applied to the fields of aerospace, national defense, next-generation wearable flexible electronic products and the like, and has a wide market application prospect.

Description

Technical Field

[0001] The present invention relates to a nanofilm for electromagnetic shielding, a preparation method thereof and an application thereof, and belongs to the technical field of electromagnetic shielding materials. Background Art

[0002] With the rapid development of electronic devices and wireless communication technologies, the problem of electromagnetic pollution has become increasingly serious, and the development of high-performance electromagnetic shielding materials has become a research hotspot. Although traditional metal-based electromagnetic shielding materials (such as copper, aluminum, etc.) have excellent shielding effectiveness, their disadvantages such as high density, easy corrosion, and poor processing flexibility are difficult to meet the requirements of modern electronic devices for flexible and lightweight electromagnetic shielding materials. Therefore, the development of new high-performance lightweight flexible electromagnetic shielding materials has important practical significance.

[0003] Electrospinning technology is an effective method for preparing nanofibers. The nanofibers prepared by it have a large specific surface area and a high aspect ratio, and are widely used in fields such as electromagnetic shielding, optics, and thermal management. As a natural polymer material with rich reserves and renewable resources, lignin has the advantages of low cost, biodegradability, and rich aromatic ring structures. However, its utilization rate is relatively low, resulting in waste of resources. It should be noted that by using a spinning aid, lignin can be made into a nanofiber membrane by electrospinning, which has the characteristics of light weight, flexibility, and porosity, providing an effective way for the resource utilization of lignin.

[0004] As a new type of two-dimensional material, MXene has high conductivity, a large specific surface area, and good surface activity, and has attracted much attention in the field of electromagnetic shielding in recent years. However, the cost of pure MXene films is high and their mechanical properties are poor, which are difficult to meet the actual application requirements. In addition, MXene sheets are prone to stacking, making it difficult to fully exert their surface effects and interfacial effects. Therefore, how to solve the above problems through material composite and structure design has become the key to the research of MXene-based electromagnetic shielding materials.

[0005] The literature (Zhou B, Zhang Z, Li Y, et al. Flexible, robust, and multifunctional electromagnetic interference shielding film with alternating cellulose nanofiber and MXene layers [J]. ACS applied materials & interfaces, 2020, 12(4): 4895-4905.) discloses the preparation of a multilayer film containing alternating cellulose nanofiber (CNF) layers and MXene layers by an alternating vacuum filtration method. However, due to the serious stacking phenomenon of MXene, its electromagnetic shielding performance is only 39.6 dB when the addition amount of MXene is 44%. Summary of the Invention

[0006] To solve the above problems, in the present invention, lithium fluoride (LiF) and hydrochloric acid (HCl) are first mixed, aluminum titanium carbide (Ti3AlC2) is added, and after stirring and reacting for 48 hours, centrifuging and washing, and ultrasonic exfoliation, an MXene dispersion is obtained; then the MXene suspension is mixed with absolute ethanol to obtain an electrospraying solution; then polyacrylonitrile (PAN) and N,N-dimethylformamide (DMF) are mixed, enzymatic lignin is added, and after stirring for 24 hours, a spinning solution is obtained; finally, the electrospraying solution and the spinning solution are respectively placed in syringes, and the electrospinning and electrospraying parameters are adjusted to prepare a "spin + spray" nanofilm with a sandwich layer structure assembled from an upper lignin / PAN nanofiber film, a middle layer MXene@lignin / PAN composite film, and a lower lignin / PAN nanofiber film. The "spin + spray" nanofilm for electromagnetic shielding prepared by the present invention has light weight, flexibility, and good electromagnetic shielding performance, and has a wide range of market application scenarios in the fields of aerospace, national defense, or next-generation flexible wearable electronic devices, etc.

