Composite microwave absorbing materials with interpenetrating interfaces across dimensions, their preparation methods and applications

Abstract

This invention belongs to the field of electromagnetic materials technology, and discloses a composite microwave absorbing material with a cross-dimensional interpenetrating interface, its preparation method, and its applications. The material comprises, in its thickness direction, a loose fibrous layer, a dense conductive carbon layer, and electromagnetic functional particles anchored to the inner walls of pores, the surface of the layers, and / or the interlayer gaps. The roots of the fibrous carbon extend into and are anchored to the pores and / or interlayer gaps of the framework, forming a cross-dimensional interpenetrating interface to achieve continuous conductive connections and / or local fusion connections. The electromagnetic functional particles are in close contact with the carbon framework, providing magnetic loss and / or dielectric loss. The preparation method includes: employing a stepwise energy beam-induced carbonization strategy on the first and second carbonizable precursor layers to induce the generation of fibrous carbon and in-situ carbonization of the infiltrated portions, achieving interpenetrating anchoring and particle conversion anchoring. This material is suitable for low-frequency absorption-dominant electromagnetic shielding, microwave absorbing patches, and flexible electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic materials technology, specifically relating to a composite microwave absorbing material with a cross-dimensional interpenetrating interface and its preparation method, as well as the application of this composite material in the fields of electromagnetic shielding, microwave absorption and flexible electronic devices. Background Technology

[0002] With the development of high-density integration of electronic devices and wireless communication, electromagnetic interference (EMI) and electromagnetic radiation problems are becoming increasingly prominent. For low-frequency microwave bands such as S-band and C-band, due to the long wavelength and strong penetration of electromagnetic waves, the realization of absorption-dominant electromagnetic protection materials requires simultaneous impedance matching, sufficient loss capacity and structural stability. Existing high-performance solutions often adopt multi-layer gradient structures, but traditional preparation usually involves obtaining different functional layers separately and then assembling them between layers through calendering or adhesives. This generally has the following shortcomings: (1) the adhesive interface layer blocks electron / heat transfer and weakens the interface polarization loss; (2) the interlayer bonding force is insufficient, and it is easy to delaminate and fail during bending and stretching; (3) the absorption mechanism in the low-frequency band is insufficient, and the reflection ratio is too high. Therefore, there is an urgent need for an integrated gradient material that achieves a smooth impedance transition in the thickness direction, has a strong loss mechanism and a strong interface.

[0003] Furthermore, introducing electromagnetic functional particles (such as magnetic nanoparticles, ferrites, high-entropy alloys, conductive two-dimensional sheets, etc.) that can generate magnetic loss, dielectric loss, or conductive loss can improve low-frequency absorption, but it is necessary to solve the problems of stable anchoring of electromagnetic functional particles in the carbon framework, interface compatibility, and overall forming of gradient structures. Summary of the Invention

[0004] This invention aims to provide an integrally molded gradient carbon-based integrated material that utilizes the synergistic effect of gradient structure, cross-dimensional interpenetrating interface and electromagnetic functional particles to improve the problems of insufficient interlayer bonding, low low-frequency absorption efficiency and poor bending reliability of traditional multilayer composite materials, and reduce the potential bypass risk caused by changes in particle type.

[0005] To achieve the above objectives, the present invention employs the following technical solution: a composite microwave absorbing material with a cross-dimensional interpenetrating interface, wherein the composite microwave absorbing material comprises, in the thickness direction, a loose fiber layer, a dense conductive carbon layer, and electromagnetic functional particles anchored in the pore walls, sheet surfaces, and / or interlayer gaps of the two structural layers; the average conductivity of the dense conductive carbon layer is higher than that of the loose fiber layer; the loose fiber layer is composed of interwoven fibrous carbon, and the dense conductive carbon layer is composed of interconnected three-dimensional porous sheet-like carbon skeletons; at the junction of the loose fiber layer and the dense conductive carbon layer, the roots of the fibrous carbon extend into and anchor in the pores and / or interlayer gaps of the three-dimensional porous sheet-like carbon skeleton, forming a cross-dimensional interpenetrating interface, and achieving continuous conductive connection and / or local fusion connection.

[0006] Further improvements to composite absorbing materials with cross-dimensional interpenetrating interfaces:

[0007] Preferably, the composite absorbing material is in the form of a flexible thin film with a total thickness of 150 μm-1000 μm; the dense conductive carbon layer has a thickness of 50 μm-200 μm; the loose fiber layer has a thickness of 100 μm-800 μm and is composed of carbon fiber or graphene fiber with an aspect ratio of (10-5000):1; the root of the fibrous carbon is inserted / anchored in the dense conductive carbon layer to a depth ≥5 μm and does not exceed 20% of the total thickness of the dense conductive carbon layer.

[0008] Preferably, the conductivity of the dense conductive carbon layer is more than 5 times that of the loose fiber layer, and the average conductivity of the loose fiber layer is 500 S / m-5000 S / m.

[0009] Preferably, the electromagnetic functional particles are selected from one or more of the following three types of materials: magnetic loss phase nanoparticles, dielectric loss phase nanoparticles, and conductive two-dimensional sheet materials.

[0010] The magnetic loss phase nanoparticles have an average particle size of 5 nm-200 nm and are selected from one or more of iron, nickel, cobalt and their alloys or compounds, spinel-type or hexagonal ferrites, and carbon-based coated magnetic particles.

[0011] The dielectric loss phase nanoparticles are selected from one or more of transition metal sulfide nanoparticles (such as MoS2), conductive ceramic or oxide nanoparticles (such as TiO2, BaTiO3).

