Aerogel with electromagnetic shielding effect and preparation method and application thereof

Abstract

The invention relates to the field of functional materials, in particular to aerogel with an electromagnetic shielding effect as well as a preparation method and application thereof, and the aerogel comprises a silicon dioxide porous gel material, modified functional particles uniformly embedded in a framework of the silicon dioxide porous gel material, and a polyaniline conductive layer distributed in pores of the silicon dioxide porous gel material; the composite material comprises the following components in parts by mass: 100 parts of a silicon dioxide porous gel material; 0.5 to 20 parts of modified functional particles; and 5-50 parts of a polyaniline conductive layer. According to the scheme, the frequency response smoothness of the shielding effectiveness is improved by optimizing the uniform distribution of the conductive network in the aerogel.

Description

Technical Field

[0001] The present invention relates to the field of functional materials, and in particular to an aerogel with electromagnetic shielding effect, a preparation method and an application thereof. Background Art

[0002] With the rapid development of electromagnetic shielding materials, aerogels, due to their unique porous structure and lightweight properties, have gradually become a research hotspot in the field of electromagnetic shielding. However, existing aerogel-based electromagnetic shielding materials still have some shortcomings in terms of conductive medium distribution uniformity, shielding effectiveness, and preparation process optimization, which affect their comprehensive performance and large-scale application in high- and low-frequency electromagnetic environments.

[0003] CN112261859B discloses an electromagnetic shielding material and a preparation method thereof, with a publication date of April 21, 2023. This patent makes carbon nanotubes into a membrane-structured aerogel and coats its surface with nanosilver and cobalt, nickel or ferroferric oxide as a shielding layer, thereby producing a high-performance electromagnetic shielding coil. However, in this technical solution, the conductive medium of the carbon nanotube aerogel has a poor distribution uniformity, which may lead to unstable local shielding effectiveness, especially in high-frequency electromagnetic environments, where the shielding effect is easily affected by the uneven distribution of the conductive medium. In addition, this preparation method has high requirements for the control of the coating thickness and uniformity, which increases the process complexity and production cost.

[0004] CN108394148B discloses a method for preparing an electromagnetic shielding composite material, with a publication date of December 8, 2020. This patent prepares a lightweight and wide-shielding electromagnetic shielding composite material by combining a metal foam layer or a metal mesh layer with a thermosetting resin and a carbon fiber woven cloth. However, in this technical solution, due to the limited interfacial bonding strength between the metal layer and the resin matrix, delamination may occur after long-term use, affecting the stability of the shielding performance. In addition, the conductive network of the composite material depends on the distribution of the metal layer and the carbon fiber, which may cause the frequency response of the shielding effectiveness to be not smooth enough, making it difficult to meet the requirements of wide-band electromagnetic shielding.

[0005] The above problems indicate that existing aerogel-based electromagnetic shielding materials still have certain shortcomings in terms of uniformity of conductive medium distribution, stability of shielding effectiveness, and optimization of preparation process. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides an aerogel with electromagnetic shielding effect and its preparation method and application, aiming to improve the frequency response smoothness of the shielding effectiveness by optimizing the uniform distribution of the conductive network inside the aerogel.

[0007] The technical solution adopted by the present invention to solve the technical problem is: to provide an aerogel with electromagnetic shielding effect, comprising a porous silica gel material, modified functional particles uniformly embedded in the skeleton of the porous silica gel material, and a polyaniline conductive layer distributed in the pores of the porous silica gel material;

[0008] The following components are included in parts by mass:

[0009] Silica porous gel material: 100 parts;

[0010] Modified functional particles: 0.5-20 parts;

[0011] Polyaniline conductive layer: 5 to 50 parts.

[0012] The core principle of the electromagnetic shielding aerogel in this scheme is to achieve in-situ directional growth of the polyaniline conductive layer through the nano-scale pore confinement of the silica porous gel skeleton and the pre-positioning of the modified functional particles, and to construct a three-dimensional continuous gradient composite structure: the silica skeleton forms a low dielectric constant substrate to induce multiple scattering of electromagnetic waves, and the surface silanols are covalently bonded with the modified functional particles, such as the ferroferric oxide / carbon nanotube complex anchored by the silane coupling agent, so that the particles are evenly dispersed at the network nodes; the aniline monomer is preferentially adsorbed on the particle surface and in the pores. The inner layer is polymerized layer by layer to form a polyaniline conductive network that runs through the skeleton. At the same time, with the help of the magnetic loss of ferroferric oxide and the electrical conductivity loss of carbon materials, a multi-mechanism synergy is produced with the dielectric polarization loss of polyaniline at the nano-interface - the conjugated molecular chain of polyaniline provides high-frequency dipole polarization and electron migration energy consumption, the magnetic particles generate low-frequency eddy current loss, and the heterogeneous interface between silicon dioxide and particles forms a local Schottky barrier to enhance the interface polarization, ultimately realizing electromagnetic energy-thermal energy conversion in a wide frequency band; the structure of this scheme replaces physical mixing with chemical bonding to make the conductive network evenly distributed.

[0013] This solution proposes a method for preparing the above-mentioned aerogel with electromagnetic shielding effect, comprising the following steps:

[0014] Step (1), preparation of magnetic thermoresponsive microcapsules;

[0015] Step (2), preparing a composite wet gel;

[0016] Step (3), solvent replacement and monomer adsorption;

[0017] Step (4), magnetic field triggered in situ polymerization;

[0018] Step (5), washing and drying.

[0019] Preferably, the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0020] Step (1-1), placing 3-5 μm silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 15-30 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.8±0.05 μm to prepare primary capsules;

[0021] Step (1-2), dispersing 1.5 to 7.5 parts of ferrosoferric oxide nanoparticles with a particle size of 10 to 20 nm in molten paraffin containing 1.0% to 1.2% polyethylene wax by mass at 80°C, and homogenizing by high-speed shearing at 9000 to 11000 rpm to obtain a uniform dispersion with a viscosity of 850 ± 50 cP;

[0022] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 200-400 rpm and 80°C, and then quickly transferring it to a -5°C salt water bath. After screening, it is immersed in an ethanol solution of 0.5wt% polyacrylic acid containing 0.1M hydrochloric acid at a constant temperature of 60°C, and continuously stirred for 1 hour to allow the polyacrylic acid to be grafted onto the paraffin surface through an acid-catalyzed esterification reaction. After the reaction, it is washed with deionized water to remove free acid and unreacted products, and the surface carboxyl layer is vacuum dried and solidified at 40°C to obtain magnetic thermal responsive microcapsules with a diameter of 5-15 μm.

[0023] Preparation of silane-modified ammonium persulfate crystals: 100 parts of ammonium sulfate crystals were added to 300 parts of anhydrous ethanol solution containing 2 parts of polymethylhydrogensiloxane, stirred at 70°C for reaction, filtered, and then vacuum-dried at 80°C to obtain silane-modified ammonium persulfate crystals with a contact angle of ≤20°.

