Preparation method of multilayer asymmetric wave-absorbing film material

Abstract

The application discloses a kind of preparation methods of multilayer asymmetric wave-absorbing film material, belong to electromagnetic wave absorbing material field.Mainly include the following steps: after surface modification of magnetic particle in aqueous phase, load on graphene oxide, with water-soluble polymer solution is mixed evenly, under negative pressure, film is formed by volatilization to obtain magnetic film;Electrically conductive nano-filler is mixed evenly with water-soluble polymer, under negative pressure, film is formed by volatilization to obtain conductive film;Magnetic film and conductive film are stacked with different layers, and are bonded and solidified with thermosetting resin, to obtain multilayer asymmetric film material.The preparation process of the application is simple and reliable, the obtained film is thin, has high absorption loss characteristics under Ka band, and the number of layers of magnetic film and conductive film can be adjusted to realize the adjustment of wave-absorbing performance.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing materials, and particularly relates to a method for preparing a multilayer asymmetric absorbing thin film material. Background Technology

[0002] In today's society, with the rapid development of 5G technology and the widespread adoption of related electronic devices, the resulting electromagnetic pollution and electromagnetic compatibility issues have attracted the attention of governments and manufacturers worldwide. Developing high-performance absorbing materials with low surface reflection loss and high absorption loss for the 5G frequency band is crucial. Materials with asymmetric structures can help reduce surface reflection loss, thereby allowing electromagnetic waves to penetrate the material and improving its absorption capacity. Developing materials with asymmetric structures holds promise for solving the problem of efficient electromagnetic wave absorption in the 5G frequency band.

[0003] Chinese patent CN115103582A discloses an asymmetric alternating multilayer electromagnetic interference shielding nanocomposite film and its preparation method. This method uses cellulose nanofibers as a matrix and alternately stacks an absorption layer containing different proportions of magnetic nanoparticles and a conductive layer containing different proportions of conductive nanoparticles to prepare the nanocomposite film.

[0004] Chinese patent CN116715870A discloses an asymmetric chitosan gel, a chitosan film, and a method for preparing the same. The method first prepares an asymmetric chitosan gel, which is then subjected to particle washing and freeze-drying to obtain a chitosan film with an asymmetric structure.

[0005] Existing technologies suffer from complex processes and high preparation costs, and there is a lack of research and development on asymmetric thin film preparation methods for the Ka band (26.5–40 GHz). Summary of the Invention

[0006] To address the shortcomings and drawbacks of the existing technology, the present invention aims to provide a method for preparing a multilayer asymmetric absorbing thin film material. The preparation process is simple and reliable, the resulting film is thin, exhibits high absorption loss characteristics in the Ka band, and the absorption performance can be adjusted by regulating the number of magnetic and conductive thin film layers.

[0007] The technical solution adopted in this invention is:

[0008] 1. A method for preparing a multilayer asymmetric microwave absorbing thin film material, which is formed by bonding several layers of magnetic thin film and several layers of conductive thin film together by hot pressing and curing with thermosetting resin.

[0009] 2. As described above, in the preparation method of a multilayer asymmetric absorbing thin film material, the multilayer asymmetric absorbing thin film is composed of at least one magnetic thin film and one conductive thin film.

[0010] 3. As described above, the preparation method of a multilayer asymmetric microwave absorbing thin film material, wherein the magnetic thin film is prepared by: firstly, loading surface-modified magnetic particles such as iron oxide and cobalt oxide onto graphene oxide, then mixing them uniformly with water-soluble polymers such as chitosan, polyvinyl alcohol, polyethylene glycol, and sodium alginate in an aqueous phase, and finally evaporating them under negative pressure to form a film, thereby obtaining a magnetic thin film.

[0011] 4. As described above, the preparation method of a multilayer asymmetric microwave absorbing film material, wherein the conductive film is prepared by mixing one or more of the conductive nanofillers such as carbon nanotubes, graphene, and two-dimensional titanium carbide with water-soluble polymers such as chitosan, polyvinyl alcohol, polyethylene glycol, and sodium alginate in an aqueous phase, and then volatilizing under negative pressure to form a film, thereby obtaining a conductive film.

