Preparation method of three-dimensional porous electromagnetic shielding composite material

Abstract

The invention provides a preparation method of a three-dimensional porous electromagnetic shielding composite material, and belongs to the technical field of nano materials. Comprising the following steps of hydrotalcite-like compound auxiliary assembly, freeze drying, high-temperature calcination and polymer backfilling. The technical bottleneck that carbon black is difficult to self-assemble into a stable three-dimensional network is fundamentally broken through, and compared with a blending technology which depends on high filling amount and filler random distribution, the preparation method has the advantages that a complete and continuous three-dimensional conductive / magnetic conductive network is constructed in advance, so that efficient utilization of the filler is realized, and better shielding performance can be obtained under the condition of lower filling amount.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology and relates to a method for preparing a three-dimensional porous electromagnetic shielding composite material. Background Technology

[0002] With the development of electronic devices towards higher frequencies and greater integration, electromagnetic interference problems are becoming increasingly serious, making the development of high-performance electromagnetic shielding materials an urgent priority. Polymer-based electromagnetic shielding composites are polymer materials with conductive properties formed by uniformly dispersing functional fillers (such as conductive fillers, magnetic fillers, etc.) in a one-phase or multi-phase polymer matrix through different processing methods (melting, solution, or other molding methods). Polymer-based composites have become a research focus due to their advantages such as lightweight, corrosion resistance, and ease of processing.

[0003] However, nanoscale functional fillers (such as carbon nanotubes and iron oxide) are prone to agglomeration when blended with polymers due to their significant surface effects, resulting in uneven distribution within the matrix and severely limiting further improvements in the electromagnetic shielding performance of composite materials. To address this issue, existing technologies primarily focus on surface modification of the fillers. For example, CN2022112977483 discloses a method for preparing a flexible electromagnetic shielding PVC composite film. This method modifies hydroxyl-containing carbon nanotubes and iron oxide (Fe3O4) using polymer / hydrotalcite-like monolayer nanomaterials. After modification, on the one hand, the interaction force between the carbon nanotubes / Fe3O4 and PVC is increased, solving the problem of easy detachment of carbon nanotubes / Fe3O4 from the PVC matrix. It also creates more interfaces, generating interfacial polarization, which is beneficial for improving the absorption of electromagnetic waves, thereby enhancing electromagnetic shielding performance. On the other hand, the introduced hydrotalcite-like material helps increase the dielectric loss of the PVC composite film, further improving electromagnetic shielding performance. Furthermore, the entanglement between the PVC chains and the polymer chains connecting the carbon nanotubes / Fe3O4 after film formation further improves the dispersibility and compatibility of carbon nanotubes / Fe3O4 in the polymer matrix. It is evident that the above patent achieves improved electromagnetic shielding performance through modification of functional materials. Similarly, CN2022112977549 discloses a multi-component composite flexible conductive film and its preparation method. A polymer / hydrotalcite-like substance is grown in situ on the surface of carbon nanotubes using a co-precipitation method, effectively reducing the surface energy of the carbon nanotubes. A highly dispersed polymer / hydrotalcite-like substance / carbon nanotube suspension is then obtained through solution exfoliation, significantly improving the uniformity and stability of the carbon nanotubes in the solvent. Furthermore, the entanglement between polymer chains enhances its fixation effect in the matrix. Likewise, related English literature (such as "Fabrication of PVA-based electromagnetic interference shielding composite film by improving the dispersibility of carbon nanomaterial via m-LDH modification") describes the preparation of a single-layer hydrotalcite-like substance using a co-precipitation method and intercalation with a styrene-maleic anhydride copolymer. Utilizing its layered structure and the steric hindrance effect generated by the polymer chains adsorbed on the surface, the dispersion of carbon filler in the aqueous PVA matrix is ​​effectively improved, thereby enhancing the conductivity and electromagnetic shielding performance of the composite film. In summary, the current mainstream technical approach is essentially "modifying the filler first, then blending and dispersing," with the goal of improving the dispersion state of the filler in the matrix.

[0004] While the aforementioned modification methods can improve electromagnetic shielding performance to some extent, their fundamental limitation lies in the fact that when the filler content is low, even with good dispersion, the filler remains randomly and isolated within the matrix, making it difficult to form a continuous, interconnected conductive / magnetic network. Electromagnetic shielding effectiveness, especially shielding mechanisms primarily based on reflection loss, highly depends on the construction of a continuous conductive network. Therefore, ensuring the formation of an efficient and stable three-dimensional functional network with low filler content is a key challenge in overcoming current performance bottlenecks and achieving both lightweight and high-performance materials.