[0024] Ammonium persulfate begins to decompose at 65°C in air, but the decomposition temperature can rise to over 120°C in an oxygen-free, water-free environment. Therefore, ammonium persulfate does not decompose during this process. The polyacrylic acid grafting process occurs via an acid-catalyzed dehydration condensation mechanism: ethanol solvent penetrates the micropores of the paraffin wax, bringing the carboxyl groups of the polyacrylic acid into contact with the paraffin alkane chains. Hydrochloric acid protonates the carboxyl groups, enhancing their electrophilicity. At 60°C, the alkane carbons undergo dehydrogenation to form paraffin ester bonds, creating a uniformly carboxylated surface and rendering the magnetic thermoresponsive microcapsules hydrophilic.

[0025] Preferably, the composite wet gel preparation process is:

[0026] Step (2-1), 100 parts of tetraethyl orthosilicate, 80-120 parts of anhydrous ethanol, and 0.1-0.5 parts of hydrochloric acid catalyst are mixed, and hydrolyzed at 40-60° C. for 30-90 minutes to obtain a precursor solution;

[0027] In step (2-2), 0.5 to 20 parts of modified functional particles and 3 to 5 parts of magnetic thermoresponsive microcapsules are added to the precursor solution, ultrasonically dispersed for 10 to 30 minutes, and then ammonia water is added dropwise to a pH of 5.5 to 6.5. The mixture is allowed to stand at 25 to 35° C. for 10 to 30 minutes for gelation, and then aged at 40 to 60° C. for 12 to 24 hours to obtain a composite wet gel.

[0028] The modified functional particles are silane-modified nanocarbon particles or ferrosoferric oxide nanoparticles;

[0029] The modified functional particles are prepared by dispersing carbon nanoparticles or ferrosoferric oxide nanoparticles in ethanol, adding γ-aminopropyltriethoxysilane at a concentration of 5% to 20% of the particle mass, and refluxing at 70°C for 2 to 4 hours. During the preparation of the composite wet gel, pH control is crucial for ensuring the porous nature of the resulting gel.

[0030] Preferably, the modified functional particle base material is ferrosoferric oxide nanoparticles and carbon nanotubes in a mass ratio of 1 to 3:1.

[0031] Preferably, in step (3), during the solvent replacement process, the replacement liquid solvent is an ethanol aqueous solution containing 1-3 mol / L hydrochloric acid, and the volume ratio of ethanol to water is 7-9:3-1; the solute is aniline monomer, and the mass ratio of the solute to the silica skeleton of the composite wet gel is 0.1-0.5:1;

[0032] Replacement process: The composite wet gel is placed in a replacement solution and soaked for 4 to 8 hours at a temperature of 0 to 5° C. The replacement is repeated multiple times to obtain an aniline monomer-loaded composite wet gel.

[0033] Preferably, the aniline monomer-loaded composite wet gel is placed in an alternating magnetic field with an alternating magnetic field frequency of 100 to 500 kHz, an intensity of 15 to 25 kA / m, a triggering time of 2 to 10 minutes, during which the water bath temperature is maintained at 0 to 5° C. After triggering, the polymer is allowed to stand for 30 to 90 minutes to obtain a polyaniline-loaded composite wet gel.

[0034] Preferably, in step (5), the washing process is to wash 3 to 5 times with an ethanol solution containing 0.1 mol / L hydrochloric acid; and the drying process is to use a carbon dioxide flow rate of 20 to 30 L / min, a pressure of 7.5 to 10 MPa, a temperature of 40 to 50° C., and dry for 4 to 8 hours.

[0035] The core of this technical solution lies in constructing a microscopically ordered electromagnetic shielding structure through multi-stage controlled reactions, achieving functional uniformity. First, the alkoxy groups of γ-aminopropyltriethoxysilane undergo simultaneous hydrolysis and condensation with the silica precursor, anchoring the modified functional particles to the gel backbone nodes via -Si-O- covalent bonds. The ammonium persulfate within the prepared magnetic microcapsules is sealed and protected by a paraffin layer, while the surface-dispersed ferroferric oxide serves as a magnetothermal conversion medium. The outermost layer is a hydrophilic grafted polyacrylic acid, which is hydrophilic and can be evenly dispersed in the precursor solution. Specifically, ethyl orthosilicate undergoes acid-catalyzed hydrolysis to generate active silanols, which form a three-dimensional silica network. The ethoxy groups of γ-aminopropyltriethoxysilane condense with the surface hydroxyl groups of the functional particles to form chemical bonds, while the residual amino groups selectively adsorb aniline monomers, making the modified functional particles polarization loss sites within the framework. The paraffin coating acts as an intelligent barrier to seal the ammonium persulfate, while the ferroferric oxide nanoparticles doped within it convert the energy of the alternating magnetic field into heat. When the wet gel absorbs aniline monomers, an alternating magnetic field stimulates ferroferric oxide to generate heat through magnetic hysteresis. The molten paraffin releases ammonium persulfate into the pores of the silica gel. The ammonium persulfate acts as an oxidant, diffusing along the three-dimensional skeleton to trigger in-situ polymerization of aniline. Due to the amino-catalytic effect of the silane, it preferentially nucleates on the surface of the functional particles, then extends along the pore walls to form a continuous polyaniline conductive layer. This conductive network forms a local heterojunction with the magnetic particles at the interface, coupling conductivity loss, dipole polarization, and magnetic eddy current loss. The resulting aerogel with electromagnetic shielding properties can guide multiple reflections and scattering of electromagnetic waves within the pores, achieving broadband conversion of incident electromagnetic energy into thermal energy. Supercritical drying locks in this hierarchical ordered structure. The entire process uses the gel skeleton as a template, achieving precise spatial arrangement of functional units and coordinated loss mechanisms through a three-step cascade reaction: chemical bonding positioning, precise magnetic field triggering, and confined spatial polymerization.

[0036] The aerogel with electromagnetic shielding effect prepared by this scheme is used in the shielding cover of 5G communication equipment or aerospace instrument cabin.

[0037] The beneficial effects of the present invention are:

[0038] 1. This scheme uses porous silica as a low-dielectric substrate to guide the multiple scattering of electromagnetic waves. The surface-bonded modified functional particles serve as polarization nodes. Polyaniline grows directionally within the pores to form a continuous conductive network, which enables the three loss mechanisms of dielectric-magnetic-conductive to be intrinsically coupled at the nano-interface.

[0039] 2. The process uses a magnetic field to precisely trigger confined polymerization: hydrophilic modified microcapsules deliver the oxidant to the gel pores at a specific point. The alternating magnetic field stimulates the ferroferric oxide to instantly generate heat, melting the paraffin and releasing the oxidant. Under the catalysis of silane amino groups, aniline is driven to preferentially nucleate and polymerize along the surface of the functional particles, achieving precise three-dimensional interpenetration between the polyaniline conductive network and the skeleton structure, ensuring the uniformity of the polyaniline conductive network. DETAILED DESCRIPTION

[0040] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] In the embodiments and comparative examples of this solution, the preparation method of the modified functional particles used and the preparation method of the silane-modified ammonium persulfate crystals are as follows:

[0042] Preparation of silane-modified ammonium persulfate crystals: 100 parts of 3-5 μm ammonium sulfate crystals were added to 300 parts of anhydrous ethanol solution containing 2 parts of polymethylhydrogensiloxane, stirred at 70°C, filtered, and then vacuum-dried at 80°C to obtain silane-modified ammonium persulfate crystals with a contact angle of ≤20°.

