Preparation method of double-layer electromagnetic shielding material for Ka wave band and double-layer electromagnetic shielding material

Abstract

The invention discloses a preparation method of a double-layer electromagnetic shielding material for a Ka wave band and the double-layer electromagnetic shielding material, and belongs to the technical field of electromagnetic shielding materials. The invention discloses a preparation method of a double-layer electromagnetic shielding material. The preparation method comprises the following steps: providing conductive layer dispersion liquid and magnetic layer dispersion liquid; laterally freezing the conductive layer dispersion liquid to obtain a conductive layer frozen sample; the magnetic layer dispersion liquid is poured above the conductive layer frozen sample and is laterally frozen again, a double-layer frozen sample is obtained, the double-layer aerogel is obtained through sublimation drying, the double-layer aerogel comprises conductive layer aerogel and magnetic layer aerogel stacked with the conductive layer aerogel, and the magnetic layer aerogel is prepared from the conductive layer aerogel and the magnetic layer aerogel. The pore orientation of the magnetic layer aerogel is consistent with that of the conductive layer aerogel; and carrying out surface hydrophobic modification on the double-layer aerogel, then filling the double-layer aerogel with a macromolecular prepolymer, and carrying out curing treatment to obtain the double-layer electromagnetic shielding material. According to the invention, the preparation of the low-reflection and high-electromagnetic shielding effectiveness material for the Ka wave band is realized.

Description

Preparation method of double-layer electromagnetic shielding material for Ka-band and double-layer electromagnetic shielding material Technical Field

[0001] This application relates to the field of electromagnetic shielding materials technology, and in particular to a method for preparing a double-layer electromagnetic shielding material for the Ka band and the double-layer electromagnetic shielding material itself. Background Technology

[0002] In the field of electromagnetic shielding materials research, asymmetric composite materials based on magnetic / conductive bilayer structures have attracted much attention because they can simultaneously achieve high shielding effectiveness and low reflection. These materials promote electromagnetic wave incidence by designing a magnetic layer on the surface and efficiently dissipate electromagnetic energy using a conductive layer at the bottom, thus theoretically demonstrating great potential to solve the problem of electromagnetic secondary pollution.

[0003] Currently, most electromagnetic shielding materials prepared using existing technologies are single-layer materials, which cannot avoid the problem of increased reflectivity due to increased material conductivity. For the case of using bilayer aerogels as low-reflection shielding materials, the mechanical strength of the aerogel and the optimization of interlayer bonding have not been considered, thus limiting its application scenarios. Furthermore, existing technologies lack shielding materials specifically for Ka-band electromagnetic waves in the millimeter-wave band. Summary of the Invention

[0004] The main objective of this application is to provide a method for preparing a double-layer electromagnetic shielding material for the Ka band and the double-layer electromagnetic shielding material itself, aiming to solve the technical problem that Ka-band electromagnetic shielding materials are difficult to achieve both low reflection and high shielding effectiveness.

[0005] To achieve the above objectives, this application provides a method for preparing a double-layer electromagnetic shielding material for the Ka-band, comprising the following steps: providing a conductive layer dispersion and a magnetic layer dispersion; laterally freezing the conductive layer dispersion to obtain a frozen conductive layer sample; pouring the magnetic layer dispersion onto the frozen conductive layer sample and laterally freezing it again to obtain a double-layer frozen sample; sublimating and drying the double-layer frozen sample to obtain a double-layer aerogel, wherein the double-layer aerogel includes the conductive layer aerogel and a magnetic layer aerogel stacked with the conductive layer aerogel, the pore orientation of the magnetic layer aerogel being consistent with the pore orientation of the conductive layer aerogel; and after surface hydrophobic modification of the double-layer aerogel, filling it with a polymer prepolymer and curing it to obtain the double-layer electromagnetic shielding material.

[0006] In one embodiment, the step of providing the conductive layer dispersion and the magnetic layer dispersion includes: dispersing the conductive nanomaterial in a first water-soluble polymer solution to obtain the conductive layer dispersion; performing cationic surface modification treatment on the magnetic nanomaterial to obtain the modified magnetic nanomaterial; and mixing the modified magnetic nanomaterial, the dispersion of the dielectric nanomaterial, and the second water-soluble polymer solution to obtain the magnetic layer dispersion.

[0007] In one embodiment, the mass concentration ratio of the conductive nanomaterial to the first water-soluble polymer is 5:5 mg / mL, wherein the concentration of the conductive nanomaterial is 2-10 mg / mL, the concentration of the first water-soluble polymer is 5-20 mg / mL, and the total concentration of the conductive nanomaterial and the first water-soluble polymer is 10-30 mg / mL; and / or, in the cationic surface modification treatment, the mass ratio of the magnetic nanomaterial to the surface cationic modifier is 1:1-4:1.

[0008] In one embodiment, the conductive nanomaterial includes: carbon nanotubes; and / or, the first water-soluble polymer includes: chitosan, polyacrylamide, chitosan quaternary ammonium salt; and / or, the magnetic nanomaterial includes: iron oxide hollow nanospheres; and / or, the dielectric nanomaterial includes: graphene oxide; and / or, the second water-soluble polymer includes: sodium alginate, polyacrylic acid, polymethacrylic acid, polyvinyl alcohol.

[0009] In one embodiment, the volume ratio of the magnetic layer dispersion to the conductive layer dispersion is 1:2 to 2:1.

[0010] In one embodiment, before the step of modifying the surface of the bilayer aerogel to be hydrophobic, filling it with a polymer prepolymer, and then curing it to obtain a bilayer electromagnetic shielding material, the method includes: placing the bilayer aerogel and volatile silane in a vacuum dryer for hydrophobic modification to obtain a hydrophobically modified bilayer aerogel; filling the hydrophobically modified bilayer aerogel with a polymer prepolymer and then curing it to obtain a bilayer electromagnetic shielding material.

[0011] In one embodiment, the hydrophobic modification treatment includes: heat treatment at -80 kPa and 55°C for 12 to 48 hours; and / or, the volatile silane includes: methyltrichlorosilane, methyldichlorosilane, and dimethylchlorosilane; and / or, the volume ratio of the bilayer aerogel to the volatile silane is 20:1 to 60:1.

[0012] In one embodiment, the step of filling the hydrophobically modified bilayer aerogel with a polymer prepolymer and then curing it to obtain a bilayer electromagnetic shielding material includes: placing the hydrophobically modified bilayer aerogel in a first organic solvent to obtain a pore-wetted aerogel; placing one end of the pore-wetted aerogel in a filling liquid for filling treatment to obtain a filled aerogel, wherein the pore direction of the pore-wetted aerogel is perpendicular to the liquid surface of the filling liquid, and the filling liquid includes: a polymer prepolymer and a second organic solvent compatible with the polymer prepolymer, wherein the second organic solvent and the first organic solvent are compatible; and curing the filled aerogel to obtain a bilayer electromagnetic shielding material.

[0013] In one embodiment, the first organic solvent includes n-hexane; and / or, the second organic solvent includes n-hexane, tetrahydrofuran, and acetone; and / or, the polymer prepolymer includes silicone rubber, polyurethane, epoxy resin, and polyacrylate; and / or, the mass ratio of the second organic solvent to the polymer prepolymer in the filling liquid is 1:2 to 2:1; and / or, the filling treatment time is 12 to 72 hours; and / or, the curing treatment includes heat treatment at 140 to 160°C for 0.5 to 2 hours.

[0014] This application also provides a double-layer electromagnetic shielding material, which is prepared by the method described above.

[0015] In this embodiment, the conductive layer dispersion is first subjected to lateral freezing, causing the solute and nanofiller in the original dispersion to form a laterally oriented microstructure within the frozen conductive layer sample. Subsequent sublimation drying forms a laterally oriented porous structure that extends through both sides of the material, forming microchannels similar to directional arrangement, effectively shielding electromagnetic waves. When the magnetic layer dispersion is poured onto the frozen conductive layer sample, it promotes the melting of a small amount of the frozen conductive layer sample at the interface. The negatively charged polymer molecules in the magnetic layer dispersion interact electrostatically with the positively charged polymer molecules in the small amount of melted conductive layer dispersion, enhancing the interfacial bonding force. A subsequent lateral freezing process causes the magnetic layer dispersion to grow ice crystals laterally, in the same direction as the pores of the conductive layer, ensuring consistency in the orientation of the pores. Finally, sublimation drying yields a bilayer aerogel. The uniform pore orientation of the bilayer aerogel leads to a mechanical interlocking effect at the interlayer interface. During co-freezing, the directional growth of ice crystals guides the pore arrangement of the magnetic layer, enabling the pore networks of the two aerogels to interconnect and intertwine at the interface. The solid skeletons of the conductive and magnetic layers form a continuous structure at the nanoscale, rather than a simple physical contact. This significantly enhances the interfacial bonding force and reduces interfacial defects and stress concentration.

[0016] Then, the bilayer aerogel was filled with a polymer prepolymer and cured to further lock and strengthen the interfacial bonding. In its liquid state, the polymer prepolymer can penetrate into the pores of the two aerogel layers. Due to the consistent pore orientation, the prepolymer can uniformly fill the interfacial region and the interior of the aerogel. During the curing process, the polymer prepolymer polymerizes into a solid, forming a three-dimensional network that firmly binds the two aerogel layers together, filling microscopic defects and further consolidating the interfacial bonding between the reflective layer and the impedance matching layer.

[0017] Therefore, this application embodiment prepares a bilayer aerogel with different electromagnetic properties by stacking lateral freezing technology. The conductive layer at the bottom provides excellent electromagnetic shielding performance for the material, while the magnetic layer at the top has impedance matching function, which can reduce the reflection of electromagnetic waves, thereby solving the technical problem that electromagnetic shielding materials in the Ka band are difficult to have both low reflection and high shielding effectiveness. Attached Figure Description

[0018] Figure 1 is a flowchart illustrating the preparation method of the double-layer electromagnetic shielding material according to the embodiments of this application; Figure 2 is a diagram of the lateral freezing device involved in the preparation method of the double-layer electromagnetic shielding material according to this application; Figure 3 is a microscopic scanning electron microscope image of the double-layer aerogel during the preparation process of the double-layer electromagnetic shielding material in Embodiment 1 of this application; Figure 4 is a microscopic scanning electron microscope image of the double-layer electromagnetic shielding material in Embodiment 1 of this application, (a) is an illustration of the magnetic layer, and (b) is an illustration of the conductive layer; Figure 5 is a characteristic impedance curve of the single-layer electromagnetic shielding material of Comparative Examples 1-2 of this application in the Ka band; Figure 6 is a conductivity curve of the double-layer electromagnetic shielding material of Comparative Example 1 and Embodiments 1-3 of this application; Figure 7 is a curve of the reflection efficiency, absorption efficiency, and electromagnetic shielding efficiency of the single-layer electromagnetic shielding material of Comparative Examples 1-2 of this application in the Ka band; Figure 8 is a curve of the reflection efficiency SE of the double-layer electromagnetic shielding material of Embodiments 1-3 of this application in the Ka band. R Absorption efficiency SE A and shielding effectiveness SE T curve.