[0005] To address this issue, a more advanced strategy has been proposed: pre-constructing a complete three-dimensional filler network within the polymer matrix. This strategy aims to fundamentally avoid the uncontrollability of random filler dispersion, enabling the formation of complete three-dimensional conductive pathways for conductive flow even at extremely low filler concentrations, thus maximizing the utilization of the filler's electromagnetic properties. However, realizing this strategy faces a crucial prerequisite: how to first assemble the filler into a structurally stable, interconnected three-dimensional macroscopic body for subsequent polymer backfilling.

[0006] Carbon black, as a traditional filler with low cost and good conductivity, has been widely studied. However, to achieve the aforementioned "pre-built network" strategy, carbon black itself needs to be assembled into a stable three-dimensional porous macrostructure (i.e., aerogel) for subsequent polymer backfilling. However, carbon black particles exhibit extremely strong van der Waals forces and have very weak self-assembly capabilities, making it difficult to form a stable sol in aqueous phases or other media, let alone spontaneously construct a long-range ordered three-dimensional network structure. This has become the main technical bottleneck in preparing high-performance shielding materials using carbon black through the "pre-built network" strategy.

[0007] In existing technologies, two-dimensional materials (such as graphene and graphene oxide) are often used as supporting frameworks to assist in the dispersion and assembly of carbon black. However, these carbon materials are costly, and their interfacial bonding with carbon black is often limited, resulting in unsatisfactory assembly effects. Layered double hydroxides (LDHs), also known as hydrotalcite-like materials, are a class of artificially synthesized two-dimensional nanostructured anionic clays, formed by the combination of positively charged hydroxide layers and negatively charged anions in the interlayer space. LDHs not only possess a stable layered structure but also have a high aspect ratio, specific surface area, and abundant interlayer interfaces. Due to their simple synthesis method, LDHs are easily combined with other functional fillers, not only passivating the filler surface and inhibiting agglomeration but also generating significant interfacial polarization effects through their layered structure and the composite interface formed with the filler. These properties theoretically make them an ideal "nanoglue" and "structural scaffold." However, the application of LDHs in existing technologies has always been limited to their role as "dispersing aids" or "dielectric fillers," that is, using them to modify fillers before blending. For example, CN2023101629109 discloses the application of LDH / polymer in the preparation of electromagnetic shielding films. An LDH / polymer solution is prepared by co-precipitation, which improves the binding between the polymer and LDH and avoids the problem of LDH peeling off from the polymer matrix. Then, a certain water-soluble solvent is added to the LDH / polymer mixture, so that some polymer precipitates and deposits on the surface of the LDH layer. The LDH / polymer settles in the solution. Due to the entanglement between the polymer chains, the LDH / polymer has extensibility and film-forming characteristics. It can be seen that the above patent introduces the dielectric material LDH and further improves the performance of the electromagnetic shielding film through the strong interaction between the dielectric material LDH and the polymer.

[0008] However, no research has yet utilized monolayer hydrotalcite-like structures to proactively address the fundamental assembly challenge of carbon black's weak self-gelling ability. In particular, the use of monolayer hydrotalcite-like structures for in-situ growth on the carbon black surface, guiding and stabilizing carbon black particles, and synergistically constructing a stable three-dimensional porous aerogel structure suitable for polymer backfilling remains a gap in research.

[0009] Therefore, the core technical problem to be solved by this patent is to provide a method to overcome the defect that carbon black cannot form a three-dimensional porous structure on its own due to its weak self-gelling ability. Unlike the existing technology that only uses hydrotalcite-like materials as dispersing agents, this method innovatively uses controllably grown monolayer hydrotalcite-like materials as the assembly core and structural template to guide carbon black particles to build a stable three-dimensional interconnected network, thereby laying a crucial structural foundation for the final preparation of high-performance electromagnetic shielding composite materials with low filler content. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a three-dimensional porous electromagnetic shielding composite material. This method utilizes a single-layer hydrotalcite-like material to solve the problems of weak self-gelling ability of carbon black, high cost of assisted assembly of traditional two-dimensional carbon materials, and weak interfacial bonding, and assists in assembling it into a three-dimensional network structure.

