Terahertz wave-absorbing foam based on magnetically-induced gradient-distributed carbon nanotubes and preparation method of terahertz wave-absorbing foam

Abstract

The invention discloses terahertz wave-absorbing foam based on magnetically-induced gradient distribution carbon nanotubes and a preparation method, and belongs to the technical field of photoelectric materials and devices. The terahertz wave-absorbing foam comprises a porous framework and a wave-absorbing agent distributed in the porous framework, wherein the porous skeleton is a PDMS matrix with holes, the wave-absorbing agent is MWCNT modified by Fe3O4 nanoparticles, and the mass percentage of the wave-absorbing agent in the wave-absorbing foam is 3-7wt%. The dielectric constant of the wave-absorbing foam is regulated and controlled by controlling the concentration of the MWCNT modified by the Fe3O4 nanoparticles, and the concentration of the MWCNT can be guided to be distributed in a longitudinal gradient manner by using an external magnetic field, so that surface electromagnetic impedance matching is realized, and finally reflection suppression and absorption enhancement of electromagnetic waves are completed; meanwhile, large-area preparation can be realized by using white granulated sugar as a sacrificial template, and the method is suitable for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of optoelectronic materials and devices, and particularly relates to a terahertz absorbing foam based on magnetically induced gradient distributed carbon nanotubes and a preparation method thereof. Background Art

[0002] To achieve faster data transmission rates and wider wireless communication bandwidths, the new generation of electronic information technology requires that carrier waves expand to higher frequency bands such as millimeter / terahertz waves. In particular, for many emerging technologies such as 6G Internet of Things, chip-to-chip wireless interconnection, and holographic technology, for highly integrated electronic systems, there is electromagnetic interference between different electronic components such as transceiver antennas, compilers, decoders, and modulators, which will greatly affect the efficiency of information transmission. It can be seen that absorption technology in the millimeter / terahertz frequency band is the key to the next generation of wireless communication systems.

[0003] In recent years, metasurface absorbers have gained popularity due to their high-Q absorption and dynamic modulation capabilities. However, their complex and costly manufacturing processes, poor conformality to curved surfaces, narrow absorption bandwidth, and directional sensitivity have limited their widespread application. In contrast, composite materials, which can be easily fabricated on large surfaces and exhibit broadband absorption, have shown great potential. Research has shown that conductive lossy absorbers can also achieve efficient broadband absorption of millimeter / terahertz waves. Various conductive absorber materials, including MXene, carbon black, and graphene, have been extensively studied to prepare high-performance composite absorbers for millimeter / terahertz electromagnetic waves. However, highly conductive materials often suffer from surface impedance mismatch, resulting in a large portion of the energy being reflected, which is not conducive to electromagnetic wave absorption. Therefore, a low dielectric environment should be introduced between the absorbers to allow electromagnetic waves to enter the material and dissipate energy. More importantly, by controlling the distribution of the absorbers in the composite material, better impedance matching can be achieved, resulting in more perfect absorption performance. At present, there are relatively few studies on distribution-controllable absorbing materials and preparation processes. Research on broadband absorption in the millimeter / terahertz frequency bands needs to focus on the preparation of absorbing materials and the development of methods to control the distribution of absorbers.

[0004] Multi-walled carbon nanotubes (MWCNTs) are a preferred filler for electromagnetic absorption due to their unique electrical properties, excellent mechanical strength, and chemical and temperature stability. By introducing a conductive MWCNT network into a polymer matrix, the dielectric constant of the composite can be regulated by adjusting the concentration of the carbon nanotubes. Furthermore, MWCNTs modified with magnetic nanoparticles can achieve a magnetic field-guided concentration gradient distribution. The gradient distribution of the foam structure and absorber can further enhance the electromagnetic shielding capability of MWCNT-based composites. The composite's gradient dielectric environment and porous skeleton can simultaneously enhance reflection suppression and multiple scattering absorption of incident electromagnetic waves. Summary of the Invention

[0005] The purpose of the present invention is to address the problems existing in the background technology and propose a terahertz absorbing foam based on magnetically induced gradient distributed carbon nanotubes and a preparation method thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A terahertz absorbing foam based on magnetically induced gradient distributed carbon nanotubes, comprising a porous skeleton and an absorbing agent distributed in the porous skeleton;

[0008] The porous skeleton is a PDMS matrix with holes, the absorber is MWCNT modified with Fe3O4 nanoparticles, and the mass percentage of the absorber in the absorbing foam is 3 to 7 wt%.

[0009] Furthermore, in the PDMS substrate with holes, the pore size is 50-100 μm, 150-250 μm or 300-500 μm.