[0012] 5. The preparation method of the above-mentioned multilayer asymmetric absorbing thin film material includes the following steps:

[0013] Step 1: Add the magnetic particles to the aqueous solution of the modifier, disperse them evenly under the action of ultrasound, and then place them on a shaker to make the modifier and magnetic particles fully contact each other. Finally, wash with deionized water to obtain surface-modified magnetic particles.

[0014] Step 2: Add the surface-modified magnetic particles to the aqueous dispersion of graphene oxide, mix them evenly under ultrasonic dispersion, and then place them on a shaker to load the surface-modified magnetic particles onto the graphene oxide to obtain graphene oxide loaded with magnetic particles.

[0015] Step 3: Mix the graphene oxide-loaded magnetic particles obtained in Step 2 with a certain concentration of water-soluble polymer solution. After mechanical stirring and ultrasonic dispersion, remove the air bubbles in the dispersion and volatilize under negative pressure to form a film, thus obtaining a magnetic thin film.

[0016] Step 4: Ultrasonically disperse graphene oxide in a 1% acetic acid aqueous solution, add conductive nanofiller, and then mix with a certain concentration of water-soluble polymer solution. Under ultrasonic dispersion, a conductive nanofiller / graphene oxide / water-soluble polymer mixed dispersion is obtained. After removing bubbles, it is volatilized under negative pressure to form a film, thus obtaining a conductive film.

[0017] Step 5: Stack the magnetic film obtained in Step 3 and the conductive film obtained in Step 4 with different numbers of layers, apply a small amount of thermosetting resin between each layer, place them in a hot press, and bond and cure them under certain pressure and temperature to obtain a multilayer asymmetric microwave absorbing film material.

[0018] Furthermore, in step one, the magnetic particles are one or a mixture of iron(III) oxide and cobalt(III) oxide, preferably iron(III) oxide, the modifier is a quaternary ammonium salt surface modifier with long-chain alkyl groups, preferably hexadecyltrimethylammonium bromide, the concentration of the aqueous solution of the modifier is 1-5 mg / mL, preferably 2 mg / mL, the mass ratio of magnetic particles to modifier is 1:1-5:1, preferably 2.5:1, the shaking time is 10 min-12 h, preferably 1 h, and the mixture is washed twice with deionized water.

[0019] Furthermore, in step two, the concentration of the graphene oxide aqueous dispersion is 1-5 mg / mL, preferably 4 mg / mL; the mass ratio of magnetic particles to graphene oxide is 1:5-1:1, preferably 1:3; the ultrasonic time is 5-30 min, preferably 10 min; and the shaking time is 1-12 h, preferably 10 h.

[0020] Furthermore, in step three, the water-soluble polymer is preferably chitosan, the solution concentration is 5-20 mg / mL, preferably 10 mg / mL, the mass ratio of graphene oxide-loaded magnetic particles to water-soluble polymer is 1:2-1:1, preferably 2:5, the mechanical stirring time is 10-30 min, preferably 30 min, the ultrasonic treatment time is 10 min-1 h, preferably 30 min, the vacuum degree of the drying oven is -60 kPa to atmospheric pressure, preferably -40 kPa, and the temperature is 40-80℃, preferably 45℃.

[0021] Furthermore, in step four, in the conductive nanofiller / graphene oxide / water-soluble polymer mixed dispersion, the conductive nanofiller is preferably carbon nanotubes with a concentration between 1 and 5 mg / mL, preferably 5 mg / mL; the graphene oxide concentration is 0.5 to 2 mg / mL, preferably 2 mg / mL; the water-soluble polymer is preferably chitosan with a concentration between 5 and 20 mg / mL, preferably 10 mg / mL; the ultrasonic treatment time is 10 min to 1 h, preferably 30 min; the vacuum degree of the drying oven is -60 kPa to atmospheric pressure, preferably -40 kPa; and the temperature is 40 to 80 °C, preferably 45 °C.

[0022] Furthermore, in step five, the thermosetting resin is a thermosetting resin such as epoxy resin, acrylate, or polyurethane, preferably epoxy resin E51, the curing agent is 4,4′-diaminodiphenylmethane, the curing conditions are preferably 80°C for 1 hour, then 120°C for 2 hours, and finally 150°C for 1 hour, and the pressure is 0.2-0.6 MPa, preferably 0.4 MPa.