[0011] In view of the shortcomings of existing technologies, such as the difficulty in assembling carbon black into a stable three-dimensional porous structure due to its weak self-gelling ability, which hinders the "pre-construction network" strategy, and the high cost and weak interfacial bonding of traditional two-dimensional carbon materials for assisted assembly, this invention aims to provide a novel and highly operable method for preparing three-dimensional porous electromagnetic shielding composite materials.

[0012] This invention, by controlling the growth process of a single-layer hydrotalcite-like material, cleverly utilizes its functions as both a "nano-glue" and a "structural scaffold" to achieve in-situ guided and stable bonding of carbon black particles, synergistically constructing a structurally stable three-dimensional composite aerogel precursor. This method not only solves the key technical challenge of carbon black's inability to self-assemble but also transforms the hydrotalcite-like material into a magnetic oxide through subsequent calcination, jointly constructing a biphase filler network with carbon black that possesses both electrical and magnetic conductivity. This network structure provides an ideal framework for subsequent polymer backfilling, ultimately yielding a composite material with excellent electromagnetic shielding performance.

[0013] Specifically, this is achieved through the following technical solutions: A method for preparing a three-dimensional porous electromagnetic shielding composite material includes the following steps: (1) Hydrotalcite-assisted assembly: Carbon black and the interlayer anions of hydrotalcite are dispersed in 50 ml of deionized water and treated under the condition of stirring and sonication for 30~120 min. The pH of the system is adjusted to 10 with alkaline solution to obtain mixed solution A. Then, 50 ml of mixed metal salt solution containing divalent metal ions and trivalent metal ions is added dropwise to mixed solution A. The pH value during the reaction process is adjusted with alkaline solution so that the pH value of the system does not exceed 7 to obtain hydrogel. Among them, the characteristic of the interlayer anions to gel and precipitate when the pH is below 7 is utilized to form a synergistic gelation effect with the monolayer hydrotalcite gel system generated in situ during the precipitation process of the mixed metal salt solution, thereby forming a stable three-dimensional hydrogel network. In the hydrotalcite-assisted assembly process of step (1), this invention cleverly utilizes the unique pH-responsive characteristics of the selected interlayer anions. When the pH of the system is adjusted to below 7, these anions undergo gelation and precipitation due to the change in charge environment. This process significantly enhances the gelation degree of the entire system, acting as a "physical cross-linking point." This gelation effect synergizes with the gel system formed when a mixed metal salt solution is added and a monolayer hydrotalcite (m-LDH) is generated in situ on the carbon black surface and in the solution. This synergy is not a simple addition, but rather a mutual support and interweaving between the macroscopic framework provided by the anionic gel and the microstructure provided by the hydrotalcite nanosheets, jointly constructing a more stable composite hydrogel with a more complete three-dimensional network. This design is the key to the successful preparation of the subsequent porous aerogel by this method.

[0014] (2) The hydrogel obtained in step (1) was placed on a copper plate immersed in liquid nitrogen and frozen. Then it was freeze-dried by ice crystal sublimation at -60℃ and 10 Pa to form an aerogel with a honeycomb porous structure. (3) The aerogel obtained in step (2) is calcined to convert the hydrotalcite-like material into a magnetic metal oxide, thereby obtaining a three-dimensional carbon black aerogel modified with a magnetic metal oxide. (4) Using the polymer backfilling method, the polymer solution is impregnated into the pores of the three-dimensional carbon black aerogel obtained in step (3) under vacuum conditions, and then heat-treated at 40~60℃ for 12~24 h. After curing, the three-dimensional porous electromagnetic shielding composite material is finally obtained.

[0015] Furthermore, the mass ratio of the carbon black to the interlayer anions of the hydrotalcite-like material is 1:5-15.

[0016] Furthermore, the interlayer anion of the hydrotalcite-like material is one of ethylene-acrylic acid copolymer and polystyrene / carboxylic anhydride functional group copolymer; the molar ratio of the interlayer anion to the trivalent metal ion is 15:1-20:1.

[0017] Furthermore, the divalent metal ion is a divalent nickel ion, the trivalent metal ion is a trivalent iron ion, and the molar ratio of the divalent nickel ion to the trivalent iron ion is 2:1-4:1.

[0018] Furthermore, the calcination is carried out at 400°C for 5 hours.

[0019] Furthermore, the polymer solution is a polydimethylsiloxane solution, which is prepared by mixing polydimethylsiloxane, a curing agent and n-hexane and stirring vigorously for 30 minutes.

