Lightweight rebounding wave-absorbing aerogel and preparation method thereof

Abstract

The invention relates to a lightweight rebounding wave-absorbing aerogel and a preparation method thereof, the aerogel is prepared from the following raw materials: graphene oxide, metal compound particles and water-based resin, the metal compound particles are loaded on the graphene oxide, and the water-based resin is loaded on the metal compound particles. Pores of the porous aerogel formed by the graphene oxide and the metal compound particles are filled with the water-based resin; the scheme of the invention has the advantages of high efficiency, light weight, wide frequency band and rebound resilience.

Description

Technical Field

[0001] This application relates to the technical field of microwave absorbing materials, and in particular to a lightweight, resilient microwave absorbing aerogel and its preparation method. Background Technology

[0002] With the rapid development of modern communication technology, the widespread application of electromagnetic waves has led to increasingly severe electromagnetic pollution, especially in high-frequency bands (such as microwave and millimeter-wave bands). The impact of electromagnetic interference on the environment and equipment is becoming increasingly significant. Therefore, the demand for electromagnetic wave absorbing materials, also known as microwave absorbing materials, is growing rapidly. Microwave absorbing materials are commonly used in fields such as communications, radar, aerospace, and military protection. In these applications, the lightweight, wide bandwidth, high absorption, and resilience of microwave absorbing materials are crucial.

[0003] Traditional absorbing materials, such as iron-based alloys, carbon-based materials, and conductive polymers, while exhibiting good absorption effects in certain specific frequency bands, typically suffer from the following problems: They are relatively heavy, as some traditional absorbing materials have high density due to their solid nature, making them unsuitable for applications requiring lightweight materials; they have narrow bandwidth, as most materials only exhibit good absorption performance within a narrow frequency band, failing to meet broadband requirements; and they have poor resilience, as some absorbing materials have poor mechanical properties, making them prone to deformation or loss of absorption capacity under external forces, affecting their long-term use. Summary of the Invention

[0004] This application addresses the aforementioned shortcomings of the prior art by providing a lightweight, high-efficiency, wide-bandwidth, and resilient lightweight elastic aerogel for absorbing microwaves.

[0005] To solve the above-mentioned technical problems, the technical solution adopted in this application is: a lightweight, resilient, microwave-absorbing aerogel, wherein the raw materials for preparing the aerogel include graphene oxide, metal compound particles, and aqueous resin, wherein the metal compound particles are loaded on the graphene oxide, and the aqueous resin fills the pores of the porous aerogel formed by the graphene oxide and the metal compound particles.

[0006] Furthermore, the aerogel is a stepped structure composed of multiple layers of materials, and the aerogel layers in the multi-layered stepped aerogel have different densities.

[0007] Furthermore, the density of the aerogel layers in the multi-layered stepped aerogel increases or decreases sequentially along the thickness direction (depending on the final placement of the aerogel, the density of the aerogel in each stacked layer is inconsistent along the thickness direction, and the inconsistent density is either increasing or decreasing sequentially along the thickness direction).

[0008] Furthermore, the mass ratio of the metal compound particles to the graphene oxide is 0.01 to 1:1.

[0009] Furthermore, the average density of the lightweight, resilient microwave-absorbing aerogel is 75-125 mg / cm³. 3 The dielectric tangent is 0.4-0.6. The dielectric tangent (tanδ) is expressed as ε” / ε. The larger the tanδ, the higher the dielectric loss of the material. Electromagnetic waves are more easily converted into heat energy rather than reflected or transmitted after entering the material. Carbon-based materials have lightweight broadband absorption in the frequency range of 1-18GHz and dielectric tangent of 0.3-1.0.

[0010] Furthermore, the metal compound particles are selected from at least one of Fe, Co, and Ni compounds.

[0011] Furthermore, the waterborne resin is selected from at least one of waterborne polyurethane resin (WPU), pure acrylic resin, styrene-acrylic resin, bisphenol A type epoxy resin, brominated epoxy resin, hydroxyl-terminated polyester, carboxyl-terminated polyester, and polyethylene resin.