[0019] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the method for preparing the double-layer electromagnetic shielding material of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0022] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0023] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0024] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0025] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0026] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0027] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0028] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the technical solution of this application is further described below in conjunction with the accompanying drawings and embodiments. However, this application is not limited to the listed embodiments, but should also include any other well-known modifications within the scope of the claims made in this application.

[0029] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0030] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0031] Electromagnetic shielding materials prepared using existing technologies are mostly single-layer materials, which cannot avoid the problem of increased reflectivity due to increased material conductivity. For the case of double-layer aerogels as low-reflection shielding materials, the mechanical strength of the aerogel and the optimization of interlayer bonding have not been considered, resulting in limited application scenarios. Furthermore, existing technologies lack shielding materials specifically for Ka-band electromagnetic waves in the millimeter-wave band.

[0032] In this embodiment, the conductive layer dispersion is first subjected to lateral freezing, causing the solute and nanofiller in the original dispersion to form a laterally oriented microstructure within the frozen conductive layer sample. Subsequent sublimation drying forms a laterally oriented porous structure that extends through both sides of the material, forming microchannels similar to directional arrangement, effectively shielding electromagnetic waves. When the magnetic layer dispersion is poured onto the frozen conductive layer sample, it promotes the melting of a small amount of the frozen conductive layer sample at the interface. The negatively charged polymer molecules in the magnetic layer dispersion interact electrostatically with the positively charged polymer molecules in the small amount of melted conductive layer dispersion, enhancing the interfacial bonding force. A subsequent lateral freezing process causes the magnetic layer dispersion to grow ice crystals laterally, in the same direction as the pores of the conductive layer, ensuring consistency in the orientation of the pores. Finally, sublimation drying yields a bilayer aerogel. The uniform pore orientation of the bilayer aerogel leads to a mechanical interlocking effect at the interlayer interface. During co-freezing, the directional growth of ice crystals guides the pore arrangement of the magnetic layer, enabling the pore networks of the two aerogels to interconnect and intertwine at the interface. The solid skeletons of the conductive and magnetic layers form a continuous structure at the nanoscale, rather than a simple physical contact. This significantly enhances the interfacial bonding force and reduces interfacial defects and stress concentration.

[0033] Then, the bilayer aerogel was filled with a polymer prepolymer and cured to further lock and strengthen the interfacial bonding. In its liquid state, the polymer prepolymer can penetrate into the pores of the two aerogel layers. Due to the consistent pore orientation, the prepolymer can uniformly fill the interfacial region and the interior of the aerogel. During the curing process, the polymer prepolymer polymerizes into a solid, forming a three-dimensional network that firmly binds the two aerogel layers together, filling microscopic defects and further consolidating the interfacial bonding between the reflective layer and the impedance matching layer.

[0034] Therefore, this application embodiment prepares a bilayer aerogel with different electromagnetic properties by stacking lateral freezing technology. The conductive layer at the bottom provides excellent electromagnetic shielding performance for the material, while the magnetic layer at the top has impedance matching function, which can reduce the reflection of electromagnetic waves, thereby solving the technical problem that electromagnetic shielding materials in the Ka band are difficult to have both low reflection and high shielding effectiveness.

[0035] The first aspect of this application provides a method for preparing a double-layer electromagnetic shielding material for the Ka band, as shown in Figure 1, including the following steps: Step S10, providing a conductive layer dispersion and a magnetic layer dispersion.

[0036] The conductive layer dispersion is subsequently subjected to lateral freeze-drying to form a conductive layer aerogel. Its core function lies in utilizing a continuous conductive network constructed from conductive nanomaterials to achieve highly efficient shielding of electromagnetic waves. When external electromagnetic waves are incident on the material surface, due to the significant impedance difference between the conductive layer and air, most of the electromagnetic waves are reflected at the interface, thus shielding them. The high conductivity of the conductive layer effectively enhances both reflection and electromagnetic shielding performance. Simultaneously, the conductive network within the conductive layer can rapidly conduct and dissipate the current induced by some of the electromagnetic waves penetrating the interface into heat energy, further enhancing the shielding effect.

[0037] The magnetic layer formed by the magnetic layer dispersion primarily functions to absorb electromagnetic wave losses. Simultaneously, the dielectric properties of the dielectric nanomaterials further enhance absorption performance, providing impedance matching and forming an asymmetric connection with the conductive layer. The magnetic nanomaterials possess unique permeability characteristics, enabling magnetic coupling with incident electromagnetic waves and converting their energy into heat energy through hysteresis loss and eddy current loss. The dielectric nanomaterials, due to changes in their dielectric constant, exhibit polarization under the influence of electromagnetic waves, further absorbing energy through polarization losses. This absorption-dominant mechanism effectively reduces secondary reflections of electromagnetic waves, preventing secondary electromagnetic interference to surrounding electronic equipment. This is one of the key advantages of asymmetric electromagnetic shielding materials compared to traditional symmetric shielding materials. Furthermore, the stacked structure of the magnetic layer and the conductive layer can first reduce the reflection of electromagnetic waves on the material surface, allowing more electromagnetic waves to enter the material. Secondly, it allows the remaining part of the electromagnetic waves that have entered the material to be fully absorbed by the magnetic layer after being reflected by the conductive layer. The small amount of electromagnetic waves that are not completely absorbed by the magnetic layer will be reflected and dissipated again by the conductive layer, forming a multi-layer shielding effect of reflection-absorption-re-reflection, which improves the overall shielding effectiveness of the material.

[0038] In one feasible embodiment, the conductive layer dispersion comprises conductive nanomaterials and a first water-soluble polymer. The conductive nanomaterials primarily function to construct an efficient conductive network within the conductive layer. Their excellent conductivity provides a good conductive loss path for electromagnetic shielding. When electromagnetic waves are incident on the material surface, the conductive nanomaterials can generate current through induction, converting electromagnetic energy into heat energy using Joule heating, thereby achieving initial shielding against electromagnetic waves. The first water-soluble polymer mainly plays a dispersing and binding role. It can uniformly disperse the conductive nanomaterials, preventing their aggregation and ensuring a stable and uniform distribution of the conductive nanomaterials in the dispersion. Simultaneously, during the subsequent freezing process, the first water-soluble polymer can act as a framework support, helping to maintain the stability of the formed pore structure and providing a structural basis for the formation of the conductive layer aerogel.

[0039] In one feasible embodiment, the magnetic layer dispersion comprises: magnetic nanomaterials, dielectric nanomaterials, and a second water-soluble polymer. Magnetic nanomaterials, due to their unique magnetic properties, can absorb and attenuate electromagnetic waves through hysteresis loss and eddy current loss, exhibiting particularly good shielding effects for low-frequency electromagnetic waves. They can complement the conductive layer, enhancing the overall electromagnetic shielding performance of the material. Dielectric nanomaterials possess a high dielectric constant and can polarize under the influence of electromagnetic waves. Through dielectric polarization loss, they convert electromagnetic energy into other forms of energy, further enhancing the material's absorption capacity for electromagnetic waves. Simultaneously, their structural characteristics help optimize the microstructure of the magnetic layer and improve the dispersibility of the magnetic nanomaterials. The second water-soluble polymer primarily functions as a dispersant, binder, and shaper in the magnetic layer dispersion. It can uniformly disperse the magnetic and dielectric nanomaterials in the system, ensuring the stability of the dispersion. During freezing, the second water-soluble polymer forms a supporting framework, achieving good interlayer bonding with the conductive layer aerogel, jointly constructing a stable bilayer aerogel structure, laying the foundation for subsequent filling and curing processes.

[0040] In one feasible embodiment, the volume ratio of the magnetic layer dispersion to the conductive layer dispersion is 1:2 to 2:1, for example, 1:2, 1:1, or 2:1. If the volume ratio of the magnetic layer dispersion to the conductive layer dispersion is less than 1:2, i.e., the volume of the magnetic layer dispersion is relatively small, the proportion of the magnetic layer aerogel in the bilayer structure will be low. In this case, the total amount of magnetic nanomaterials and dielectric nanomaterials is insufficient, and their ability to absorb electromagnetic waves and impedance matching function through hysteresis loss, dielectric polarization loss, etc., will be weakened, making it difficult to effectively reduce the reflection efficiency of electromagnetic waves on the material surface, thus significantly increasing the material's reflection efficiency. At the same time, a thinner magnetic layer may not be able to fully cover the conductive layer surface, and performance discontinuities are likely to occur at the junction of the bilayer structure, affecting the uniformity of the overall electromagnetic shielding performance of the material. In addition, an excessively thin magnetic layer may deform or break due to insufficient structural support during subsequent filling and curing processes, further reducing the structural stability and shielding efficiency of the material. If the volume ratio of the magnetic layer dispersion to the conductive layer dispersion is greater than 2:1, meaning the volume of the magnetic layer dispersion is relatively too large, the magnetic aerogel layer will be too thick. On one hand, an excessively high proportion of magnetic aerogel results in an insufficient proportion of conductive aerogel, significantly reducing the material's electromagnetic shielding capability and causing overall insufficient shielding performance. On the other hand, an excessively thin conductive layer reduces the stability and uniformity of the material structure, leading to unstable shielding performance. Furthermore, an excessive amount of magnetic layer material may increase manufacturing costs and reduce the material's cost-effectiveness.

[0041] Step S20: Laterally freeze the conductive layer dispersion to obtain a frozen conductive layer sample.

[0042] Lateral freezing is a type of unidirectional freezing, a freezing technique that controls the freezing direction to cause the solvent in the dispersion to crystallize and grow in a single direction. The difference is that unidirectional freezing does not specify any freezing direction; unless otherwise specified, unidirectional freezing generally refers to freezing from the bottom to the top of the container. Lateral freezing involves freezing from one side of the container to the other. In this process, the dispersion is placed in a specific freezing device. By applying a low-temperature gradient to one end of the dispersion, the temperature gradually decreases from that end to the other. Solvent molecules thus align themselves in the direction of decreasing temperature and grow into ice crystals. As the ice crystals grow, solid particles in the dispersion (such as conductive materials and polymers) are gradually squeezed into the gaps between the ice crystals, forming an alignment structure consistent with the ice crystal growth direction. After the freezing process is complete, the ice crystals are removed by methods such as freeze-drying. The spaces originally occupied by the ice crystals become pores, ultimately yielding a material with a unidirectionally aligned porous structure.