[0023] Furthermore, in step five, the number of layers of the magnetic thin film and the conductive thin film shall be no less than one and no more than five.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The present invention provides a method for preparing a multilayer asymmetric absorbing thin film material, which is a high absorption loss thin film material developed for the high-frequency millimeter-wave band, namely the Ka band (26.5-40 GHz). A magnetic thin film is used as an impedance matching layer to reduce the surface impedance of the material, which is beneficial for reducing the reflection of electromagnetic waves on the material surface. A thin film with strong conductivity is used as an electromagnetic wave absorbing layer, which is beneficial for the absorption of electromagnetic waves inside the material. Through asymmetric structural design, high absorption loss can be achieved at a relatively thin thickness.

[0026] (2) The present invention provides a method for preparing a multilayer asymmetric absorbing thin film material, which can achieve precise control of the absorbing performance of the multilayer thin film by changing the number of layers of the magnetic thin film and the conductive thin film.

[0027] (3) The present invention provides a method for preparing a multilayer asymmetric microwave absorbing film material, which can easily and conveniently obtain a microwave absorbing film material with a multilayer asymmetric structure. By curing and bonding the magnetic film and the conductive film with a thermosetting resin under certain pressure and temperature, the mass production of multilayer asymmetric films can be achieved rapidly, which is beneficial to industrialization. Attached Figure Description

[0028] Figure 1 This is a scanning electron microscope image of the multilayer asymmetric absorbing film material obtained in Example 1 of the present invention.

[0029] Figure 2 These are the absorption loss (SEA) curves of the multilayer asymmetric absorbing thin film materials obtained in Examples 1 to 3 of the present invention in the Ka band (26.5 to 40 GHz).

[0030] Figure 3 The absorption loss (SE) of the magnetic thin film obtained in Comparative Example 1 of this invention in the Ka band (26.5–40 GHz) is... A )curve.

[0031] Figure 4 The absorption loss (SE) of the conductive thin film obtained in Comparative Example 2 of this invention in the Ka band (26.5–40 GHz) is... A )curve.

[0032] Figure 5 This is a scanning electron microscope image of the surface of the magnetic thin film obtained in Comparative Example 1 of the present invention.

[0033] Figure 6 This is a scanning electron microscope image of the surface of the conductive thin film obtained in Comparative Example 2 of the present invention.

[0034] Figure 7The absorption loss (SE) of the multilayer asymmetric absorbing thin film material obtained in Example 4 of this invention in the Ka band (26.5-40 GHz) is... A )curve.

[0035] Figure 8 The absorption loss (SE) of the multilayer asymmetric absorbing thin film material obtained in Example 5 of this invention in the Ka band (26.5-40 GHz) is... A )curve. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0037] Example 1:

[0038] Step 1: Add 100 mg of iron oxide nanospheres to 20 mL of a 2 mg / mL hexadecyltrimethylammonium bromide aqueous solution, disperse for 5 min under ultrasonic treatment in a water bath, then mix on a shaker for 1 h, and finally wash twice with deionized water to obtain surface-modified iron oxide microspheres.

[0039] Step 2: Add 100 mg of surface-modified iron oxide microspheres to 75 mL of an aqueous dispersion of graphene oxide with a concentration of 4 mg / mL, sonicate in a water bath for 10 min, and then mix on a shaker for 10 h to obtain graphene oxide-supported iron oxide microspheres.

[0040] Step 3: Mix the graphene oxide-supported iron oxide microspheres obtained in Step 2 with 10 mg / mL chitosan solution at a volume ratio of 1:1, stir mechanically for 30 min, then sonicate for 30 min, and after vacuum degassing, take 32 mL and add it to a petri dish with a bottom diameter of 90 mm. At a temperature of 45 °C and a negative pressure of -40 kPa, volatilize to form a film to obtain a magnetic thin film.