[0012] The conductive two-dimensional sheet material is one or more of MXene or its composite sheet, graphene or its composite sheet, and conductive transition metal sulfide or its composite sheet.

[0013] Preferably, the magnetic loss phase nanoparticles are Fe3O4 and / or Fe3C, with a particle size of 5 nm-200 nm.

[0014] The second objective of this invention is to provide a method for preparing the above-mentioned composite microwave absorbing material with a cross-dimensional interpenetrating interface, comprising the following steps:

[0015] S1. Mix the carbonizable precursor solution with the electromagnetic functional particle source solution to obtain a carbonizable precursor mixture. The concentration of the carbonizable precursor in the mixture is 50-200 g / L, and the concentration of the electromagnetic functional particle source is 0.01-1.0 mol / L.

[0016] S2. A film is prepared using the carbonizable precursor mixture obtained in step S1, with a wet film thickness of 400-1500 μm, to obtain the first carbonizable precursor layer.

[0017] The first carbonizable precursor layer is subjected to a first CO2 laser-induced carbonization treatment with a laser power of 8-12 W, a scanning speed of 50-200 mm / s, and a scanning interval of 0.05-0.12 mm to form a dense conductive carbon layer composed of a three-dimensional porous layered carbon skeleton. At the same time, the electromagnetic functional particle source is converted and / or fixed and anchored in situ into electromagnetic functional particles.

[0018] S3. Using the carbonizable precursor mixture obtained in step S1, a film is formed on the surface of a dense conductive carbon layer. The wet film thickness is 200-750 μm. Part of the mixture penetrates into the surface pores of the dense conductive carbon layer to form a second carbonizable precursor layer.

[0019] The second carbonizable precursor layer is subjected to a second CO2 laser-induced carbonization treatment with a laser power of 14-25 W, a scanning speed of 200-500 mm / s, and a scanning interval of 0.13-0.40 mm. The generated fibrous carbon forms a loose fibrous layer, and the roots of the fibrous carbon are anchored in the three-dimensional porous layered carbon skeleton to form a cross-dimensional interpenetrating interface. The electromagnetic functional particle source is converted and / or fixed and anchored in situ into electromagnetic functional particles, thus obtaining a composite microwave absorbing material with a cross-dimensional interpenetrating interface.

[0020] As a further improvement to the preparation method of the above-mentioned composite absorbing material with cross-dimensional interpenetrating interface:

[0021] Preferably, the carbonizable precursor is polyamic acid or polyethersulfone.

[0022] Preferably, the electromagnetic functional particle source includes electromagnetic functional particle precursors and / or pre-made electromagnetic functional particles.

[0023] The electromagnetic functional particle precursor is selected from one or more of the following: metal salts, organometallic complexes, metal oxide / hydroxide precursors, and polymer complex precursors.

[0024] The prefabricated electromagnetic functional particles are selected from one or more of the following: prefabricated magnetic loss phase nanoparticles, dielectric loss phase nanoparticles, and conductive two-dimensional sheet materials.

[0025] Preferably, the electromagnetic functional particle source is an iron source;

[0026] The iron source is an iron salt and / or an iron complex, wherein the iron salt is selected from one or more of ferric chloride, ferric nitrate, and ferric sulfate;

[0027] The concentration of the iron source in the carbonizable precursor mixture is 0.01 mol / L-1.0 mol / L.

[0028] The third objective of this invention is to provide an application of the aforementioned composite absorbing material with a cross-dimensional interpenetrating interface in an electromagnetic functional device, which is an absorption-dominant electromagnetic shielding film, a microwave absorbing patch, or a flexible wearable electronic device. The loose fiber layer in the composite absorbing material serves as the electromagnetic wave incident surface for impedance matching and absorption, while the dense conductive carbon layer serves as the backplane surface for reflection shielding and charge transfer.

[0029] The advantages of this invention compared to the prior art are as follows:

[0030] (1) This invention discloses an electromagnetic functional particle / laser-induced graphene composite absorbing material with a cross-dimensional interpenetrating interface structure. The material is an integrated structure comprising a loose fiber layer, a dense conductive carbon layer, and electromagnetic functional particles anchored in the pore walls, sheet surfaces, and / or interlayer gaps of the two structural layers. The average conductivity of the dense conductive carbon layer is higher than that of the loose fiber layer, and there is no external binder interface layer between the functional regions. At the cross-dimensional interpenetrating interface at the junction of the loose fiber layer and the dense conductive carbon layer, the roots of the fibrous carbon extend into and anchor in the pores and / or interlayer gaps of the three-dimensional porous sheet-like carbon skeleton, forming a spatially nested interlocking structure (i.e., a cross-dimensional interpenetrating network), and achieving continuous conductive connection and / or local fusion connection. The three-dimensional porous sheet-like carbon skeleton is formed by stacking and overlapping graphene-like sheets to form a network structure with interconnected pores. The three-dimensional porous sheet-like carbon skeleton is preferably a laser-induced graphene skeleton.

[0031] (2) This invention provides a method for preparing a composite microwave absorbing material with a cross-dimensional interpenetrating interface: A stepwise energy beam-induced carbonization strategy is employed. First, a first carbonizable precursor layer containing a particle source is treated with CO2 laser to form a three-dimensional porous layered carbon skeleton. Then, a second carbonizable precursor layer containing a particle source is introduced onto the surface of the skeleton, and at least a portion of the second carbonizable precursor is controlled to penetrate into the surface pores and / or interlayer gaps of the skeleton. Subsequently, the second carbonizable precursor is treated with CO2 laser to induce the formation of fibrous carbon, and under thermal influence, the precursor penetrating into the pores and / or interlayer gaps is carbonized in situ, thereby achieving interpenetrating anchoring and forming a cross-dimensional interpenetrating interface. Simultaneously, the particle source is transformed into and / or fixedly anchored to form electromagnetic functional particles. The energy beam is a laser beam. By controlling the laser's linear energy density, scanning speed, scanning spacing, and / or scanning path overlap rate, a three-dimensional porous layered carbon skeleton and fibrous carbon are formed respectively, achieving interpenetrating anchoring. Electromagnetic functional particles can be formed in situ or directly added and anchored, thus being compatible with different particle systems and reducing the risk of being bypassed, and having process adaptability and scalability.

