Preparation method of asymmetric electromagnetic shielding material for X wave band and asymmetric electromagnetic shielding material

Abstract

The invention discloses a preparation method of an asymmetric electromagnetic shielding material for an X wave band and the asymmetric electromagnetic shielding material, and belongs to the technical field of electromagnetic shielding materials.The method comprises the steps that impedance matching layer dispersion liquid and reflecting layer dispersion liquid are provided; laterally freezing the reflecting layer dispersion liquid to obtain a reflecting layer frozen sample; the impedance matching layer dispersion liquid is poured above the reflection layer frozen sample and subjected to lateral freezing again, an asymmetric frozen sample is obtained, finally, the asymmetric aerogel is obtained through sublimation drying, the asymmetric aerogel comprises reflection layer aerogel and impedance matching layer aerogel stacked with the reflection layer aerogel, and the impedance matching layer aerogel is stacked with the reflection layer aerogel. The pore orientation of the aerogel of the impedance matching layer is consistent with that of the aerogel of the reflecting layer; and carrying out liquid-phase hydrophobic surface modification on the asymmetric aerogel, filling the asymmetric aerogel with a high-molecular prepolymer, and carrying out curing treatment to obtain the asymmetric electromagnetic shielding material. According to the invention, the preparation of the low-reflection and high-electromagnetic shielding effectiveness material for the X wave band is realized.

Description

Technical Field

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

[0002] The demand for electromagnetic shielding materials is shifting from simply high shielding effectiveness to a comprehensive performance profile that combines low reflection, high shielding effectiveness, and robust reliability. Asymmetric structural designs, which combine impedance matching layers with electromagnetic loss layers, are considered an ideal way to achieve this goal. The impedance matching layer effectively promotes electromagnetic wave incidentness rather than reflection, while the internal conductive / magnetic loss layer is responsible for efficiently dissipating electromagnetic energy, thus synergistically achieving low secondary radiation and high shielding effectiveness.

[0003] However, when two aerogel layers with different components and functions are simply combined to construct an asymmetric structure, the weak interlayer bonding force has become a core technical bottleneck restricting its practical application. Once interlayer separation occurs, it will not only severely weaken the overall mechanical properties of the material, making it prone to structural damage in practical applications, but also sever the originally designed asymmetric attenuation path from an electromagnetic function perspective. Electromagnetic waves will encounter impedance abrupt changes at the separation interface, resulting in strong undesigned reflections and affecting the electromagnetic shielding performance of the material.

[0004] The above content is only used to help understand the technical solution of this application and does not represent an admission that the above content is prior art. Summary of the Invention

[0005] The main objective of this application is to provide a method for preparing an asymmetric electromagnetic shielding material for the X-band and the asymmetric electromagnetic shielding material itself, aiming to solve the technical problems that X-band electromagnetic shielding materials are difficult to combine with low reflection, high shielding effectiveness, and poor interlayer bonding of asymmetric materials.

[0006] To achieve the above objectives, this application provides a method for preparing an asymmetric electromagnetic shielding material for the X-band, the method comprising the following steps: Provides impedance matching layer dispersion and reflective layer dispersion; The reflective layer dispersion was laterally frozen to obtain a frozen reflective layer sample; The impedance matching layer dispersion is poured onto the frozen sample of the reflective layer and then laterally frozen again to obtain an asymmetric frozen sample. The asymmetric frozen sample is then sublimated and dried to obtain an asymmetric aerogel. The asymmetric aerogel includes the reflective layer aerogel and an impedance matching layer aerogel stacked with the reflective layer aerogel. The pore orientation of the impedance matching layer aerogel is consistent with that of the reflective layer aerogel. After the asymmetric aerogel is modified with a hydrophobic surface in the liquid phase, it is filled with a polymer prepolymer and then cured to obtain an asymmetric electromagnetic shielding material.

[0007] In one embodiment, the step of providing the impedance matching layer dispersion and the reflective layer dispersion includes: Magnetic nanomaterials were subjected to cationic surface modification treatment to obtain modified magnetic nanomaterials. The modified magnetic nanomaterial, the dispersion of the first two-dimensional conductive material, and the first water-soluble polymer solution are mixed to obtain an impedance matching layer dispersion. A dispersion of a one-dimensional conductive material, a second water-soluble polymer solution, and a second two-dimensional conductive material is mixed to obtain a reflective layer dispersion.

[0008] In one embodiment, in the cationic surface modification treatment, the mass ratio of the magnetic nanomaterial to the cationic modifier is 1:1 to 4:1; And / or, the concentration of the one-dimensional conductive material is 2~10 mg / mL, the concentration of the second two-dimensional conductive material is 2~5 mg / mL, the concentration of the second water-soluble polymer is 5~20 mg / mL, and the total concentration of the one-dimensional conductive material, the second two-dimensional conductive material and the second water-soluble polymer is between 10~30 mg / mL.

[0009] In one embodiment, the magnetic nanomaterial comprises: hollow iron oxide nanospheres; And / or, the first two-dimensional conductive material includes: MXene; And / or, the first water-soluble polymer includes: sodium alginate, polyacrylic acid, polymethacrylic acid, and polyvinyl alcohol; And / or, the one-dimensional conductive material includes: carbon nanotubes; And / or, the second two-dimensional conductive material includes: MXene, graphene; And / or, the second water-soluble polymer includes: chitosan, polyacrylamide, or chitosan quaternary ammonium salt.

[0010] In one embodiment, the volume ratio of the impedance matching layer dispersion to the reflective layer dispersion is 1:2 to 2:1.

[0011] In one embodiment, the step of modifying the asymmetric aerogel with a hydrophobic surface in the liquid phase, filling it with a polymer prepolymer, and then curing it to obtain an asymmetric electromagnetic shielding material includes: The asymmetric aerogel is immersed in a mixture to obtain a hydrophobically modified asymmetric aerogel, wherein the mixture includes a liquid-phase modified silane and a first organic solvent compatible with the liquid-phase modified silane, and the first organic solvent is compatible with the polymer prepolymer. The hydrophobically modified asymmetric aerogel is filled with a polymer prepolymer and then cured to obtain an asymmetric electromagnetic shielding material.

[0012] In one embodiment, the hydrophobic modification treatment includes: soaking for 10-14 hours; And / or, the liquid-phase modified silane includes: methyltrichlorosilane, hexyltriethoxysilane, propyltriethoxysilane, octyltriethoxysilane; And / or, the first organic solvent includes: n-hexane, tetrahydrofuran; And / or, the concentration of the liquid-phase modified silane in the first organic solvent is 1~3 mg / mL.

[0013] In one embodiment, the step of filling the hydrophobically modified asymmetric aerogel with a polymer prepolymer and then curing it to obtain an asymmetric electromagnetic shielding material includes: One end of the hydrophobically modified asymmetric aerogel is placed in a filling liquid for filling treatment to obtain a filled asymmetric aerogel, wherein the pore direction of the asymmetric 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. The filled asymmetric aerogel is cured to obtain an asymmetric electromagnetic shielding material.

[0014] In one embodiment, the mass ratio of the polymer prepolymer to the second organic solvent in the filling liquid is 1:2 to 2:1; And / or, the polymer prepolymer includes: silicone rubber, polyurethane, epoxy resin, polyacrylate; And / or, the first organic solvent includes: n-hexane, tetrahydrofuran; And / or, the filling process takes 12h to 24h; And / or, the curing process includes: heat treatment at 140~160℃ for 0.5~2h.

[0015] This application also provides an asymmetric electromagnetic shielding material, which is prepared by the method described above.

[0016] In this embodiment, the reflective layer dispersion is first subjected to lateral freezing, causing the solute and nanofiller in the original dispersion to form a laterally oriented microstructure inside the frozen reflective layer sample. Subsequent sublimation drying forms a laterally oriented pore structure penetrating both sides of the material. This laterally oriented structure effectively hinders electromagnetic wave propagation, thus effectively shielding electromagnetic waves. When the impedance matching layer dispersion is poured onto the frozen reflective layer sample, the dispersion promotes the melting of a small amount of the frozen reflective layer sample at the interface. The negatively charged polymer molecules in the impedance matching layer dispersion form electrostatic interactions with the positively charged polymer molecules in the small amount of melted reflective layer dispersion. This intermolecular force at the interface enhances the interfacial bonding force, thereby improving the interfacial bonding performance of the asymmetric aerogel. During a second lateral freezing, since the frozen reflective layer sample already has oriented pores, it acts as a substrate to guide the growth of ice crystals in the impedance matching layer dispersion, ensuring that the growth direction of the new ice crystals aligns with the existing pore direction, thus achieving continuity in the pore orientation of the two aerogel layers. When the pore orientations of the two aerogel layers are consistent, the pore channels are continuously connected at the interface between the reflective layer and the impedance matching layer, thereby increasing the effective contact area and mechanical interlocking effect at the interface.