[0041] Step 4: Disperse 200 mg of graphene oxide in 100 mL of 1% acetic acid aqueous solution to prepare a dispersion of 2 mg / mL. Add 1000 mg of carbon nanotubes and mix with an equal volume of 10 mg / mL chitosan solution. Disperse ultrasonically for 30 min to obtain a carbon nanotube / graphene oxide / chitosan mixed dispersion. After removing air bubbles under vacuum, take 32 mL and add it to a petri dish with a bottom diameter of 90 mm. Volatilize at 45 °C and under a negative pressure of -40 kPa to form a film, thus obtaining a conductive film.

[0042] Step 5: Stack the magnetic film layer 1 obtained in Step 3 and the conductive film layer 1 obtained in Step 4 together. Mix epoxy resin E51 and curing agent 4,4′-diaminodiphenylmethane evenly and apply it between the two film layers. Place it in a hot press, set the pressure to 0.4MPa, first heat to 80℃ and hold for 1 hour, then heat to 120℃ and hold for 2 hours, and finally heat to 150℃ and hold for 1 hour. Remove it and let it cool to room temperature to obtain the (1 magnetic + 1 conductive) dual-functional layer asymmetric absorbing film material.

[0043] The multilayer asymmetric absorbing thin film material prepared in this embodiment has an average thickness of 80.4 μm. It consists of a bifunctional layer composed of one magnetic thin film and one conductive thin film, with an epoxy resin adhesive layer in between. A scanning electron microscope image of its cross-section is shown below. Figure 1 As shown, this thin film material has a multilayer structure. The thicker layer on the left is a conductive film, and the thinner layer on the right is a magnetic film. The gap between the two is an epoxy resin adhesive layer. This dual-functional layer of 1 magnetic + 1 conductive layer exhibits excellent wave absorption performance, such as... Figure 2 As shown. Its absorption loss SE is [value missing] across the entire frequency range of the Ka band (26.5–40 GHz). A All are above 22.7 dB. Its absorption performance is significantly better than that of... Figure 3 The single-layer magnetic thin film shown in Comparative Example 1 is also superior to that shown in Comparative Example 1. Figure 4 The single-layer conductive film shown in Comparative Example 2. Taking the absorption loss at 33.52 GHz as an example, the SE at this frequency in Example 1 is... A The value was 24.26 dB, which is not only significantly higher than 0.42 dB in Comparative Example 1 and 20.26 dB in Comparative Example 2, but also higher than the sum of the two. Therefore, the structure of the asymmetric multilayer thin film material in Example 1 is more conducive to the absorption of electromagnetic waves than that of a single-layer thin film.

[0044] Comparative Example 1:

[0045] Step 1: Add 100 mg of iron oxide nanospheres to 20 mL of a 2 mg / mL hexadecyltrimethylammonium bromide aqueous solution, disperse for 5 min under ultrasonic treatment in a water bath, then mix on a shaker for 1 h, and finally wash twice with deionized water to obtain surface-modified iron oxide microspheres.

[0046] Step 2: Add 100 mg of surface-modified iron oxide microspheres to 75 mL of an aqueous dispersion of graphene oxide with a concentration of 4 mg / mL, sonicate in a water bath for 10 min, and then mix on a shaker for 10 h to obtain graphene oxide-supported iron oxide microspheres.

[0047] Step 3: Mix the graphene oxide-supported iron oxide microspheres obtained in Step 2 with 10 mg / mL chitosan solution at a volume ratio of 1:1, stir mechanically for 30 min, then sonicate for 30 min, and after vacuum degassing, take 32 mL and add it to a petri dish with a bottom diameter of 90 mm. At a temperature of 45 °C and a negative pressure of -40 kPa, volatilize to form a film to obtain a magnetic thin film.

[0048] Comparative Example 1 is the same as Example 1 in the first three steps, the main difference being that Comparative Example 1 only prepares a magnetic thin film.

[0049] The average thickness of the monolayer magnetic film prepared in Comparative Example 1 is 33.1 μm, and its surface is shown in the scanning electron microscope image as follows. Figure 5 As shown in the figure, the spherical particles are magnetic iron oxide microspheres, uniformly dispersed. The absorption loss curve of the monolayer magnetic thin film for Ka-band electromagnetic waves is shown in the figure. Figure 3 As shown, the magnetic thin film has a very weak absorption capacity for electromagnetic waves, with a SEA of 0.05–0.70 dB in the Ka band, which is far lower than the absorption loss of the asymmetric thin film in Example 1. The role of the magnetic thin film in the asymmetric thin film is to improve the impedance matching between the material surface and free space, thereby reducing reflection loss and improving absorption loss.