[0043] Preparation method of modified functional particles: disperse ferrosoferric oxide nanoparticles and carbon nanotubes in ethanol at a mass ratio of 1 to 3:1, add γ-aminopropyltriethoxysilane in an amount of 20% of the particle mass, and reflux at 70°C for 4 hours to obtain modified functional particles.

[0044] Example 1

[0045] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0046] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0047] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 22 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.82 μm to prepare primary capsules;

[0048] Step (1-2), dispersing 5 parts of 15 nm ferrosoferric oxide nanoparticles in molten paraffin containing 1.1% polyethylene wax at 80°C, and homogenizing by high-speed shearing at 10,000 rpm to obtain a uniform dispersion with a viscosity of 850 cP;

[0049] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 300 rpm and 80°C, and then quickly transferring it to a -5°C salt water bath. After screening, it is immersed in an ethanol solution containing 0.5 wt% polyacrylic acid containing 0.1 M hydrochloric acid at a constant temperature of 60°C, and stirred for 1 hour. After the reaction, it is washed with deionized water to remove free acid and unreacted products, and then vacuum dried and solidified at 40°C to obtain magnetic thermoresponsive microcapsules with a diameter of 10 μm;

[0050] Step (2), the composite wet gel preparation process is:

[0051] Step (2-1), 100 parts of tetraethyl orthosilicate, 100 parts of anhydrous ethanol, and 0.3 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 50°C for 60 minutes to obtain a precursor solution;

[0052] Step (2-2): adding 12 parts of modified functional particles and 3 parts of magnetic thermoresponsive microcapsules to the precursor solution, ultrasonically dispersing for 20 minutes, then adding ammonia water dropwise to a pH of 6.0, standing at 30°C for 20 minutes for gelation, and then aging at 50°C for 18 hours to obtain a composite wet gel;

[0053] Step (3), solvent replacement and monomer adsorption:

[0054] The displacement solution was an ethanol-water solution containing 2 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 8.5:1.5. The solute was aniline monomer, with a mass ratio of 0.35:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 6 hours at 2°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0055] Step (4), magnetic field triggered in-situ polymerization:

[0056] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 200 kHz, an intensity of 22 kA / m, and a triggering time of 6 minutes, during which the water bath temperature was maintained at 2°C. After triggering, the polymerized gel was allowed to stand for 60 minutes to obtain a polyaniline-loaded composite wet gel.

[0057] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0058] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid 4 times; the drying process is to use a carbon dioxide flow rate of 25 L / min, a pressure of 8.5 MPa, a temperature of 45° C., and dry for 6 hours.

[0059] Example 2

[0060] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0061] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0062] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 20 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.75 μm to prepare primary capsules;

[0063] Step (1-2): dispersing 4 parts of 15 nm ferrosoferric oxide nanoparticles in molten paraffin containing 1.1% polyethylene wax at 80°C, and homogenizing by high-speed shearing at 9500 rpm to obtain a uniform dispersion with a viscosity of 830 cP;

[0064] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 300 rpm and 80°C, and then quickly transferring it to a -5°C salt water bath. After screening, it is immersed in an ethanol solution containing 0.5 wt% polyacrylic acid containing 0.1 M hydrochloric acid at a constant temperature of 60°C, and stirred for 1 hour. After the reaction, it is washed with deionized water to remove free acid and unreacted products, and then vacuum dried and solidified at 40°C to obtain magnetic thermoresponsive microcapsules with a diameter of 8 μm;

[0065] Step (2), the composite wet gel preparation process is:

[0066] Step (2-1), 100 parts of tetraethyl orthosilicate, 100 parts of anhydrous ethanol, and 0.3 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 50°C for 60 minutes to obtain a precursor solution;

[0067] Step (2-2), adding 10 parts of modified functional particles and 3 parts of magnetic thermoresponsive microcapsules to the precursor solution, ultrasonically dispersing for 20 minutes, then adding ammonia water dropwise to a pH of 6.0, standing at 30°C for 20 minutes for gelation, and then aging at 50°C for 18 hours to obtain a composite wet gel;

[0068] Step (3), solvent replacement and monomer adsorption:

[0069] The displacement solution was an ethanol-water solution containing 2 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 8:2. The solute was aniline monomer, with a mass ratio of 0.3:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 6 hours at 2°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0070] Step (4), magnetic field triggered in-situ polymerization:

[0071] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 300 kHz, an intensity of 20 kA / m, a triggering time of 5 minutes, and a water bath temperature of 2°C. After triggering, the polymerized gel was allowed to stand for 60 minutes to obtain a polyaniline-loaded composite wet gel.

[0072] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0073] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid 4 times; the drying process is to use a carbon dioxide flow rate of 25 L / min, a pressure of 8.5 MPa, a temperature of 45° C., and dry for 6 hours.

[0074] Example 3

[0075] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0076] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0077] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 25 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.85 μm to prepare primary capsules;

[0078] Step (1-2): dispersing 2 parts of 18 nm ferrosoferric oxide nanoparticles in molten paraffin containing 1.2% polyethylene wax at 80°C, and homogenizing the mixture at 10,000 rpm to obtain a uniform dispersion with a viscosity of 870 cP.

[0079] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 250 rpm and 80°C, and then quickly transferring it to a -5°C salt water bath. After screening, the functional microcapsules were obtained, and immersed in a 0.5 wt% polyacrylic acid ethanol solution containing 0.1 M hydrochloric acid at a constant temperature of 60°C, stirring was continued for 1 hour, and after the reaction, the free acid and unreacted products were removed by washing with deionized water, and then vacuum drying and curing at 40°C to obtain magnetic thermoresponsive microcapsules with a diameter of 12 μm;

[0080] Step (2), the composite wet gel preparation process is:

[0081] Step (2-1), 100 parts of tetraethyl orthosilicate, 90 parts of anhydrous ethanol, and 0.2 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 45° C. for 45 minutes to obtain a precursor solution;

[0082] Step (2-2), adding 15 parts of modified functional particles and 4 parts of magnetic thermoresponsive microcapsules to the precursor solution, ultrasonically dispersing for 20 minutes, then adding ammonia water dropwise to a pH of 5.8, standing at 25°C for 15 minutes for gelation, and then aging at 45°C for 15 hours to obtain a composite wet gel;

[0083] Step (3), solvent replacement and monomer adsorption:

[0084] The displacement solution was an ethanol-water solution containing 1.5 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 8.5:1.5. The solute was aniline monomer, with a mass ratio of 0.4:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 5 hours at 0°C, and the displacement was repeated three times to obtain an aniline monomer-loaded composite wet gel.

[0085] Step (4), magnetic field triggered in-situ polymerization:

[0086] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 200 kHz, an intensity of 18 kA / m, and a triggering time of 8 minutes, during which the water bath temperature was maintained at 0°C. After triggering, the polymerized gel was allowed to stand for 40 minutes to obtain a polyaniline-loaded composite wet gel.