[0032] The first CO2 laser treatment employs a high linear energy density and a small scanning interval. The laser energy causes the first carbonizable precursor layer to carbonize in situ, forming a dense, conductive carbon layer. The second CO2 laser treatment uses a lower linear energy density and a larger scanning interval, aiming to induce the formation of fibrous carbon in the second carbonizable precursor layer, constructing a loose fibrous layer. Simultaneously, during the two laser-induced carbonization processes, the electromagnetic functional particle source is converted in situ into electromagnetic functional particles, achieving fixed anchoring.

[0033] (3) The composite microwave absorbing material with a cross-dimensional interpenetrating interface of the present invention has the following performance advantages: The cross-dimensional interpenetrating interface enables the two regions to form a mechanical interlock and continuous conductive connection, avoiding the weak interface caused by the adhesive layer, and the interface is firmly bonded. Gradient impedance matching makes it easier for electromagnetic waves to enter the interior of the material; the heterogeneous interface improves the interface polarization loss; electromagnetic functional particles provide a magnetic loss / dielectric loss / conductive loss mechanism, which works in synergy with the dielectric loss of the carbon skeleton to increase the absorption ratio in the low-frequency to microwave band. The integrated structure is not easy to delaminate in bending cycles, making it suitable for flexible electromagnetic protection devices with high reliability. Therefore, it is suitable for low-frequency absorption-dominant electromagnetic shielding, microwave absorbing patches and flexible electronic devices. Among them, electromagnetic functional particles are used to provide magnetic loss and / or dielectric loss and / or conductive loss to improve the absorption-dominant electromagnetic protection performance in the low-frequency to microwave band. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of the composite absorbing material with a cross-dimensional interpenetrating interface of the present invention.

[0035] Figure 2This is an enlarged schematic diagram of the inter-dimensional interpenetrating interface in the composite absorbing material of the present invention.

[0036] Figure 3 This is a flowchart of the preparation of composite microwave absorbing material in Example 1 of the present invention (using Fe3O4 as an example of electromagnetic functional particles).

[0037] Figure 4 This is a schematic diagram / characterization image of the cross-sectional microstructure of the composite absorbing material prepared in Example 1 of the present invention.

[0038] Figure 5 This is an EDS surface scan of the cross-sectional microstructure of the composite absorbing material prepared in Example 1 of the present invention.

[0039] Figure 6 These are transmission electron microscope (TEM) images and high-resolution images of the composite absorbing material prepared in Example 1 of this invention, wherein (a) is the morphology image of the interface between the loose fiber layer and the dense conductive carbon layer, and (b) and (c) are high-resolution images of electromagnetic functional particles on the surface of the loose fiber layer and the dense conductive carbon layer.

[0040] Figure 7 This is a schematic diagram of the XRD and XPS test results of the composite absorbing material prepared in Example 1 of the present invention, wherein (a) is the XRD characterization result of the composite absorbing material, and (b) is the peak fitting result of iron element in the XPS characterization of the composite absorbing material.

[0041] Figure 8 This is a schematic diagram comparing the electromagnetic shielding effectiveness and absorption coefficient of the composite absorbing material prepared in Embodiment 1 of the present invention before and after bending.

[0042] Figure 9 This is a schematic diagram comparing the electromagnetic shielding effectiveness and absorption coefficient of the composite materials prepared in Example 1 of the present invention with those prepared in Comparative Examples 1, 2, and 3, corresponding to (a) and (b) in the figure respectively.

[0043] Figure 10 These are schematic / characterization diagrams of the microstructure of the composite absorbing materials prepared in Examples 2-3 of the present invention, wherein (a) is a microstructure scan of the composite absorbing material prepared in Example 2 using Fe3O4 nanoparticles as an electromagnetic functional particle source, and (b) is a microstructure scan of the composite absorbing material prepared in Example 3 using nickel-cobalt alloy nanoparticles as an electromagnetic functional particle source.

[0044] Figure 11 This is a schematic diagram / characterization image of the microstructure of the composite absorbing material obtained in Example 4 of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0046] In this specification, "interpenetrating interface" refers to an interface structure in which the root / end of fibrous carbon extends at least partially into the pores and / or interlayer gaps of a three-dimensional porous layered carbon skeleton, forming a spatially nested, interlocking interface that generates continuous conductive connections and / or local fusion connections. In this specification, "electromagnetic functional particles" refers to particle or sheet units capable of providing magnetic loss, dielectric loss, and / or conductive loss to materials, including but not limited to magnetic loss phase nanoparticles (such as iron-based, nickel-based, cobalt-based and their alloys / compounds, ferrites, high-entropy alloys, etc.), dielectric loss phase nanoparticles (such as TiO2, BaTiO3, etc.), conductive two-dimensional materials (such as MXene, graphene, etc.), and combinations thereof; electromagnetic functional particles can be particles formed through in-situ transformation, or they can be physically introduced and anchored from pre-fabricated particles / sheets. Unless otherwise stated, the "electrical conductivity" mentioned in this specification can be characterized by bulk conductivity or in-plane conductivity measured using the four-probe method or equivalent electrical methods.