[0007] The first object of the present invention is to provide a preparation method of a nanofilm for electromagnetic shielding, comprising the following steps:

[0008] (1) Mix lithium fluoride and hydrochloric acid, add aluminum titanium carbide to react, and after the reaction, perform ultrasonic exfoliation to obtain an MXene suspension;

[0009] (2) Mix the MXene suspension with a volatile organic solvent to obtain an electrospraying solution;

[0010] (3) Add polyacrylonitrile to an organic solvent to mix, add enzymatic lignin, and fully stir to obtain a spinning solution;

[0011] (4) Prepare the upper-layer lignin / polyacrylonitrile nanofiber membrane by electrospinning the spinning solution in step (3), prepare the middle-layer MXene@lignin / polyacrylonitrile composite membrane by simultaneously performing electrostatic spraying and electrospinning with the electrospraying solution in step (2) and the spinning solution in step (3), and prepare the lower-layer lignin / polyacrylonitrile nanofiber membrane by electrospinning the spinning solution in step (3). Assemble the three layers of membranes in sequence to form the nanofilm for electromagnetic shielding.

[0012] In one embodiment of the present invention, the concentration of the MXene suspension in step (1) is 10 mg / mL to 25 mg / mL.

[0013] In one embodiment of the present invention, the mass ratio of lithium fluoride to aluminum titanium carbide in step (1) is 1:0.5 to 2.

[0014] In one embodiment of the present invention, the reaction temperature in step (1) is 35°C to 40°C, and the reaction time is 40 to 60 h.

[0015] In one embodiment of the present invention, the concentration of hydrochloric acid in step (1) is 6 to 10 M.

[0016] In one embodiment of the present invention, the ultrasonic time in step (1) is 0.5 - 3 h, and the ultrasonic power is 300 - 500 W.

[0017] In one embodiment of the present invention, after the reaction in step (1), it further includes a washing step, and the washing is centrifugal washing at 3000 - 7000 rpm for 1 - 5 min.

[0018] In one embodiment of the present invention, in step (2), the volatile organic solvent is anhydrous ethanol, and the volume ratio of the MXene suspension to anhydrous ethanol is 1 - 2:2 - 1.

[0019] In one embodiment of the present invention, in step (3), the mass ratio of polyacrylonitrile to enzymatically hydrolyzed lignin is 6 - 8:3.

[0020] In one embodiment of the present invention, in step (3), the organic solvent is one of N,N-dimethylformamide, dimethyl sulfoxide, acetone, a mixed solvent of N,N-dimethylformamide, a mixed solvent of tetrahydrofuran and N,N-dimethylformamide.

[0021] In one embodiment of the present invention, in step (3), the solid content of the spinning solution is 10 wt% to 20 wt%.

[0022] In one embodiment of the present invention, in step (4), the voltages for the upper and lower electrospinning are 12 - 20 kV, the injection speed is 0.5 - 1 mL / h, and the spinning time is 1 - 5 h.

[0023] In one embodiment of the present invention, in step (4), the preparation of the middle layer is carried out by simultaneous electrospinning and electrostatic spraying. The injection speed of the electrostatic spraying is 0.5 - 7 mL / h, the voltage is 12 - 20 kV, and the time is 6 - 11 h.

[0024] In one embodiment of the present invention, in step (4), the loading amount of MXene in the nanofilm is 2.5% - 15%.

[0025] The second object of the present invention is a nanofilm for electromagnetic shielding prepared by the method of the present invention.

[0026] The third object of the present invention is the application of the nanofilm for electromagnetic shielding of the present invention in the fields of aerospace, national defense or next-generation flexible wearable electronic devices.

[0027] The fourth object of the present invention is to provide an electromagnetic shielding material which uses the nanofilm for electromagnetic shielding of the present invention.

[0028] Advantages of the present invention:

[0029] (1) By combining electrospinning and electrostatic spraying techniques, the present invention successfully prepares an electromagnetic shielding composite film with a sandwich layer structure. This method is simple and easy to control, can uniformly load MXene on the surface of nanofibers, reduce the stacking phenomenon of MXene, not only improve the utilization rate of MXene and the surface conductivity, but also create a heterojunction interface to improve the electromagnetic wave loss.

[0030] (2) Through continuous electrostatic spraying and electrospinning operations, the present invention self-assembles under the entanglement of strong van der Waals forces to form a three-dimensional nanofiber network layered structure, which consists of a conductive layer formed by the self-deposited layer of MXene and a void layer formed by a small number of nanofibers, constituting a continuous alternation of conductive layers and insulating layers, which helps the loss of electromagnetic wave energy. The electromagnetic shielding nanofilm prepared by the present invention has the advantage of high electromagnetic shielding performance with low conductive fillers. When the MXene content is 15%, the electromagnetic shielding effectiveness (EMI SE) of the film reaches 44.1 dB.