[0012] This application also provides a method for preparing the above-described lightweight, resilient microwave-absorbing aerogel, comprising the following steps:

[0013] (1) The metal compound particles and the graphene oxide dispersion were mixed evenly by physical stirring to obtain the Me@GO dispersion;

[0014] (2) Prepare Me@GO dispersions with different water contents using the Me@GO dispersion obtained in step (1);

[0015] (3) Add aqueous resin to each of the various Me@GO dispersions with different water contents obtained in step (2) and stir evenly. Then take at least one of the above-mentioned evenly stirred Me@GO dispersions, freeze and dry them to obtain Me@GO-aqueous resin aerogel.

[0016] Furthermore, the specific operation process of step (1) is as follows: add metal compound particles to the prepared graphene oxide dispersion, the mass ratio of metal compound particles to graphene oxide powder is 0.01 to 1:1, and then stir at a speed of 1500 rpm to 2000 rpm for 2 to 3 hours to obtain a uniformly dispersed Me@GO dispersion.

[0017] Furthermore, the various Me@GO dispersions with different water contents mentioned in step (2) are Me@GO dispersion a, Me@GO dispersion b, and Me@GO dispersion c.

[0018] Furthermore, the specific operation process of step (3) is as follows: Me@GO dispersion a is added to aqueous resin and stirred evenly, and then frozen to obtain intermediate 1; Me@GO dispersion b is added to aqueous resin and stirred evenly, and then added to intermediate 1, and frozen to obtain intermediate 2; Me@GO dispersion c is added to aqueous resin and stirred evenly, and then added to intermediate 2, and frozen to obtain intermediate 3; intermediate 3 is dried to obtain gradient Me@GO-aqueous resin aerogel.

[0019] Furthermore, the water content of Me@GO dispersion a is 10-20%; the water content of Me@GO dispersion b is 20-30%; and the water content of Me@GO dispersion c is 30-40%.

[0020] Furthermore, the freezing process in step (3) involves introducing the Me@GO dispersion with added water-based resin into a mold and then freezing it in liquid nitrogen for 0.5-1.5 hours to form the product.

[0021] Furthermore, after being frozen and molded in liquid nitrogen, the product is then frozen and demolded, and then dried for 48-72 hours to obtain an aerogel.

[0022] Furthermore, the method for drying the product shall be at least one of atmospheric pressure drying, supercritical drying, or freeze drying.

[0023] Furthermore, the mass ratio of the aqueous resin to the corresponding Me@GO dispersion is (1-2):20.

[0024] Furthermore, the metal compound particles are selected from at least one of Fe, Co, and Ni compounds.

[0025] Furthermore, the waterborne resin is selected from at least one of waterborne polyurethane resin (WPU), pure acrylic resin, styrene-acrylic resin, bisphenol A type epoxy resin, brominated epoxy resin, hydroxyl-terminated polyester, carboxyl-terminated polyester, and polyethylene resin.

[0026] The advantages and beneficial effects of this application are as follows:

[0027] 1. The magnetic and electrical advantages of graphene oxide loaded with metal compound particles (Me@GO) in this application: The combination of metal compound particles and graphene oxide in Me@GO can significantly enhance the magnetic and electrical properties of the material, thereby improving the electromagnetic wave absorption efficiency of the absorbing material, especially exhibiting excellent broadband absorption performance in the high-frequency band. This is because graphene oxide has a huge specific surface area, and its surface is rich in oxygen-containing functional groups (such as hydroxyl, carboxyl, and epoxy groups) and structural defects, which will generate interfacial polarization and dipole polarization (dielectric loss mechanism); the metal compound particles have high saturation magnetization and magnetocrystalline anisotropy, especially cobalt metal compound particles. The introduction of cobalt metal compound particles significantly improves the permeability of the composite material and provides magnetic loss. Combined with graphene oxide, it can increase dielectric loss. By rationally designing the ratio, distribution, and structure of the two components, the impedance of the Me@GO composite material can be made as close as possible to the impedance of free space, thereby maximizing the chance of electromagnetic waves being incident and entering the interior of the material.