[0047] Example 1

[0048] This embodiment provides a method for preparing a composite microwave absorbing material with a cross-dimensional interpenetrating interface, comprising the following steps:

[0049] S1. A thermoplastic polyamic acid (PI, Donglin Polymer Materials) solution with a concentration of 200 g / L is selected as the carbonizable precursor solution.

[0050] FeCl3·6H2O (ACS grade, Aladdin reagent) was used as the electromagnetic functional particle source and dissolved in N,N-dimethylacetamide (DMAc, 99% purity, Aladdin reagent) to prepare an electromagnetic functional particle source solution with a concentration of 0.9 mol / L.

[0051] The carbonizable precursor solution and the electromagnetic functional particle source solution were mixed at a volume ratio of 2:1 and stirred continuously for 2 hours to obtain a homogeneous carbonizable precursor mixture. The concentration of the carbonizable precursor was 133 g / L, of which the concentration of the electromagnetic functional particle source was 0.3 mol / L.

[0052] S2. The carbonizable precursor mixture is poured onto a clean glass plate (150 mm × 150 mm), and the wet film thickness is controlled to be 800 μm using a doctor blade. It is then placed in an oven and gradually heated to evaporate the solvent and complete the imidization process: successively heated at 60 ℃, 90 ℃, 120 ℃, 150 ℃, and 180 ℃ for 2 hours each. Finally, an iron-containing polyimide solid film with a thickness of approximately 150 μm is formed, serving as the first carbonizable precursor layer.

[0053] A glass plate with the first carbonizable precursor layer attached was placed on the stage of a CO2 laser engraving machine (HANS Laser CO2-D200, wavelength 10.6 μm, spot diameter approximately 100 μm). The laser power was set to 10 W, the scanning speed to 80 mm / s, and the scanning interval to 0.08 mm. A 30 mm × 30 mm area was laser-scanned. This formed a three-dimensional porous layered carbon framework, constituting a dense conductive carbon layer. Simultaneously, an electromagnetic functional particle source was converted in situ into electromagnetic functional particles (Fe3O4 and / or Fe3C), anchoring them to the pore walls and surface of the three-dimensional porous layered carbon framework.

[0054] S3. The carbonizable precursor mixture is poured onto the surface of the dense conductive carbon layer and coated using a spin coating method. The specific spin coating parameters are: first, spin coating at a low speed of 400 rpm for 30 seconds, then spin coating at a high speed of 1000 rpm for 10 seconds. The spin-coated sample is then placed on a hot plate at 120 ℃ for pre-curing for 8 minutes, allowing partial imidization of the polyamic acid (PAA) to form a semi-solid layer, and allowing some of the mixture to penetrate into the surface pores of the dense conductive carbon layer. The sample is then transferred to an oven for further heating and curing: sequentially heated at 120 ℃ for 2 hours, 150 ℃ for 1 hour, and 180 ℃ for 1 hour, until the surface layer is completely cured, forming a second carbonizable precursor layer containing a particle source that covers the dense conductive carbon layer and is partially embedded in its surface.

[0055] The glass plate with the dense conductive carbon layer and the second carbonizable precursor layer attached was placed again on the stage of a CO2 laser engraving machine (HANS Laser CO2-D200, wavelength 10.6 μm, spot diameter approximately 100 μm). The laser power was set to 18W, the scanning speed to 300 mm / s, and the scanning interval to 0.2 mm. The carbonizable precursor, which had penetrated into the surface pores and interlayer gaps of the dense conductive carbon layer, underwent carbonization under the action of the laser. The roots of the in-situ generated fibrous carbon were firmly anchored and locally fused into the three-dimensional porous layered carbon skeleton at the bottom, thereby constructing a cross-dimensional interpenetrating interface between the two layers. At the same time, the FeCl3 in the second carbonizable precursor layer was re-thermally transformed, generating Fe3O4 / Fe3C nanoparticles in situ, which were then anchored to the surface of the newly generated fibrous carbon, the skeleton pores, and the interpenetrating interface region.

[0056] The prepared composite film was peeled off from the glass plate and cleaned three times each with deionized water and ethanol to remove impurities. Finally, it was dried in a vacuum drying oven at 60 °C for 8 hours to obtain a composite microwave absorbing material film with a cross-dimensional interpenetrating interface.

[0057] The average conductivity of the loose fiber layer was 2930 S / m, and that of the dense conductive carbon layer was 28430 S / m, using the PM5 four-probe system (Cascade Microtech, USA). The ratio of the two was approximately 9.7 times.

[0058] Figure 1 This is a schematic diagram of the overall structure of the composite absorbing material with a cross-dimensional interpenetrating interface of the present invention. Figure 2 This is an enlarged schematic diagram of the interdimensional interpenetrating interface in the composite absorbing material of this invention. Figure 1 and Figure 2 As shown, the composite microwave absorbing material of the present invention is an integrated monolithic structure, comprising a loose fiber layer, a dense conductive carbon layer, and electromagnetic functional particles anchored in the pore walls, sheet surfaces, and / or interlayer gaps of the two structural layers. No external adhesive interface layer is added between the functional regions. At the cross-dimensional interpenetrating interface at the junction of the loose fiber layer and the dense conductive carbon layer, the roots of the fibrous carbon extend into and anchor in the pores and / or interlayer gaps of the three-dimensional porous sheet-like carbon skeleton, forming a spatially nested interlocking structure (i.e., a cross-dimensional interpenetrating network), achieving continuous conductive connection and / or local fusion connection.