[0087] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0088] The washing process is to wash three times with an ethanol solution containing 0.1 mol / L hydrochloric acid; the drying process is to use a carbon dioxide flow rate of 22 L / min, a pressure of 9.0 MPa, a temperature of 42° C., and dry for 5 hours.

[0089] Example 4

[0090] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0091] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0092] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 28 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.80 μm to prepare primary capsules;

[0093] Step (1-2): 6 parts of 12 nm ferrosoferric oxide nanoparticles were dispersed in molten paraffin containing 1.0% polyethylene wax at 80°C, and homogenized at 10,500 rpm to obtain a uniform dispersion with a viscosity of 820 cP.

[0094] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 380 rpm and 80°C, and then quickly transferring it to a -5°C salt water bath. After screening, it is immersed in an ethanol solution containing 0.5 wt% polyacrylic acid containing 0.1 M hydrochloric acid at a constant temperature of 60°C, and continuously stirred for 1 hour. After the reaction, it is washed with deionized water to remove free acid and unreacted products, and then vacuum dried and solidified at 40°C to obtain magnetic thermoresponsive microcapsules with a diameter of 5 μm;

[0095] Step (2), the composite wet gel preparation process is:

[0096] Step (2-1), 100 parts of tetraethyl orthosilicate, 110 parts of anhydrous ethanol, and 0.4 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 55° C. for 75 minutes to obtain a precursor solution;

[0097] Step (2-2): 18 parts of modified functional particles and 4 parts of magnetic thermoresponsive microcapsules were added to the precursor solution, ultrasonically dispersed for 20 minutes, and then ammonia water was added dropwise to a pH of 6.3. The mixture was allowed to stand at 33°C for 25 minutes for gelation, and then aged at 55°C for 20 hours to obtain a composite wet gel;

[0098] Step (3), solvent replacement and monomer adsorption:

[0099] The displacement solution was an ethanol-water solution containing 2.5 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 7.5:2.5. The solute was aniline monomer, with a mass ratio of 0.15:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 7 hours at 4°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0100] Step (4), magnetic field triggered in-situ polymerization:

[0101] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 450 kHz, an intensity of 22 kA / m, a triggering time of 3 minutes, and a water bath temperature of 4°C. After triggering, the gel was allowed to polymerize for 80 minutes to obtain a polyaniline-loaded composite wet gel.

[0102] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0103] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid for 5 times; the drying process is to use a carbon dioxide flow rate of 28 L / min, a pressure of 7.8 MPa, a temperature of 48° C., and dry for 7 hours.

[0104] Example 5

[0105] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0106] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0107] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 18 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.78 μm to prepare primary capsules;

[0108] Step (1-2): Dispersing 3 parts of 10 nm ferrosoferric oxide nanoparticles in molten paraffin containing 1.1% polyethylene wax at 80°C, and homogenizing by high-speed shearing at 9800 rpm to obtain a uniform dispersion with a viscosity of 860 cP;

[0109] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 320 rpm and 80°C, and then quickly transferring it to a -5°C salt water bath. After screening, it is immersed in an ethanol solution containing 0.5 wt% polyacrylic acid containing 0.1 M hydrochloric acid at a constant temperature of 60°C, and continuously stirred for 1 hour. After the reaction, it is washed with deionized water to remove free acid and unreacted products, and then vacuum dried and solidified at 40°C to obtain magnetic thermoresponsive microcapsules with a diameter of 15 μm;

[0110] Step (2), the composite wet gel preparation process is:

[0111] Step (2-1), 100 parts of tetraethyl orthosilicate, 85 parts of anhydrous ethanol, and 0.5 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 42° C. for 85 minutes to obtain a precursor solution;

[0112] Step (2-2): 5 parts of modified functional particles and 3 parts of magnetic thermoresponsive microcapsules were added to the precursor solution, ultrasonically dispersed for 20 minutes, and then ammonia water was added dropwise to a pH of 5.5. The mixture was allowed to stand at 28°C for 28 minutes for gelation, and then aged at 42°C for 22 hours to obtain a composite wet gel;

[0113] Step (3), solvent replacement and monomer adsorption:

[0114] The displacement solution was an ethanol-water solution containing 3 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 9:1. The solute was aniline monomer, with a mass ratio of 0.5:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 4 hours at 1°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0115] Step (4), magnetic field triggered in-situ polymerization:

[0116] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 100 kHz, an intensity of 25 kA / m, and a triggering time of 10 min, during which the water bath temperature was maintained at 0°C. After triggering, the polymer was allowed to stand for 90 min to obtain a polyaniline-loaded composite wet gel.

[0117] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0118] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid for 4 times; the drying process is to use a carbon dioxide flow rate of 30 L / min, a pressure of 10 MPa, a temperature of 50° C., and dry for 8 hours.

[0119] Comparative Example 1 is pure silica gel.

[0120] Comparative Example 2

[0121] The difference from Example 1 is that only modified functional particles are added:

[0122] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0123] Step (1), the composite wet gel preparation process is:

[0124] Step (1-1), 100 parts of tetraethyl orthosilicate, 100 parts of anhydrous ethanol, and 0.3 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 50° C. for 60 minutes to obtain a precursor solution;

[0125] Step (1-2): 12 parts of modified functional particles were added to the precursor solution, ultrasonically dispersed for 20 minutes, and then ammonia water was added dropwise to a pH of 6.0. The mixture was allowed to stand at 30°C for 20 minutes for gelation, and then aged at 50°C for 18 hours to obtain a composite wet gel.

[0126] Step (2), washing and drying the composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0127] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid 4 times; the drying process is to use a carbon dioxide flow rate of 25 L / min, a pressure of 8.5 MPa, a temperature of 45° C., and dry for 6 hours.

[0128] Comparative Example 3

[0129] The difference from Example 1 is that magnetic thermal response microcapsules are not selected:

[0130] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0131] Step (1), the composite wet gel preparation process is:

[0132] Step (1-1), 100 parts of tetraethyl orthosilicate, 100 parts of anhydrous ethanol, and 0.3 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 50° C. for 60 minutes to obtain a precursor solution;

[0133] Step (1-2): 12 parts of modified functional particles were added to the precursor solution, ultrasonically dispersed for 20 minutes, and then ammonia water was added dropwise to a pH of 6.0. The mixture was allowed to stand at 30°C for 20 minutes for gelation, and then aged at 50°C for 18 hours to obtain a composite wet gel.

[0134] Step (2), solvent replacement and monomer adsorption:

[0135] The displacement solution was an ethanol-water solution containing 2 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 8.5:1.5. The solute was aniline monomer, with a mass ratio of 0.35:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 6 hours at 2°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0136] Step (3), polyaniline polymerization:

[0137] The aniline monomer-loaded composite wet gel was placed in an ammonium persulfate aqueous solution, the water bath temperature was maintained at 2°C, and after triggering, the polymer was allowed to stand for 60 minutes to obtain a polyaniline-loaded composite wet gel.