[0028] 2. The resilient lightweight aerogel prepared in this application has a porous structure: As a material with high porosity and extremely low density, aerogel can effectively reduce material weight and provide a large surface area, enhancing the interaction between electromagnetic waves and the material and improving the wave absorption efficiency of the aerogel; at the same time, the porous structure of the aerogel also improves the resilience of the material, while pure aerogel only has a certain strength but no resilience. In this application, the addition of aqueous resin fills the porous structure with resin, thereby endowing the material with a certain degree of resilience and giving it better stability.

[0029] 3. The resilient lightweight aerogel prepared in this application can realize the multi-gradient structure design of impedance gradient layer: by designing different density gradients and porosity gradients in the structure of the aerogel, the aerogel can achieve the best wave absorption effect in different frequency ranges; the gradient structure not only improves the electromagnetic wave absorption capacity of the aerogel, but also improves its mechanical properties, making the aerogel have better resilience.

[0030] 4. The resilient lightweight aerogel prepared in this application can achieve self-rebound. After the material undergoes compression deformation, it can recover its shape and maintain stable elasticity after 10 cycles of compression, overcoming the defects of irreversible deformation and easy pulverization of traditional aerogels.

[0031] 5. This application uses Me@GO dispersions with water contents of 10-20%, 20-30%, and 30-40% to prepare a three-layer gradient resilient lightweight aerogel, significantly improving the microwave absorption performance of the aerogel. Furthermore, Me@GO dispersions with progressively increasing or decreasing water contents are stacked layer by layer along the thickness direction, cooled, and dried to prepare a three-layer gradient resilient lightweight aerogel with a mass fraction that increases or decreases along the thickness direction of the aerogel. The three-layer structure is designed to minimize the interaction between electromagnetic waves and the material. The lowest mass fraction on one side of the thickness direction is to make the impedance of the aerogel as close as possible to the impedance of air, allowing electromagnetic waves to penetrate as much as possible into the aerogel. The middle layer has a medium mass fraction to minimize the loss of electromagnetic waves within the aerogel. The highest mass fraction on the other side of the thickness direction is to reduce the transmission or reflection of electromagnetic waves from the aerogel. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope image of the multigradient Co@GO-WPU aerogel prepared in Example 4 of this application.

[0033] Figure 2 This is a reflection loss diagram of the Co@GO-WPU aerogel prepared in Example 3 of this application.

[0034] Figure 3 This is a reflection loss diagram of the multi-gradient Co@GO-WPU aerogel prepared in Example 4 of this application.

[0035] Figure 4 This is a reflection loss diagram of the Co@GO-PP aerogel prepared by Comparative Example 1 of this application. Detailed Implementation

[0036] The present application will be described in further detail below with reference to specific embodiments, but the implementation of the present application includes, but is not limited to, the scope represented by the following embodiments.

[0037] Example 1:

[0038] (1) Take 50 mL of graphene oxide dispersion with a mass fraction of 2%, then add 0.05 g of Fe3O4 particles, and stir for 1 h using a high-speed disperser at 1500 rpm to prepare Fe@GO dispersion.

[0039] (2) Add water to the obtained Fe@GO dispersion to prepare a Fe@GO dispersion with a water content of 20%.

[0040] (3) Take 20g of Fe@GO dispersion with a water content of 20% obtained in step (2), add 1g of WPU (waterborne polyurethane with a solid content of 32%, purchased from Yoshida New Materials, and the following examples are all waterborne polyurethane with a solid content of 32%), stir evenly to prepare Fe@GO-WPU suspension, then pour Fe@GO-WPU suspension into polytetrafluoroethylene mold, freeze in liquid nitrogen for 1h to form, demold and dry for 48h to obtain Fe@GO-WPU aerogel.

[0041] Example 2:

[0042] (1) Take 50 mL of graphene oxide dispersion with a mass fraction of 2%, then add 0.05 g of Ni3O4 particles, and stir at 1500 rpm for 1 h using a high-speed disperser to prepare Ni@GO dispersion.