[0059] Figure 3 This is a flowchart of the preparation of composite microwave absorbing materials in Example 1 of the present invention (using Fe3O4 as an example of electromagnetic functional particles). This method prepares composite films under environmental conditions through a stepwise laser-induced carbonization strategy. First, FeCl3·6H2O is added to a polyamic acid (PAA) solution, coated onto a glass plate, and then cured by gradient heating, causing the solvent to evaporate and imidization to occur, forming Fe3O4-containing... + A polyimide film was formed. This film was then subjected to a first laser scan using a CO2 laser engraving machine to induce the formation of a laser-induced graphene film modified with Fe3O4. Subsequently, a layer containing Fe³⁺ was spin-coated onto the surface of the aforementioned film. + The PAA solution was cured and then subjected to a second laser ablation to finally obtain the Fe3O4@LIGF / LIG composite film.

[0060] Figure 4This is a cross-sectional microstructure characterization image of the composite absorbing material prepared in Example 1 of this invention. Field emission scanning electron microscopy (SEM, Sirion 200, FEI Corporation, USA) reveals a continuous, integrated structure from the surface layer to the bottom layer: a loose fiber network, an interpenetrating transition region, and a dense lamellar skeleton, with no external adhesive layer at the interface. Testing showed that the total thickness of the obtained composite film is approximately 400 μm, with a dense conductive carbon layer thickness of approximately 80 μm and a loose fiber layer thickness of approximately 200 μm. The roots of the fibrous carbon are inserted / anchored within the dense conductive carbon layer at a depth ranging from 5 to 16 μm.

[0061] Figure 5 This is an EDS surface scan of the cross-sectional microstructure of the composite absorbing material prepared in Example 1 of this invention. The elemental distribution was investigated using an EDS surface scan method with a field emission scanning electron microscope (SEM, Sirion 200, FEI Corporation, USA). Figure 5 It can be seen that LIG exhibits a continuous porous structure, with a framework composed of carbon elements and iron elements uniformly distributed on the surface of the carbon framework.

[0062] Figure 6 These are transmission electron microscopy (TEM) images and high-resolution images of the composite absorbing material prepared in Example 1 of this invention. Figure (a) shows the morphology of the interface between the loose fibrous layer and the dense conductive carbon layer, while Figures (b) and (c) are high-resolution images of electromagnetic functional particles on the surfaces of the loose fibrous layer and the dense conductive carbon layer. The TEM powder sample was obtained by scraping from a Fe3O4@LIGF / LIG film, ultrasonically treated in ethanol for 4 h, and then dropped onto a molybdenum grid for observation using a transmission electron microscope (TEM, JEM 2100F, Nippon Electron Ltd.). Figure 6 As shown in (a), multiple fibrous carbon strands are anchored to the sheet-like framework, which is the basic bonding mode between fibrous graphene and sheet-like graphene at the interpenetrating interface layer. Figure 6 As shown in (a), (b), and (c), electromagnetic functional particles are uniformly distributed on the surface of graphene sheets, interlayer gaps, and fiber surface, with a particle size of 5-50 nm. By analyzing the lattice fringes under high-resolution images, the interplanar spacing was measured to correspond to the (002) crystal plane of graphene, the (311) and (220) crystal planes of Fe3O4, and the (002) crystal plane of Fe3C. Furthermore, Fe3O4 particles are the majority phase.

[0063] Figure 7Figure 1 shows the XRD and XPS test results of the composite microwave absorbing material prepared in Example 1 of this invention. Figure (a) shows the XRD characterization results of the composite microwave absorbing material, and Figure (b) shows the peak fitting results of iron element in the XPS characterization of the composite microwave absorbing material. Powder samples were directly scraped from the Fe3O4@LIGF / LIG film, and XRD spectra were obtained using an X'Pert Pro X-ray diffractometer (PAN alytical, Netherlands) under Cu Kα radiation. X-ray photoelectron spectroscopy (XPS) analysis was performed on an electron spectrometer (ESCALAB 250Xi, Thermo Fisher Scientific, USA), with the C 1s peak (284.8 eV) used to calibrate all XPS spectra. The XRD in Figure (a) shows that in addition to graphene as the framework, there are two main components: Fe3O4 and Fe3C. The XPS in Figure (b) shows that iron element exists mainly in the form of divalent and trivalent iron in the material, and Fe... 3+ with Fe 2+ The content ratio is approximately 2:1, indicating that iron oxides mainly exist in the form of Fe3O4.

[0064] Figure 8 This is a schematic diagram comparing the electromagnetic shielding effectiveness and absorption coefficient of the composite absorbing material prepared in Embodiment 1 of the present invention before and after bending. A self-made telescopic bending fixture was used in conjunction with a stepper motor. Figure 8 It can be seen that there is no obvious delamination after repeated bending. After 1000 bending, the electromagnetic shielding effectiveness decreases by 15% and the absorption coefficient decreases by 34%.

[0065] In summary, the test results of the composite absorbing material prepared in Example 1 are as follows: SEM cross-section observation shows that the composite absorbing material has a continuous integrated structure from the surface layer to the bottom layer, consisting of a loose fiber network, an interpenetrating transition zone, and a dense sheet skeleton, with no external adhesive layer at the interface. EDS surface scanning shows the distribution of metal elements in the skeleton surface and interpenetrating interface region of the composite absorbing material; XRD, XPS, or a combination thereof were used to verify the Fe3O4 and Fe3C phases. TEM morphology shows that the fiber-sheet structure still exists after the obtained sample is ultrasonically treated for 3 hours. Mechanical reliability shows no obvious delamination after repeated bending, and the electromagnetic shielding effectiveness decreases by 15% after 1000 bending cycles. The electromagnetic parameters of the material in the S-band and other frequency bands were tested using a vector network analyzer combined with the coaxial line method or waveguide method, and the electromagnetic shielding effectiveness and absorption ratio were calculated. The material exhibits an absorption-dominant characteristic with an increased absorption ratio and a decreased reflection ratio.