[0017] After sublimation drying to obtain an asymmetric aerogel, it is filled with a polymer prepolymer and cured. The uniform pore channels allow the polymer prepolymer to more easily penetrate and fill the entire structure, including the interfacial region. After curing, the polymer forms a solid-phase network that binds the two aerogel layers together, filling microscopic defects and further strengthening the interfacial bond between the reflective layer and the impedance matching layer.

[0018] Therefore, this embodiment of the application achieves the consistency of the pore orientation of the two aerogel layers through secondary lateral freezing, ensuring the continuity and interlocking at the interface from the microstructure. Then, the overall structure is strengthened by polymer filling and curing, thereby improving the interlayer bonding strength of the asymmetric electromagnetic shielding material. This technology has prepared asymmetric electromagnetic shielding materials with different electromagnetic properties. The impedance matching layer located above can reduce the reflection of electromagnetic waves on the material surface, while the reflective layer located below provides the material with excellent electromagnetic shielding performance. Through the synergistic effect of the two, the technical problem that X-band electromagnetic shielding materials are difficult to have low reflection, high shielding effectiveness and poor interlayer bonding of asymmetric residual layers is solved. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart illustrating the preparation method of the asymmetric electromagnetic shielding material for the X-band involved in the embodiments of this application; Figure 2 This is a diagram of the lateral freezing device designed for the preparation method of the asymmetric electromagnetic shielding material in this application; Figure 3These are scanning electron microscope images of the asymmetric aerogel during the preparation of the asymmetric electromagnetic shielding material in Example 1 of this application. Figure 4 These are scanning electron microscope images of the asymmetric electromagnetic shielding materials in Examples 1-3 of this application, where (a) is the impedance matching layer and (b) is the reflective layer. Figure 5 These are the reflection efficiency, absorption efficiency, and electromagnetic shielding efficiency curves of the electromagnetic shielding materials of Comparative Example 1 (impedance matching layer) and Comparative Example 2 (reflection layer) in the X-band. Figure 6 The reflection efficiency, absorption efficiency, and electromagnetic shielding efficiency (SE) of the asymmetric electromagnetic shielding materials in Embodiments 1-3 of this application in the X-band are described. T Total Shielding Effectiveness (TPE) curve; Figure 7 These are the reflection, absorption, and shielding performance curves of the asymmetric electromagnetic shielding materials in Embodiments 3-5 of this application in the X-band.

[0020] 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

[0021] 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.

[0022] The following detailed description, with appropriate reference to the accompanying drawings, discloses specific embodiments for the preparation of the asymmetric electromagnetic shielding material of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically 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.

[0023] 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.

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

[0025] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0026] 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.

[0027] 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.

[0028] 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).

[0029] 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.

[0030] 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.

[0031] 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.

[0032] When constructing asymmetric structures by simply combining two aerogel layers with different components and functions, the weak interlayer bonding has become a core technical bottleneck restricting its practical application. This interlayer separation problem mainly stems from several fundamental reasons: First, different functional layers are usually composed of material systems with significantly different chemical properties, and their surface energy and chemical compatibility are mismatched, resulting in only weak physical contact between the layers rather than a strong chemical bond; second, existing preparation processes, such as simple physical stacking or stepwise freezing, are unable to establish effective molecular-level entanglement or chemical bonding at the interface between the two layers, making the interface a weak link in mechanical properties and mass transfer pathways; during subsequent drying or curing processes, due to the inconsistent shrinkage behavior of different layer materials, significant residual stress will be generated at the interface, further exacerbating the risk of interlayer debonding and delamination.

[0033] In this embodiment, the reflective 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 reflective 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 impedance matching layer dispersion is poured onto the frozen reflective layer sample, it promotes the melting of a small amount of the frozen reflective layer sample at the interface. The negatively charged polymer molecules in the impedance matching layer dispersion interact electrostatically with the positively charged polymer molecules in the small amount of melted reflective layer dispersion, enhancing the interfacial bonding force. A subsequent lateral freezing process causes the impedance matching layer dispersion to grow ice crystals laterally, in the same direction as the pore orientation of the reflective layer, ensuring consistency in the pore orientation of both. Finally, sublimation drying yields an asymmetric aerogel. When the pore orientations of the two aerogel layers are aligned, the pore channels are continuously connected at the interface between the reflective layer and the impedance matching layer, thereby increasing the effective contact area and mechanical interlocking effect at the interface. Furthermore, during the co-freezing process, slight interdiffusion or cross-linking may occur between the two dispersions at the interface, further promoting chemical bonding.

[0034] After obtaining the asymmetric aerogel, a polymer prepolymer was gradually filled and cured. The uniform pore channels allowed the polymer prepolymer to more easily penetrate and fill the entire structure, including the interfacial region. After curing, the polymer formed a solid-phase network that firmly bound the two aerogel layers together, filling microscopic defects and further consolidating the interfacial bond between the reflective layer and the impedance matching layer.

[0035] Thus, the embodiments of this application achieve the consistency of the pore orientation of the two aerogel layers through secondary lateral freezing, ensuring the continuity and interlocking at the interface from the microstructure. Furthermore, the overall structure is strengthened by polymer filling and curing, thereby improving the interlayer bonding strength of the asymmetric electromagnetic shielding material.

[0036] The first aspect of this application provides a method for preparing an asymmetric electromagnetic shielding material for the X-band. Please refer to... Figure 1 The preparation method includes the following steps: Step S10: Provide the impedance matching layer dispersion and the reflective layer dispersion.

[0037] The primary function of the impedance matching layer is to reduce the reflection of electromagnetic waves at the material surface, allowing more electromagnetic waves to penetrate the material's interior. When electromagnetic waves reach the material surface, if the surface impedance does not match the air impedance, a large amount of electromagnetic waves will be reflected, failing to effectively penetrate the material for absorption, thus causing secondary electromagnetic pollution. The impedance matching layer, through specific composition design, can adjust the impedance characteristics of the material surface, making it easier for electromagnetic waves to penetrate the surface and enter the material's interior. The reflective layer is mainly responsible for reflecting and scattering electromagnetic waves entering the material's interior. Through multiple reflections, the electromagnetic waves continuously interact with the conductive orientation structure within the material, converting electromagnetic energy into other forms of energy such as heat, achieving electromagnetic wave attenuation and thus shielding the electromagnetic waves. The two layers work together to form a synergistic mechanism of first matching and then reflecting and attenuating, jointly improving the overall electromagnetic shielding effectiveness of the material.

[0038] In one feasible embodiment, the impedance matching layer dispersion comprises: magnetic nanomaterials, a first two-dimensional conductive material, and a first water-soluble polymer. The magnetic nanomaterials can absorb electromagnetic waves through magnetic loss; their unique nanoscale structure increases the contact area with electromagnetic waves, enhancing the absorption effect. The first two-dimensional conductive material has good conductivity and can participate in the attenuation process of electromagnetic waves through conductive loss. Simultaneously, its sheet-like structure helps form a continuous conductive network, enhancing the charge transport capability within the material. The first water-soluble polymer serves as a dispersion medium and structural support, uniformly dispersing the magnetic nanomaterials and the first two-dimensional conductive material in the system, ensuring the subsequent formation of a stable aerogel structure.

[0039] In one feasible embodiment, the reflective layer dispersion comprises: a one-dimensional conductive material, a second two-dimensional conductive material, and a second water-soluble polymer. The one-dimensional conductive material has a high aspect ratio, enabling it to form interwoven conductive pathways in the dispersion, which is beneficial for the reflection and conduction of electromagnetic waves, thereby promoting the conversion of electromagnetic energy. The second two-dimensional conductive material is similar to the first two-dimensional conductive material, possessing good conductivity and a sheet-like structure, but its role in the reflective layer is more focused on synergistically constructing a dense conductive network with the one-dimensional conductive material to enhance the reflection capability of electromagnetic waves. The second water-soluble polymer, as a dispersing and supporting component, enables the one-dimensional and two-dimensional conductive materials to be evenly distributed, ensuring that the subsequently formed reflective layer aerogel has a stable structure and performance.

[0040] In one feasible embodiment, the volume ratio of the impedance matching layer dispersion to the reflective layer dispersion is 1:2 to 2:1, for example, 1:2, 1:1, or 2:1. An imbalance in the volume ratio of the impedance matching layer dispersion to the reflective layer dispersion may lead to a mismatch in the interlayer structure of the asymmetric aerogel. Specifically, when the impedance matching layer is too thin or too thick, it cannot form a consistent pore orientation, resulting in insufficient interfacial bonding and damage to the reflective layer's orientation structure, ultimately affecting electromagnetic shielding performance and mechanical stability. When the volume ratio of the impedance matching layer dispersion is too large (exceeding 2:1), during subsequent co-directional freezing, excessive dispersion may cause insufficient reflective layer samples to melt, thus disrupting the laterally oriented porous structure formed during the first lateral freezing and reducing reflective performance. Conversely, when the volume ratio is too large (below 1:2), the impedance matching layer becomes too thin, failing to fully utilize its impedance matching function. This results in a large amount of electromagnetic waves being reflected at the material surface, unable to penetrate and be effectively attenuated. Furthermore, the bonding force between the thin impedance matching layer and the reflective layer weakens, leading to uneven distribution and affecting the overall stability and lifespan of the material. Therefore, controlling the volume ratio between the two within the range of 1:2 to 2:1 ensures that the impedance matching layer and reflective layer form a structurally coordinated and tightly bonded asymmetric aerogel, providing a structural basis for achieving excellent electromagnetic shielding performance.