[0020] Furthermore, the three-dimensional porous electromagnetic shielding composite material contains a three-dimensional continuous porous framework composed of carbon black and magnetic metal oxides derived from a single layer of hydrotalcite, and this framework is completely filled and coated with polydimethylsiloxane.

[0021] Furthermore, the magnetic metal oxide is a mixture of nickel oxide and iron oxide formed by calcining magnetic hydrotalcite.

[0022] The present invention also provides an application of the aforementioned three-dimensional porous electromagnetic shielding composite material in the fabrication of flexible electronic devices, portable communication devices, and electromagnetic compatibility components.

[0023] In the process of preparing flexible electronic devices, portable communication devices, and electromagnetic compatibility components, the composite material prepared by this invention has excellent comprehensive performance. Its unique three-dimensional continuous network and porous structure are conducive to impedance matching and multiple absorption of electromagnetic waves, enhancing electromagnetic shielding performance and facilitating the formation of a shielding mechanism dominated by absorption, significantly reducing secondary electromagnetic pollution. At the same time, after polymer backfilling, the material combines the stability of rigid network with the flexibility of polymer, expanding its application potential in the fields of flexible electronics and wearable devices.

[0024] Invention Principle: This invention first utilizes the pH-responsive characteristics of interlayer anions. Under alkaline conditions (pH=10), the anions are well dispersed; when the pH drops below 7, these anionic chains gel due to charge neutralization, forming the first layer of physical cross-linking network. Simultaneously, the added metal salt solution generates monolayer hydrotalcite-like nanosheets in situ on the carbon black surface and in the solution, which themselves also form a gel network. These two gelation effects are not simply additive but synergistic: the anionic gel acts as the macroscopic framework, and the hydrotalcite-like gel acts as the microscopic reinforcement, intertwining to firmly "lock" the carbon black particles in a stable three-dimensional hydrogel network, fundamentally solving the problem of weak self-gelling ability of carbon black. Furthermore, by using liquid nitrogen copper disk cryogenic freezing to induce vertical growth of ice crystals, an aerogel skeleton with a vertically oriented honeycomb porous structure is formed, creating favorable conditions for multiple reflections and scattering of electromagnetic waves and enhancing shielding effectiveness. Finally, by calcination, hydrotalcite-like material is converted in situ into magnetic metal oxide, forming a three-dimensional continuous skeleton composed of conductive carbon black and magnetic metal oxide, realizing the synergistic effect of conductive loss and magnetic loss, and further enhancing electromagnetic shielding performance.

[0025] Beneficial effects Compared with existing technologies, this invention exhibits significant advancements and comprehensive advantages: First, it fundamentally overcomes the technical bottleneck of carbon black's inability to self-assemble into a stable three-dimensional network. Compared to blending techniques that rely on high filler content and random filler distribution, this invention achieves efficient utilization of fillers by pre-constructing a complete and continuous three-dimensional conductive / magnetic network, enabling superior shielding performance with lower filler content. Simultaneously, compared to solutions using expensive graphene as a supporting framework, this invention uses low-cost, easily prepared hydrotalcite-like materials as "nanoglue," constructing a more stable and uniform network system through a "synergistic gelation" mechanism, significantly reducing costs. Second, this invention achieves a perfect fusion of "structural design" and "functional integration." By constructing an oriented porous framework through directional freezing and combining it with in-situ calcination, structural units are directly transformed into magnetic functional units, avoiding the problem of uneven magnetic filler distribution and effectively promoting uniform matching and synergistic enhancement of conductive and magnetic losses. Furthermore, the composite material of this invention exhibits excellent overall performance. Its unique three-dimensional continuous network and porous structure are conducive to impedance matching and multiple absorption of electromagnetic waves, enhancing electromagnetic shielding performance and facilitating the formation of an absorption-dominant shielding mechanism, significantly reducing secondary electromagnetic pollution. It is particularly suitable for precision electronic equipment. At the same time, after polymer backfilling, the material combines the stability of a rigid network with the flexibility of a polymer, expanding its application potential in the fields of flexible electronics and wearable devices. In addition, the main raw materials are inexpensive and the process is highly controllable, giving it good prospects for large-scale production and commercial value. Attached Figure Description