[0050] Comparative Example 2:

[0051] Step 1: 200 mg of graphene oxide was ultrasonically dispersed in 100 mL of 1% acetic acid aqueous solution to prepare a dispersion of 2 mg / mL. 1000 mg of carbon nanotubes was added, and then mixed with an equal volume of 10 mg / mL chitosan solution. The mixture was ultrasonically dispersed for 30 min to obtain a carbon nanotube / graphene oxide / chitosan mixed dispersion. After removing air bubbles under vacuum, 32 mL of the dispersion was added to a petri dish with a bottom diameter of 90 mm. The mixture was then evaporated to form a film at 45 °C and under a negative pressure of -40 kPa to obtain a conductive film.

[0052] Comparative Example 2 is the same as step four of Example 1, except that Comparative Example 2 only prepares a conductive thin film.

[0053] The average thickness of the monolayer conductive film prepared in Comparative Example 2 was 46.3 μm, and its surface scanning electron microscope image is shown below. Figure 6 As shown in the figure, the conductive film is composed of coiled and intertwined carbon nanotubes, thus exhibiting excellent conductivity. The absorption loss curve of a single-layer conductive film for Ka-band electromagnetic waves is shown in the figure. Figure 4As shown, the conductive thin film exhibits strong electromagnetic wave absorption, with an SEA of 20.20–24.21 dB in the Ka band, lower than the absorption loss of the asymmetric thin film in Example 1. The conductive thin film in the asymmetric thin film acts as an electromagnetic wave absorption layer; however, its high conductivity results in strong electromagnetic wave reflection. To reduce electromagnetic wave reflection, combining the conductive thin film with a magnetic thin film to form an asymmetric multilayer thin film material can achieve the goal of reducing reflection loss and improving absorption loss.

[0054] Example 2:

[0055] Step 5: Stack two magnetic films and one conductive film together. Mix epoxy resin E51 and curing agent 4,4′-diaminodiphenylmethane evenly and apply it between the two films. Place it in a hot press, set the pressure to 0.4 MPa, first heat to 80℃ and hold for 1 hour, then heat to 120℃ and hold for 2 hours, and finally heat to 150℃ and hold for 1 hour. Remove it and let it cool to room temperature to obtain the (2 magnetic + 1 conductive) three-functional layer asymmetric absorbing film material.

[0056] The remaining steps are the same as in Example 1.

[0057] The multilayer asymmetric absorbing thin film material prepared in Example 2 has an average thickness of 114.5 μm and is a three-functional layer asymmetric structure with 2 magnetic layers and 1 conductive layer. The absorption loss curve for Ka-band electromagnetic waves is shown below. Figure 2 As shown, its absorption loss SEA is between 23.20 and 31.18 dB across the entire frequency range of 26.5–40 GHz, which is higher than that of Example 1. This indicates that adding a magnetic layer helps to further reduce the surface loss of the material, thereby achieving higher absorption loss.

[0058] Example 3:

[0059] Step 5: Stack 3 layers of magnetic film and 1 layer of conductive film together. Mix epoxy resin E51 and curing agent 4,4′-diaminodiphenylmethane evenly and apply it between the two layers of film. Place it in a hot press, set the pressure to 0.4MPa, first heat to 80℃ and hold for 1 hour, then heat to 120℃ and hold for 2 hours, and finally heat to 150℃ and hold for 1 hour. Remove it and let it cool to room temperature to obtain the (3 magnetic + 1 conductive) four-functional layer asymmetric absorbing film material.

[0060] The remaining steps are the same as in Example 1.

[0061] The multilayer asymmetric absorbing thin film material prepared in Example 3 has an average thickness of 148.6 μm and is a four-functional layer asymmetric structure with 3 magnetic layers and 1 conductive layer. The absorption loss curve for Ka-band electromagnetic waves is shown below. Figure 2 As shown. Its absorption loss SE is [value missing] across the entire frequency range of 26.5–40 GHz. AThe values ​​ranged from 24.80 to 33.29 dB, all of which were higher than those in Examples 1 and 2.