[0138] Step (4), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel with electromagnetic shielding effect;

[0139] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid 4 times; the drying process is to use a carbon dioxide flow rate of 25 L / min, a pressure of 8.5 MPa, a temperature of 45° C., and dry for 6 hours.

[0140] Comparative Example 4

[0141] The difference from Example 1 is that the modified functional particles are excessive:

[0142] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0143] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0144] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 22 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.82 μm to prepare primary capsules;

[0145] Step (1-2), dispersing 5 parts of 15 nm ferrosoferric oxide nanoparticles in molten paraffin containing 1.1% polyethylene wax at 80°C, and homogenizing by high-speed shearing at 10,000 rpm to obtain a uniform dispersion with a viscosity of 850 cP;

[0146] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 300 rpm and 80°C, and then quickly transferring it to a -5°C salt water bath. After screening, it is immersed in an ethanol solution containing 0.5 wt% polyacrylic acid containing 0.1 M hydrochloric acid at a constant temperature of 60°C, and stirred for 1 hour. After the reaction, it is washed with deionized water to remove free acid and unreacted products, and then vacuum dried and solidified at 40°C to obtain magnetic thermoresponsive microcapsules with a diameter of 10 μm;

[0147] Step (2), the composite wet gel preparation process is:

[0148] Step (2-1), 100 parts of tetraethyl orthosilicate, 100 parts of anhydrous ethanol, and 0.3 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 50°C for 60 minutes to obtain a precursor solution;

[0149] Step (2-2): adding 25 parts of modified functional particles and 3 parts of magnetic thermoresponsive microcapsules to the precursor solution, ultrasonically dispersing for 20 minutes, then adding ammonia water dropwise to a pH of 6.0, standing at 30°C for 20 minutes for gelation, and then aging at 50°C for 18 hours to obtain a composite wet gel;

[0150] Step (3), solvent replacement and monomer adsorption:

[0151] The displacement solution was an ethanol-water solution containing 2 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 8.5:1.5. The solute was aniline monomer, with a mass ratio of 0.35:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 6 hours at 2°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0152] Step (4), magnetic field triggered in-situ polymerization:

[0153] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 200 kHz, an intensity of 22 kA / m, and a triggering time of 6 minutes, during which the water bath temperature was maintained at 2°C. After triggering, the polymerized gel was allowed to stand for 60 minutes to obtain a polyaniline-loaded composite wet gel.

[0154] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0155] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid 4 times; the drying process is to use a carbon dioxide flow rate of 25 L / min, a pressure of 8.5 MPa, a temperature of 45° C., and dry for 6 hours.

[0156] Comparative Example 5

[0157] The difference from Example 1 is that polyethylene wax is not added in step (1-2):

[0158] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0159] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0160] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 22 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.82 μm to prepare primary capsules;

[0161] Step (1-2): Disperse 5 parts of 15 nm ferrosoferric oxide nanoparticles in molten paraffin at 80°C and homogenize at 10,000 rpm to obtain a uniform dispersion with a viscosity of 850 cP.

[0162] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 300 rpm and 80°C, and then quickly transferring it to a -5°C salt water bath. After screening, it is immersed in an ethanol solution containing 0.5 wt% polyacrylic acid containing 0.1 M hydrochloric acid at a constant temperature of 60°C, and stirred for 1 hour. After the reaction, it is washed with deionized water to remove free acid and unreacted products, and then vacuum dried and solidified at 40°C to obtain magnetic thermoresponsive microcapsules with a diameter of 10 μm;

[0163] Step (2), the composite wet gel preparation process is:

[0164] Step (2-1), 100 parts of tetraethyl orthosilicate, 100 parts of anhydrous ethanol, and 0.3 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 50°C for 60 minutes to obtain a precursor solution;

[0165] Step (2-2): adding 12 parts of modified functional particles and 3 parts of magnetic thermoresponsive microcapsules to the precursor solution, ultrasonically dispersing for 20 minutes, then adding ammonia water dropwise to a pH of 6.0, standing at 30°C for 20 minutes for gelation, and then aging at 50°C for 18 hours to obtain a composite wet gel;

[0166] Step (3), solvent replacement and monomer adsorption:

[0167] The displacement solution was an ethanol-water solution containing 2 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 8.5:1.5. The solute was aniline monomer, with a mass ratio of 0.35:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 6 hours at 2°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0168] Step (4), magnetic field triggered in-situ polymerization:

[0169] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 200 kHz, an intensity of 22 kA / m, and a triggering time of 6 minutes, during which the water bath temperature was maintained at 2°C. After triggering, the polymerized gel was allowed to stand for 60 minutes to obtain a polyaniline-loaded composite wet gel.

[0170] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0171] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid 4 times; the drying process is to use a carbon dioxide flow rate of 25 L / min, a pressure of 8.5 MPa, a temperature of 45° C., and dry for 6 hours.

[0172] Comparative Example 6

[0173] The difference from Example 1 is that steps (1-3) are not grafted with polyacrylic acid:

[0174] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0175] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0176] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 22 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.82 μm to prepare primary capsules;

[0177] Step (1-2), dispersing 5 parts of 15 nm ferrosoferric oxide nanoparticles in molten paraffin containing 1.1% polyethylene wax at 80°C, and homogenizing by high-speed shearing at 10,000 rpm to obtain a uniform dispersion with a viscosity of 850 cP;

[0178] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 300 rpm and 80°C, and then quickly transferring to a -5°C salt water bath, sieving, washing, and vacuum drying and curing at 40°C to obtain magnetic thermoresponsive microcapsules with a diameter of 10 μm;

[0179] Step (2), the composite wet gel preparation process is:

[0180] Step (2-1), 100 parts of tetraethyl orthosilicate, 100 parts of anhydrous ethanol, and 0.3 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 50°C for 60 minutes to obtain a precursor solution;

[0181] Step (2-2): adding 12 parts of modified functional particles and 3 parts of magnetic thermoresponsive microcapsules to the precursor solution, ultrasonically dispersing for 20 minutes, then adding ammonia water dropwise to a pH of 6.0, standing at 30°C for 20 minutes for gelation, and then aging at 50°C for 18 hours to obtain a composite wet gel;

[0182] Step (3), solvent replacement and monomer adsorption:

[0183] The displacement solution was an ethanol-water solution containing 2 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 8.5:1.5. The solute was aniline monomer, with a mass ratio of 0.35:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 6 hours at 2°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0184] Step (4), magnetic field triggered in-situ polymerization:

[0185] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 200 kHz, an intensity of 22 kA / m, and a triggering time of 6 minutes, during which the water bath temperature was maintained at 2°C. After triggering, the polymerized gel was allowed to stand for 60 minutes to obtain a polyaniline-loaded composite wet gel.

[0186] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0187] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid 4 times; the drying process is to use a carbon dioxide flow rate of 25 L / min, a pressure of 8.5 MPa, a temperature of 45° C., and dry for 6 hours.