[0031] (3) Due to the reasonable sandwich structure design of the electromagnetic shielding nanofilm prepared by the present invention, the oxidation of MXene is slowed down and its durability is improved. Description of the drawings

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0033] Figure 1 It is the preparation mechanism diagram of the "spin + spray" nanofilm for electromagnetic shielding in the present invention.

[0034] Figure 2 It is the physical diagram of the "spin + spray" nanofilm for electromagnetic shielding in Example 1 folded into different shapes.

[0035] Figure 3 It is the scanning electron microscope image of the "spin + spray" nanofilm for electromagnetic shielding in Example 1, where (a) is the plane scanning electron microscope of the middle layer, with a scale of 4μm; (b) is the cross-sectional electron microscope of the middle layer, with a scale of 20μm.

[0036] Figure 4 It is the electromagnetic shielding performance diagram of the "spin + spray" nanofilm for electromagnetic shielding in Examples 1 - 4.

[0037] Figure 5 It is the durability test result of the "spin + spray" nanofilm for electromagnetic shielding in Example 4. Specific Embodiments

[0038] The following are the preferred embodiments of the present invention. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0039] Test Methods:

[0040] 1. Microscopic Morphology Test:

[0041] Use a cold field emission scanning electron microscope, model Regulus8100 for testing.

[0042] 2. Electromagnetic Shielding Effect Test:

[0043] Use a network vector analyzer, model DR-S to conduct tests in the X-band (8.2 - 12.4 GHz).

[0044] Raw Materials Used in the Embodiments:

[0045] Titanium aluminum carbide (Ti3AlC2): 400 mesh, purchased from the Eleventh Institute of Science and Technology Co., Ltd.

[0046] Lithium fluoride (LiF): Analytically pure, purchased from Shanghai Aladdin Chemical Reagent Co., Ltd.

[0047] Hydrochloric acid (HCl): Analytical reagent grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0048] N,N-Dimethylformamide (DMF): Analytical reagent grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0049] Polyacrylonitrile (PAN), Mw = 150000, purchased from Suzhou Great Pharmaceutical Technology Co., Ltd.

[0050] Absolute ethanol: Analytical reagent grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0051] Enzymatic lignin was prepared by the following method: Straw was crushed into 1 - 5 mm particles by a hammer mill, treated with 1.5 MPa saturated steam for 5 - 10 minutes, then rinsed with 60 °C hot water. After solid-liquid separation, the pretreated raw material was obtained, and the pretreated raw material was formulated into a 15 wt% lignocellulose slurry with pH 4.8 phosphate buffer solution; Laccase and ABTS were covalently immobilized on a porous resin (enzyme loading = 120 U / g carrier) to obtain a laccase-mediator composite carrier. The composite carrier was filled into a fixed-bed continuous flow reactor, and the lignocellulose slurry passed through the reactor at a flow rate of 0.5 BV / h, the reaction temperature was 50 °C, and the oxygen supply rate was 0.1 vvm; The reaction effluent was intercepted by a ceramic membrane ultrafiltration (50 kDa) to retain the undegraded components. The permeate contained soluble lignin fragments. The pH of the permeate was adjusted to 2.0, and after lignin precipitation, it was separated by a disc centrifuge (3000 rpm, 10 min), and spray-dried (inlet air temperature 180 °C, outlet air temperature 80 °C) to obtain powdered enzymatic lignin.

[0052] In the examples, % without specific indication of meaning refers to mass percentage.

[0053] The following combines specific examples to elaborate in detail on the technical solutions of the present invention. In the following examples, unless otherwise specified, the reagents, materials, and equipment used can be obtained through commercial channels, or prepared by conventional methods, or commonly used in this industry.