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

[0042] Lateral freezing and unidirectional freezing share the same principle: both are freezing techniques that control the freezing direction to cause the solvent in the dispersion to crystallize and grow in a single direction. Traditional unidirectional freezing typically involves controlling the freezing temperature gradient from the bottom of the container upwards, in the same direction as gravity. Lateral freezing, however, involves the temperature gradient moving 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 to the reflective 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 reflective layer. This increases the chances of interaction between the electromagnetic waves and the conductive components, significantly enhancing the reflective layer's attenuation capability. Secondly, the laterally oriented pore structure helps improve the mechanical properties of the reflective 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 impedance matching 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 the reflective layer dispersion into a specific mold, with one end of the mold in contact with a low-temperature cold source (such as a liquid nitrogen cooling stage, a low-temperature metal plate, etc.), and the other end in a relatively high-temperature environment, forming a stable unidirectional temperature gradient. For example, the temperature gradient range can be controlled between 5 and 20 °C / 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 to 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 reflective layer aerogel can be precisely controlled to meet the performance requirements of subsequent asymmetric electromagnetic shielding materials. For example, please refer to... Figure 2 In this embodiment, the following is adopted: Figure 2 The mold shown undergoes lateral unidirectional freezing. The liquid nitrogen in the central container of the mold unidirectionally freezes the liquid nitrogen in the containers on both sides. That is, in this embodiment, the mold is directly in contact with the container containing liquid nitrogen, and heat is directly transferred through the container wall. In a feasible implementation, one side of the mold can be a thermally conductive metal sheet, and the interior of the mold can be used to hold the dispersion liquid, with the thermally conductive metal sheet serving as the heat transfer medium.

[0045] Step S30: Pour the impedance matching layer dispersion onto the frozen sample of the reflective layer and perform lateral freezing again to obtain an asymmetric frozen sample. Sublime-dry the asymmetric frozen sample to obtain an asymmetric aerogel. The asymmetric aerogel includes the reflective layer aerogel and an impedance matching layer aerogel stacked with the reflective layer aerogel. The pore orientation of the impedance matching layer aerogel is consistent with the pore orientation of the reflective layer aerogel.

[0046] In one feasible embodiment, the asymmetric aerogel's layered structure is characterized by a planar superposition of a reflective aerogel layer and an impedance matching aerogel layer, with the pores of the two aerogel layers extending laterally to form continuous directional channels. The pore orientation of the asymmetric aerogel is parallel to the layer interface, i.e., extending along the side of the material, allowing the pores to penetrate from one side of the impedance matching layer to the other, forming a mutually parallel directional pore network of asymmetric aerogels. It is understood that the pore orientation parallel to the layer interface allows vertically incident electromagnetic waves to be effectively blocked, first being guided through the impedance matching layer for adjustment, and then entering the reflective layer for multiple reflections and attenuation, maximizing the functional division of the two layers. Furthermore, the directionally arranged pores penetrate the entire layered 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 mechanical weak point, and significantly improving the structural consistency of the asymmetric electromagnetic shielding material.

[0047] Secondary lateral freezing ensures that the impedance matching layer dispersion and the already frozen reflective layer sample are tightly bonded before the second freezing through interfacial fusion and electrostatic interactions formed by the polymers in their dispersions, avoiding the risk of subsequent interlayer separation. Under lateral freezing, the solvent in the impedance matching layer dispersion crystallizes along a direction consistent with the pore orientation of the reflective layer, allowing the newly formed impedance matching layer aerogel to form a continuous structural transition with the reflective layer aerogel at the interface, rather than a simple mechanical superposition. On the other hand, co-freezing guides the functional particles (such as magnetic nanomaterials, first-dimensional and second-dimensional conductive materials, etc.) in the impedance matching layer dispersion to align along a predetermined direction, providing a structural basis for the subsequent impedance matching function and attenuation, ensuring the synergistic effect of the two layers in the electromagnetic shielding process.

[0048] In one feasible embodiment, the common unidirectional freezing treatment conditions are consistent with the lateral freezing treatment 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 treatment conditions simplify the process operation, reduce the error risk 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 asymmetric aerogel, and reduce the possibility of cracking or deformation.

[0049] In one feasible embodiment, after freezing, the frozen sample is placed at -40 to -60°C under a vacuum of less than 10 Pa for drying. 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 asymmetric aerogels, the pore orientation of the impedance matching layer aerogel is consistent with that of the reflective layer aerogel. This consistent pore orientation provides a continuous transmission channel for electromagnetic waves, allowing them to smoothly enter the reflective layer after passing through the impedance matching layer. This reduces electromagnetic wave scattering loss or enhanced reflection caused by abrupt changes in pore direction, 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 the asymmetric aerogel is modified with a hydrophobic liquid phase, it is filled with a polymer prepolymer and then cured to obtain an asymmetric electromagnetic shielding material.

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

[0053] In one feasible embodiment, the hydrophobic modification treatment may include: immersing the asymmetric aerogel in a mixed solution to obtain a hydrophobically modified asymmetric aerogel, wherein the mixed solution includes a liquid-phase modified silane and a first organic solvent compatible with the liquid-phase modified silane. The active groups in the silane molecules react with the hydroxyl groups on the aerogel surface, introducing hydrophobic organic groups into the aerogel surface, thereby altering the surface energy of the aerogel and making it hydrophobic. The first organic solvent dissolves and disperses the liquid-phase modified silane, allowing it to uniformly penetrate into the pores of the aerogel, ensuring the uniformity of the modification. The hydrophobic modification treatment can improve the water resistance of the aerogel, preventing structural damage and performance degradation caused by water absorption in humid environments; furthermore, it can enhance the compatibility of the aerogel with the subsequently filled polymer prepolymer, reduce interfacial defects, improve the overall performance of the material, and simultaneously reduce the surface energy of the aerogel, facilitating the uniform filling of the polymer prepolymer into the pores.

[0054] In one feasible embodiment, the shaping process may include: pressing the asymmetric aerogel into a sheet-like asymmetric 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 asymmetric aerogel has a thickness of 2-8 mm, such as 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, or 8 mm. If the thickness is less than 2 mm, the material is too thin, resulting in a short propagation path for electromagnetic waves and limited reflection and absorption effects, making it difficult to achieve ideal shielding performance. If the thickness is greater than 8 mm, although it may improve shielding performance, it increases the weight and volume of the material, which is not conducive to use in lightweight and miniaturized applications, and also increases manufacturing costs. Therefore, in this embodiment, the shaping process includes pressing to a thickness of 2-8 mm.

[0055] In one feasible embodiment, an organic solvent is used to wet the pores of an asymmetric aerogel, and then one end of the asymmetric aerogel is placed in a filling liquid for filling treatment to obtain a filled asymmetric aerogel. The filled asymmetric 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 organic solvent that wets the asymmetric aerogel. 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.

[0056] In one feasible embodiment, the first organic solvent used in the hydrophobic modification process is an organic solvent compatible with the second organic solvent. In conventional processes, hydrophobic modification and pore wetting typically need to be performed separately. However, using a compatible organic solvent allows both tasks to be completed simultaneously in a single treatment, reducing operational steps and time costs. Furthermore, during the hydrophobic modification process, the organic solvent has already fully penetrated into the pores, creating favorable conditions for subsequent filling with the packing solution and avoiding uneven filling problems caused by insufficient wetting.

[0057] In one feasible embodiment, the pore orientation of the asymmetric 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 material 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: providing the impedance matching layer dispersion and the reflective layer dispersion, includes: Step S101: The magnetic nanomaterial is subjected to cationic surface modification treatment to obtain the modified magnetic nanomaterial.

[0059] In one feasible embodiment, the cationic surface modification treatment includes: dispersing magnetic nanomaterials in deionized water, adding a cationic modifier, stirring and reacting at room temperature for 2-6 hours, and obtaining the modified magnetic nanomaterials by centrifugation after the reaction is completed. Magnetic nanomaterials are prone to aggregation due to their high surface energy. The 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 impedance matching layer dispersion, ensuring the uniformity of material properties. Furthermore, the hydrophobic groups of the 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.