[0043] Lateral freezing provides a unique laterally oriented pore structure for the conductive aerogel. When electromagnetic waves are incident perpendicularly to the material surface, this structure effectively blocks their propagation, causing most waves to be reflected at the surface. The small number of waves that do penetrate the material can undergo multiple reflections between the multi-layered oriented structures, extending the propagation path within the conductive layer. This increases the interaction opportunities between the electromagnetic waves and the conductive components, significantly enhancing the conductive layer's attenuation capability. Secondly, the laterally oriented pore structure helps improve the mechanical properties of the conductive aerogel. The oriented pores allow for more uniform stress distribution under load, reducing stress concentration and enhancing structural stability and compressive strength. Furthermore, this ordered pore structure creates favorable conditions for subsequent bonding with magnetic layers and the filling of polymer prepolymers, ensuring tight interlayer bonding and uniform distribution of the filling material.

[0044] In one feasible embodiment, the lateral freezing process includes injecting a conductive layer dispersion into a specific mold. One end of the mold is in contact with a low-temperature cold source (such as a liquid nitrogen cooling stage or a low-temperature metal plate), while the other end is in a relatively high-temperature environment, forming a stable unidirectional temperature gradient. For example, the temperature gradient can be controlled within the range of 5~20℃ / cm. During the freezing process, the dispersion is kept stationary to avoid interference with the directional growth of ice crystals due to vibration or flow. The freezing time is adjusted according to the volume and concentration of the dispersion and can be 5~30 minutes to ensure complete freezing. By controlling parameters such as the temperature gradient, freezing time, and drying conditions, the pore size, orientation, and structural integrity of the conductive layer aerogel can be precisely controlled to meet the performance requirements of subsequent preparation of asymmetric electromagnetic shielding materials. For example, please refer to Figure 2. In this embodiment, the mold shown in Figure 2 is used for lateral freezing. One side of the mold is a heat-conducting metal sheet, and the mold is used to place the dispersion liquid. It should be noted that the double-layer electromagnetic shielding material prepared in this embodiment is developed for Ka-band electromagnetic waves. In this embodiment, a heat-conducting metal sheet is used as the heat transfer medium. In some feasible embodiments, the mold can also be in contact with a container containing liquid nitrogen, and the heat can be transferred directly by the container wall.

[0045] Step S30: Pour the magnetic layer dispersion onto the conductive layer frozen sample and perform lateral unidirectional freezing again to obtain a double-layer frozen sample. Sublime dry the double-layer frozen sample to obtain a double-layer aerogel. The double-layer aerogel includes the conductive layer aerogel and a magnetic layer aerogel stacked with the conductive layer aerogel. The pore orientation of the magnetic layer aerogel is consistent with the pore orientation of the conductive layer aerogel.

[0046] In one feasible embodiment, the stacked structure of the bilayer aerogel is characterized by a planar superposition of a conductive aerogel layer and a magnetic aerogel layer, with the pores of the two aerogel layers extending laterally to form continuous directional channels. The pore orientation of the bilayer aerogel is parallel to the stacking interface, that is, extending along the lateral direction of the material, so that the pores penetrate from one side of the magnetic layer to the other, forming a mutually parallel directional pore network of the bilayer aerogel. It can be understood that the pore orientation parallel to the stacking interface allows vertically incident electromagnetic waves to be effectively blocked, first being guided through the magnetic layer with impedance matching function, and then entering the conductive layer for multiple reflections and attenuation, maximizing the functional division of the two layers. Furthermore, the directionally arranged pores penetrate the entire stacked structure, allowing stress to be uniformly transmitted through the pore walls when the material is subjected to stress along the thickness direction, preventing the interlayer interface from becoming a weak point in mechanical strength, and significantly improving the overall compressive strength and structural stability of the bilayer aerogel.

[0047] Performing two lateral freezing cycles ensures that the magnetic layer dispersion and the already frozen conductive layer sample achieve a tight bond through interfacial fusion and electrostatic forces formed by the polymers with different charges in their dispersions before the second freezing, avoiding the risk of subsequent interlayer separation. Under lateral freezing, the solvent in the magnetic layer dispersion crystallizes along a direction consistent with the pore orientation of the conductive layer, allowing the magnetic layer aerogel formed after drying to form a continuous structural transition with the conductive layer aerogel at the interface, rather than a simple mechanical superposition. Furthermore, the lateral freezing method guides the functional particles in the magnetic layer dispersion to align in a predetermined direction, providing a structural basis for subsequent impedance matching and electromagnetic wave attenuation, ensuring the synergistic effect of the two layers in the electromagnetic shielding process.

[0048] In one feasible embodiment, the common unidirectional freezing conditions are consistent with the lateral freezing conditions in step S20. It is understood that uniform freezing conditions, such as temperature gradient and freezing rate, can maximize the consistency of pore orientation and avoid interlayer pore direction deviations caused by differences in process parameters, thereby ensuring that the two aerogel layers form a continuous and coordinated pore network. Secondly, identical processing conditions simplify the process flow, reduce the risk of errors caused by parameter adjustments, and facilitate quality stability in large-scale production. Furthermore, consistent freezing conditions can reduce internal stress caused by different shrinkage rates between layers, improve the overall structural stability of the bilayer aerogel, and reduce the possibility of cracking or deformation.

[0049] In one feasible embodiment, after freezing, the frozen sample is dried at -40 to -60°C under a vacuum of less than 10 Pa. In a vacuum environment, water molecules on the surface of ice crystals can directly change from solid to gaseous state. Ice crystal sublimation drying can preserve the original pore structure of the aerogel to the maximum extent, avoid pore collapse caused by liquid water evaporation, and ensure that the aerogel has high porosity and a complete unidirectional oriented pore structure.

[0050] In the bilayer aerogel, the pore orientation of the magnetic aerogel layer is consistent with that of the conductive aerogel layer. This consistent pore orientation provides a continuous transmission channel for electromagnetic waves, allowing them to smoothly enter the conductive layer after passing through the magnetic layer. This reduces electromagnetic wave scattering loss or enhanced reflection caused by abrupt changes in pore orientation, ensuring the efficient synergy of the matching-reflection mechanism. From a material structure perspective, the consistent pore orientation enhances the interfacial bonding between the two aerogel layers. The oriented pore walls form an interlocking structure at the interface, improving the mechanical bonding strength between the layers. Simultaneously, this structure facilitates the subsequent filling process of the polymer prepolymer, enabling the prepolymer to permeate uniformly along the pores in a unified direction, ensuring the uniformity of the material properties after filling.

[0051] Step S40: After surface hydrophobic modification, the bilayer aerogel is filled with a polymer prepolymer and then cured to obtain a bilayer electromagnetic shielding material.

[0052] In one feasible embodiment, the bilayer aerogel is hydrophobically modified to obtain a hydrophobically modified bilayer aerogel, the hydrophobically modified bilayer aerogel is shaped and degassed to obtain a pretreated bilayer aerogel, and the pretreated bilayer aerogel is filled with a polymer prepolymer and cured to obtain a bilayer electromagnetic shielding material.

[0053] In one feasible embodiment, the hydrophobic modification treatment may include: placing the bilayer aerogel and volatile silane into a vacuum dryer for hydrophobic modification treatment to obtain a hydrophobically modified bilayer aerogel. In this embodiment, the hydrophobic modification method is chemical vapor deposition, the principle of which is that in a vacuum environment, low-boiling-point modifier molecules volatilize and enter the pore structure of the bilayer aerogel in the form of gaseous molecules.

[0054] The active groups in silane molecules react with the hydroxyl groups on the aerogel surface, introducing hydrophobic organic groups into the aerogel surface, thereby altering the surface energy and making it hydrophobic. Hydrophobic modification improves the water resistance of the aerogel, preventing it from absorbing water in humid environments, which could lead to structural damage and performance degradation. Furthermore, hydrophobic modification enhances the compatibility of the aerogel with subsequent polymer prepolymer filling, reduces interfacial defects, improves filling efficiency, and lowers the surface energy of the aerogel, facilitating the uniform filling of the pores by the polymer prepolymer.

[0055] In one feasible embodiment, the shaping process may include: pressing the bilayer aerogel into a sheet-like bilayer aerogel of a certain thickness to meet the size requirements of practical applications. The pressing process also appropriately compresses the pores of the aerogel, improving the material's density and mechanical properties, and reducing deformation and damage during subsequent use. For example, the sheet-like bilayer aerogel is 2mm thick. It is understood that, from the perspective of practical use of shielding materials, thinner is better while still providing sufficient shielding performance. However, due to the wavelength difference between the X-band and Ka-band, longer wavelength X-band electromagnetic waves are more difficult to shield. Therefore, the thickness of X-band shielding materials is usually higher than that of Ka-band shielding materials. During testing, the maximum sample thickness that the Ka-band electromagnetic shielding testing device can accommodate is 2mm. Therefore, in this embodiment, all samples are controlled to have a thickness of 2mm. In this embodiment, the shielding effectiveness SE of each embodiment with a thickness of 2mm is... TThe shielding performance is excellent within the range of 37.9–59.3 dB. However, a thickness <2 mm may affect the filling effect, and further reduction in thickness can negatively impact electromagnetic shielding performance. In summary, under the specific filling process conditions and Ka-band application scenario of this embodiment, a thickness of 2 mm is the most suitable thickness for demonstrating sample performance. However, this does not mean that the method presented in this embodiment can only prepare samples with a thickness of 2 mm. Furthermore, the advantage of bilayer aerogel materials compared to monolayers lies in the presence of an impedance matching layer, which can reduce the reflection efficiency (SE). R It also has high electromagnetic shielding performance (SET).

[0056] In one feasible embodiment, the pores of the bilayer aerogel are wetted with a first organic solvent, and then one end of the bilayer aerogel is placed in a filling liquid to obtain a filled bilayer aerogel. The filled bilayer aerogel is then cured to obtain an asymmetric electromagnetic shielding material. The filling liquid includes a polymer prepolymer and a second organic solvent compatible with the polymer prepolymer. The second organic solvent is compatible with the first organic solvent. When the pores of the aerogel are wetted by the organic solvent compatible with the filling liquid, the adhesion between the molecules in the filling liquid and the pore walls, as well as the cohesive force between the molecules in the filling liquid, work together to generate capillary attraction. The capillary force allows the filling liquid to rise automatically along the pores and gradually fill the entire pore space. Specifically, the wetted pore walls have a strong adsorption force on the filling liquid, while the surface tension of the filling liquid promotes its diffusion into the pores. Driven by the capillary force, the filling liquid can uniformly penetrate into each pore of the aerogel, achieving full filling.