[0026] Figure 1 This is a SEM image of the three-dimensional porous aerogel in Example 1. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be described in detail below with reference to several embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] One objective of this invention is to provide a method for preparing a three-dimensional porous electromagnetic shielding composite material, comprising the following steps: (1) Hydrotalcite-assisted assembly: Carbon black and the interlayer anions of hydrotalcite are dispersed in 50 ml of deionized water and treated under the condition of stirring and sonication for 30~120 min. The pH of the system is adjusted to 10 with alkaline solution to obtain mixed solution A. Then, 50 ml of mixed metal salt solution containing divalent metal ions and trivalent metal ions is added dropwise to mixed solution A. The pH value during the reaction process is adjusted with alkaline solution so that the pH value of the system does not exceed 7 to obtain hydrogel. Among them, the characteristic of the interlayer anions to gel and precipitate when the pH is below 7 is utilized to form a synergistic gelation effect with the monolayer hydrotalcite gel system generated in situ during the precipitation process of the mixed metal salt solution, thereby forming a stable three-dimensional hydrogel network. In the hydrotalcite-assisted assembly process of step (1), this invention cleverly utilizes the unique pH-responsive characteristics of the selected interlayer anions. When the pH of the system is adjusted to below 7, these anions undergo gelation and precipitation due to the change in charge environment. This process significantly enhances the gelation degree of the entire system, acting as a "physical cross-linking point." This gelation effect synergizes with the gel system formed when a mixed metal salt solution is added and a monolayer hydrotalcite (m-LDH) is generated in situ on the carbon black surface and in the solution. This synergy is not a simple addition, but rather a mutual support and interweaving between the macroscopic framework provided by the anionic gel and the microstructure provided by the hydrotalcite nanosheets, jointly constructing a more stable composite hydrogel with a more complete three-dimensional network. This design is the key to the successful preparation of the subsequent porous aerogel by this method.

[0029] (2) The hydrogel obtained in step (1) is placed on a copper disk immersed in liquid nitrogen and frozen. Then, it is freeze-dried by ice crystal sublimation at -60℃ and 10 Pa to form an aerogel with a honeycomb porous structure. The ultra-low temperature freezing of the liquid nitrogen copper disk induces the vertical growth of ice crystals to form an aerogel skeleton with a vertically oriented honeycomb porous structure, which creates favorable conditions for multiple reflections and scattering of electromagnetic waves and enhances the shielding effectiveness.

[0030] (3) The aerogel obtained in step (2) is calcined to convert the hydrotalcite-like material into a magnetic metal oxide, thereby obtaining a three-dimensional carbon black aerogel modified with a magnetic metal oxide. (4) Using the polymer backfilling method, the polymer solution is impregnated into the pores of the three-dimensional carbon black aerogel obtained in step (3) under vacuum conditions, and then heat-treated at 40~60℃ for 12~24 h. After curing, the three-dimensional porous electromagnetic shielding composite material is finally obtained. The three-dimensional porous electromagnetic shielding composite material contains a three-dimensional continuous porous framework composed of carbon black and magnetic metal oxides derived from single-layer hydrotalcite, and the framework is completely filled and coated with polydimethylsiloxane.

[0031] The mass ratio of carbon black to interlayer anions of hydrotalcite is 1:5-15.

[0032] The interlayer anion of the hydrotalcite-like material is one of ethylene-acrylic acid copolymer and polystyrene / carboxylic anhydride functional group copolymer; the molar ratio of the interlayer anion to the trivalent metal ion is 15:1-20:1.

[0033] The divalent metal ion is a divalent nickel ion, the trivalent metal ion is a trivalent iron ion, and the molar ratio of the divalent nickel ion to the trivalent iron ion is 2:1-4:1.

[0034] The calcination was carried out at 400°C for 5 hours.

[0035] The polymer solution is a polydimethylsiloxane solution, which is prepared by mixing polydimethylsiloxane, a curing agent and n-hexane and stirring vigorously for 30 min.

[0036] The magnetic metal oxide is a mixture of nickel oxide and iron oxide formed by calcining magnetic hydrotalcite.

[0037] Another object of the present invention is to provide the application of the three-dimensional porous electromagnetic shielding composite material in the fabrication of flexible electronic devices, portable communication devices, and electromagnetic compatibility components.

[0038] In the process of preparing flexible electronic devices, portable communication devices, and electromagnetic compatibility components, the composite material prepared by this invention has excellent comprehensive performance. Its unique three-dimensional continuous network and porous structure are conducive to impedance matching and multiple absorption of electromagnetic waves, enhancing electromagnetic shielding performance and facilitating the formation of a shielding mechanism dominated by absorption, significantly reducing secondary electromagnetic pollution. At the same time, after polymer backfilling, the material combines the stability of rigid network with the flexibility of polymer, expanding its application potential in the fields of flexible electronics and wearable devices.