[0188] Comparative Example 7

[0189] The difference from Example 1 is that the magnetic field strength is too large:

[0190] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0191] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0192] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 22 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.82 μm to prepare primary capsules;

[0193] Step (1-2), dispersing 5 parts of 15 nm ferrosoferric oxide nanoparticles in molten paraffin containing 1.1% polyethylene wax at 80°C, and homogenizing by high-speed shearing at 10,000 rpm to obtain a uniform dispersion with a viscosity of 850 cP;

[0194] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 300 rpm and 80°C, and then quickly transferring it to a -5°C salt water bath. After screening, it is immersed in an ethanol solution containing 0.5 wt% polyacrylic acid containing 0.1 M hydrochloric acid at a constant temperature of 60°C, and stirred for 1 hour. After the reaction, it is washed with deionized water to remove free acid and unreacted products, and then vacuum dried and solidified at 40°C to obtain magnetic thermoresponsive microcapsules with a diameter of 10 μm;

[0195] Step (2), the composite wet gel preparation process is:

[0196] Step (2-1), 100 parts of tetraethyl orthosilicate, 100 parts of anhydrous ethanol, and 0.3 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 50°C for 60 minutes to obtain a precursor solution;

[0197] Step (2-2): adding 12 parts of modified functional particles and 3 parts of magnetic thermoresponsive microcapsules to the precursor solution, ultrasonically dispersing for 20 minutes, then adding ammonia water dropwise to a pH of 6.0, standing at 30°C for 20 minutes for gelation, and then aging at 50°C for 18 hours to obtain a composite wet gel;

[0198] Step (3), solvent replacement and monomer adsorption:

[0199] The displacement solution was an ethanol-water solution containing 2 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 8.5:1.5. The solute was aniline monomer, with a mass ratio of 0.35:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 6 hours at 2°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0200] Step (4), magnetic field triggered in-situ polymerization:

[0201] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 200 kHz, an intensity of 30 kA / m, and a triggering time of 6 minutes, during which the water bath temperature was maintained at 2°C. After triggering, the polymer was allowed to stand for 60 minutes to obtain a polyaniline-loaded composite wet gel.

[0202] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0203] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid 4 times; the drying process is to use a carbon dioxide flow rate of 25 L / min, a pressure of 8.5 MPa, a temperature of 45° C., and dry for 6 hours.

[0204] Comparative Example 8

[0205] The difference from Example 1 is that the amount of magnetic thermal responsive microcapsules added is too small:

[0206] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0207] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0208] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 22 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.82 μm to prepare primary capsules;

[0209] Step (1-2), dispersing 5 parts of 15 nm ferrosoferric oxide nanoparticles in molten paraffin containing 1.1% polyethylene wax at 80°C, and homogenizing by high-speed shearing at 10,000 rpm to obtain a uniform dispersion with a viscosity of 850 cP;

[0210] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 300 rpm and 80°C, and then quickly transferring it to a -5°C salt water bath. After screening, it is immersed in an ethanol solution containing 0.5 wt% polyacrylic acid containing 0.1 M hydrochloric acid at a constant temperature of 60°C, and stirred for 1 hour. After the reaction, it is washed with deionized water to remove free acid and unreacted products, and then vacuum dried and solidified at 40°C to obtain magnetic thermoresponsive microcapsules with a diameter of 10 μm;

[0211] Step (2), the composite wet gel preparation process is:

[0212] Step (2-1), 100 parts of tetraethyl orthosilicate, 100 parts of anhydrous ethanol, and 0.3 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 50°C for 60 minutes to obtain a precursor solution;

[0213] Step (2-2), adding 12 parts of modified functional particles and 2 parts of magnetic thermoresponsive microcapsules to the precursor solution, ultrasonically dispersing for 20 minutes, then adding ammonia water dropwise to a pH of 6.0, standing at 30°C for 20 minutes for gelation, and then aging at 50°C for 18 hours to obtain a composite wet gel;

[0214] Step (3), solvent replacement and monomer adsorption:

[0215] The displacement solution was an ethanol-water solution containing 2 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 8.5:1.5. The solute was aniline monomer, with a mass ratio of 0.35:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 6 hours at 2°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0216] Step (4), magnetic field triggered in-situ polymerization:

[0217] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 200 kHz, an intensity of 22 kA / m, and a triggering time of 6 minutes, during which the water bath temperature was maintained at 2°C. After triggering, the polymerized gel was allowed to stand for 60 minutes to obtain a polyaniline-loaded composite wet gel.

[0218] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0219] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid 4 times; the drying process is to use a carbon dioxide flow rate of 25 L / min, a pressure of 8.5 MPa, a temperature of 45° C., and dry for 6 hours.

[0220] Comparative Example 9

[0221] The difference from Example 1 is that drying is carried out by drying:

[0222] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0223] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0224] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 22 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.82 μm to prepare primary capsules;

[0225] Step (1-2), dispersing 5 parts of 15 nm ferrosoferric oxide nanoparticles in molten paraffin containing 1.1% polyethylene wax at 80°C, and homogenizing by high-speed shearing at 10,000 rpm to obtain a uniform dispersion with a viscosity of 850 cP;

[0226] Step (1-3), immersing the primary capsule in the uniform dispersion, stirring at a low speed of 300 rpm and 80°C, and then quickly transferring it to a -5°C salt water bath. After screening, it is immersed in an ethanol solution containing 0.5 wt% polyacrylic acid containing 0.1 M hydrochloric acid at a constant temperature of 60°C, and stirred for 1 hour. After the reaction, it is washed with deionized water to remove free acid and unreacted products, and then vacuum dried and solidified at 40°C to obtain magnetic thermoresponsive microcapsules with a diameter of 10 μm;

[0227] Step (2), the composite wet gel preparation process is:

[0228] Step (2-1), 100 parts of tetraethyl orthosilicate, 100 parts of anhydrous ethanol, and 0.3 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 50°C for 60 minutes to obtain a precursor solution;

[0229] Step (2-2): adding 12 parts of modified functional particles and 3 parts of magnetic thermoresponsive microcapsules to the precursor solution, ultrasonically dispersing for 20 minutes, then adding ammonia water dropwise to a pH of 6.0, standing at 30°C for 20 minutes for gelation, and then aging at 50°C for 18 hours to obtain a composite wet gel;

[0230] Step (3), solvent replacement and monomer adsorption:

[0231] The displacement solution was an ethanol-water solution containing 2 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 8.5:1.5. The solute was aniline monomer, with a mass ratio of 0.35:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 6 hours at 2°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0232] Step (4), magnetic field triggered in-situ polymerization:

[0233] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 200 kHz, an intensity of 22 kA / m, and a triggering time of 6 minutes, during which the water bath temperature was maintained at 2°C. After triggering, the polymerized gel was allowed to stand for 60 minutes to obtain a polyaniline-loaded composite wet gel.

[0234] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0235] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid 4 times; the drying process is to dry at a temperature of 45° C. for 10 hours.