[0057] In one feasible embodiment, the pore orientation of the bilayer aerogel is controlled to be perpendicular to the liquid surface during the filling process. Because the pore orientation is perpendicular to the liquid surface, the filling liquid can directly permeate upwards along the pore axis under the drive of capillary forces, reducing resistance during the filling process and accelerating the filling speed. Simultaneously, the oriented pore structure guides the filling liquid to distribute evenly, avoiding the formation of dead zones or air bubbles in the pores and ensuring the integrity of the filling. In contrast, if the pore orientation is not perpendicular to the liquid surface, the flow path of the filling liquid in the pores becomes tortuous, increasing filling resistance and potentially leading to slower filling speed and uneven filling. Furthermore, a non-perpendicular orientation may cause the filling liquid to accumulate in some pores while insufficiently filling others, affecting the consistency of the material's performance. Therefore, controlling the pore orientation to be perpendicular to the liquid surface can significantly improve the filling effect and ensure the performance stability of the final material.

[0058] In one feasible embodiment, step S10, the step of providing magnetic layer dispersion and conductive layer dispersion, includes: step S101, dispersing conductive nanomaterials in a first water-soluble polymer solution to obtain conductive layer dispersion.

[0059] In one feasible embodiment, mixing the conductive nanomaterial with the second water-soluble polymer solution includes ultrasonic dispersion at a power of 400W for 20-40 minutes. Too short an ultrasonic duration may cause the aggregates to be broken up, forming a micron-sized dispersion system; if the ultrasonic duration is too long, the heat generated by prolonged ultrasonication will cause the solution temperature to rise, which may cause thermal denaturation of the second water-soluble polymer and loss of its dispersion stabilizing effect.

[0060] In one feasible embodiment, the conductive nanomaterial includes carbon nanotubes. Carbon nanotubes possess extremely high aspect ratios and excellent conductivity. Their tubular structure enables the construction of a continuous and efficient three-dimensional conductive network within the conductive layer, providing a smooth path for electromagnetic wave conduction loss. Simultaneously, the nanoscale size of carbon nanotubes allows them to be uniformly dispersed in the first water-soluble polymer solution, reducing agglomeration and ensuring the structural uniformity of the conductive layer aerogel. Furthermore, carbon nanotubes also possess good mechanical properties, enhancing the structural strength of the conductive layer aerogel and preventing damage due to external forces during subsequent processing, thus balancing electromagnetic shielding performance and structural stability.

[0061] In one feasible embodiment, the first water-soluble polymer includes chitosan, which has good film-forming and gelling properties. During the subsequent unidirectional freezing process, its molecular chains can form a continuous skeletal structure in the gaps between ice crystals, supporting the pore morphology of the conductive layer aerogel, preventing pore collapse after freeze-drying, and ensuring the integrity of the conductive network. At the same time, when it is subsequently combined with the magnetic layer, the polar groups of chitosan can also form intermolecular forces with the second water-soluble polymer in the magnetic layer, improving the interfacial bonding strength of the two aerogel layers and reducing the risk of interlayer separation.

[0062] In one feasible embodiment, the mass concentration of the conductive nanomaterial is between 2 and 10 mg / mL, for example, it can be 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, 7 mg / mL, 8 mg / mL, 9 mg / mL, or 10 mg / mL. The mass concentration of the first water-soluble polymer is between 5 and 30 mg / mL, for example, it can be 5 mg / mL, 6 mg / mL, 7 mg / mL, 8 mg / mL, 9 mg / mL, 10 mg / mL, 11 mg / mL, 12 mg / mL, 13 mg / mL, 14 mg / mL, 15 mg / mL, 16 mg / mL, 17 mg / mL, 18 mg / mL, 19 mg / mL, 20 mg / mL, 21 mg / mL, 22 mg / mL, 23 mg / mL, 24 mg / mL, 25 mg / mL, 26 mg / mL, 27 mg / mL, 28 mg / mL, 29 mg / mL, or 30 mg / mL.The total concentration of the conductive nanomaterial and the first water-soluble polymer is between 10 and 30 mg / mL, for example, it can be 10 mg / mL, 11 mg / mL, 12 mg / mL, 13 mg / mL, 14 mg / mL, 15 mg / mL, 16 mg / mL, 17 mg / mL, 18 mg / mL, 19 mg / mL, 20 mg / mL, 21 mg / mL, 22 mg / mL, 23 mg / mL, 24 mg / mL, 25 mg / mL, 26 mg / mL, 27 mg / mL, 28 mg / mL, 29 mg / mL, or 30 mg / mL. For example, it can be: the concentration of the conductive nanomaterial is 2 mg / mL, the concentration of the first water-soluble polymer is 8 mg / mL, and the total concentration is 10 mg / mL; the concentration of the conductive nanomaterial is 5 mg / mL, the concentration of the first water-soluble polymer is 5 mg / mL, and the total concentration is 10 mg / mL; the concentration of the conductive nanomaterial is 3 mg / mL, and the concentration of the first water-soluble polymer is 12 mg / mL. The concentrations of conductive nanomaterials and the first water-soluble polymer are as follows: 15 mg / mL; 6 mg / mL for conductive nanomaterials and 9 mg / mL for the first water-soluble polymer; 8 mg / mL for conductive nanomaterials and 10 mg / mL for the first water-soluble polymer; 10 mg / mL for conductive nanomaterials and 5 mg / mL for the first water-soluble polymer; 10 mg / mL for conductive nanomaterials and 15 mg / mL for the first water-soluble polymer; and 20 mg / mL for conductive nanomaterials and 30 mg / mL for the first water-soluble polymer. The optimal mass concentration ratio of conductive nanomaterials to the first water-soluble polymer is 5:5 mg / mL. If the concentration ratio is too low, meaning the proportion of conductive nanomaterials is too low, the amount of conductive nanomaterials in the dispersion is insufficient, making it difficult to form a continuous conductive network. This results in a significant decrease in the conductivity loss capacity of the conductive layer, making it unable to effectively shield electromagnetic waves. If the concentration ratio is too high, meaning the proportion of conductive nanomaterials is too high, excessive conductive nanomaterials are prone to agglomeration, disrupting the uniformity of the dispersion. Furthermore, the insufficient content of the first water-soluble polymer makes it difficult to form a complete framework structure. Subsequently, the pores of the aerogel are prone to collapse after freeze-drying, leading to the breakage of the conductive network. At the same time, the interlayer bonding force will also be weakened, affecting the stability of the bilayer structure.

[0063] Step S102: The magnetic nanomaterial is subjected to cationic surface modification treatment to obtain the modified magnetic nanomaterial.

[0064] In one feasible embodiment, the cationic surface modification treatment includes: dispersing magnetic nanomaterials in deionized water, adding a surface cationic modifier, stirring and reacting at room temperature for 2-6 hours, and obtaining the modified magnetic nanomaterials by centrifugation after the reaction. Magnetic nanomaterials are prone to aggregation due to their high surface energy. The surface cationic modifier, by adsorbing onto the surface of the magnetic nanomaterials, can form a charge layer on its surface. Utilizing the repulsive force between like charges, it effectively prevents the aggregation of nanoparticles, allowing the magnetic nanomaterials to be uniformly dispersed in the subsequent magnetic layer dispersion, ensuring the uniformity of material properties. Furthermore, the hydrophobic groups of the surface cationic modifier can interact with the organic components in the dispersion, while the hydrophilic groups are compatible with the aqueous environment, thus acting as a bridge between the magnetic nanomaterials and other components, improving the binding force between the components, and facilitating the formation of a stable dispersion system.

[0065] In one feasible embodiment, the magnetic nanomaterial comprises: hollow iron oxide nanospheres. The internal cavity structure of the hollow iron oxide nanospheres reduces the material density and enhances the magnetic loss capability. The hollow characteristic is beneficial for the multiple reflection absorption of electromagnetic waves, thereby improving the electromagnetic wave absorption efficiency.

[0066] In one feasible embodiment, in the cationic surface modification treatment, the mass ratio of the magnetic nanomaterial to the surface cationic modifier is between 1:1 and 4:1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, or 4:1. The modification efficiency is highest when the mass ratio of the magnetic nanomaterial to the surface cationic modifier is 5:2. If the mass ratio is lower than this, the amount of surface cationic modifier is insufficient, the surface of the magnetic nanomaterial cannot be fully covered, and some areas will still agglomerate due to high surface energy, resulting in poor dispersion and affecting the uniformity of the subsequent magnetic layer dispersion. If the mass ratio is higher than this, excessive surface cationic modifier will be free in the dispersion, which will not only increase costs but may also cause surfactant molecules to aggregate, interfering with the dispersion of the magnetic nanomaterial. At the same time, excessive surfactant may affect the magnetic properties of the magnetic nanomaterial itself and its interaction with other components, thereby reducing the overall performance of the material.

[0067] Step S103: Mix the modified magnetic nanomaterial, the dispersion of dielectric nanomaterial, and the second water-soluble polymer solution to obtain a magnetic layer dispersion.

[0068] In one feasible embodiment, the modified magnetic nanomaterial is mixed with a dispersion of dielectric nanomaterial. During the mixing process, electrostatic self-assembly occurs to obtain a magnetic carrier. The cation-modified magnetic nanomaterial carries a positive charge on its surface, while the surface of the dielectric nanomaterial, due to oxygen-containing functional groups or defect sites retained during the preparation process, easily dissociates into a negative charge in aqueous solution, forming a negatively charged surface. When the two dispersions are mixed, the positive and negative charges generate a strong electrostatic attraction, driving the modified magnetic nanomaterial to spontaneously migrate to the negatively charged surface of the dielectric nanomaterial and uniformly adsorb onto the surface and edge defects of the sheet. This electrostatic self-assembly does not require the addition of an additional binder, which can both prevent the magnetic nanomaterial from agglomerating and allow the two functional materials to form a tightly bonded composite structure, laying the foundation for the subsequent magnetic layer to possess both magnetic and electrical loss capabilities. The magnetic carrier is then mixed with a second water-soluble polymer solution. The molecular chains of the water-soluble polymer wrap around the surface of the magnetic carrier and bind to the magnetic carrier through hydrogen bonds and van der Waals forces, ultimately forming a uniform and stable magnetic layer dispersion.