[0066] The material of this invention can be used as an absorption-dominant electromagnetic shielding film, microwave absorbing patch, or flexible electromagnetic protection layer in fields such as communication equipment, radar dome, wearable electronics, and flexible circuit packaging.

[0067] Example 2-3

[0068] This embodiment provides a method for preparing a composite microwave absorbing material with a cross-dimensional interpenetrating interface. The specific steps are the same as in Embodiment 1, except that the preparation steps of the carbonizable precursor mixture in step S1 are as follows:

[0069] A thermoplastic polyamic acid (PI, Donglin Polymer Materials) solution with a concentration of 200 g / L was selected as the carbonizable precursor solution.

[0070] Fe3O4 nanoparticles and nickel-cobalt alloy nanoparticles were used as electromagnetic functional particle sources in sequence and dispersed in N,N-dimethylacetamide (DMAc, 99% purity, Aladdin reagent) by ultrasonication for 30 min to prepare an electromagnetic functional particle source dispersion with a concentration of 0.4 mol / L.

[0071] The carbonizable precursor solution and the electromagnetic functional particle source dispersion were mixed at a volume ratio of 3:1 and stirred continuously for 2 hours to obtain a homogeneous carbonizable precursor mixture. The concentration of the carbonizable precursor in the mixture was 150 g / L, and the concentration of the electromagnetic functional particle source was 0.1 mol / L.

[0072] The microstructure scanning images of the composite absorbing materials prepared in Example 2 using Fe3O4 nanoparticles as the electromagnetic functional particle source and in Example 3 using nickel-cobalt alloy nanoparticles as the electromagnetic functional particle source are shown below. Figure 10 As shown in (a) and (b), by Figure 10 It is known that by adding pre-made electromagnetic functional particles as the source of electromagnetic functional particles, after CO2 laser-induced treatment, the pre-made electromagnetic functional particles are fixedly anchored in the pore walls, sheet surfaces and / or interlayer gaps of the loose fiber layer and the dense conductive carbon layer.

[0073] Example 4

[0074] This embodiment provides a method for preparing a composite microwave absorbing material with a cross-dimensional interpenetrating interface. The specific steps are the same as in Embodiment 1, except that the preparation steps of the carbonizable precursor mixture in step S1 are as follows:

[0075] A thermoplastic polyamic acid (PI, Donglin Polymer Materials) solution with a concentration of 250 g / L was selected as the carbonizable precursor solution.

[0076] MXene conductive two-dimensional sheet material (Ti3C2T) xMXene (98% purity, 100-500 nm sheet thickness, 2-20 μm lateral size, Xinxi Technology Co., Ltd.) was used as an electromagnetic functional particle source. It was added to N,N-dimethylacetamide (DMAc, 99% purity, Aladdin reagent) and ultrasonically dispersed for 30-60 minutes (power 200-300 W) to prepare an electromagnetic functional particle source solution with a concentration of 0.05 mol / L.

[0077] The carbonizable precursor solution and the electromagnetic functional particle source solution were mixed at a volume ratio of 4:1 and stirred continuously for 2 hours (stirring rate 200-300 r / min) to obtain a homogeneous carbonizable precursor mixture. The concentration of the carbonizable precursor was 200 g / L, and the concentration of the electromagnetic functional particle source was 0.01 mol / L.

[0078] Finally, a composite absorbing material with a cross-dimensional interpenetrating interface was obtained.

[0079] The microstructure scan of the composite absorbing material prepared in Example 4 is shown below. Figure 11 As shown in the figure, after CO2 laser treatment, the conductive two-dimensional sheet material is transformed into electromagnetic functional particles in situ, which are fixed in the pores / interlayer gaps and form multi-interface contact with the carbon skeleton, thereby enhancing the conductivity loss and interfacial polarization loss.

[0080] Example 5

[0081] This embodiment provides a method for preparing a composite microwave absorbing material with a cross-dimensional interpenetrating interface. The specific steps are the same as in Example 1, except that in step S1, polyethersulfone powder (PES, Wanlihong Plastics Co., Ltd.) is added to N,N-dimethylacetamide (DMAc, 99% purity, Aladdin reagent) at a concentration of 20 wt%, and stirred for 8 hours until completely dissolved, serving as a carbonizable precursor source solution. In steps S2 and S3, the film formation does not require imidization treatment; it is simply placed at 80°C until the solvent evaporates, resulting in a first carbonizable precursor layer and a second carbonizable precursor layer. Finally, a composite microwave absorbing material with a cross-dimensional interpenetrating interface is obtained.

[0082] Comparative Example 1

[0083] This comparative example provides a method for preparing a composite absorbing material, with specific steps as described in Example 1. First, a porous layered carbon film is obtained through steps S1 and S2. The preparation steps for the fibrous carbon film are the same as steps S1 and S2 in Example 1, except that the laser power is set to 18 W, the scanning speed to 300 mm / s, and the scanning spacing to 0.2 mm. Then, conductive adhesive or bonding agent is used to physically bond the prepared porous layered carbon film to form a sandwich structure.

[0084] The electromagnetic shielding performance of the composite absorbing material prepared in Comparative Example 1 was tested, and the results are as follows: Figure 9 As shown, the overall electromagnetic shielding effectiveness is less than 23 dB, and the absorption coefficient is less than 0.25. The cross-sectional morphology was tested, and a distinct adhesive layer was observed in the cross-section after the electromagnetic shielding test results; delamination occurred after 20 bends.