[0043] (2) Add water to the obtained Ni@GO dispersion to prepare a Ni@GO dispersion with a water content of 20%.

[0044] (3) Take 20g of Ni@GO dispersion with a water content of 20% obtained in step (2), add 1g of WPU to it, stir evenly to prepare Ni@GO-WPU suspension, then pour the Ni@GO-WPU suspension into a polytetrafluoroethylene mold, freeze it in liquid nitrogen for 1h to form, demold and dry for 72h to obtain Ni@GO-WPU aerogel.

[0045] Example 3:

[0046] (1) Take 50 mL of graphene oxide dispersion with a mass fraction of 2%, then add 0.05 g of Co3O4 particles, and stir for 1 h using a high-speed disperser at 1500 rpm to prepare Co@GO dispersion.

[0047] (2) Add water to the obtained Co@GO dispersion to prepare a Co@GO dispersion with a water content of 20%.

[0048] (3) Take 20g of the Co@GO dispersion with a water content of 20% obtained in step (2), add 1g of WPU to it, stir evenly to prepare Co@GO-WPU suspension, then pour the Co@GO-WPU suspension into a polytetrafluoroethylene mold, freeze it in liquid nitrogen for 1h to form, demold and dry for 72h to obtain Co@GO-WPU aerogel.

[0049] Example 4:

[0050] (1) Take 50 mL of graphene oxide dispersion with a mass fraction of 2%, then add 0.05 g of Co3O4 particles, and stir for 1 h using a high-speed disperser at 1500 rpm to prepare Co@GO dispersion.

[0051] (2) Add water to the Co@GO dispersion obtained in step (1) to prepare Co@GO dispersion with a water content of 20%, Co@GO dispersion with a water content of 30%, and Co@GO dispersion with a water content of 40%.

[0052] (3) Take 20g of the Co@GO dispersion with a water content of 20% obtained in step (2), add 1g of WPU to it, stir evenly to prepare Co@GO-WPU suspension 1, then pour Co@GO-WPU suspension 1 into a polytetrafluoroethylene mold, freeze it in liquid nitrogen for 1h to form intermediate 1, i.e., single-layer Co@GO-WPU frozen block; Take 20g of the Co@GO dispersion with a water content of 30% obtained in step (2), add 1g of WPU to it WPU was stirred evenly to prepare Co@GO-WPU suspension 2. Co@GO-WPU suspension 2 was added to a polytetrafluoroethylene mold with a single layer of Co@GO-WPU frozen block and frozen in liquid nitrogen for 1 hour to form intermediate 2, i.e., double layer Co@GO-WPU frozen block. 20g of Co@GO dispersion with a water content of 40% obtained in step (2) was added to 1g of WPU and stirred evenly to prepare Co@GO-WPU suspension 3. Co@GO-WPU suspension 3 was added to a polytetrafluoroethylene mold with a double layer of Co@GO-WPU frozen block and frozen in liquid nitrogen for 1 hour to form intermediate 3, i.e. triple layer Co@GO-WPU. Finally, the triple layer Co@GO-WPU frozen block was demolded and dried for 72 hours to obtain multi-gradient Co@GO-WPU aerogel.

[0053] Comparative Example 1:

[0054] (1) Take 50 mL of graphene oxide dispersion with a mass fraction of 2%, then add 0.05 g of Co3O4 particles, and stir at 1500 rpm for 60 min using a high-speed disperser to prepare Co@GO dispersion.

[0055] (2) Add water to the obtained Co@GO dispersion to prepare a Co@GO dispersion with a water content of 20%.

[0056] (3) Take 20g of the Co@GO dispersion with a water content of 20% obtained in step (2), add 1g of polypropylene resin (PP) to it, stir evenly to prepare Co@GO-PP suspension, then pour the Co@GO-PP suspension into a polytetrafluoroethylene mold, freeze it in liquid nitrogen for 1h to form it, demold and dry for 72h to obtain Co@GO-PP aerogel.

[0057] Performance testing

[0058] 1. Aerogel resilience test:

[0059] The aerogels prepared in Examples 1-4 and Comparative Example 1 were placed on a 100g copper block for 30s, then removed, and the aerogel recovery phenomenon was observed. This was repeated 10 times.