[0069] In one feasible embodiment, the mixing of the modified magnetic nanomaterial and the dielectric nanomaterial dispersion includes: ultrasonic dispersion at 400W for 10-30 min, followed by shaking on a shaker for 0.5-4 h. Ultrasonic dispersion utilizes high-frequency vibration to rapidly break up initial agglomerates, ensuring sufficient contact between the two charged nanomaterials and creating a uniform reaction environment for electrostatic self-assembly. Subsequent shaking on a shaker promotes molecular-level interactions through gentle mechanical stirring, ensuring full utilization of electrostatic attraction and allowing the magnetic nanomaterial to be uniformly and firmly adsorbed onto the surface of the dielectric nanomaterial. If the ultrasonic or shaking time is too short, the contact between the modified magnetic nanomaterial and the dielectric nanomaterial is insufficient, resulting in incomplete electrostatic self-assembly and potentially causing some magnetic nanomaterial to remain free in the system, forming localized agglomerates and affecting the structural uniformity of the magnetic carrier. If the time is too long, excessive mechanical action may destroy the already formed electrostatic assembly structure, causing the magnetic nanomaterial to detach from the surface of the dielectric nanomaterial, thus reducing the stability of the composite structure. Furthermore, excessive processing time increases energy consumption and reduces preparation efficiency.

[0070] In one feasible embodiment, the mass ratio of magnetic nanomaterials to dielectric nanomaterials is between 1:3 and 1:1, for example, 1:3, 1:2, or 1:1. If the ratio is lower than 1:3, i.e., the proportion of magnetic nanomaterials is too low, there are insufficient magnetic loss sites, the material's absorption capacity for low-frequency electromagnetic waves is weakened, and an effective broadband shielding effect cannot be formed. If the ratio is higher than 1:1, i.e., the proportion of magnetic nanomaterials is too high, the loading capacity of dielectric nanomaterials reaches saturation, and the excess magnetic nanomaterials will agglomerate due to the lack of sufficient negatively charged surface support. This not only reduces magnetic loss efficiency but also disrupts the continuous distribution of dielectric nanomaterials, leading to a decrease in dielectric polarization loss capability and ultimately impairing the overall shielding performance.

[0071] In one feasible embodiment, the dielectric nanomaterial includes graphene oxide. The surface of graphene oxide sheets is rich in oxygen-containing functional groups such as hydroxyl and carboxyl groups, which can dissociate into negative charges in aqueous solution, providing sufficient interaction sites for electrostatic self-assembly with cation-modified magnetic nanomaterials. Its unique two-dimensional sheet structure has a large specific surface area, enabling efficient loading of magnetic nanomaterials. Simultaneously, the sheets can form an interlaced network structure, providing channels for dielectric polarization loss. Furthermore, graphene oxide itself possesses localized conductivity, which can synergistically construct a composite conductive network with magnetic nanomaterials, enhancing the conductivity loss capability of the magnetic layer and further improving the overall electromagnetic shielding effectiveness of the material.

[0072] In one feasible embodiment, the mass concentration of the dielectric nanomaterial in the dispersion is between 0.5 and 2 mg / mL, for example, 0.5 mg / mL, 0.6 mg / mL, 0.7 mg / mL, 0.8 mg / mL, 0.9 mg / mL, 1.0 mg / mL, 1.1 mg / mL, 1.2 mg / mL, 1.3 mg / mL, 1.4 mg / mL, 1.5 mg / mL, 1.6 mg / mL, 1.7 mg / mL, 1.8 mg / mL, 1.9 mg / mL, and 2.0 mg / mL. If the concentration is too low, the content of the dielectric nanomaterial in the dispersion is insufficient, the distribution density of its two-dimensional sheet structure decreases, and the effective interaction sites for electrostatic self-assembly with magnetic nanomaterials are reduced. At this point, magnetic nanomaterials are difficult to fully load and are prone to ionized aggregation, leading to a decrease in the formation efficiency of magnetic attachments. Insufficient overall proportion of dielectric nanomaterials weakens the dielectric polarization loss capability, resulting in a reduced attenuation effect of the magnetic layer on high-frequency electromagnetic waves. This prevents effective synergy with the magnetic loss of the magnetic nanomaterials, ultimately affecting the broadband shielding performance of the bilayer material. If the concentration is too high, the layers of dielectric nanomaterials are prone to stacking and agglomeration due to van der Waals forces, disrupting the uniformity of the dispersion, reducing the effective surface area for electrostatic self-assembly, leading to uneven loading of magnetic nanomaterials, and increasing the viscosity of the dispersion, affecting the subsequent mixing effect with the second water-soluble polymer solution. Furthermore, excessive dielectric nanomaterials may form localized dense regions in the magnetic layer, hindering the unidirectional growth of ice crystals during freezing, disrupting the orientation pore structure of the magnetic layer aerogel, and thus reducing the structural stability of the material and the continuity of the electromagnetic wave transmission path.

[0073] In one feasible embodiment, the second water-soluble polymer includes sodium alginate, wherein the carboxylic acid group of sodium alginate can form a stable framework by ionic crosslinking with the cations on the surface of the magnetic carrier, while the viscosity of the dispersion is adjusted to adapt to the lateral freezing process, thereby ensuring the stability of the magnetic layer structure.

[0074] In one feasible embodiment, the mass concentration of the second water-soluble polymer in the second water-soluble polymer solution is 5-10 mg / mL, for example, it can be 5.0 mg / mL, 5.5 mg / mL, 6.0 mg / mL, 6.5 mg / mL, 7.0 mg / mL, 7.5 mg / mL, 8.0 mg / mL, 8.5 mg / mL, 9.0 mg / mL, 9.5 mg / mL, or 10.0 mg / mL. Within this concentration range, the second water-soluble polymer, such as sodium alginate, can form a moderately viscous solution, which can effectively coat the surface of the magnetic carrier, maintain the stability of the dispersion through intermolecular forces, and form a uniform framework structure during subsequent unidirectional freezing to support the pore morphology of the magnetic aerogel layer. If the concentration is too low, the number of polymer chains is insufficient, which cannot fully encapsulate the magnetic carrier, easily leading to stratification or aggregation of the dispersion. Furthermore, the skeleton structure formed after freezing is weak, and the pores are prone to collapse. If the concentration is too high, the solution viscosity is too high, which will hinder the uniform dispersion of the magnetic carrier. At the same time, the growth of ice crystals is hindered during freezing, making it difficult to form regular lateral orientation pores, affecting the structural integrity of the magnetic layer and the subsequent filling effect.

[0075] In one feasible embodiment, the mass concentration ratio of the magnetic support to the second water-soluble polymer is between 0.5:10 and 2:5 mg / mL, for example, it can be 0.5:10 mg / mL, 1:10 mg / mL, 1.5:10 mg / mL (3:20 mg / mL), 2:10 mg / mL (1:5 mg / mL), 2:9 mg / mL, 2:8 mg / mL (1:4 mg / mL), 2:7 mg / mL, 2:6 mg / mL (1:3 mg / mL), or 2:5 mg / mL, wherein the optimal concentration ratio is 2:5 mg / mL. At this concentration ratio, the magnetic support provides sufficient magnetic and dielectric loss sites, while the second water-soluble polymer ensures the stability of the dispersion and the structural strength of the subsequent aerogel. If the proportion is too low, meaning the magnetic carrier is insufficient, the content of functional nanomaterials in the magnetic layer is too small, making it impossible to achieve effective electromagnetic wave absorption and attenuation, resulting in a significant decrease in shielding performance. If the proportion is too high, meaning the magnetic carrier is too high, the second water-soluble polymer cannot completely encapsulate and disperse the magnetic carrier, easily leading to aggregation. Furthermore, the aerogel's skeletal support is insufficient after freezing, and the pore structure is easily damaged, affecting the overall performance of the bilayer material.

[0076] In one feasible embodiment, before step S40: modifying the surface of the bilayer aerogel, filling it with a polymer prepolymer, and then curing it to obtain a bilayer electromagnetic shielding material, the method further includes: step S50: placing the bilayer aerogel and volatile silane into a vacuum dryer for hydrophobic modification treatment to obtain a hydrophobically modified bilayer aerogel; in one feasible embodiment, the hydrophobic modification treatment includes: placing the bilayer aerogel and volatile silane into a vacuum dryer for chemical vapor phase modification. By utilizing a vacuum environment to promote the vaporization and diffusion of volatile silanes, they can fully penetrate into the porous structure of the bilayer aerogel. Simultaneously, heating conditions can activate the chemical reaction between silane molecules and aerogel surface groups. Silane molecules are grafted onto the aerogel framework surface through chemical bonding. Since silane molecules have hydrophobic organic groups, the grafted silane molecules can cover the hydrophilic sites on the aerogel surface, thereby significantly reducing the surface energy of the material and endowing the bilayer aerogel with good hydrophobicity. This avoids problems such as uneven solution penetration or structural swelling caused by excessive hydrophilicity of the material when filling polymer prepolymers later.

[0077] In one feasible embodiment, the hydrophobic modification treatment includes: heat treatment at -80 kPa and 55°C for 12 to 48 hours.

[0078] In one feasible embodiment, the volatile silanes include: methyltrichlorosilane, methyldichlorosilane, and dimethylchlorosilane. Methyltrichlorosilane has high volatility, readily vaporizes under vacuum conditions, and penetrates deep into the fine pores of the aerogel, ensuring the uniformity of modification. The three chlorine atoms in the methyltrichlorosilane molecule have high reactivity, capable of undergoing substitution reactions with the hydroxyl groups on the aerogel surface to form stable covalent bonds, firmly grafting the hydrophobic groups onto the material surface and preventing them from easily detaching. Furthermore, the reaction byproduct of methyltrichlorosilane is hydrogen chloride, which is easily removed under vacuum and heating conditions, leaving no impurities inside the aerogel and ensuring the purity and structural stability of the modified material. Methyldichlorosilane achieves a better balance between high reactivity and moderate steric hindrance. Compared with methyltrichlorosilane, it has one less chlorine atom, which reduces its reactivity and heat of reaction, thus reducing the risk of stress corrosion and structural damage to the fragile aerogel framework during vapor deposition. At the same time, compared with dimethylchlorosilane, which has only one chlorine atom, it retains enough reaction sites (two chlorine atoms) to form a medium-density siloxane crosslinking network on the aerogel surface, giving the material stable and durable hydrophobicity and maintaining good pore permeability, leaving ample space for subsequent polymer filling. Dimethylchlorosilane's greatest steric hindrance and lowest reactive functionality enable it to form a highly uniform and ordered monomolecular hydrophobic layer. Its molecular structure contains two methyl groups and one chlorine atom. During the reaction, the single chlorine atom bonds with a single hydroxyl group on the aerogel surface, and the two large methyl groups extend outward to form a densely packed hydrophobic surface. This structure can minimize the surface energy of the material and provide excellent hydrophobic effects. At the same time, due to the mild reaction and few byproducts, it causes minimal damage to the aerogel nanostructure and can best maintain its original fine pore morphology and mechanical integrity.