[0062] Example 4:

[0063] Step 2: Add 200 mg of surface-modified iron oxide microspheres to 75 mL of an aqueous dispersion of graphene oxide with a concentration of 4 mg / mL, sonicate in a water bath for 10 min, and then mix on a shaker for 10 h to obtain graphene oxide-supported iron oxide microspheres.

[0064] The remaining steps are the same as in Example 1.

[0065] The difference between Example 4 and Example 1 is that the amount of modified iron oxide microspheres used is twice that of Example 1.

[0066] The multilayer asymmetric absorbing thin film material prepared in Example 4 has an average thickness of 80.8 μm and is a bifunctional asymmetric structure with one magnetic layer and one conductive layer. The absorption loss curve for Ka-band electromagnetic waves is shown below. Figure 7 As shown. Its absorption loss SE is [value missing] across the entire frequency range of 26.5–40 GHz. A The range is 22.31–33.41 dB.

[0067] Example 5:

[0068] Step 3: Mix the graphene oxide-supported iron oxide microspheres obtained in Step 2 with 20 mg / mL chitosan solution at a volume ratio of 1:1, stir mechanically for 30 min, then sonicate for 30 min, and after vacuum degassing, take 32 mL and add it to a petri dish with a bottom diameter of 90 mm. At a temperature of 45 °C and a negative pressure of -40 kPa, volatilize to form a film to obtain a magnetic thin film.

[0069] Step 4: Disperse 200 mg of graphene oxide in 100 mL of 1% acetic acid aqueous solution to prepare a dispersion of 2 mg / mL. Add 1000 mg of carbon nanotubes and mix with an equal volume of 20 mg / mL chitosan solution. Disperse ultrasonically for 30 min to obtain a carbon nanotube / graphene oxide / chitosan mixed dispersion. After removing air bubbles under vacuum, take 32 mL and add it to a petri dish with a bottom diameter of 90 mm. Volatilize at 45 °C and under a negative pressure of -40 kPa to form a film, thus obtaining a conductive film.

[0070] The remaining steps are the same as in Example 1.

[0071] The difference between Example 5 and Example 1 is that the amount of chitosan used in the magnetic film and conductive film is twice that in Example 1.

[0072] The multilayer asymmetric absorbing thin film material prepared in Example 5 has an average thickness of 176.2 μm and is a bifunctional asymmetric structure with one magnetic layer and one conductive layer. The absorption loss curve for Ka-band electromagnetic waves is shown below. Figure 7 As shown, the overall wave absorption capability of the material weakens due to the increased chitosan content in the magnetic and conductive layers. Its absorption loss SEA is 17.05–19.05 dB across the entire frequency range of 26.5–40 GHz.

[0073] In summary, this invention provides a method for preparing a multilayer asymmetric microwave absorbing thin film material. First, magnetic particles are surface-modified in an aqueous phase and then loaded onto graphene oxide. After being uniformly mixed with a water-soluble polymer solution, the mixture is volatilized under negative pressure to form a magnetic thin film. Next, conductive nanofillers are uniformly mixed with a water-soluble polymer and volatilized under negative pressure to form a conductive thin film. Finally, the magnetic and conductive thin films are stacked with different numbers of layers and bonded and cured with a thermosetting resin to obtain a multilayer asymmetric thin film material. The preparation process is simple and reliable, the resulting film is thin, exhibits high absorption loss characteristics in the Ka band, and the microwave absorption performance can be adjusted by changing the number of magnetic and conductive thin films.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a multilayer asymmetric microwave absorbing thin film material, characterized in that, It is formed by bonding at least one magnetic film and at least one conductive film together by hot pressing with a thermosetting resin. The preparation method of the magnetic film includes the following steps: loading magnetic particles onto graphene oxide, mixing them uniformly with water-soluble polymers in an aqueous phase, and evaporating them under negative pressure to form a film, thereby obtaining a magnetic film. The mass ratio of magnetic particles to graphene oxide in the magnetic film is 1:5 to 1:

1. The water-soluble polymers include one or more of chitosan, polyvinyl alcohol, polyethylene glycol, and sodium alginate. The magnetic particles are surface-modified iron(III) oxide. The surface modification uses hexadecyltrimethylammonium bromide as a modifier, and the mass ratio of magnetic particles to surface modifier is 1:1 to 5:

1. The mass ratio of graphene oxide-loaded magnetic particles to water-soluble polymers is 1:2 to 1:

1. The conductive film is formed by uniformly mixing graphene oxide, conductive functional nanofillers, and water-soluble polymers in an aqueous phase, and evaporating them under negative pressure. The conductive functional nanofillers include one or more of carbon nanotubes, graphene, and two-dimensional titanium carbide.

2. The method for preparing a multilayer asymmetric absorbing thin film material as described in claim 1, characterized in that, Includes the following steps: Step 1: Add the magnetic particles to the aqueous solution of the modifier, disperse them evenly under the action of ultrasound, and then place them on a shaker to make the modifier and magnetic particles fully contact each other. Finally, wash with deionized water to obtain surface-modified magnetic particles. Step 2: Add the surface-modified magnetic particles to the aqueous dispersion of graphene oxide, mix them evenly under ultrasonic dispersion, and then place them on a shaker to load the surface-modified magnetic particles onto the graphene oxide to obtain graphene oxide loaded with magnetic particles. Step 3: Mix the graphene oxide-loaded magnetic particles obtained in Step 2 with a water-soluble polymer solution. After mechanical stirring and ultrasonic dispersion, remove the air bubbles in the dispersion and volatilize under negative pressure to form a film, thus obtaining a magnetic thin film. Step 4: Ultrasonically disperse graphene oxide in a 1% acetic acid aqueous solution, add conductive nanofiller, and then mix with a certain concentration of water-soluble polymer solution. Under ultrasonic dispersion, a conductive nanofiller / graphene oxide / water-soluble polymer mixed dispersion is obtained. After removing bubbles, it is volatilized under negative pressure to form a film, thus obtaining a conductive film. Step 5: Stack several layers of the magnetic film obtained in Step 3 and the conductive film obtained in Step 4 with different numbers of layers, apply a small amount of thermosetting resin between each layer of film, place them in a hot press, and bond and cure them under certain pressure and temperature to obtain a multilayer asymmetric microwave absorbing film material.

3. The method for preparing a multilayer asymmetric absorbing thin film material as described in claim 2, characterized in that: The concentration of the modifier in aqueous solution is 1-5 mg / mL, the mixing time on a shaker is 10 min-12 h, and it is washed twice with deionized water.

4. The method for preparing a multilayer asymmetric absorbing thin film material as described in claim 2 or 3, characterized in that: In step two, the concentration of the graphene oxide aqueous dispersion is 1–5 mg / mL, the ultrasonic time is 5–30 min, and the shaking time is 1–12 h.

5. The method for preparing a multilayer asymmetric absorbing thin film material as described in claim 2 or 3, characterized in that: In step three, the concentration of the water-soluble polymer solution is 5–20 mg / mL, the mechanical stirring time is 10–30 min, the ultrasonic treatment time is 10 min–1 h, the vacuum degree of the drying oven is -60 kPa to atmospheric pressure, and the temperature is 40–80 °C.

6. The method for preparing a multilayer asymmetric absorbing thin film material as described in claim 2 or 3, characterized in that, In step four, the concentration of the conductive nanofiller / graphene oxide / water-soluble polymer mixed dispersion is 1-5 mg / mL, the concentration of graphene oxide is 0.5-2 mg / mL, the concentration of water-soluble polymer is 5-20 mg / mL, the ultrasonic treatment time is 10 min-1 h, the vacuum degree of the drying oven is -60 kPa to atmospheric pressure, and the temperature is 40-80℃.

7. A method for preparing a multilayer asymmetric absorbing thin film material as described in claim 1 or 2, characterized in that, The thermosetting resin is epoxy resin, acrylate, or polyurethane. The curing temperature corresponds to the selected thermosetting resin, and the pressure is 0.2–0.6 MPa.

8. A multilayer asymmetric absorbing thin film material prepared by the preparation method of any one of claims 1-7.

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