[0085] Comparative Example 2

[0086] This comparative example provides a method for preparing a composite microwave absorbing material, which uses a single energy beam parameter for one-time processing. The specific steps are the same as in Example 1, except that the dense conductive carbon layer composed of a three-dimensional porous layered carbon skeleton containing electromagnetic functional particles (Fe3O4 and / or Fe3C) is obtained up to step S2.

[0087] The electromagnetic shielding performance of the composite absorbing material prepared in Comparative Example 2 was tested, and the test results are as follows: Figure 9 As shown, the overall electromagnetic shielding effectiveness of Comparative Example 2 is less than 25 dB, and the absorption coefficient is less than 0.15. The test results indicate that the composite absorbing material prepared in this comparative example exhibits insufficient absorption capacity in the low-frequency band or a high reflection ratio.

[0088] Comparative Example 3

[0089] This comparative example provides a method for preparing a composite microwave absorbing material. After secondary coating, the second precursor is completely cured to prevent it from penetrating downwards. The resulting material is difficult to form a clear cross-dimensional interpenetrating interface and an impedance gradient along the thickness direction. The specific steps are the same as in Example 1, except that in step S3, the carbonizable precursor mixture is first stirred and heated at 60°C for 10 minutes to evaporate some of the solvent, thereby increasing the viscosity. Then it is poured onto the surface of a dense conductive carbon layer. At the same time, the spin coating parameters are changed to spin coating at 1000 rpm for 40 seconds and then pre-curing immediately.

[0090] The electromagnetic shielding performance of the composite absorbing material prepared in Comparative Example 3 was tested, and the test results are as follows: Figure 9 As shown, the overall electromagnetic shielding effectiveness of Comparative Example 3 is less than 29 dB, and the absorption coefficient is less than 0.4. The test results indicate that the composite absorbing material prepared in this comparative example exhibits insufficient absorption capacity or a high reflection ratio in the low-frequency band.

[0091] Figure 9This is a schematic diagram comparing the electromagnetic shielding effectiveness and absorption coefficient of the composite materials prepared in Example 1 of this invention with those in Comparative Examples 1, 2, and 3. (a) is a comparison diagram of the total shielding effectiveness, and (b) is a comparison diagram of the absorption coefficient. Composite material films with dimensions of 40mm × 80mm were cut, and the S-parameters in the S-band (2.6-3.95 GHz) were measured using a vector network analyzer (N5244A, Agilent Technologies, USA). The electromagnetic shielding effectiveness and absorption coefficient A of the materials were calculated using the S-parameters. Figure 9 It can be seen that the composite material of Example 1 of the present invention achieves a total shielding effectiveness of 35.4 dB and an electromagnetic wave absorption coefficient of 0.78 in the S-band. The composite material of Example 1 of the present invention has a greater total electromagnetic shielding effectiveness than the composite materials of Comparative Examples 1, 2, and 3. The electromagnetic wave shielding of Comparative Examples 1, 2, and 3 is mainly based on reflection (absorption coefficient < 0.5), while Example 1 achieves an absorption coefficient of over 0.5, realizing an electromagnetic shielding mechanism mainly based on absorption. The comparison of the test results of Example 1 and Comparative Examples 1, 2, and 3 shows that step-by-step processing, penetration control, and interpenetrating anchoring construction are necessary to obtain the target gradient structure and absorption-dominant performance.

[0092] The electromagnetic shielding effectiveness and absorption coefficient of the electromagnetic functional particles / laser-induced graphene prepared in Example 1 were compared with those of existing microwave absorbing materials. The test data are shown in Table 1 below. The corresponding literature for the silver / polyaniline / aminated graphene oxide coated textiles is "Fabrication of silver / polyaniline / aminated graphene oxide coated textiles for electromagnetic interference shielding application within the different bands of frequency", Akram, S. et al., Synthetic Metals, Vol. 298, Article No. 117400. The corresponding literature for the silver / PET fabric is "Electroless silver plating on PET fabric initiated by in situ reduction of polyaniline", Mu, SP et al., Applied Surface Science, Vol. 353, pp. 608-614. The corresponding literature for Cu-Fe3O4@Graphene / Ni / wood is "HighHydrophobic Wood / Cu-Fe3O4@Graphene / Ni Composites for Electromagnetic Interference Shielding", Guo, Qiang et al., Journal of Inorganic and Organometallic Polymers and Materials, Vol. 33, No. 2, pp. 502-514.

[0093] Table 1. Performance comparison between Example 1 and existing composite microwave absorbing materials

[0094]

[0095] As can be seen from the test data in Table 1, in the comparison of electromagnetic shielding tests in the S-band, the composite material prepared by this invention has a higher absorption coefficient (A) than other thin film materials. The total electromagnetic shielding effectiveness of the material of this invention is greater than 30 dB, achieving absorption or reflection of more than 99.9% of electromagnetic radiation. It can be used for shielding in general industrial applications as well as industrial and commercial electronic instruments.

[0096] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A composite microwave absorbing material with a cross-dimensional interpenetrating interface, characterized in that, The composite absorbing material comprises, in the thickness direction, a loose fiber layer, a dense conductive carbon layer, and electromagnetic functional particles anchored in the pore walls, sheet surfaces, and / or interlayer gaps of the two structural layers; the average conductivity of the dense conductive carbon layer is higher than that of the loose fiber layer; the loose fiber layer is composed of interwoven fibrous carbon, and the dense conductive carbon layer is composed of interconnected three-dimensional porous sheet-like carbon skeletons; at the junction of the loose fiber layer and the dense conductive carbon layer, the roots of the fibrous carbon extend into and anchor in the pores and / or interlayer gaps of the three-dimensional porous sheet-like carbon skeleton, forming a cross-dimensional interpenetrating interface and achieving continuous conductive connection and / or local fusion connection.