[0079] In one feasible embodiment, the volume ratio of the bilayer aerogel to the volatile silane is between 20:1 and 60:1, for example, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, and 60:1, with the optimal volume ratio being 40:1. If the volume ratio is lower than 20:1, the excess volatile silane will fill the pore space of the aerogel after vaporization, causing the silane molecules to over-graft or cross-link and polymerize during the reaction. This will block the pores of the aerogel with silane polymers, destroying the original oriented pore structure and hindering the subsequent filling and penetration of the polymer prepolymer. Consequently, it will affect the mechanical properties of the bilayer material and the continuity of the electromagnetic shielding network. At the same time, excessive silane residue may lead to excessive hydrophobicity on the material surface, which will reduce the interfacial compatibility with the polymer prepolymer and cause a decrease in interlayer bonding strength. If the volume ratio is higher than 60:1, the amount of silane used is relatively insufficient. The vaporized silane molecules cannot fully cover the pore surface of the aerogel, especially the hydroxyl groups in the deep pores, which are difficult to completely replace. This results in incomplete hydrophobic modification, and the aerogel still retains many hydrophilic sites. When it comes into contact with organic solvents or polymer prepolymers in the future, it is easy to damage the pore structure due to water absorption or swelling, causing the aerogel skeleton to collapse. In addition, insufficient hydrophobicity will cause uneven permeation rate of the filling liquid in the pores, resulting in local incomplete filling and affecting the overall performance consistency of the double-layer electromagnetic shielding material.

[0080] Step S60: The hydrophobically modified double-layer aerogel is filled with a polymer prepolymer and cured to obtain a double-layer electromagnetic shielding material.

[0081] In this embodiment, the hydrophobically modified bilayer aerogel is filled with a polymer prepolymer and then cured to obtain a bilayer electromagnetic shielding material.

[0082] Before curing, aerogels can be shaped into specific forms through methods such as pressing and mold constraint to meet the dimensional requirements of electromagnetic shielding materials in practical applications. Furthermore, the pressure applied during shaping promotes further adhesion between the magnetic and conductive layers, reducing interlayer gaps and laying the foundation for interfacial fusion during subsequent polymer prepolymer filling.

[0083] In one feasible embodiment, step S60: the step of modifying the surface of the bilayer aerogel to be hydrophobic, filling it with a polymer prepolymer and curing it to obtain a bilayer electromagnetic shielding material includes: step S601, placing the hydrophobically modified bilayer aerogel in a first organic solvent to obtain a porous aerogel.

[0084] By fully impregnating the porous structure of the hydrophobically modified bilayer aerogel with the first organic solvent, air within the pores can be eliminated, creating unobstructed channels for subsequent filling with polymer prepolymers. This ensures that the filling liquid can penetrate evenly and deeply into the fine pores of the aerogel, avoiding filling blind spots caused by residual air. The wetting effect of the organic solvent can reduce the interfacial tension between the aerogel skeleton and the filling liquid, enhancing their compatibility and making it easier for the polymer prepolymer to adhere to the surface of the aerogel skeleton. This lays the foundation for subsequent curing to form a continuous composite structure, ensuring the structural integrity and performance uniformity of the bilayer material.

[0085] In one feasible embodiment, the first organic solvent has good compatibility with the second organic solvent in the subsequent filling liquid so as to achieve smooth solvent replacement during the filling process and avoid stratification or precipitation due to poor compatibility, which would affect the filling effect; the first organic solvent cannot chemically react with the skeleton material of the bilayer aerogel, nor can it dissolve or destroy the pore structure of the aerogel, so as to ensure the original orientation pores and structural stability of the aerogel.

[0086] In one feasible embodiment, the first organic solvent includes n-hexane. n-Hexane can stably dissolve the polymer prepolymer to form a uniform filling liquid without causing cross-linking or agglomeration of the prepolymer. Furthermore, n-hexane has low surface tension, which allows it to quickly wet the hydrophobic surface of the aerogel, promoting the penetration of the filling liquid along the pores and improving filling efficiency. n-Hexane is chemically stable and does not react with the aerogel framework, ensuring a smooth filling process. The volatility of n-hexane can also be gradually removed during subsequent curing, avoiding defects such as bubbles forming inside the material.

[0087] Step S602: Place one end of the pore-wetted aerogel in the filling liquid to obtain a filled aerogel, wherein the pore direction of the pore-wetted aerogel is perpendicular to the liquid surface of the filling liquid, and the filling liquid includes: a polymer prepolymer and a second organic solvent compatible with the polymer prepolymer, wherein the second organic solvent and the first organic solvent are compatible.

[0088] In one feasible embodiment, the pore-wetted aerogel is suspended on a container containing a filling liquid, one end of the pore-wetted aerogel is placed in the filling liquid, and the filling liquid is filled into the sample from bottom to top by capillary action. After filling is completed, the clamping device is removed.

[0089] In one feasible embodiment, the mass ratio of the polymer prepolymer to the second organic solvent is 1:2 to 2:1. If the prepolymer content is too high, the viscosity of the filling liquid is too high, the fluidity is poor, and it cannot penetrate into the fine pores, resulting in incomplete filling; if the solvent content is too high, the prepolymer content is insufficient, the polymer network is sparse after curing, the material has poor mechanical properties, and the solvent is prone to forming internal pores after evaporation.

[0090] In one feasible embodiment, the polymer prepolymer comprises: silicone rubber, polyurethane, epoxy resin, and polyacrylate. After curing, silicone rubber exhibits high elasticity, buffering the brittleness of the double-layer aerogel, enhancing the overall material's impact and bending resistance, and preventing the aerogel from breaking under stress during use. Furthermore, silicone rubber maintains stable performance within a temperature range of -60 to 200°C, making it suitable for electromagnetic shielding applications in various temperature environments. Silicone rubber also possesses high chemical stability, does not react with the conductive materials in the aerogel, and is resistant to aging and moisture, providing long-term protection for the aerogel's conductive network. In addition, the dielectric properties of silicone rubber are adjustable; by selecting different types of silicone rubber, the dielectric constant of the cured material can be controlled to ensure impedance matching with the aerogel, avoiding any impact on electromagnetic shielding effectiveness. Polyurethane, as a polymer prepolymer filler material, boasts core advantages in its excellent toughness, high elasticity, and adjustable mechanical properties. By adjusting the composition ratio of its isocyanate and polyol and its crosslinking density, the hardness, tensile strength, and resilience of the cured material can be precisely controlled, effectively buffering and dispersing stress and preventing the brittle aerogel skeleton from cracking under stress. Furthermore, polyurethane typically exhibits good wear resistance, low-temperature resistance, and adhesion to various substrates, further enhancing the overall durability and interlayer bonding of the composite material. Epoxy resin, on the other hand, offers significant advantages in its extremely high adhesive strength, excellent dimensional stability, and chemical corrosion resistance. The dense and rigid three-dimensional network structure formed after curing provides strong support for the porous aerogel skeleton, significantly improving the rigidity, strength, and creep resistance of the composite material. It exhibits excellent adhesion to metals, ceramics, and most polymer substrates, ensuring a firm bond between the electromagnetic shielding functional layer and the device housing or internal structure. Simultaneously, epoxy resin has low curing shrinkage, which helps maintain material dimensional accuracy and prevents interfacial delamination due to internal stress. The main advantages of polyacrylates (and their polymer acrylic resins) lie in their excellent optical transparency, good weather resistance, and diverse modification possibilities, making them irreplaceable in special applications that require both electromagnetic shielding and light transmission (such as display window shielding and optical equipment). By selecting different monomers for copolymerization, their flexibility, heat resistance, and viscosity can be flexibly adjusted. In addition, polyacrylates are generally resistant to ultraviolet aging and can maintain stable performance for a long time in outdoor or light-exposed environments, and they also have good electrical insulation properties.

[0091] In one feasible embodiment, the second organic solvent and the first organic solvent are compatible. If the two solvents are incompatible, the first organic solvent remaining in the aerogel pores after hydrophobic modification will form layers or precipitates with the second organic solvent, hindering the penetration of the polymer prepolymer in the filling liquid and resulting in uneven filling. At the same time, the incompatible solvents will create interfacial tension in the aerogel pores, preventing the prepolymer from fully contacting the aerogel surface, and making it prone to interfacial delamination after curing, reducing the overall stability of the material. When the solvents are compatible, the filling liquid can seamlessly integrate with the first organic solvent remaining in the pores, and the prepolymer can be uniformly dispersed and penetrate deep into the pores, ensuring the consistency of filling effect and material performance.

[0092] In one feasible embodiment, the first organic solvent and the second organic solvent are the same solvent. If the two solvents are different, the difference in polarity may cause stratification or decreased solubility during mixing, affecting the dissolution and penetration of the polymer prepolymer. When the solvents are the same, the portion of the first organic solvent remaining in the aerogel pores after hydrophobic modification can seamlessly fuse with the second organic solvent and the polymer prepolymer, avoiding interface defects caused by solvent replacement, and reducing the amount of solvent residue in the aerogel pores, thus reducing the risk of material shrinkage or cracking due to solvent evaporation during subsequent curing. For example, the first organic solvent includes n-hexane, and the second organic solvent includes n-hexane.

[0093] In one feasible embodiment, the filling treatment time is 12h to 72h, for example, 12h, 24h, 36h, 48h, 60h, or 72h. If the filling time is too short, there will be insufficient filling liquid in the tiny pores, which will form voids after curing, affecting the mechanical strength and electromagnetic shielding performance of the material; if the filling time is too long, the concentration of the filling liquid may increase due to solvent evaporation, forming an accumulation on the aerogel surface and blocking the pores.

[0094] Step S603: The filled aerogel is cured to obtain a double-layer electromagnetic shielding material.

[0095] In one feasible embodiment, the curing process includes heat treatment at 140~160℃ for 0.5~2 hours. If the temperature is below 150℃, the crosslinking reaction rate is slow, curing is insufficient, the material's mechanical properties are poor, and it is easily deformed. If the temperature is above 150℃, the conductive material in the aerogel may oxidize, leading to the breakage of the conductive network. At the same time, the silicone rubber may become brittle due to excessive crosslinking and lose its elasticity. Regarding the curing time, if the time is too long, it will lead to over-curing of the silicone rubber and a decrease in mechanical properties; if the time is too short, the prepolymer will not crosslink sufficiently and will not be able to form a polymer network.

[0096] In order to enable those skilled in the art to clearly understand the details and operations of the above embodiments of this application, and to demonstrate the significant improvement in performance of the embodiments of this application, the above technical solutions are illustrated below through multiple embodiments.

[0097] It should be noted that in the following embodiments and comparative examples, in the magnetic layer dispersion, hollow iron oxide nanospheres (HFO) are used as the magnetic nanomaterial, graphene oxide (GO) is used as the dielectric, sodium alginate (SA) is used as the second water-soluble polymer, and hexadecyltrimethylammonium bromide (CTAB) is used as the surface cationic modifier. In the reflective layer dispersion, carbon nanotubes (CNTs) are used as the conductive nanomaterial, and chitosan (CS) is used as the first water-soluble polymer.