[0039] This section presents different embodiments based on adjustments to different raw material ratios and parameter settings. Example 1 A method for preparing a three-dimensional porous electromagnetic shielding composite material includes the following steps: (1) Hydrotalcite-assisted assembly: 1g carbon black and 5g ethylene acrylic acid copolymer were dispersed in 50 ml of deionized water and treated under the condition of stirring and sonication for 30 min. The pH of the system was adjusted to 10 with alkaline solution to obtain mixed solution A. Then, 50 ml of mixed metal salt solution containing 2 mol / L divalent nickel ions and 1 mol / L trivalent iron ions was added dropwise to mixed solution A. The pH value during the reaction process was adjusted with alkaline solution so that the pH value of the system did not exceed 7 to obtain hydrogel. (2) The hydrogel obtained in step (1) was placed on a copper plate immersed in liquid nitrogen and frozen. Then it was freeze-dried by ice crystal sublimation at -60℃ and 10 Pa to form an aerogel with a honeycomb porous structure. (3) Calcine the aerogel obtained in step (2) at 400°C for 5 hours to convert the hydrotalcite into a mixture of nickel oxide and iron oxide to obtain a three-dimensional magnetic carbon black aerogel. (4) Using the polymer backfilling method, the polydimethylsiloxane solution is impregnated into the pores of the three-dimensional carbon black aerogel obtained in step (3) under vacuum conditions, and then heat-treated at 40°C for 12 h. After curing, the three-dimensional porous electromagnetic shielding composite material is finally obtained.

[0040] Example 2 A method for preparing a three-dimensional porous electromagnetic shielding composite material includes the following steps: (1) Hydrotalcite-assisted assembly: 1g carbon black and 15g polystyrene / carboxylic anhydride functional group copolymer were dispersed in 50ml of deionized water and treated under the condition of stirring and sonication for 120 min. The pH of the system was adjusted to 10 with alkaline solution to obtain mixed solution A. Then, 50 ml of mixed metal salt solution containing 4mol / L divalent nickel ions and 1mol / L trivalent iron ions was added dropwise to mixed solution A. The pH value during the reaction process was adjusted with alkaline solution so that the pH value of the system did not exceed 7 to obtain hydrogel. (2) The hydrogel obtained in step (1) was placed on a copper plate immersed in liquid nitrogen and frozen. Then it was freeze-dried by ice crystal sublimation at -60℃ and 10 Pa to form an aerogel with a honeycomb porous structure. (3) Calcine the aerogel obtained in step (2) at 400°C for 5 hours to convert the hydrotalcite into a mixture of nickel oxide and iron oxide to obtain a three-dimensional magnetic carbon black aerogel. (4) Using the polymer backfilling method, polydimethylsiloxane solution is impregnated into the pores of the three-dimensional carbon black aerogel obtained in step (3) under vacuum conditions, and then heat-treated at 60°C for 24 h. After curing, the three-dimensional porous electromagnetic shielding composite material is finally obtained.

[0041] Example 3 A method for preparing a three-dimensional porous electromagnetic shielding composite material includes the following steps: (1) Hydrotalcite-assisted assembly: 1g of carbon black and 10g of ethylene-acrylic acid copolymer were dispersed in 50ml of deionized water and treated under the condition of stirring and sonication for 80min. The pH of the system was adjusted to 10 with alkaline solution to obtain mixed solution A. Then, 50ml of mixed metal salt solution containing 3mol / L divalent nickel ions and 1mol / L trivalent iron ions was added dropwise to mixed solution A. The pH value during the reaction process was adjusted with alkaline solution so that the pH value of the system did not exceed 7 to obtain hydrogel. (2) The hydrogel obtained in step (1) was placed on a copper plate immersed in liquid nitrogen and frozen. Then it was freeze-dried by ice crystal sublimation at -60℃ and 10 Pa to form an aerogel with a honeycomb porous structure. (3) Calcine the aerogel obtained in step (2) at 400°C for 5 hours to convert the hydrotalcite into a mixture of nickel oxide and iron oxide to obtain a three-dimensional magnetic carbon black aerogel. (4) Using the polymer backfilling method, the polydimethylsiloxane solution is impregnated into the pores of the three-dimensional carbon black aerogel obtained in step (3) under vacuum conditions, and then heat-treated at 50°C for 18 h. After curing, the three-dimensional porous electromagnetic shielding composite material is finally obtained.