[0060] 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.

[0061] In one feasible embodiment, in the cationic surface modification treatment, the mass ratio of the magnetic nanomaterial to the cationic modifier is between 1:1 and 4:1, for example, it can be 1:1, 2:1, 2.5:1, 3:1, or 4:1. Among these, the modification efficiency is highest when the mass ratio of the magnetic nanomaterial to the cationic modifier is 2:5. If the ratio is lower than 4:1, the amount of cationic modifier is insufficient, and the surface of the magnetic nanomaterial cannot be fully covered. Some areas will still agglomerate due to high surface energy, resulting in poor dispersion and affecting the uniformity of the subsequent impedance matching layer dispersion. If the ratio is higher than 1:1, excessive cationic modifier will be free in the dispersion, which not only increases the cost 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.

[0062] Step S102: Mix the modified magnetic nanomaterial, the dispersion of the first two-dimensional conductive material, and the first water-soluble polymer solution to obtain an impedance matching layer dispersion.

[0063] In one feasible embodiment, the modified magnetic nanomaterial is mixed with a dispersion of a first two-dimensional conductive material. During the mixing process, electrostatic self-assembly occurs to obtain a magnetic load. The cation-modified magnetic nanomaterial carries a positive charge on its surface, while the surface of the first two-dimensional conductive material, 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 first two-dimensional conductive material 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 impedance matching layer to possess both magnetic and electrical loss capabilities. The magnetic load is then mixed with a first water-soluble polymer solution. The molecular chains of the water-soluble polymer wrap around the surface of the magnetic load and bind to the magnetic load through hydrogen bonds and van der Waals forces, ultimately forming a uniform and stable impedance matching layer dispersion.

[0064] In one feasible embodiment, the mixing of the modified magnetic nanomaterial with the dispersion of the first two-dimensional conductive material includes: stirring at room temperature for 30-60 minutes, for example, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, and 60 minutes. Room temperature (typically 20-25°C) minimizes the interference of temperature on the charge characteristics and dispersion stability of the material. If the temperature is too high, it will accelerate the thermal motion of water molecules, which may disrupt the charge balance on the surface of the first two-dimensional conductive material sheets, leading to weakened interlayer repulsion and causing sheet stacking. If the temperature is too low, it will reduce ionic activity, slow down the rate of electrostatic self-assembly, prolong the reaction time, and may lead to incomplete assembly. If the stirring time is too short, the modified magnetic nanomaterial and the first two-dimensional conductive material cannot achieve sufficient contact; if the stirring time is too long, the shear force generated by high-speed stirring may destroy the sheet structure of the first two-dimensional conductive material, or cause the assembled magnetic load to dissociate due to shear force exceeding electrostatic attraction, thereby reducing the uniformity of the dispersion.

[0065] In one feasible embodiment, the mass ratio of the magnetic nanomaterial to the first two-dimensional conductive material is 1:2 to 1:5, for example, 1:2, 1:3, 1:4, or 1:5. If the proportion of the two-dimensional conductive material is too low, the magnetic nanomaterial will easily agglomerate due to the lack of sufficient two-dimensional sheet carrier, resulting in poor dispersion uniformity and large fluctuations in the electromagnetic loss performance of the subsequent aerogel. If the proportion of the two-dimensional conductive material is too low, the dielectric constant of the impedance matching layer will increase significantly, causing an excessive difference in impedance between the material and air. This will cause the reflectivity of electromagnetic waves on the material surface to soar, making it impossible to achieve the impedance matching function of reducing reflection and guiding electromagnetic waves into the interior.

[0066] In one feasible embodiment, the first two-dimensional conductive material includes MXene. The surface of the MXene sheets contains a large number of functional groups such as hydroxyl and oxygen atoms. These functional groups form hydrogen bonds with the hydroxyl and carboxyl groups of the first water-soluble polymer, enhancing the stability of the dispersion. Furthermore, the thin sheet thickness and large specific surface area of ​​MXene provide ample attachment sites for magnetic nanomaterials, and its flexible sheet structure is not easily broken during subsequent unidirectional freezing and curing processes, which helps to preserve the integrity of the aerogel's pore structure, thereby ensuring unobstructed transmission paths of electromagnetic waves within the material.

[0067] In one feasible embodiment, the mass concentration of the first two-dimensional conductive material in the dispersion is 1 mg / mL. In another feasible embodiment, the first water-soluble polymer includes sodium alginate, wherein the carboxylate groups of sodium alginate can form a stable framework by ionic crosslinking with the cations on the surface of the magnetic support, and the viscosity of the dispersion is adjusted to adapt to the unidirectional freezing process, thereby ensuring the stability of the impedance matching layer structure. It should be noted that if the mass concentration of the dispersion of the first two-dimensional conductive material is less than 1 mg / mL, the distribution density of its sheets in the solution will be too low. This will result in a lack of sufficient effective action sites when electrostatically self-assembling with the surface-cation-modified magnetic nanomaterials. This will not only reduce the formation efficiency and loading of the magnetic load, but also weaken the dielectric polarization loss capability of the final material against high-frequency electromagnetic waves due to insufficient dielectric components. Conversely, if the concentration is higher than 1 mg / mL, the excessive two-dimensional sheets will easily stack and agglomerate due to van der Waals forces, destroying the uniformity and stability of the dispersion. At the same time, the high concentration of sheets will severely hinder the directional growth of ice crystals during the subsequent unidirectional freezing process, thereby destroying the oriented pore structure of the aerogel and forming stress concentration points inside the material, damaging its structural integrity and mechanical properties.

[0068] In one feasible embodiment, the mass concentration ratio of the magnetic loading material to the first water-soluble polymer is 6:5 mg / mL to 7:5 mg / mL, for example, 6:5 mg / mL, 6.5:5 mg / mL, or 7:5 mg / mL. If the mass concentration ratio is higher than 7:5, the concentration of the first water-soluble polymer is too low, the cross-linking backbone strength is insufficient, and the aerogel is prone to cracking during drying or subsequent filling processes; if the mass concentration ratio is lower than 6:5, the concentration of the magnetic loading material is too low, the electromagnetic loss capability decreases, and the performance requirements of the impedance matching layer cannot be met.

[0069] In one feasible embodiment, the mass concentration ratio of the magnetic nanomaterial, the first two-dimensional conductive material, and the first water-soluble polymer is 1.7:5:5 mg / mL, that is, the mass concentration ratio of the magnetic loading material to the first water-soluble polymer is 6.7:5 mg / mL. If the proportion of the magnetic loading material is too low, the total amount of functional nanomaterials in the dispersion is insufficient, resulting in a scarcity of magnetic and dielectric loss sites in the final impedance matching layer. This prevents the formation of an effective synergistic electromagnetic wave absorption network, which not only weakens the overall electromagnetic shielding effectiveness of the material but also damages its key impedance matching function, increasing the reflection of electromagnetic waves on the material surface and failing to achieve the design goal of low reflection. Conversely, if the proportion of the magnetic loading material is too high, the excessive nanoparticles will exceed the dispersion and encapsulation capacity of the first water-soluble polymer, leading to severe particle aggregation, disrupting the uniformity and stability of the dispersion, and thus hindering the directional growth of ice crystals during subsequent freeze-drying, damaging the integrity of the directional pore structure of the aerogel, and potentially reducing the mechanical strength of the material due to local stress concentration.

[0070] Step S103: Mix the one-dimensional conductive material, the second water-soluble polymer solution, and the dispersion of the second two-dimensional conductive material to obtain the reflective layer dispersion.

[0071] In one feasible embodiment, a one-dimensional conductive material is mixed with a second water-soluble polymer solution to obtain a one-dimensional conductive material dispersion, and the one-dimensional conductive material dispersion is mixed with a dispersion of a second two-dimensional conductive material to obtain a reflective layer dispersion.

[0072] In one feasible embodiment, mixing the one-dimensional conductive material 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, potentially causing thermal denaturation of the second water-soluble polymer and loss of its dispersing and stabilizing effect.

[0073] In one feasible embodiment, the one-dimensional conductive material includes carbon nanotubes, whose aspect ratio characteristics allow them to be oriented along the orientation pores formed by freezing, and to work in conjunction with the second two-dimensional conductive material to construct a three-dimensional conductive network, thereby enhancing the electromagnetic wave reflection efficiency.

[0074] In one feasible embodiment, the second water-soluble polymer is chitosan. Chitosan has good film-forming and gelling properties. During the subsequent unidirectional freezing process, its molecular chains can form a continuous skeleton structure in the gaps between ice crystals, supporting the pore morphology of the reflective aerogel, preventing pore collapse after freeze-drying, and ensuring the integrity of the conductive network. Furthermore, the amino and hydroxyl groups of chitosan can form hydrogen bonds with the oxygen-containing functional groups on the surface of the second two-dimensional conductive material, enhancing the bonding force between the conductive material and the water-soluble polymer. At the same time, when it is subsequently combined with the impedance matching layer, the polar groups of chitosan can also form intermolecular forces with the first water-soluble polymer in the impedance matching layer, improving the interfacial bonding strength of the two aerogel layers and reducing the risk of interlayer separation.