[0060] 2. Electromagnetic parameter testing of aerogels:

[0061] The electromagnetic parameters of the aerogels prepared in Examples 3, 4, and Comparative Example 1 were tested using the waveguide method, specifically as follows: Figures 2-4 .

[0062] 3. Aerogel Reflection Loss Test

[0063] The reflection loss capability of the aerogels prepared in Examples 1-4 and Comparative Example 1 was assessed. The reflection loss was calculated using electromagnetic parameters. Z in Z0 is the input impedance of the material, measured in Ω, and is related to the material's dielectric constant, permeability, thickness, and the wavelength of the electromagnetic wave in free space; Z0 is the impedance in free space (approximately 377Ω).

[0064] 4. Aerogel density test

[0065] Density is calculated by weighing the mass before and after drying (i.e., before and after drying; after drying, the aerogel is a square block, and the weight and dimensions are measured, and the density is calculated according to the formula) and the volume of the block after drying, according to the formula ρ = m / V.

[0066] 5. Aerogel effective absorption bandwidth test

[0067] Effective absorption bandwidth refers to the frequency band where the reflection loss RL < 10dB.

[0068] 6. Aerogel dielectric tangent test

[0069] The tangent value is calculated based on the real and imaginary parts of the dielectric constant obtained from the electromagnetic parameters. The dielectric tangent value (tanδ) is expressed as ε” / ε.

[0070] Figure 1 The scan images show the multi-gradient Co@GO-WPU aerogel and porous layered Co@GO-WPU aerogel prepared in Example 4. It can be seen that there are a large number of gaps between the layers. These gaps can increase the reflection path of electromagnetic waves. At the same time, when external stress is applied, the stress is stored between the aerogel layers. When the external force is unloaded, the aerogel can quickly return to its initial state, thereby improving the overall resilience of the aerogel.

[0071] The electromagnetic parameters of the multi-gradient Co@GO-WPU absorbing aerogel prepared in Example 4 were tested using the waveguide method, and its corresponding reflection loss was calculated. The results are shown in the appendix. Figure 3 middle; Figure 3 The diagram shows the reflection loss corresponding to the reflection loss capability of the Co@GO-WPU absorbing aerogel prepared in Example 4.

[0072] Table 1. Performance test results of Me@GO-WPU aerogel in Examples 1-4

[0073]

[0074]

[0075] As can be seen from the above embodiments, the addition of aqueous resin can effectively improve the resilience of aerogel (especially WPU, which acts as a binder to combine aerogels into a whole, giving the aerogel a certain degree of resilience). The aerogel obtained by this application has an average density of 75 mg / cm³. 3 Its lightweight properties are evident; even with the addition of water-based resins, the density of the aerogel obtained can still be less than 100 mg / cm³. 3 The broadband nature of the aerogel obtained in this application is reflected in the following: in the X-band (4.2 GHz), the effective absorption bandwidth of the aerogel in this application can reach 3.4 GHz; when preparing the multi-gradient Co@GO-WPU absorbing aerogel, there are a large number of gaps between the aerogel layers. These gaps can increase the reflection path of electromagnetic waves. At the same time, when external stress is applied, the stress is stored between the aerogel layers. When the external force is unloaded, the aerogel can quickly return to its initial state, thereby further improving the overall resilience of the aerogel; this application sets the multi-gradient aerogel into a three-layer structure, which is designed from the perspective of maximizing the consumption of electromagnetic waves when they interact with the material. The mass fraction is lowest on one side along the thickness direction of the aerogel to make the impedance of the aerogel as close as possible to the impedance of air, so that the electromagnetic waves can enter the interior of the aerogel as much as possible; the mass fraction of the middle layer is moderate to maximize the loss of electromagnetic waves inside the aerogel; and the mass fraction is highest on the other side along the thickness direction to reduce the transmission or reflection of electromagnetic waves from the aerogel.