[0054] Example 1

[0055] A method for preparing a "spin + spray" nanofilm for electromagnetic shielding, comprising the following steps:

[0056] (1) 2 g of lithium fluoride (LiF) and 40 mL of 9 M hydrochloric acid (HCl) were mixed evenly and then added to 2 g of titanium aluminum carbide (Ti3AlC2), and stirred at 35 °C for 48 hours. After centrifugal washing and ultrasonic treatment for 1 h, the supernatant was collected by centrifugation to obtain a MXene dispersion;

[0057] (2) The MXene dispersion of 20 mg / mL was mixed with an equal volume of absolute ethanol to obtain an electrospraying solution;

[0058] (3) 1.33 g of polyacrylonitrile (PAN) was added to 10 g of N,N-dimethylformamide (DMF) and stirred evenly. Then, 0.57 g of enzymatically hydrolyzed lignin was added and stirred for 24 hours to obtain a homogeneous spinning solution with a solid content of 16 wt%, where the mass ratio of polyacrylonitrile (PAN) to enzymatically hydrolyzed lignin was 7:3;

[0059] (4) 4.9 mL of electrospraying solution and 12 mL of spinning solution were respectively placed in syringes. The electrospinning injection speed was adjusted to 0.8 mL / h, the electrospraying speed was 0.5 mL / h, the common applied voltage was 17 kV, the roller rotation speed was 100 rpm, and the receiving distance was 15 cm. First, the lower layer lignin / PAN nanofiber membrane was prepared, and the electrospinning time was 3 h; then, the middle layer MXene@lignin / PAN composite membrane was prepared, and the "spinning + spraying" time was 9 h; finally, the upper layer lignin / PAN nanofiber membrane was prepared, and the spinning time was 3 h. Eventually, a "spinning + spraying" nanofilm with a sandwich layer structure was assembled, where the MXene loading was 2.5%.

[0060] Figure 2 Figure of the "spinning + spraying" nanofilm with a sandwich layer structure folded into different shapes, Figure 3 Scanning electron microscope image of the "spinning + spraying" nanofilm with a sandwich layer structure.

[0061] Comparative Example 1:

[0062] The present application also optimized the mass ratio of polyacrylonitrile to enzymatically hydrolyzed lignin as follows:

[0063] Other steps were the same as those in Example 1, and the solid content in step (3) was fixed at 16 wt%. Only the ratio of polyacrylonitrile to lignin was adjusted to 5:5, and electrospinning was carried out. As a result, the obtained spinning film was brittle, and the fibers had a certain amount of beading and lacked a certain degree of flexibility.

[0064] Other steps were the same as those in Example 1, and the solid content in step (3) was fixed at 16 wt%. Only the ratio of polyacrylonitrile to lignin was adjusted to 6:4, and electrospinning was carried out. As a result, the obtained spinning film had relative flexibility but was still not flexible enough.

[0065] When the ratio of polyacrylonitrile to lignin in Example 1 was 7:3 and electrospinning was carried out, the obtained spinning film had good flexibility, the fibers had no beading, and the sizes were uniform.

[0066] Example 2

[0067] The volume of the electrospraying solution in step (4) of Example 1 was adjusted to 10 mL, and the electrospraying speed was 1.1 mL / h. Other conditions were the same as those in Example 1, and a "spinning + spraying" nanofilm was obtained; where the MXene loading was 5%.

[0068] Example 3

[0069] Adjust the volume of the electrospraying liquid in step (4) of Example 1 to 21 mL, and the electrostatic spraying speed to 2.3 mL / h. Keep the others the same as in Example 1 to obtain the "spinning + spraying" nanofilm; the MXene loading is 10%.

[0070] Example 4

[0071] Adjust the volume of the electrospraying liquid in step (4) of Example 1 to 33.5 mL, and the electrostatic spraying speed to 3.7 mL / h. Keep the others the same as in Example 1 to obtain the "spinning + spraying" nanofilm; the MXene loading is 15%.

[0072] Perform performance tests on the obtained "spinning + spraying" nanofilm, and the test results are as follows:

[0073] Figure 4 It is the electromagnetic shielding performance diagram of the "spinning + spraying" nanofilm used for electromagnetic shielding in Examples 1 - 4. From Figure 4 it can be seen that: when the solid content of MXene in the nanofilm is 2.5% (Example 1), the electromagnetic shielding performance can reach 19 dB; when the solid content of MXene in the nanofilm is 5% (Example 2), the electromagnetic shielding performance can reach 23.3 dB; when the solid content of MXene in the nanofilm is 10% (Example 3), the electromagnetic shielding performance can reach 33.1 dB; when the solid content of MXene in the nanofilm is 15% (Example 4), the electromagnetic shielding performance can reach 44.1 dB.