[0075] In one feasible embodiment, the second two-dimensional conductive material includes MXene and graphene. MXene's high specific surface area and surface functional groups enhance the continuity of the conductive network and improve the electromagnetic wave reflection effect. Simultaneously, MXene can tightly bind with cation-modified magnetic nanomaterials through electrostatic interactions, ensuring the uniform dispersion of each component in the impedance matching layer. Graphene possesses intrinsically high electrical conductivity and carrier mobility, enabling the construction of an extremely efficient conductive network and providing a strong electrical conduction loss mechanism for electromagnetic shielding. Furthermore, graphene exhibits high mechanical strength and excellent chemical stability, significantly improving the mechanical properties of composite materials and maintaining performance stability under various environments. In addition, its extremely high thermal conductivity also helps dissipate Joule heat generated by electromagnetic wave conversion.

[0076] In one feasible embodiment, the mass concentration of the second two-dimensional conductive material in the dispersion of the second two-dimensional conductive material is 10 mg / mL.

[0077] In one feasible embodiment, the mass concentration ratio of the one-dimensional conductive material, the second two-dimensional conductive material, and the second water-soluble polymer is 5:5:5 mg / mL. The concentration of the one-dimensional conductive material is between 2 and 10 mg / mL, for example, 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 concentration of the second two-dimensional conductive material is between 2 and 5 mg / mL, for example, 2 mg / mL, 3 mg / mL, 4 mg / mL, or 5 mg / mL. The concentration of the second water-soluble polymer is between 5 and 20 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, or 20 mg / mL. The total concentration of the one-dimensional conductive material, the second two-dimensional conductive material, and the second 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, the concentrations could be: 2 mg / mL for the one-dimensional conductive material, 2 mg / mL for the second two-dimensional conductive material, 6 mg / mL for the second water-soluble polymer, and a total concentration of 10 mg / mL; 2 mg / mL for the one-dimensional conductive material, 3 mg / mL for the second two-dimensional conductive material, 5 mg / mL for the second water-soluble polymer, and a total concentration of 10 mg / mL; 5 mg / mL for the one-dimensional conductive material, 5 mg / mL for the second two-dimensional conductive material, 5 mg / mL for the second water-soluble polymer, and a total concentration of 15 mg / mL; 6 mg / mL for the one-dimensional conductive material, 4 mg / mL for the second two-dimensional conductive material, 10 mg / mL for the second water-soluble polymer, and a total concentration of 20 mg / mL; 8 mg / mL for the one-dimensional conductive material, 3 mg / mL for the second two-dimensional conductive material, 15 mg / mL for the second water-soluble polymer, and a total concentration of 26 mg / mL; or 10 mg / mL for the one-dimensional conductive material. The concentration of the second two-dimensional conductive material is 5 mg / mL, the concentration of the second water-soluble polymer is 15 mg / mL, and the total concentration is 30 mg / mL.

[0078] In one feasible embodiment, before step S40: filling the asymmetric aerogel with a polymer prepolymer and curing it to obtain the asymmetric electromagnetic shielding material, the method further includes: Step S50: Immerse the asymmetric aerogel in a mixture to obtain a hydrophobically modified asymmetric aerogel, wherein the mixture includes a liquid-phase modified silane and a first organic solvent compatible with the liquid-phase modified silane, and the first organic solvent is compatible with the polymer prepolymer. In one feasible embodiment, the hydrophobic modification treatment includes: soaking for 10-14 hours. The asymmetric aerogel is soaked in a mixed solution to obtain a hydrophobically modified asymmetric aerogel, wherein the mixed solution includes a liquid-phase modified silane and a first organic solvent compatible with the liquid-phase modified silane, and the first organic solvent is compatible with the polymer prepolymer.

[0079] 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.

[0080] In one feasible embodiment, the liquid-phase modified silane includes: methyltrichlorosilane, hexyltriethoxysilane, propyltriethoxysilane, and octyltriethoxysilane. Methyltrichlorosilane, as a liquid-phase modifier, can rapidly undergo a substitution reaction with the hydroxyl groups on the aerogel surface in organic solvents, exhibiting high grafting efficiency and short processing time. Simultaneously, its small molecular size allows it to penetrate deep into nanoscale pores, achieving deep modification. Hexyltriethoxysilane provides excellent hydrophobicity while significantly improving compatibility with organic polymers. Its hexyl carbon chain has a moderate length, forming an effective hydrophobic barrier without causing severe steric hindrance due to excessive chain length, thus ensuring good diffusion in solution and its ability to permeate pores. Propyltriethoxysilane has a small molecular size, mild reaction, and effectively maintains the porous structure of the material. Its short propyl chain occupies little space after grafting onto the aerogel surface, minimizing blockage or impact on the original nanoporous structure of the material. After the long-chain octyl groups of octyltriethoxysilane are assembled on the surface, they can form a tightly packed hydrophobic layer, which greatly reduces the surface energy of the material and increases the contact angle significantly, thereby obtaining the best anti-wetting, moisture-proof and even self-cleaning potential.

[0081] In one feasible embodiment, the concentration of the liquid-phase modified silane in the first organic solvent is 1~3 mg / mL. If the concentration is too low, the number of silane molecules is insufficient to completely cover the hydrophilic groups on the aerogel surface, resulting in poor hydrophobic effect; if the concentration is too high, excess silane molecules will form siloxane polymer precipitates in the pores after the reaction, blocking the unidirectional orientation pores of the aerogel and hindering the subsequent penetration of polymer prepolymers; within the concentration range of 1~3 mg / mL, silane molecules can fully react to form a complete hydrophobic film while ensuring the unobstructed pore structure, and at the same time avoiding the increase in material cost caused by excessive silane.

[0082] Step S60: The hydrophobically modified asymmetric aerogel is filled with a polymer prepolymer and cured to obtain an asymmetric electromagnetic shielding material.

[0083] In this embodiment, the hydrophobically modified asymmetric aerogel is filled with a polymer prepolymer and then cured to obtain an asymmetric electromagnetic shielding material.

[0084] 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 bonding between the impedance matching layer and the reflective layer, reducing interlayer gaps and laying the foundation for interfacial fusion during subsequent polymer prepolymer filling.

[0085] In one feasible embodiment, step S60: filling the hydrophobically modified asymmetric aerogel with a polymer prepolymer and performing a curing treatment to obtain the asymmetric electromagnetic shielding material, includes: Step S601: Place one end of the hydrophobically modified asymmetric aerogel in a filling liquid for filling treatment to obtain a filled asymmetric aerogel, wherein the pore direction of the asymmetric 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.

[0086] In one feasible embodiment, an asymmetric aerogel is suspended on a container filled with a filling liquid, one end of the asymmetric 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.

[0087] 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.

[0088] In one feasible embodiment, the polymer prepolymer includes: silicone rubber, polyurethane, epoxy resin, and polyacrylate. Silicone rubber, after curing, exhibits high elasticity, buffering the brittleness of the asymmetric aerogel, improving 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, possesses core advantages in its excellent toughness, high elasticity, and adjustable mechanical properties. By adjusting the composition ratio and crosslinking density of its isocyanate and polyol, 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 possesses good abrasion resistance, low-temperature resistance, and adhesion to various substrates, further enhancing the overall durability and interlayer bonding of composite materials. Epoxy resins offer significant advantages such as extremely high adhesive strength, excellent dimensional stability, and chemical 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 resins have low curing shrinkage, which helps maintain material dimensional accuracy and avoids interfacial delamination due to internal stress. Polyacrylates (and their polymers, acrylic resins) offer the main advantages of excellent optical transparency, good weather resistance, and diverse modification possibilities. This characteristic makes it 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, its 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 have good electrical insulation properties.

[0089] 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.

[0090] In one feasible embodiment, the first organic solvent comprises n-hexane. n-Hexane can stably dissolve the polymer prepolymer to form a uniform filling liquid without causing cross-linking or aggregation 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. In one feasible embodiment, the filling treatment time is 12h to 24h, for example, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, or 24h. 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.

[0091] Step S402: The filled asymmetric aerogel is cured to obtain an asymmetric electromagnetic shielding material.

[0092] In one feasible embodiment, the curing process includes heat treatment at 140~160℃ for 0.5~2 hours. If the temperature is below 140℃, 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 160℃, 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 elastic advantage. The temperature range of 140~160℃ can achieve complete crosslinking of the prepolymer within 2 hours, forming a stable polymer network. 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.