Claims

1. A lightweight, resilient, microwave-absorbing aerogel, characterized in that: The raw materials for preparing the aerogel include graphene oxide, metal compound particles, and aqueous resin. The metal compound particles are loaded on the graphene oxide, and the aqueous resin fills the pores of the porous aerogel formed by the graphene oxide and metal compound particles.

2. The lightweight, resilient, microwave-absorbing aerogel according to claim 1, characterized in that: The aerogel is a stepped structure composed of multiple layers of materials, and the aerogel layers in the multi-layered stepped aerogel have different densities.

3. The lightweight, resilient, microwave-absorbing aerogel according to claim 2, characterized in that: The density of the aerogel layers in the multilayer stepped aerogel increases or decreases sequentially along the thickness extension direction.

4. The lightweight, resilient, microwave-absorbing aerogel according to claim 1, characterized in that: The mass ratio of the metal compound particles to the graphene oxide is 0.01 to 1:

1.

5. The lightweight, resilient, microwave-absorbing aerogel according to claim 1, characterized in that: The average density of the lightweight, resilient microwave-absorbing aerogel is 75-125 mg / cm³. 3 The dielectric tangent is 0.4-0.

6.

6. The lightweight, resilient, microwave-absorbing aerogel according to claim 1, characterized in that: The metal compound particles are selected from at least one of Fe, Co, and Ni compounds; the waterborne resin is selected from at least one of waterborne polyurethane resin, pure acrylic resin, styrene-acrylic resin, bisphenol A type epoxy resin, brominated epoxy resin, hydroxyl-terminated polyester, carboxyl-terminated polyester, and polyethylene resin.

7. A method for preparing a lightweight, resilient, microwave-absorbing aerogel according to any one of claims 1-6, characterized in that: step include: (1) The metal compound particles and the graphene oxide dispersion were mixed evenly by physical stirring to obtain the Me@GO dispersion; (2) Prepare Me@GO dispersions with different water contents using the Me@GO dispersion obtained in step (1); (3) Add aqueous resin to each of the various Me@GO dispersions with different water contents obtained in step (2) and stir evenly. Then take at least one of the above-mentioned evenly stirred Me@GO dispersions, freeze and dry them to obtain Me@GO-aqueous resin aerogel.

8. The method for preparing the lightweight, resilient, microwave-absorbing aerogel according to claim 7, characterized in that: The various Me@GO dispersions with different water contents mentioned in step (2) are Me@GO dispersion a, Me@GO dispersion b and Me@GO dispersion c; Step (3) Specifically: Add the aqueous resin to Me@GO dispersion a and stir evenly, then freeze to obtain intermediate 1; add the aqueous resin to Me@GO dispersion b and stir evenly, then add it to intermediate 1 and freeze to obtain intermediate 2; Aqueous resin was added to Me@GO dispersion c and stirred until homogeneous. Then it was added to intermediate 2 and frozen to obtain intermediate 3. Intermediate 3 was dried to obtain gradient Me@GO-aqueous resin aerogel.

9. The method for preparing the lightweight, resilient, microwave-absorbing aerogel according to claim 8, characterized in that: The mass ratio of the aqueous resin to the corresponding Me@GO dispersion is (1-2):

20.

10. The method for preparing the lightweight, resilient, microwave-absorbing aerogel according to claim 8, characterized in that: The water content of Me@GO dispersion a is 10-20%; the water content of Me@GO dispersion b is 20-30%; and the water content of Me@GO dispersion c is 30-40%.

11. The method for preparing the lightweight, resilient, microwave-absorbing aerogel according to claim 8, characterized in that: The mass ratio of the metal compound particles to graphene oxide is (0.01-1):

1.

12. The method for preparing the lightweight, resilient, microwave-absorbing aerogel according to claim 9, characterized in that: The metal compound particles are selected from at least one of Fe, Co, and Ni compounds; the waterborne resin is selected from at least one of waterborne polyurethane resin, pure acrylic resin, styrene-acrylic resin, bisphenol A type epoxy resin, brominated epoxy resin, hydroxyl-terminated polyester, carboxyl-terminated polyester, and polyethylene resin.

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