[0074] Perform durability tests on the "spinning + spraying" nanofilm prepared in Example 4, and use the unassembled middle - layer MXene@lignin / PAN composite film in Example 4 as a control for durability tests. Among them, the electromagnetic shielding performance of the sandwich structure only decreased by 4.1 dB after being placed for 4 months, while that of the single middle - layer decreased by 9 dB after being placed for four months. The comparison is as Figure 5 shown.

[0075] Example 5

[0076] Adjust the electrospinning time of the upper and lower layers in step (4) of Example 4 to 1 h respectively, the "spinning + spraying" time of the middle layer to 13 h, and the electrostatic spraying injection speed to 2.58 mL / h; keep the others the same as in Example 1 to obtain the "spinning + spraying" nanofilm.

[0077] Example 6

[0078] Adjust the electrospinning time of the upper and lower layers in step (4) of Example 4 to 2 h respectively, the "spinning + spraying" time of the middle layer to 11 h, and the electrostatic spraying injection speed to 3.05 mL / h; keep the other conditions the same as those in Example 1 to obtain the "spinning + spraying" nanofilm.

[0079] Example 7

[0080] Adjust the electrospinning time of the upper and lower layers in step (4) of Example 4 to 4 h respectively, the "spinning + spraying" time of the middle layer to 7 h, and adjust the electrostatic spraying injection speed to 4.79 mL / h;

[0081] Keep the other conditions the same as those in Example 1 to obtain the "spinning + spraying" nanofilm.

[0082] Example 8

[0083] Adjust the electrospinning time of the upper and lower layers in step (4) of Example 4 to 5 h respectively, the "spinning + spraying" time of the middle layer to 5 h, and adjust the electrostatic spraying injection speed to 6.7 mL / h;

[0084] Keep the other conditions the same as those in Example 1 to obtain the "spinning + spraying" nanofilm.

[0085] In this application, by controlling the speed of electrostatic spraying, the solid content of MXene in the nanofilms prepared in Examples 5 to 8 is 15% finally.

[0086] Comparative Example 2: Prepare a nanofilm with the same MXene loading by blending

[0087] Adjust steps (2), (3), and (4) of Example 4 as follows:

[0088] Place the MXene dispersion in a refrigerator at -20 °C and pre-freeze it for 12 h, then place it in a freeze dryer and freeze-dry it to obtain MXene powder. Take 335 mg and dissolve it in 11.6 g of N,N-dimethylformamide (DMF), stir evenly, add 1.33 g of polyacrylonitrile (PAN) and 0.57 g of enzymatically hydrolyzed lignin, stir evenly to obtain a spinning solution with a solid content of 16 wt%, where the MXene loading is 15%, and carry out electrospinning according to the electrospinning conditions in step (4) of Example 4.

[0089] Keep the other conditions the same as those in Example 1 to obtain a blended nanofilm.

[0090] Comparative Example 3: Prepare a nanofilm by the method of electrospinning first and then spraying

[0091] Adjust step (4) of Example 4 as follows:

[0092] First carry out electrospinning for 15 h, and then carry out electrostatic spraying for 9 h;

[0093] The rest is the same as in Example 1 to obtain a nanofilm with single-sided sprayed MXene.

[0094] Comparative Example 4: Prepare a nanofiber with an electrospun nanofiber as the intermediate layer and electrosprayed MXene nanosheets on both sides

[0095] Adjust step (4) of Example 4 to:

[0096] First, perform electrospinning for 15 h, then perform electrospraying for 4.5 h, and then peel the nanofilm from the tin foil and perform electrospraying on the reverse side for 4.5 h;

[0097] The rest is the same as in Example 1 to obtain a nanofilm with double-sided sprayed MXene.