[0093] This application further proposes an asymmetric electromagnetic shielding material, including an impedance matching layer and a reflective layer. The impedance matching layer comprises an impedance matching layer aerogel framework composed of magnetic nanomaterials, a first two-dimensional conductive material, and a first water-soluble polymer, and a polymer matrix solidified in the framework voids. The reflective layer comprises a reflective layer aerogel framework composed of a one-dimensional conductive material, a second two-dimensional conductive material, and a second water-soluble polymer, and a polymer matrix solidified in the framework voids.

[0094] 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.

[0095] It should be noted that in the following embodiments and comparative examples, in the impedance layer matching dispersion, hollow iron oxide nanospheres (HFO) are used as magnetic nanomaterials, MXene is used as the first two-dimensional conductive material, sodium alginate (SA) is used as the first water-soluble polymer, and hexadecyltrimethylammonium bromide (CTAB) is used as a cationic modifier. In the reflective layer dispersion, carbon nanotubes (CNTs) are used as the one-dimensional conductive material, MXene is used as the second two-dimensional conductive material, and chitosan (CS) is used as the second water-soluble polymer.

[0096] Comparative Example 1 Step 1: First, weigh 50 mg HFO and 20 mg CTAB and disperse them evenly in 10 mL of deionized water by shaking on a shaker for 1 h. Then, wash with deionized water under magnetic force and collect to obtain surface-cationized HFO (HFO). Add all the prepared HFO to 150 mL of MXene dispersion with a concentration of 1 mg / mL, shake on a shaker for 12 h under an inert gas atmosphere, and finally wash with deionized water under magnetic force and make up to volume to obtain 15 mL of loaded material (HFO@MXene) dispersion with a concentration of 10 mg / mL.

[0097] Step 2: Add 15 mL of SA solution with a concentration of 10 mg / mL to the above 15 mL HFO@MXene dispersion, and shake on an argon atmosphere for 4 h to obtain 30 mL of HFO@MXene / SA impedance matching layer dispersion with a concentration ratio of 5 / 5 mg / mL. Step 3: Take 15 mL of the matching layer dispersion obtained in Step 2 and pour it into a self-made mold for unidirectional freezing; after complete freezing, obtain magnetic aerogel by sublimation drying.

[0098] Step 4: Soak the magnetic aerogel obtained in Step 3 in 50 mL of methyltrichlorosilane / n-hexane solution with a concentration of 2 mg / mL for 12 h, then press it into a 4 mm thick sheet, and finally soak the pressed sheet in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1 for 12 h for filling. Step 6: Remove the fully filled sample and place it in a 150℃ oven to cure for 1 hour to obtain a matching layer aerogel / silicone rubber composite material.

[0099] The composite material obtained in this comparative example contains only an impedance matching layer, and the average impedance of the resulting aerogel / silicone rubber composite with the matching layer is 1.3 × 10⁻⁶. -1 It has a certain impedance matching performance.

[0100] Comparative Example 2 Step 1: Add 300 mg CNT to 30 mL of CS solution with a concentration of 10 mg / mL, and disperse by ultrasonication for 30 min to prepare 30 mL of CNT / CS dispersion with a concentration ratio of 10 / 10 mg / mL. Then add 30 mL of MXene aqueous dispersion with a concentration of 10 mg / mL, and disperse by ultrasonication for 10 min to obtain 60 mL of MXene / CNT / CS reflective layer dispersion with a concentration ratio of 5 / 5 / 5. Step 2: Pour 15 mL of the reflective layer dispersion obtained in Step 1 into a self-made mold and freeze it unidirectionally; after complete freezing, a frozen sample of the reflective layer is obtained; finally, the reflective layer aerogel is obtained by sublimation drying. Step 3: Soak the reflective aerogel obtained in Step 2 in 50 mL of methyltrichlorosilane / n-hexane solution with a concentration of 2 mg / mL for 12 h, then press it into a 4 mm thick sheet, and finally soak the pressed sheet in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1 for 12 h for filling. Step 6: Remove the fully filled sample and place it in a 150℃ oven to cure for 1 hour to obtain the reflective layer aerogel / silicone rubber composite material.

[0101] The composite material obtained in this comparative example contains only a reflective performance layer, and the average impedance of the prepared reflective layer aerogel / silicone rubber composite is 6.02 × 10⁻⁶. -2 It is a material with significant impedance mismatch.

[0102] Example 1 Step 1: First, weigh 50 mg HFO and 20 mg CTAB and disperse them evenly in 10 mL of deionized water by shaking on a shaker for 1 h. Then, wash with deionized water under magnetic force and collect the surface-cationized HFO. Add all the prepared HFO to 150 mL of MXene dispersion with a concentration of 1 mg / mL, shake on a shaker for 12 h under an inert gas atmosphere, and finally wash with deionized water under magnetic force and make up to volume to obtain 15 mL of the loaded material (HFO@MXene) dispersion with a concentration of 10 mg / mL.

[0103] Step 2: Add 15 mL of SA solution with a concentration of 10 mg / mL to the above 15 mL HFO@ MXene dispersion, and shake on a shaker for 4 h in an argon atmosphere to obtain 30 mL of HFO@ MXene / SA impedance matching layer dispersion with a concentration ratio of 5 / 5 mg / mL.

[0104] Step 3: Add 300 mg CNT to 30 mL of CS solution with a concentration of 10 mg / mL, and disperse by ultrasonication for 30 min to prepare 30 mL of CNT / CS dispersion with a concentration ratio of 10 / 10 mg / mL. Then add 30 mL of MXene aqueous dispersion with a concentration of 10 mg / mL, and disperse by ultrasonication for 10 min to obtain 60 mL of MXene / CNT / CS reflective layer dispersion with a concentration ratio of 5 / 5 / 5 mg / mL. Step 4: Pour 5 mL of the reflective layer dispersion obtained in Step 3 into a self-made mold and freeze it unidirectionally. After freezing is complete, pour 10 mL of the impedance matching layer dispersion obtained in Step 2 on top of it. Obtain an asymmetric aerogel with a matching layer to reflective layer volume ratio of 2:1 by unidirectional freezing. Finally, obtain a bilayer asymmetric aerogel with a matching layer to reflective layer volume ratio of 2:1 by sublimation drying. Step 5: The bilayer asymmetric aerogel with a matching layer to reflective layer volume ratio of 2:1 obtained in Step 4 is immersed in 50 mL of methyltrichlorosilane / n-hexane solution with a concentration of 2 mg / mL for 12 h, then pressed into a 4 mm thick sheet, and finally immersed in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1 for 12 h for filling. Step 6: Remove the fully filled sample and place it in a 150℃ oven to cure for 1 h to obtain a double-layer asymmetric aerogel / silicone rubber composite material with a matching layer to reflective layer volume ratio of 2:1.

[0105] Figure 3 These are scanning electron microscope images of the asymmetric electromagnetic shielding material of Embodiment 1 of this application. (a) shows the impedance matching layer, and (b) shows the reflective layer. Figure 3As shown, the aerogel / silicone rubber forms a uniform cross-linked network.

[0106] The low-reflection double-layer electromagnetic shielding material prepared in this embodiment has a thickness of 4 mm, an impedance matching layer to reflective layer volume ratio of 2:1, and an average reflection efficiency (SE). R The average absorption efficiency (SE) is 4.8 dB. A With an average electromagnetic shielding effectiveness (SE) of 15.4 dB, the shielding effectiveness is... T It is 20.1 dB.

[0107] Example 2 Step 1: First, weigh 50 mg of HFO and 20 mg of CTAB and disperse them evenly in 10 mL of deionized water by shaking on a shaker for 1 h. Then, wash with deionized water under magnetic force and collect to obtain surface-cationized HFO (HFO). Add all the prepared HFO to 150 mL of MXene dispersion with a concentration of 1 mg / mL, shake on a shaker for 12 h under an inert gas atmosphere, and finally wash with deionized water under magnetic force and make up to volume to obtain 15 mL of loaded material (HFO@MXene) dispersion with a concentration of 10 mg / mL.

[0108] Step 2: Add 15 mL of SA solution with a concentration of 10 mg / mL to the above 15 mL HFO@ MXene dispersion, and shake on a shaker for 4 h in an argon atmosphere to obtain 30 mL of HFO@ MXene / SA impedance matching layer dispersion with a concentration ratio of 5 / 5 mg / mL.