[0098] Comparative Example 1: Step 1: 0.15 g CNT and 30 mL of 5 mg / mL CS solution were dispersed by ultrasonication in a water bath for 0.5 h and by ultrasonication with a probe for 0.5 h to obtain 30 mL of CNT / CS dispersion with a concentration ratio of 5 / 5 mg / mL; 2.7 mL of this dispersion was poured into a self-made mold with a side-mounted metal heat-conducting plate and a cavity size of 15 mm × 15 mm × 15 mm, and the conductive layer was frozen by lateral freezing to obtain a frozen sample; Step 2: The frozen sample of the conductive layer was sublimated and dried for 3 days to obtain a conductive layer aerogel; Step 3: The total volume of 40 cm³ was... 3 The conductive aerogel layer was placed in a vacuum container with 1 mL of methyltrichlorosilane. The desiccator was sealed with vacuum silicone grease, and the bilayer aerogel was chemically modified in the vapor phase at -80 kPa and 50°C for 48 h to obtain a surface-hydrophobically modified conductive aerogel. In step four, the surface-hydrophobically modified conductive aerogel obtained in step three was pressed into a 2 mm thick sheet and immersed in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1. After vacuum degassing, it was allowed to stand and fill at room temperature and normal pressure for 1 day to obtain a conductive aerogel / silicone rubber composite. In step five, the conductive aerogel / silicone rubber composite obtained in step four was heat-treated at 150°C for 1 h to obtain a cured conductive aerogel / silicone rubber composite material.

[0099] In Comparative Example 2, Step 1, 20 mg of hexadecyltrimethylammonium bromide and 50 mg of HFO were added to 10 mL of deionized water and stirred until homogeneous. The surface-cationized HFO was collected under the action of a magnet. 150 mg of GO was ultrasonically dispersed in 150 mL of deionized water to prepare 150 mL of 1 mg / mL GO dispersion. All the obtained GO dispersion and the obtained cationized HFO were mixed, ultrasonically dispersed for 20 min, and then shaken on a shaker for 1 h to obtain HFO@GO. This HFO@GO was added to 75 mL of 5 mg / mL SA solution and ultrasonically dispersed for 10 min to obtain 75 mL of HFO@GO / SA dispersion with a concentration ratio of 2 / 5 mg / mL. 2.7 mL of this dispersion was poured into a self-made mold with a side-mounted metal heat-conducting plate. The mold cavity dimensions were 15 mm × 15 mm × 15 mm. Magnetic layer frozen samples were obtained by lateral freezing. Step 2, the total volume was 40 cm³. 3Magnetic aerogel and 1 mL of methyltrichlorosilane were placed in a vacuum container, and the desiccator was sealed with vacuum silicone grease. The aerogel was chemically modified in the vapor phase at -80 kPa and 50°C for 2 days to obtain a surface-hydrophobic modified magnetic aerogel. In step two, the surface-hydrophobic modified magnetic aerogel obtained in step two was pressed into a 2 mm thick sheet and immersed in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1. After vacuum degassing, the aerogel was allowed to stand and fill at room temperature and normal pressure for 1 day to obtain a magnetic aerogel / silicone rubber composite. In step four, the magnetic aerogel / silicone rubber composite obtained in step three was heat-treated at 150°C for 1 h to obtain a cured magnetic aerogel / silicone rubber composite material. Example 1: In step one, 0.15 g of CNT and 30 mL of 5 mg / mL CS solution were sonicated in a water bath for 0.5 h and then sonicated with a probe for 0.5 h to obtain 30 mL of a CNT / CS dispersion with a concentration ratio of 5 / 5 mg / mL. 1.35 mL of the dispersion was poured into a self-made mold with a side-mounted metal heat-conducting plate. The mold cavity size was 15 mm × 15 mm × 15 mm. A conductive aerogel was obtained by lateral freezing. In step two, 20 mg of hexadecyltrimethylammonium bromide and 50 mg of HFO were added to 10 mL of deionized water and mechanically stirred to mix them evenly. A layer of CTAB molecules was attached to the surface of HFO by electrostatic self-assembly. Finally, the surface-cationized HFO was collected by a magnet. 150 mg of GO was ultrasonically dispersed in 150 mL of deionized water to prepare 150 mL of GO dispersion with a concentration of 1 mg / mL. All the GO dispersion and all the cationized HFO obtained above were mixed and ultrasonically dispersed for 20 min, then shaken on a shaker for 1 h to obtain HFO@GO. The HFO@GO was added to 75 mL of SA solution with a concentration of 5 mg / mL and ultrasonically dispersed for 10 min to obtain 75 mL of HFO@GO / SA dispersion with a concentration ratio of 2 / 5 mg / mL. 1.35 mL of the dispersion was poured onto the conductive aerogel prepared in step one, and then a bilayer aerogel with a magnetic layer to conductive layer volume ratio of 1:1 was obtained by lateral freezing. Finally, the bilayer aerogel was obtained after 3 days of sublimation drying. In step three, a total volume of 40 cm³ was... 3The bilayer aerogel and 1 mL of methyltrichlorosilane were placed in a vacuum container, and the desiccator was sealed with vacuum silicone grease. The surface was chemically modified in the gas phase at -80 kPa and 50°C for 48 h to obtain a surface-hydrophobic modified bilayer aerogel. In step four, the surface-hydrophobic modified bilayer aerogel obtained in step three was pressed into a 2 mm thick sheet and immersed in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1. After vacuum degassing, it was allowed to stand and fill at room temperature and normal pressure for 3 days. In step five, the bilayer aerogel / silicone rubber composite obtained in step four was heat-treated at 150°C for 1 h to obtain a bilayer electromagnetic shielding material. Figure 3 is a microscopic scanning electron microscope image of the bilayer electromagnetic shielding material of Example 1 of this application. (a) is the magnetic layer and (b) is the conductive layer. As shown in Figure 3, the aerogel / silicone rubber forms a uniform cross-linked network.

[0100] The double-layer electromagnetic shielding material prepared in this embodiment has a magnetic layer to conductive layer volume ratio of 1:1 and an average reflection efficiency (SE) of 1 / 100%. R The average absorption efficiency (SE) is 5.3 dB. A The average electromagnetic shielding effectiveness (SE) is 44.2 dB. T It is 49.5 dB.

[0101] In Example 2, step one, 0.15 g of CNT and 30 mL of 5 mg / mL CS solution were ultrasonicated in a water bath for 0.5 h and then ultrasonicated with a probe for 0.5 h to obtain 30 mL of CNT / CS dispersion with a concentration ratio of 5 / 5 mg / mL. 1.8 mL of this dispersion was poured into a self-made mold with a side-mounted metal heat-conducting plate. The mold cavity dimensions were 15 mm × 15 mm × 15 mm. A conductive aerogel layer was obtained by lateral freezing. In step two, 20 mg of hexadecyltrimethylammonium bromide and 50 mg of HFO were dissolved in 10 mL of deionized water and mechanically stirred until homogeneous. Electrostatic self-assembly was used to attach a layer of CTAB molecules to the surface of the HFO. Finally, the surface-cationized HFO was collected using a magnet. 150 mg of GO was ultrasonically dispersed in 150 mL of deionized water to prepare 150 mL of 1 mg / mL GO dispersion. All the GO dispersions and cationized HFOs obtained above were mixed and ultrasonically dispersed for 20 min, then shaken on a shaker for 1 h to obtain HFO@GO. This HFO@GO was added to 75 mL of a 5 mg / mL SA solution and ultrasonically dispersed for 10 min to obtain 75 mL of an HFO@GO / SA dispersion with a concentration ratio of 2 / 5 mg / mL. 0.9 mL of this dispersion was poured onto the conductive aerogel prepared in step one, and then lateral freezing was performed to obtain a bilayer aerogel with a magnetic layer to conductive layer volume ratio of 1:2. Finally, after 3 days of sublimation drying, the bilayer aerogel was obtained. In step three, a total volume of 40 cm³ was...3 A bilayer aerogel was placed in a vacuum container with 1 mL of methyltrichlorosilane. The desiccator was sealed with vacuum silicone grease and chemically modified in the vapor phase at -80 kPa and 50°C for 2 days to obtain a surface-hydrophobic modified bilayer aerogel. In step four, the surface-hydrophobic modified bilayer aerogel obtained in step three was pressed into a 2 mm thick sheet and immersed in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1. After vacuum degassing, it was allowed to stand and fill at room temperature and normal pressure for 3 days. In step five, the bilayer aerogel / silicone rubber composite obtained in step four was heat-treated at 150°C for 1 h to obtain a bilayer electromagnetic shielding material. The bilayer electromagnetic shielding material prepared in this example has a magnetic layer to conductive layer volume ratio of 1:2 and an average reflection efficiency SE. R With an average absorption efficiency of 6.8 dB, SE A The average electromagnetic shielding effectiveness (SE) is 52.5 dB. T It is 59.3 dB.

[0102] In Example 3, Step 1, 0.15 g of CNT and 30 mL of 5 mg / mL CS solution were ultrasonicated in a water bath for 0.5 h and then ultrasonicated with a probe for 0.5 h to obtain 30 mL of CNT / CS dispersion with a concentration ratio of 5 / 5 mg / mL. 0.9 mL of this dispersion was poured into a self-made mold with a metal heat-conducting plate on the side, and a conductive aerogel was obtained by lateral freezing. Step 2, 20 mg of hexadecyltrimethylammonium bromide and 50 mg of HFO were dissolved in 10 mL of deionized water and mechanically stirred until homogeneous. Electrostatic self-assembly was used to attach a layer of CTAB molecules to the surface of HFO. Finally, the surface-cationized HFO was collected using a magnet. 150 mg of GO was ultrasonically dispersed in 150 mL of deionized water to prepare 150 mL of 1 mg / mL GO dispersion. All the GO dispersions and cationized HFOs obtained above were mixed, ultrasonically dispersed for 20 min, and then shaken on a shaker for 1 h to obtain HFO@GO. This HFO@GO was added to 75 mL of a 5 mg / mL SA solution and ultrasonically dispersed for 10 min to obtain 75 mL of an HFO@GO / SA dispersion with a concentration ratio of 2 / 5 mg / mL. 1.8 mL of this dispersion was poured onto the conductive aerogel prepared in step one, and then lateral freezing was performed to obtain a bilayer aerogel with a magnetic layer to conductive layer volume ratio of 2:1. Finally, after 3 days of sublimation drying, the bilayer aerogel was obtained. In step three, 40 cm... 3A bilayer aerogel was placed in a vacuum container with 1 mL of methyltrichlorosilane. The desiccator was sealed with vacuum silicone grease, and the aerogel was chemically modified in the gas phase at -80 kPa and 50°C for 48 h to obtain a surface-hydrophobic modified bilayer aerogel. In step four, the surface-hydrophobic modified bilayer aerogel obtained in step three was pressed into a 2 mm thick sheet and immersed in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1. After vacuum degassing, the mixture was allowed to stand and fill at room temperature and normal pressure for 3 days. In step five, the bilayer aerogel / silicone rubber composite obtained in step four was heat-treated at 150°C for 1 h to obtain a bilayer electromagnetic shielding material. The bilayer electromagnetic shielding material prepared in this example has a magnetic layer to conductive layer volume ratio of 2:1 and an average reflection efficiency SE. R The average absorption efficiency (SE) is 4.9 dB. A The average electromagnetic shielding effectiveness (SE) is 33.0 dB. T It is 37.9 dB.