[0042] Example 4 A method for preparing a three-dimensional porous electromagnetic shielding composite material includes the following steps: (1) Hydrotalcite-assisted assembly: 1g carbon black and 15g polystyrene / carboxylic anhydride functional group copolymer were dispersed in 50ml of deionized water and treated under the condition of stirring and sonication for 30 min. The pH of the system was adjusted to 10 with alkaline solution to obtain mixed solution A. Then, 50 ml of mixed metal salt solution containing 2mol / L divalent nickel ions and 1mol / L trivalent iron ions was added dropwise to mixed solution A. The pH value during the reaction process was adjusted with alkaline solution so that the pH value of the system did not exceed 7 to obtain hydrogel. (2) The hydrogel obtained in step (1) was placed on a copper plate immersed in liquid nitrogen and frozen. Then it was freeze-dried by ice crystal sublimation at -60℃ and 10 Pa to form an aerogel with a honeycomb porous structure. (3) Calcine the aerogel obtained in step (2) at 400°C for 5 hours to convert the hydrotalcite into a mixture of nickel oxide and iron oxide to obtain a three-dimensional magnetic carbon black aerogel. (4) Using the polymer backfilling method, the polydimethylsiloxane solution is impregnated into the pores of the three-dimensional carbon black aerogel obtained in step (3) under vacuum conditions, and then heat-treated at 60°C for 12 h. After curing, the three-dimensional porous electromagnetic shielding composite material is finally obtained.

[0043] Experiment 1 Performance Test Test subjects: Electromagnetic shielding composite materials prepared in Examples 1-4; Experimental method: The test was conducted using a vector network analyzer (Agilent E5071C) with the coaxial method.

[0044] Experimental results: Table 1 test subjects Example 1 Example 2 Example 3 Example 4 Electromagnetic shielding performance (EMI SE) 20.1 24.5 23.3 21.8 As shown in Table 1, the composite materials prepared in Examples 1-4 all exhibited effective electromagnetic shielding performance. This strongly demonstrates the effectiveness and adjustability of the preparation method described in this invention. By adjusting key parameters such as the ratio of carbon black to interlayer anions and the concentration of metal ions, the three-dimensional network structure of the final composite material can be optimized, thereby achieving effective control over the electromagnetic shielding performance. This provides clear data support and directional guidance for subsequent material performance optimization and industrialization development.

[0045] Other embodiments Example 5 For specific implementation details, please refer to Example 1. The key difference is that the carbon black weighs 2g, while the ethylene-acrylic acid copolymer is 1g and undergoes ultrasonic treatment; (this is intended to highlight the auxiliary role of interlayer anions in the case of excess carbon black). Example 6 For specific implementation details, please refer to Example 1. The key difference lies in the mass of carbon black (5g) and the ultrasonic treatment of ethylene-acrylic acid copolymer (1g); this is intended to highlight the auxiliary effect of interlayer anions on carbon black in cases of excess carbon black. Example 7 For specific implementation details, please refer to Example 1. The key difference lies in the substitution of a hydrotalcite-like interlayer anionic ethylene-acrylic acid copolymer with a hydrotalcite-like material (Mg6Al2(OH)CO3·4H2O). (This is intended to highlight the auxiliary effect on carbon black in the presence of both metal cations and anions.) Examples 8-9 For specific implementation details, please refer to Example 1. The key difference is that, in step (1) of the hydrotalcite-assisted assembly process, after adding mixed metal ions to the mixed solution A, the pH value during the reaction process is adjusted to 8 or 9 with an alkaline solution; (this is to highlight the pH-responsive gelation characteristics of interlayer anions on the triggering effect of the entire "synergistic gelation" process). Experiment 2 Performance Testing Test subjects: electromagnetic shielding composite materials prepared in Examples 5-9; control group: electromagnetic shielding composite material prepared in Example 1.

[0046] Experimental method: The test was conducted using a vector network analyzer (Agilent E5071C) with the coaxial method.