[0109] Step 3: Add 300 mg CNT to 30 mL of CS solution with a concentration of 10 mg / mL, and disperse by ultrasonication for 30 min to prepare 30 mL of CNT / CS dispersion with a concentration ratio of 10 / 10 mg / mL. Then add 30 mL of MXene aqueous dispersion with a concentration of 10 mg / mL, and disperse by ultrasonication for 10 min to obtain 60 mL of MXene / CNT / CS reflective layer dispersion with a concentration ratio of 5 / 5 / 5 mg / mL. Step 4: Pour 7.5 mL of the reflective layer dispersion obtained in Step 3 into a self-made mold and perform unidirectional freezing; after complete freezing, pour 7.5 mL of the impedance matching layer dispersion obtained in Step 2 on top of it, and obtain an asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:1 by unidirectional freezing; finally, obtain a bilayer asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:1 by sublimation drying. Step 5: The bilayer asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:1 obtained in Step 4 is immersed in 50 mL of methyltrichlorosilane / n-hexane solution with a concentration of 2 mg / mL for 12 h, then pressed into a 4 mm thick sheet, and finally immersed in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1 for 12 h for filling. Step 6: Remove the fully filled sample and place it in a 150℃ oven to cure for 1 h to obtain a double-layer asymmetric aerogel / silicone rubber composite material with a matching layer to reflective layer volume ratio of 1:1.

[0110] The low-reflection double-layer electromagnetic shielding material prepared in this embodiment has a thickness of 4 mm, an impedance matching layer to reflective layer volume ratio of 1:1, and an average reflection efficiency (SE). R With an average absorption efficiency of 8.9 dB and SE A The average electromagnetic shielding effectiveness (SE) is 23.4 dB. T It is 32.3 dB.

[0111] Example 3 Step 1: First, weigh 50 mg of HFO and 20 mg of CTAB and disperse them evenly in 10 mL of deionized water by shaking on a shaker for 1 h. Then, wash with deionized water under magnetic force and collect to obtain surface-cationized HFO (HFO). Add all the prepared HFO to 150 mL of MXene dispersion with a concentration of 1 mg / mL, shake on a shaker for 12 h under an inert gas atmosphere, and finally wash with deionized water under magnetic force and make up to volume to obtain 15 mL of loaded material (HFO@MXene) dispersion with a concentration of 10 mg / mL.

[0112] Step 2: Add 15 mL of SA solution with a concentration of 10 mg / mL to the above 15 mL HFO@ MXene dispersion, and shake on an argon atmosphere for 4 h to obtain 30 mL of HFO@ MXene / SA impedance matching layer dispersion with a concentration ratio of 5 / 5 mg / mL.

[0113] Step 3: Add 300 mg CNT to 30 mL of CS solution with a concentration of 10 mg / mL, and disperse by ultrasonication for 30 min to prepare 30 mL of CNT / CS dispersion with a concentration ratio of 10 / 10 mg / mL. Then add 30 mL of MXene aqueous dispersion with a concentration of 10 mg / mL, and disperse by ultrasonication for 10 min to obtain 60 mL of MXene / CNT / CS reflective layer dispersion with a concentration ratio of 5 / 5 / 5. Step 4: Pour 10 mL of the reflective layer dispersion obtained in Step 3 into a self-made mold and freeze it unidirectionally. After freezing is complete, pour 5 mL of the impedance matching layer dispersion obtained in Step 2 on top of it. Obtain an asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:2 by unidirectional freezing. Finally, obtain a bilayer asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:2 by sublimation drying. Step 5: The bilayer asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:2 obtained in Step 4 is immersed in 50 mL of methyltrichlorosilane / n-hexane solution with a concentration of 2 mg / mL for 12 h, then pressed into a 4 mm thick sheet, and finally immersed in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1 for 12 h for filling. Step 6: Remove the fully filled sample and place it in a 150℃ oven to cure for 1 h to obtain a double-layer asymmetric aerogel / silicone rubber composite material with a matching layer to reflective layer volume ratio of 1:2.

[0114] The low-reflection double-layer electromagnetic shielding material prepared in this embodiment has a thickness of 4 mm, an impedance matching layer to reflective layer volume ratio of 1:2, and an average reflection efficiency SE. R With an average absorption efficiency of 9.4 dB, SE A The average electromagnetic shielding effectiveness (SE) is 29.7 dB. T It is 39.2 dB.

[0115] Example 4 Step 1: First, weigh 50 mg of HFO and 20 mg of CTAB and disperse them evenly in 10 mL of deionized water by shaking on a shaker for 1 h. Then, wash with deionized water under magnetic force and collect to obtain surface-cationized HFO (HFO). Add all the prepared HFO to 150 mL of MXene dispersion with a concentration of 1 mg / mL, shake on a shaker for 12 h under an inert gas atmosphere, and finally wash with deionized water under magnetic force and make up to volume to obtain 15 mL of loaded material (HFO@MXene) dispersion with a concentration of 10 mg / mL.

[0116] Step 2: Add 15 mL of SA solution with a concentration of 10 mg / mL to the above 15 mL HFO@ MXene dispersion, and shake on a shaker for 4 h in an argon atmosphere to obtain 30 mL of HFO@ MXene / SA impedance matching layer dispersion with a concentration ratio of 5 / 5 mg / mL.

[0117] Step 3: Add 300 mg CNT to 30 mL of CS solution with a concentration of 10 mg / mL, and disperse by ultrasonication for 30 min to prepare 30 mL of CNT / CS dispersion with a concentration ratio of 10 / 10 mg / mL. Then add 30 mL of MXene aqueous dispersion with a concentration of 10 mg / mL, and disperse by ultrasonication for 10 min to obtain 60 mL of MXene / CNT / CS reflective layer dispersion with a concentration ratio of 5 / 5 / 5. Step 4: Pour 10 mL of the reflective layer dispersion obtained in Step 3 into a self-made mold and freeze it unidirectionally. After freezing is complete, pour 5 mL of the impedance matching layer dispersion obtained in Step 2 on top of it. Obtain an asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:2 by unidirectional freezing. Finally, obtain a bilayer asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:2 by sublimation drying. Step 5: The bilayer asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:2 obtained in Step 4 is immersed in 50 mL of methyltrichlorosilane / n-hexane solution with a concentration of 2 mg / mL for 12 h, then pressed into a 2 mm thick sheet, and finally immersed in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1 for 12 h for filling. Step 6: Remove the fully filled sample and place it in a 150℃ oven to cure for 1 h to obtain a double-layer asymmetric aerogel / silicone rubber composite material with a matching layer to reflective layer volume ratio of 1:2.

[0118] The low-reflection double-layer electromagnetic shielding material prepared in this embodiment has a thickness of 2 mm, a matching layer to reflective layer volume ratio of 1:2, and an average reflection efficiency (SE). R With an average absorption efficiency of 7.0 dB, SE A The average electromagnetic shielding effectiveness (SE) is 23.4 dB. T It is 30.4dB.

[0119] Example 5 Step 1: First, weigh 50 mg HFO and 20 mg CTAB and disperse them evenly in 10 mL of deionized water by shaking on a shaker for 1 h. Then, wash with deionized water under magnetic force and collect to obtain surface-cationized HFO (HFO). Add all the prepared HFO to 150 mL of MXene dispersion with a concentration of 1 mg / mL, shake on a shaker for 12 h under an inert gas atmosphere, and finally wash with deionized water under magnetic force and make up to volume to obtain 15 mL of loaded material (HFO@MXene) dispersion with a concentration of 10 mg / mL.

[0120] Step 2: Add 15 mL of SA solution with a concentration of 10 mg / mL to the above 15 mL HFO@ MXene dispersion, and shake on a shaker for 4 h in an argon atmosphere to obtain 30 mL of HFO@ MXene / SA impedance matching layer dispersion with a concentration ratio of 5 / 5 mg / mL.

[0121] Step 3: Add 300 mg CNT to 30 mL of CS solution with a concentration of 10 mg / mL, and disperse by ultrasonication for 30 min to prepare 30 mL of CNT / CS dispersion with a concentration ratio of 10 / 10 mg / mL. Then add 30 mL of MXene aqueous dispersion with a concentration of 10 mg / mL, and disperse by ultrasonication for 10 min to obtain 60 mL of MXene / CNT / CS reflective layer dispersion with a concentration ratio of 5 / 5 / 5. Step 4: Pour 10 mL of the reflective layer dispersion obtained in Step 3 into a self-made mold and freeze it unidirectionally. After freezing is complete, pour 5 mL of the impedance matching layer dispersion obtained in Step 2 on top of it. Obtain an asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:2 by unidirectional freezing. Finally, obtain a bilayer asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:2 by sublimation drying. Step 5: The bilayer asymmetric aerogel with a matching layer to reflective layer volume ratio of 1:2 obtained in Step 4 is immersed in 50 mL of methyltrichlorosilane / n-hexane solution with a concentration of 2 mg / mL for 12 h, then pressed into a sheet with a thickness of 8 mm, and finally immersed in a silicone rubber / n-hexane filling solution with a mass ratio of 1:1 for 24 h for filling. Step 6: Remove the fully filled sample and place it in a 150℃ oven to cure for 1 h to obtain a double-layer asymmetric aerogel / silicone rubber composite material with a matching layer to reflective layer volume ratio of 1:2.

[0122] The low-reflection double-layer electromagnetic shielding material prepared in this embodiment has a thickness of 8 mm, a matching layer to reflective 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 41.2 dB. T It is 48.0 dB.