[0103] The electromagnetic shielding materials of Comparative Examples 1 and 2 and Examples 1 and 3 were tested in the Ka band. Figure 5 shows the characteristic impedance curves of the samples of Comparative Examples 1 and 2 in the Ka band, Figure 6 shows the conductivity of the samples of Comparative Examples 1 and 3 in the Ka band, and Figure 7 shows the reflection efficiency (SE) of the samples of Comparative Examples 1 and 2 in the Ka band. R Absorption efficiency SE A and shielding effectiveness SE T The curves, shown in Figure 8, represent the reflectance performance (SE) of the samples from Examples 1-3 of this application in the Ka band. R Absorption efficiency SE A and shielding effectiveness SE T Curves. The average reflection efficiency, average absorption efficiency, and average electromagnetic shielding efficiency of each comparative example and embodiment are used as experimental results, as shown in Table 1 below: Table 1

[0104] First, as shown in Figure 3, the interface between the two aerogel layers is seamless, indicating good bonding between them. This demonstrates that a double-layer aerogel with excellent interfacial bonding can be obtained through the stacking and freezing method. After surface modification and polymer filling, the double-layer aerogel can be used to obtain a double-layer electromagnetic shielding material. As shown in Figure 4, the polymer in the double-layer electromagnetic shielding material completely fills the aerogel pores, achieving a fully filled state. These results demonstrate that the material preparation process shown in this application can produce a double-layer electromagnetic shielding material with a complete structure, no defects, and suitable for large-scale production.

[0105] Secondly, Comparative Example 1 shows the conductive layer in the double-layer electromagnetic shielding material. The conductivity of this layer is 6.1 × 10⁻⁶. -1The S / m of Comparative Example 1 is significantly higher than that of Examples 1-3. Therefore, the sample of Comparative Example 1 has higher electromagnetic shielding performance, with an average SE T The impedance is 49.6 dB. However, due to impedance mismatch caused by high conductivity, its average impedance is only 0.01 dB. This results in a low average reflection efficiency (SE). R The impedance is as high as 7.9 dB. In contrast, Comparative Example 2 is a magnetic layer in a double-layer electromagnetic shielding material, which has impedance matching capabilities. With the help of magnetic iron oxide hollow microspheres and graphene oxide, this layer exhibits good impedance matching performance, with an average impedance of 0.35, significantly higher than Comparative Example 1. Therefore, the average reflection efficiency of this layer is only 1.5 dB, exhibiting limited low reflection characteristics. However, since no conductive material is added, it lacks conductivity, resulting in weak electromagnetic shielding capability and a low average SE. T The response time is only 14.1 dB. In summary, no single-layer material, whether a high-conductivity conductive layer or a magnetic impedance matching layer, can achieve both low reflection efficiency and high electromagnetic shielding performance. The advantage of double-layer electromagnetic shielding materials is that they possess both excellent electromagnetic shielding performance (SE) and high electromagnetic shielding efficiency. T It also has low reflectivity (SE) R For example, in Embodiment 2, when the volume ratio of the magnetic layer to the conductive layer is 1:2, its SE T Up to 59.3dB, while SE R Only 6.8dB. Compared to Comparative Example 1, SE T Higher, and SE R Lower.

[0106] Furthermore, for double-layer electromagnetic shielding materials (Examples 1-3), increasing the proportion of the conductive layer directly improves the overall shielding and absorption capabilities of the material. When the volume ratio of the magnetic layer to the conductive layer changes from 2:1 (Example 3) to 1:2 (Example 2), i.e., the thickness of the conductive layer increases, its total shielding effectiveness SE... T The absorption efficiency (SE) increased significantly from 37.9 dB to 59.3 dB. A The impedance also jumped from 33.0 dB to 52.5 dB. This indicates that a thicker conductive layer provides a stronger conductive network, thereby greatly enhancing the material's loss capability. Conversely, the increased proportion of the magnetic layer effectively optimized impedance matching and further reduced reflection. Comparative Example 2 (magnetic layer to conductive layer volume ratio 1:2, SE) R =6.8 dB) and Example 3 (magnetic layer to conductive layer volume ratio 2:1, SE R =4.9 dB), showing that the thicker magnetic layer resulted in lower reflection.

[0107] This application utilizes a stacked freezing method to construct a bilayer aerogel material, and then fills the aerogel with silicone rubber using a silicone rubber / n-hexane filling solution in a specific ratio, thus preparing an electromagnetic shielding material with low reflection and high shielding effectiveness in the Ka band. The magnetic layer reduces electromagnetic wave reflection on the material surface, while the conductive layer effectively shields electromagnetic waves, enabling the material to simultaneously possess low reflection and high electromagnetic shielding properties. The magnetic layer uses sodium alginate, rich in negative charges, as the polymer matrix, while the conductive layer uses chitosan, which has a positive charge, as the polymer matrix. The electrostatic force between these two materials enhances the interlayer bonding. Furthermore, the preparation method proposed in this application is simple, effective, highly controllable, low-cost, and suitable for large-scale manufacturing and commercial production.

[0108] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the patent protection scope of this application.

Claims

1. A method for preparing a double-layer electromagnetic shielding material for the Ka-band, characterized in that, The method includes the following steps: providing a conductive layer dispersion and a magnetic layer dispersion; laterally freezing the conductive layer dispersion to obtain a frozen conductive layer sample; pouring the magnetic layer dispersion onto the frozen conductive layer sample and laterally freezing it again to obtain a double-layer frozen sample; sublimating and drying the double-layer frozen sample to obtain a double-layer aerogel, wherein the double-layer aerogel includes the conductive layer aerogel and a magnetic layer aerogel stacked with the conductive layer aerogel, the pore orientation of the magnetic layer aerogel being consistent with the pore orientation of the conductive layer aerogel; and after surface hydrophobic modification, filling the double-layer aerogel with a polymer prepolymer and curing it to obtain a double-layer electromagnetic shielding material.

2. The method as described in claim 1, characterized in that, The steps of providing the conductive layer dispersion and the magnetic layer dispersion include: dispersing the conductive nanomaterial in a first water-soluble polymer solution to obtain the conductive layer dispersion; performing cationic surface modification treatment on the magnetic nanomaterial to obtain the modified magnetic nanomaterial; and mixing the modified magnetic nanomaterial, the dispersion of the dielectric nanomaterial, and the second water-soluble polymer solution to obtain the magnetic layer dispersion.

3. The method as described in claim 2, characterized in that, The mass concentration ratio of the conductive nanomaterial to the first water-soluble polymer is 5:5 mg / mL, wherein the concentration of the conductive nanomaterial is 2~10 mg / mL, the concentration of the first water-soluble polymer is 5~20 mg / mL, and the total concentration of the conductive nanomaterial and the first water-soluble polymer is 10~30 mg / mL; and / or, in the cationic surface modification treatment, the mass ratio of the magnetic nanomaterial to the surface cationic modifier is 1:1~4:

1.

4. The method as described in claim 2, characterized in that, The conductive nanomaterials include: carbon nanotubes; and / or, the first water-soluble polymer includes: chitosan, polyacrylamide, chitosan quaternary ammonium salt; and / or, the magnetic nanomaterials include: iron(III) oxide hollow nanospheres; and / or, the dielectric nanomaterials include: graphene oxide; and / or, the second water-soluble polymer includes: sodium alginate, polyacrylic acid, polymethacrylic acid, polyvinyl alcohol.

5. The method as described in claim 1, characterized in that, The volume ratio of the magnetic layer dispersion to the conductive layer dispersion is 1:2 to 2:

1.

6. The method as described in claim 1, characterized in that, Before the step of modifying the surface of the bilayer aerogel to be hydrophobic, filling it with a polymer prepolymer, and then curing it to obtain a bilayer electromagnetic shielding material, the method includes: placing the bilayer aerogel and volatile silane in a vacuum dryer for hydrophobic modification to obtain a hydrophobically modified bilayer aerogel; filling the hydrophobically modified bilayer aerogel with a polymer prepolymer and then curing it to obtain a bilayer electromagnetic shielding material.

7. The method as described in claim 6, characterized in that, The hydrophobic modification treatment includes: heat treatment at -80 kPa and 55°C for 12 to 48 hours; and / or, the volatile silane includes: methyltrichlorosilane, methyldichlorosilane, and dimethylchlorosilane; and / or, the volume ratio of the bilayer aerogel to the volatile silane is 20:1 to 60:

1.

8. The method as described in claim 6, characterized in that, The step of filling the hydrophobically modified bilayer aerogel with a polymer prepolymer and then curing it to obtain a bilayer electromagnetic shielding material includes: placing the hydrophobically modified bilayer aerogel in a first organic solvent to obtain a pore-wetted aerogel; placing one end of the pore-wetted aerogel in a filling liquid for filling treatment to obtain a filled aerogel, wherein the pore direction of the pore-wetted aerogel is perpendicular to the liquid surface of the filling liquid, and the filling liquid includes: a polymer prepolymer and a second organic solvent compatible with the polymer prepolymer, wherein the second organic solvent and the first organic solvent are compatible; and curing the filled aerogel to obtain a bilayer electromagnetic shielding material.

9. The method as described in claim 8, characterized in that, The first organic solvent includes n-hexane; and / or, the second organic solvent includes n-hexane, tetrahydrofuran, and acetone; and / or, the polymer prepolymer includes silicone rubber, polyurethane, epoxy resin, and polyacrylate; and / or, the mass ratio of the second organic solvent to the polymer prepolymer in the filling liquid is 1:2 to 2:1; and / or, the filling treatment time is 12 to 72 hours; and / or, the curing treatment includes heat treatment at 140 to 160°C for 0.5 to 2 hours.

10. A double-layer electromagnetic shielding material, characterized in that, The double-layer electromagnetic shielding material is prepared by the method described in any one of claims 1 to 9.

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