[0047] Experimental results: Table 2 test subjects Electromagnetic shielding performance (EMI SE) Example 5 13.5 Example 6 12.7 Example 7 10.3 Example 8 11.4 Example 9 10.8 Example 1 20.1 The results of Examples 5 and 6 show that when carbon black is in excess relative to interlayer anions (the ratio changes from 1:5 to 2:1 and 5:1), the shielding performance drops sharply to 13.5 dB and 12.7 dB, respectively. This demonstrates that without sufficient interlayer anions to act as a "nanoglue" and synergistic gelation agent, carbon black cannot be effectively dispersed and assembled, resulting in defects in the three-dimensional network structure and incomplete conductive pathways. The results of Example 7 show that using pre-synthesized, non-monolayer LDH (MgAl-CO3 LDH) instead of the interlayer anion scheme of this invention results in a performance drop to a minimum of 10.3 dB. This demonstrates that ordinary LDH lacks the gelation and high dispersibility of monolayer nanosheets and cannot produce a synergistic gelation effect with interlayer anions, thus failing to effectively disperse carbon black or construct a stable three-dimensional network. The results of Examples 8 and 9 show that when the pH of the reaction system is increased to 8 and 9 (i.e., not lowered below 7), the performance also deteriorates significantly. This directly verifies that the pH-responsive gelation property of interlayer anions (precipitation at pH < 7) is the key triggering condition for the entire "synergistic gelation" process. If the pH value is not up to standard, the synergistic effect cannot be initiated, and the three-dimensional hydrogel network cannot be stably formed.

Claims

1. A method for preparing a three-dimensional porous electromagnetic shielding composite material, characterized in that, Includes the following steps: (1) Hydrotalcite-assisted assembly: Carbon black and the interlayer anions of hydrotalcite are dispersed in 50 ml of deionized water and treated under the condition of stirring and sonication for 30~120 min. The pH of the system is adjusted to 10 with alkaline solution to obtain mixed solution A. Then, 50 ml of mixed metal salt solution containing divalent metal ions and trivalent metal ions is added dropwise to mixed solution A. The pH value during the reaction process is adjusted with alkaline solution so that the pH value of the system does not exceed 7 to obtain hydrogel. (2) The hydrogel obtained in step (1) was placed on a copper plate immersed in liquid nitrogen and frozen. Then it was freeze-dried by ice crystal sublimation at -60℃ and 10 Pa to form an aerogel with a honeycomb porous structure. (3) The aerogel obtained in step (2) is calcined to convert the hydrotalcite-like material into a magnetic metal oxide, thereby obtaining a three-dimensional carbon black aerogel modified with a magnetic metal oxide. (4) Using the polymer backfilling method, the polymer solution is impregnated into the pores of the three-dimensional carbon black aerogel obtained in step (3) under vacuum conditions, and then heat-treated at 40~60℃ for 12~24 h. After curing, the three-dimensional porous electromagnetic shielding composite material is finally obtained.

2. The preparation method according to claim 1, characterized in that, The mass ratio of carbon black to interlayer anions of hydrotalcite is 1:3-10.

3. The preparation method according to claim 1, characterized in that, The interlayer anion of the hydrotalcite-like material is one of ethylene-acrylic acid copolymer and polystyrene / carboxylic anhydride functional group copolymer; the molar ratio of the interlayer anion to the trivalent metal ion of the hydrotalcite-like material is 15:1-20:

1.

4. The preparation method according to claim 1, characterized in that, The divalent metal ion is a divalent nickel ion, the trivalent metal ion is a trivalent iron ion, and the molar ratio of the divalent nickel ion to the trivalent iron ion is 2:1-4:

1.

5. The preparation method according to claim 1, characterized in that, The calcination was carried out at 400°C for 5 hours.

6. The preparation method according to claim 1, characterized in that, The polymer solution is a polydimethylsiloxane solution, which is prepared by mixing polydimethylsiloxane, a curing agent and n-hexane and stirring vigorously for 30 min.

7. The preparation method according to claim 1, characterized in that, The three-dimensional porous electromagnetic shielding composite material contains a three-dimensional continuous porous framework composed of carbon black and magnetic metal oxides derived from a single layer of hydrotalcite, and this framework is completely filled and coated with polydimethylsiloxane.

8. The preparation method according to claim 1 or 7, characterized in that, The magnetic metal oxide is a mixture of nickel oxide and iron oxide formed by calcining magnetic hydrotalcite.

9. A three-dimensional porous electromagnetic shielding composite material prepared by the preparation method according to any one of claims 1-8.

10. The application of a three-dimensional porous electromagnetic shielding composite material prepared by any one of claims 1-8 in the preparation of flexible electronic devices, portable communication devices, and electromagnetic compatibility components.

Images