[0123] The electromagnetic shielding performance of the electromagnetic shielding materials of Comparative Examples 1 to 2 and Examples 1 to 5 was tested in the X-band. Figure 5 The electromagnetic shielding materials of Comparative Example 1 (impedance matching layer) and Comparative Example 2 (reflective layer) of this application demonstrate the reflection effectiveness (SE) in the X-band. R Absorption efficiency SE A and shielding effectiveness SE T curve, Figure 6 The reflection efficiency (SE) of the asymmetric electromagnetic shielding materials in embodiments 1-3 of this application in the X-band. R Absorption efficiency SE A and shielding effectiveness SE T curve, Figure 7 The reflection efficiency (SE) of the asymmetric electromagnetic shielding materials in embodiments 3-5 of this application in the X-band. R Absorption efficiency SE A and shielding effectiveness SE T Curves. The average reflection effectiveness, average absorption effectiveness, and average electromagnetic shielding effectiveness of each embodiment are used as experimental results, as shown in Table 1 below: Table 1

[0124] First, such as Figure 3 The asymmetric aerogel interface shown is seamless, and the two aerogel layers exhibit excellent bonding, indicating that asymmetric aerogels with superior interfacial bonding can be obtained through a secondary lateral freezing method. Further surface modification and polymer filling of the asymmetric aerogel can yield asymmetric electromagnetic shielding materials. Figure 4 As can be seen, the polymer in the asymmetric 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 yield asymmetric electromagnetic shielding materials with intact structures, no defects, and suitable for large-scale production.

[0125] Secondly, Comparative Example 2 is a reflective layer in an asymmetric electromagnetic shielding material. This layer has high electromagnetic shielding performance, with an average SE... T It is 39.8 dB. However, the average reflectance efficiency (SE) of this layer is... R Up to 10.6 dB. In contrast, Comparative Example 1 is an impedance matching layer in an asymmetric electromagnetic shielding material. Through the synergistic effect of magnetic iron oxide hollow microspheres and MXene, this layer exhibits excellent impedance matching capabilities, reducing the material's reflection efficiency (SE). R The average reflection efficiency of this layer is only 0.4 dB, exhibiting limited low reflection characteristics. However, its lack of conductivity results in weak electromagnetic shielding capability, with an average SE (Sequence Response) of only 0.4 dB. T The difference is only 0.9 dB. In summary, no single-layer material, whether a reflective layer or an impedance matching layer, can achieve both low reflection efficiency and high electromagnetic shielding performance. The advantage of asymmetric 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 5, when the volume ratio of the impedance matching layer to the reflective layer is 1:2 and the material thickness is 8 mm, its SE in the X-band... TUp to 48.0 dB, while SE R Only 6.8dB. Compared to Comparative Example 2, SE T Higher, and SE R Lower.

[0126] Examples 1 to 3 clearly demonstrate the regulation of performance by the internal volume ratio of the double-layer structure: as the proportion of the reflective layer increases (volume ratio from 2:1 → 1:1 → 1:2), the average total shielding effectiveness SE... T (20.1 dB → 32.3 dB → 39.2 dB) and average absorption efficiency SE A The reflectivity (SE) shows a significant and monotonic upward trend (15.4 dB → 23.4 dB → 29.7 dB), as the thicker reflective layer provides a more complete highly conductive network, greatly enhancing the material's ability to withstand multiple internal reflections and absorption losses of incident electromagnetic waves. It is worth noting that the average reflection efficiency (SE)... R Although it also increased (4.8 dB → 8.9 dB → 9.4 dB), its increase was much smaller than that of SE. A Furthermore, the absolute value remains at a low level, proving that the asymmetric structure achieves an absorption-based mechanism and realizes green shielding.

[0127] Secondly, material thickness is another key factor determining shielding effectiveness. Comparing Examples 3, 4, and 5 (all with a volume ratio of 1:2), it can be seen that as the total thickness increases from 2mm to 8mm, the average absorption effectiveness (SE) decreases. A (23.4 dB → 29.7 dB → 41.2 dB) and average total shielding effectiveness SE T The reflectivity (SE) was significantly improved (from 30.4 dB to 39.2 dB to 48.0 dB). The thicker material provides a longer attenuation path for electromagnetic waves, allowing for more complete absorption and dissipation. As the thickness increases, the material's reflectivity (SE) also increases. R The shielding performance did not increase significantly (7.0 dB → 9.4 dB → 6.8 dB), and even decreased at 8 mm. This fully demonstrates the characteristics of this absorption-dominant shielding material: the improvement in shielding effectiveness does not depend on increasing harmful reflections, but is achieved by enhancing internal losses. This makes the material have great application potential in applications requiring high-performance shielding.

[0128] 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 an asymmetric electromagnetic shielding material for the X-band, characterized in that, The method includes the following steps: Provides impedance matching layer dispersion and reflective layer dispersion; The reflective layer dispersion was laterally frozen to obtain a frozen reflective layer sample; The impedance matching layer dispersion is poured onto the frozen sample of the reflective layer and then laterally frozen again to obtain an asymmetric frozen sample. The asymmetric frozen sample is then sublimated and dried to obtain an asymmetric aerogel. The asymmetric aerogel includes the reflective layer aerogel and an impedance matching layer aerogel stacked with the reflective layer aerogel. The pore orientation of the impedance matching layer aerogel is consistent with that of the reflective layer aerogel. After the asymmetric aerogel is modified with a hydrophobic surface in the liquid phase, it is filled with a polymer prepolymer and then cured to obtain an asymmetric electromagnetic shielding material.

2. The method as described in claim 1, characterized in that, The step of providing the impedance matching layer dispersion and the reflective layer dispersion includes: Magnetic nanomaterials were subjected to cationic surface modification treatment to obtain modified magnetic nanomaterials. The modified magnetic nanomaterial, the dispersion of the first two-dimensional conductive material, and the first water-soluble polymer solution are mixed to obtain an impedance matching layer dispersion. A dispersion of a one-dimensional conductive material, a second water-soluble polymer solution, and a second two-dimensional conductive material is mixed to obtain a reflective layer dispersion.

3. The method as described in claim 2, characterized in that, In the cationic surface modification treatment, the mass ratio of the magnetic nanomaterial to the cationic modifier is 1:1 to 4:

1. And / or, the concentration of the one-dimensional conductive material is 2~10 mg / mL, the concentration of the second two-dimensional conductive material is 2~5 mg / mL, the concentration of the second water-soluble polymer is 5~20 mg / mL, and the total concentration of the one-dimensional conductive material, the second two-dimensional conductive material and the second water-soluble polymer is between 10~30 mg / mL.

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

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

1.

6. The method as described in claim 1, characterized in that, The step of modifying the asymmetric aerogel with a hydrophobic surface in the liquid phase, filling it with a polymer prepolymer, and then curing it to obtain an asymmetric electromagnetic shielding material includes: The asymmetric aerogel is immersed in a mixture to obtain a hydrophobically modified asymmetric aerogel, wherein the mixture includes a liquid-phase modified silane and a first organic solvent compatible with the liquid-phase modified silane, and the first organic solvent is compatible with the polymer prepolymer. The hydrophobically modified asymmetric aerogel is filled with a polymer prepolymer and then cured to obtain an asymmetric electromagnetic shielding material.

7. The method as described in claim 6, characterized in that, The hydrophobic modification treatment includes: soaking for 10-14 hours; And / or, the liquid-phase modified silane includes: methyltrichlorosilane, hexyltriethoxysilane, propyltriethoxysilane, octyltriethoxysilane; And / or, the first organic solvent includes: n-hexane, tetrahydrofuran; And / or, the concentration of the liquid-phase modified silane in the first organic solvent is 1~3 mg / mL.

8. The method as described in claim 6, characterized in that, The step of filling the hydrophobically modified asymmetric aerogel with a polymer prepolymer and then curing it to obtain an asymmetric electromagnetic shielding material includes: One end of the hydrophobically modified asymmetric aerogel is placed in a filling liquid for filling treatment to obtain a filled asymmetric aerogel, wherein the pore direction of the asymmetric 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. The filled asymmetric aerogel is cured to obtain an asymmetric electromagnetic shielding material.

9. The method as described in claim 8, characterized in that, In the filling liquid, the mass ratio of the polymer prepolymer to the second organic solvent is 1:2 to 2:1; And / or, the polymer prepolymer includes: silicone rubber, polyurethane, epoxy resin, polyacrylate; And / or, the first organic solvent includes: n-hexane, tetrahydrofuran; And / or, the filling process takes 12h to 24h; And / or, the curing process includes: heat treatment at 140~160℃ for 0.5~2h.

10. An asymmetric electromagnetic shielding material, characterized in that, The asymmetric electromagnetic shielding material is prepared by the method described in any one of claims 1 to 9.

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