[0236] Comparative Example 10

[0237] The difference from Example 1 is that no ferroferric oxide nanoparticles were added during the preparation of the magnetic thermoresponsive microcapsules:

[0238] A method for preparing an aerogel having an electromagnetic shielding effect comprises the following steps:

[0239] Step (1), the preparation process of magnetic thermoresponsive microcapsules is as follows:

[0240] Step (1-1), placing silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70°C hot nitrogen, and spraying 22 parts of 75°C molten paraffin at a rate of 0.5 g / min·kg to form a dense coating layer with a thickness of 0.82 μm to prepare primary capsules;

[0241] Step (1-2), after screening the primary capsules, immerse them in a 0.5 wt% polyacrylic acid ethanol solution containing 0.1 M hydrochloric acid at a constant temperature of 60°C and stir continuously for 1 hour. After the reaction, wash with deionized water to remove free acid and unreacted products, and vacuum dry and solidify at 40°C to obtain microcapsules with a diameter of 10 μm;

[0242] Step (2), the composite wet gel preparation process is:

[0243] Step (2-1), 100 parts of tetraethyl orthosilicate, 100 parts of anhydrous ethanol, and 0.3 parts of hydrochloric acid catalyst were mixed and hydrolyzed at 50°C for 60 minutes to obtain a precursor solution;

[0244] Step (2-2): 12 parts of modified functional particles and 3 parts of microcapsules were added to the precursor solution, ultrasonically dispersed for 20 minutes, and then ammonia water was added dropwise to a pH of 6.0. The mixture was allowed to stand at 30°C for 20 minutes for gelation, and then aged at 50°C for 18 hours to obtain a composite wet gel;

[0245] Step (3), solvent replacement and monomer adsorption:

[0246] The displacement solution was an ethanol-water solution containing 2 mol / L hydrochloric acid, with a volume ratio of ethanol to water of 8.5:1.5. The solute was aniline monomer, with a mass ratio of 0.35:1 to the silica skeleton of the composite wet gel. The composite wet gel was immersed in the displacement solution for 6 hours at 2°C, and the displacement was repeated three times to obtain the aniline monomer-loaded composite wet gel.

[0247] Step (4), magnetic field triggered in-situ polymerization:

[0248] The aniline monomer-loaded composite wet gel was placed in an alternating magnetic field with a frequency of 200 kHz, an intensity of 22 kA / m, and a triggering time of 6 minutes, during which the water bath temperature was maintained at 2°C. After triggering, the polymerized gel was allowed to stand for 60 minutes to obtain a polyaniline-loaded composite wet gel.

[0249] Step (5), washing and drying the polyaniline-loaded composite wet gel to obtain an aerogel having an electromagnetic shielding effect;

[0250] The washing process is to wash with an ethanol solution containing 0.1 mol / L hydrochloric acid 4 times; the drying process is to use a carbon dioxide flow rate of 25 L / min, a pressure of 8.5 MPa, a temperature of 45° C., and dry for 6 hours.

[0251] Performance testing methods or standards:

[0252] Density: measured by displacement method;

[0253] Specific surface area and porosity: The specific surface area was measured using the BET nitrogen adsorption method (GB / T 19587-2017), and the pore size distribution and porosity were calculated using the BJH method.

[0254] Conductivity: Four-probe method, taking measurements at multiple points on the aerogel surface and taking the average value;

[0255] Electromagnetic shielding effectiveness (SE): measured using a vector network analyzer (ASTM D4935-18). SE values ​​were recorded in the frequency range of 1-18 GHz, and the average SE was calculated as: SE (dB) = 101g (Pi / Pt), where Pi is the incident power and Pt is the transmitted power.

[0256] Shielding uniformity (RSD): SE was measured at 9 points (3 × 3 grid) on the aerogel surface, and the relative standard deviation (RSD) was calculated;

[0257] Thermal stability: TGA (thermogravimetric analysis) was performed under nitrogen atmosphere by heating the sample to 800°C at a rate of 10°C / min and recording the weight loss.

[0258] The performance test results are shown in Table 1.

[0259] Table 1 Performance test results of examples and comparative examples

[0260]

[0261]

[0262] The test results show that Examples 1-5 have a significant advantage in shielding uniformity compared to Comparative Examples 2-10, and the electromagnetic shielding effectiveness is better than that of Comparative Examples 1-10.

[0263] The difference between Comparative Example 1 and Example 1 is that it only contains a pure silica skeleton without modified functional particles and a polyaniline conductive layer. Although it has high porosity and low dielectric properties, it lacks an electromagnetic loss mechanism.

[0264] The difference between Comparative Example 2 and Example 1 is that the modified functional particles are added but the polyaniline conductive layer is missing, so a complete conductive network cannot be formed: the ferroferric oxide particles provide low-frequency magnetic loss, and the carbon nanotubes bear part of the high-frequency conductivity loss, but the particle spacing leads to a high electron migration barrier and low carrier transfer efficiency; the lack of polyaniline bridging at the interface makes it impossible to establish a continuous charge transfer path, resulting in difficulty in dissipating the electric field energy in the interface polarization-conductivity synergy. Analysis of Comparative Example 3 (Non-magnetic Triggered Polymerization)

[0265] The difference between Comparative Example 3 and Example 1 is that, in the case of the exogenous ammonium persulfate solution immersion polymerization, the oxidant diffuses disorderly in the aerogel pores: the excessively high concentration at the surface pores triggers rapid stacking polymerization, while insufficient oxidant in the deep pores causes a sharp drop in the polyaniline coverage, resulting in deterioration of the spatial uniformity and structural connectivity of the polyaniline network.

[0266] The difference between Comparative Example 4 and Example 1 is that the excessive addition of functional particles easily blocks the nanopores of the aerogel skeleton, hindering the extension and growth of the polyaniline molecular chains in the pores. The accumulation of particles also easily destroys the low dielectric matrix properties of the skeleton and reduces the length of the multiple reflection path of electromagnetic waves in the pores.

[0267] The difference between Comparative Example 5 and Example 1 is that polyethylene wax is not used to disperse ferrosoferric oxide, so the magnetic particles agglomerate in the paraffin layer and the encapsulation is poor. The distribution defects of the magnetothermal conversion source directly lead to an unbalanced distribution of the polyaniline polymerization trigger points.

[0268] The difference between Comparative Example 6 and Example 1 is that the microcapsules lack polyacrylic acid grafting, and the strong hydrophobicity of the paraffin surface hinders its compatibility with the silica sol.

[0269] The difference between Comparative Example 7 and Example 1 is that the ultra-strong magnetic field induces instantaneous overheating of the microcapsules and releases a large amount of them. The high magnetothermal power of ferroferric oxide causes the paraffin layer to melt through quickly, and the instantaneous concentration of released ammonium persulfate exceeds the threshold value, resulting in rapid cross-linking and accumulation of polyaniline molecular chains on the surface of the functional particles; forming a short-chain branched structure instead of a linear conjugated long chain, which reduces the conductivity mobility and hinders the high-frequency response performance of the molecular dipole.

[0270] The difference between Comparative Example 8 and Example 1 is that the insufficient amount of microcapsules added causes the oxidant release density to be lower than the critical value, the sparsely distributed microcapsules cannot fully cover the gel network nodes, the concentration of ammonium persulfate decays to below the polymerization threshold within the diffusion range, and polyaniline fails to nucleate and grow in some areas.