[0098] Comparative Example 5:

[0099] Omit the electrospraying operations in steps (1), (2) and step (4) of Example 4, and the rest is the same as in Example 4 to obtain a lignin / PAN nanofilm.

[0100] Perform performance tests on the nanofilms prepared in Examples 4 to 8 and Comparative Examples 2 to 5, and the test results are as follows:

[0101] Table 1

[0102] Example Electromagnetic shielding performance (dB) Example 4 44.1 Example 5 42.3 Example 6 43.0 Example 7 38.4 Example 8 35.7 Comparative Example 2 1.9 Comparative Example 3 33.5 Comparative Example 4 37.1 Comparative Example 5 0.23

[0103] As can be seen from Table 1, the electromagnetic shielding effects of Examples 4 to 6 are not very different, while the electromagnetic shielding effects of Examples 7 and 8 are relatively low. This is because the intermediate layers of Examples 4 to 6 are thicker, and the formed layer structure can effectively dissipate electromagnetic waves multiple times. However, in Examples 7 and 8, due to the thinning of the intermediate layer, MXene accumulates, so the same amount of MXene will have a lower electromagnetic shielding effect. In Comparative Example 2, a nanofilm with the same MXene loading amount was prepared by a blending method, and MXene accumulated severely, resulting in a very poor electromagnetic shielding effect. For the nanofilms prepared by the single-sided spraying and double-sided spraying methods in Comparative Examples 3 and 4, the problem of MXene stacking cannot be solved, and the electromagnetic shielding effect is also weak.

[0104] The embodiments provided above are not intended to limit the scope covered by the present invention, and the described steps are not intended to limit their execution order. Obvious improvements made by those skilled in the art to the present invention in combination with the existing common general knowledge also fall within the protection scope defined by the claims of the present invention.

Claims

1. A preparation method of a nanomembrane for electromagnetic shielding, characterized in that, It includes the following steps: (1) Mix lithium fluoride and hydrochloric acid, add aluminum titanium carbide for reaction, and perform ultrasonic exfoliation after the reaction to obtain an MXene suspension; (2) Mix the MXene suspension with a volatile organic solvent to obtain an electrospray solution; (3) Add polyacrylonitrile to an organic solvent for mixing, add enzymatically hydrolyzed lignin, and fully stir to obtain a spinning solution; (4) Electrospin the spinning solution in step (3) to prepare an upper layer of lignin / polyacrylonitrile nanofiber membrane, simultaneously perform electrospraying and electrospinning on the electrospray solution in step (2) and the spinning solution in step (3) to prepare a middle layer of MXene@lignin / polyacrylonitrile composite membrane, and electrospin the spinning solution in step (3) to prepare a lower layer of lignin / polyacrylonitrile nanofiber membrane, and assemble the three layers of membranes in sequence to form the nanofilm for electromagnetic shielding.

2. The preparation method according to claim 1, wherein In step (1), the concentration of the MXene suspension is 10 mg / mL to 25 mg / mL.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of lithium fluoride to aluminum titanium carbide is 1:0.5 to 2; the reaction temperature is 35 °C to 40 °C, and the reaction time is 40 to 60 h.

4. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of polyacrylonitrile to enzymatically hydrolyzed lignin is 6 to 8:

3.

5. The preparation method according to claim 1, characterized in that, In step (3), the solid content of the spinning solution is 10 wt% to 20 wt%.

6. The preparation method according to claim 1, characterized in that, In step (4), the voltage for electrospinning the upper and lower layers is 12 to 20 kv, the injection speed is 0.5 to 1 mL / h, and the electrospinning time is 1 to 5 h.

7. The preparation method according to claim 1, characterized in that, In step (4), the preparation of the middle layer is to simultaneously perform electrospinning and electrospraying. The injection speed of electrospraying is 0.5 to 7 mL / h, the voltage is 12 to 20 kv, and the time is 6 to 11 h.

8. A nanofilm for electromagnetic shielding prepared by the preparation method according to any one of claims 1 to 7.

9. Application of the nanofilm for electromagnetic shielding according to claim 8 in the fields of aerospace, national defense, or next-generation flexible wearable electronic devices.

10. An electromagnetic shielding material, characterized in that, It uses the nanofilm for electromagnetic shielding according to claim 8.

Images