2. The composite microwave absorbing material with a cross-dimensional interpenetrating interface according to claim 1, characterized in that, The composite absorbing material is in the form of a flexible thin film with a total thickness of 150 μm-1000 μm; the dense conductive carbon layer has a thickness of 50 μm-200 μm; the loose fiber layer has a thickness of 100 μm-800 μm and is composed of carbon fiber or graphene fiber with an aspect ratio of (10-5000):1; the root of the fibrous carbon is inserted / anchored in the dense conductive carbon layer to a depth ≥5 μm and does not exceed 20% of the total thickness of the dense conductive carbon layer.

3. The composite microwave absorbing material with a cross-dimensional interpenetrating interface according to claim 1 or 2, characterized in that, The conductivity of the dense conductive carbon layer is more than 5 times that of the loose fiber layer, and the average conductivity of the loose fiber layer is 500 S / m-5000 S / m.

4. The composite microwave absorbing material with a cross-dimensional interpenetrating interface according to claim 1 or 2, characterized in that, The electromagnetic functional particles are selected from one or more of the following three types of materials: magnetic loss phase nanoparticles, dielectric loss phase nanoparticles, and conductive two-dimensional sheet materials. The magnetic loss phase nanoparticles have an average particle size of 5 nm-200 nm and are selected from one or more of iron, nickel, cobalt and their alloys or compounds, spinel-type or hexagonal ferrites, and carbon-based coated magnetic particles. The dielectric loss phase nanoparticles are selected from one or more of transition metal sulfide nanoparticles, conductive ceramics, or oxide nanoparticles. The conductive two-dimensional sheet material is one or more of MXene or its composite sheet, graphene or its composite sheet, and conductive transition metal sulfide or its composite sheet.

5. The composite microwave absorbing material with a cross-dimensional interpenetrating interface according to claim 4, characterized in that, The magnetic loss phase nanoparticles are Fe3O4 and / or Fe3C, with a particle size of 5 nm-200 nm.

6. A method for preparing a composite microwave absorbing material with a cross-dimensional interpenetrating interface as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. A carbonizable precursor solution is mixed with an electromagnetic functional particle source solution to obtain a carbonizable precursor mixture. The concentration of the carbonizable precursor in the mixture is 50-200 g / L, and the concentration of the electromagnetic functional particle source is 0.01-1.0 mol / L. S2. A film is prepared using the carbonizable precursor mixture obtained in step S1, with a wet film thickness of 400-1500 μm, to obtain the first carbonizable precursor layer. The first carbonizable precursor layer is subjected to a first CO2 laser-induced carbonization treatment with a laser power of 8-12 W, a scanning speed of 50-200 mm / s, and a scanning interval of 0.05-0.12 mm to form a dense conductive carbon layer composed of a three-dimensional porous layered carbon skeleton. At the same time, the electromagnetic functional particle source is converted and / or fixed and anchored in situ into electromagnetic functional particles. S3. A film is formed on the surface of a dense conductive carbon layer using the carbonizable precursor mixture obtained in step S1. The wet film thickness is 200-750 μm. Part of the mixture penetrates into the surface pores of the dense conductive carbon layer to form a second carbonizable precursor layer. The second carbonizable precursor layer is subjected to a second CO2 laser-induced carbonization treatment with a laser power of 14-25 W, a scanning speed of 200-500 mm / s, and a scanning spacing of 0.13-0.40 mm. The resulting fibrous carbon forms a loose fibrous layer, and the roots of the fibrous carbon are anchored in the three-dimensional porous layered carbon skeleton to form a cross-dimensional interpenetrating interface. The electromagnetic functional particle source is converted and / or fixed and anchored in situ into electromagnetic functional particles, thus obtaining a composite microwave absorbing material with a cross-dimensional interpenetrating interface.

7. The method for preparing a composite microwave absorbing material with a cross-dimensional interpenetrating interface according to claim 6, characterized in that, The carbonizable precursor is polyamic acid or polyethersulfone.

8. The method for preparing a composite microwave absorbing material with a cross-dimensional interpenetrating interface according to claim 6, characterized in that, The electromagnetic functional particle source includes electromagnetic functional particle precursors and / or pre-made electromagnetic functional particles. The electromagnetic functional particle precursor is selected from one or more of the following: metal salts, organometallic complexes, metal oxide / hydroxide precursors, and polymer complex precursors. The prefabricated electromagnetic functional particles are selected from one or more of the following: prefabricated magnetic loss phase nanoparticles, dielectric loss phase nanoparticles, and conductive two-dimensional sheet materials.

9. The method for preparing a composite microwave absorbing material with a cross-dimensional interpenetrating interface according to claim 8, characterized in that, The electromagnetic functional particle source is an iron source; The iron source is an iron salt and / or an iron complex, wherein the iron salt is selected from one or more of ferric chloride, ferric nitrate, and ferric sulfate; The concentration of the iron source in the carbonizable precursor mixture is 0.01 mol / L-1.0 mol / L.

10. The application of a composite absorbing material with a cross-dimensional interpenetrating interface as described in any one of claims 1-5 in an electromagnetic functional device, characterized in that, The electromagnetic functional device is an absorption-dominant electromagnetic shielding film, microwave absorbing patch, or flexible wearable electronic device. The loose fiber layer in the composite absorbing material serves as the electromagnetic wave incident surface for impedance matching and absorption, while the dense conductive carbon layer serves as the backplane surface for reflection shielding and charge transfer.

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