[0271] The difference between Comparative Example 9 and Example 1 is that the wet gel is subjected to ultra-high capillary force by drying at normal pressure, which causes the micropores to collapse and squeeze the functional units to aggregate. The polyaniline molecular chains are twisted and entangled due to physical compression, destroying the conjugated conductance channel.

[0272] The difference between Comparative Example 10 and Example 1 is that nano-ferroferric oxide is not incorporated into the microcapsules, and the paraffin layer loses its magnetothermal conversion function: the microcapsules without ferroferric oxide can only heat up through the weak dielectric dissipation of paraffin in the alternating magnetic field, which is far below the melting point of paraffin and cannot trigger the melting and release process.

Claims

1. An aerogel having an electromagnetic shielding effect, characterized in that: The invention comprises a porous silica gel material, modified functional particles uniformly embedded in the skeleton of the porous silica gel material, and a polyaniline conductive layer distributed in the pores of the porous silica gel material; The following components are included in parts by mass: Silica porous gel material: 100 parts; Modified functional particles: 0.5-20 parts; Polyaniline conductive layer: 5 to 50 parts.

2. The aerogel having electromagnetic shielding effect as claimed in claim 1, characterized in that: The modified functional particles are silane-modified ferrosoferric oxide nanoparticles and silane-modified carbon nanotubes in a mass ratio of 1 to 3:

1.

3. A method for preparing an aerogel having electromagnetic shielding effect according to any one of claims 1 to 2, characterized in that: The following steps are involved: Step (1), preparation of magnetic thermoresponsive microcapsules: Step (1-1), placing 3-5 μm silane-modified ammonium persulfate crystals in a fluidized bed, introducing hot nitrogen, and spraying 15-30 parts of molten paraffin to obtain primary capsules; Step (1-2), dispersing 1.5 to 7.5 parts of ferrosoferric oxide nanoparticles with a particle size of 10 to 20 nm in molten paraffin containing 1.0% to 1.2% polyethylene wax by mass, and homogenizing by high-speed shearing to obtain a uniform dispersion; Step (1-3), immersing the primary capsule in the uniform dispersion, stirring and screening to obtain functional microcapsules, and hydrophilically modifying the functional microcapsules to obtain magnetic thermal responsive microcapsules with a diameter of 5-15 μm; Step (2), preparation of composite wet gel: Step (2-1), 100 parts of tetraethyl orthosilicate, 80-120 parts of anhydrous ethanol, and 0.1-0.5 parts of hydrochloric acid catalyst are mixed, and hydrolyzed at 40-60° C. for 30-90 minutes to obtain a precursor solution; Step (2-2), adding 0.5-20 parts of modified functional particles and 3-5 parts of magnetic thermoresponsive microcapsules to the precursor solution, ultrasonically dispersing, adjusting the pH to 5.5-6.5, standing at 25-35° C. for gelation, and aging to obtain a composite wet gel; Step (3), solvent replacement and monomer adsorption: The composite wet gel is placed in a replacement solution and soaked for 4 to 8 hours at a temperature of 0 to 5°C, and the replacement is repeated multiple times to obtain an aniline monomer-loaded composite wet gel; Step (4), magnetic field triggered in-situ polymerization: The aniline monomer-loaded composite wet gel is placed in an alternating magnetic field, during which the water bath temperature is maintained at 0-5°C, and after being triggered, the polymer is allowed to stand for 30-90 minutes to obtain a polyaniline-loaded composite wet gel; Step (5): washing and drying to obtain an aerogel having an electromagnetic shielding effect.

4. The method for preparing an aerogel having an electromagnetic shielding effect according to claim 3, wherein: In step (3), the replacement liquid solvent is an ethanol aqueous solution containing 1-3 mol / L hydrochloric acid, and the volume ratio of ethanol to water is 7-9:3-1; the solute is aniline monomer, and the mass ratio of the solute to the silica skeleton of the composite wet gel is 0.1-0.5:

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5. The method for preparing an aerogel having an electromagnetic shielding effect according to claim 3, wherein: In step (5), the washing process is to wash 3 to 5 times with an ethanol solution containing 0.1 mol / L hydrochloric acid; and the drying process is to use a carbon dioxide flow rate of 20 to 30 L / min, a pressure of 7.5 to 10 MPa, a temperature of 40 to 50° C., and dry for 4 to 8 hours.

6. The method for preparing an aerogel having an electromagnetic shielding effect according to claim 3, wherein: Step (1) Preparation of magnetic thermoresponsive microcapsules: Step (1-1), placing 3-5 μm silane-modified ammonium persulfate crystals in a fluidized bed, introducing 70° C. hot nitrogen, and spraying 15-30 parts of 75° C. molten paraffin at a rate of 0.5 g / min·kg to obtain primary capsules; Step (1-2), dispersing 1.5 to 7.5 parts of ferrosoferric oxide nanoparticles with a particle size of 10 to 20 nm in molten paraffin containing 1.0% to 1.2% polyethylene wax by mass at 80°C, and homogenizing by high-speed shearing at 9000 to 11000 rpm to obtain a uniform dispersion with a viscosity of 850 ± 50 cP; Step (1-3): immerse the primary capsule in the uniform dispersion, stir evenly at a low speed of 200-400 rpm and 80°C, and then quickly transfer to a -5°C salt water bath. After screening, functional microcapsules are obtained. The functional microcapsules are hydrophilically modified to obtain magnetic thermal responsive microcapsules with a diameter of 5-15 μm.

7. The method for preparing an aerogel having an electromagnetic shielding effect according to claim 6, wherein: The hydrophilic modification process of the functional microcapsules is as follows: immersing the functional microcapsules in a 0.5 wt% polyacrylic acid ethanol solution containing 0.1 M hydrochloric acid at a constant temperature of 60° C., stirring continuously for 1 hour, washing with deionized water after the reaction, and vacuum drying at 40° C. to solidify the surface carboxyl layer.

8. The method for preparing an aerogel having an electromagnetic shielding effect according to claim 3, wherein: In step (2-2), 0.5 to 20 parts of modified functional particles and 3 to 5 parts of magnetic thermoresponsive microcapsules are added to the precursor solution, ultrasonically dispersed for 10 to 30 minutes, and then ammonia water is added dropwise to a pH of 5.5 to 6.

5. The solution is allowed to stand at 25 to 35° C. for 10 to 30 minutes for gelation, and then aged at 40 to 60° C. for 12 to 24 hours to obtain a composite wet gel.

9. The method for preparing an aerogel having an electromagnetic shielding effect according to claim 3, wherein: In step (4), the aniline monomer-loaded composite wet gel is placed in an alternating magnetic field with an alternating magnetic field frequency of 100 to 500 kHz, an intensity of 15 to 25 kA / m, a triggering time of 2 to 10 minutes, during which the water bath temperature is maintained at 0 to 5° C. After triggering, the polymer is allowed to stand for 30 to 90 minutes to obtain a polyaniline-loaded composite wet gel.

10. An application of an aerogel having electromagnetic shielding effect according to any one of claims 1 to 2, characterized in that: The aerogel with electromagnetic shielding effect is applied to the shielding cover of 5G communication equipment or aerospace instrument cabin.

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