[0010] Furthermore, the thickness of the wave-absorbing foam is 2 to 4 mm.

[0011] Furthermore, in the absorbing foam, the concentration of the absorbing agent is distributed in a gradient in the longitudinal direction, decreasing from bottom to top, and the concentration of the absorbing agent on the foam surface is almost 0.

[0012] A method for preparing terahertz absorbing foam based on magnetically induced gradient distributed carbon nanotubes, comprising:

[0013] Step 1. Surface modification of MWCNTs:

[0014] 1.1 Immerse multi-walled carbon nanotubes (MWCNTs) in a mixture of hydrochloric acid and nitric acid at a molar ratio of 1:3 at 60°C for at least 72 hours; then wash and filter with acetone and deionized water, and transfer to a vacuum oven at 75°C to dry for at least 12 hours;

[0015] 1.2 The MWCNTs treated in step 1.1 are added to deionized water to prepare a 0.3-0.9 wt% multi-walled carbon nanotube solution, and then FeCl3·6H2O and FeCl2·4H2O are added to the multi-walled carbon nanotube solution and stirred for 20-40 minutes to obtain a precursor mixed solution; wherein the mass ratio of MWCNT, FeCl3·6H2O, and FeCl2·4H2O is (3-7):8:4;

[0016] 1.3 Add ammonia water to the precursor mixed solution obtained in step 1.2, adjust its pH to above 12, and react in an oil bath at 60°C for 1.5 to 2.5 hours. After the reaction is complete, repeatedly wash with deionized water until the supernatant is clear, filter, and dry to obtain Fe3O4 nanoparticle-modified MWCNTs;

[0017] Step 2. Preparation of conductive composite slurry:

[0018] Mixing Fe3O4 nanoparticle-modified MWCNTs with PDMS to form a uniform composite slurry, wherein the mass ratio of Fe3O4 nanoparticle-modified MWCNTs to PDMS is (1-4.5):100; adding toluene of the same volume as the composite slurry to dilute the composite slurry and set aside;

[0019] Step 3. Preparation of porous framework:

[0020] Mix the white sugar granules and the diluted composite slurry from step 2, and then transfer them to a culture dish and cast them flat;

[0021] Step 4. Magnetic induced gradient distribution:

[0022] The surface and bottom of the culture dish obtained in step 3 are covered with permalloy soft magnetic sheets, and a permanent magnet is placed at the bottom; after standing at room temperature for not less than 48 hours, the conductive composite slurry is completely solidified and can be peeled off and transferred to a water bath at 60-100°C to dissolve white sugar; finally, it is rinsed with deionized water and dried to obtain a terahertz absorbing foam based on magnetically induced gradient distributed carbon nanotubes.

[0023] Furthermore, in step 3, the volume fraction of the white sugar particles is 50-70 vol%; the particle size of the white sugar particles is 50-100 μm, 150-250 μm or 300-500 μm.

[0024] Furthermore, in step 4, a magnetic field of not less than 5000 Oe is applied in a direction perpendicular to the surface of the permanent magnet.

[0025] The present invention provides a terahertz absorbing foam based on magnetically induced gradient distributed carbon nanotubes. The dielectric constant of the absorbing foam is regulated by controlling the content of MWCNT modified with Fe3O4 nanoparticles, so that the real part of the dielectric constant and the loss tangent of the absorbing foam can vary between 3 and 5 and 0.1 and 0.6, respectively. In addition, the foam exhibits an average absorption rate higher than 99.99% in the frequency band of 0.2 to 1.2 THz.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention provides a terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes. The dielectric constant of the absorbing foam is regulated by controlling the concentration of MWCNTs modified with Fe3O4 nanoparticles. The external magnetic field can be used to guide the concentration to form a longitudinal gradient distribution to achieve surface electromagnetic impedance matching, ultimately completing the reflection suppression and absorption enhancement of electromagnetic waves.

[0028] 2. The present invention provides a method for preparing terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes. The method uses white sugar as a sacrificial template to achieve large-area preparation. The method is highly repeatable and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The dielectric parameter frequency domain spectra of the composite materials modified with MWCNTs at different concentrations of Fe3O4 nanoparticles in Example 1;

[0030] Figure 2 Scanning electron photographs of four longitudinal regions of the terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes in Example 2;

[0031] Figure 3 3 is a comparison curve of the reflection and absorption frequency domain spectra of the terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes in Example 2 and the control group of the composite material without porous structure and gradient distribution. DETAILED DESCRIPTION

[0032] The technical solutions of the present invention are described in detail below with reference to the accompanying drawings and embodiments. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0033] Example 1

[0034] MWCNTs were immersed in a solution of hydrochloric acid and nitric acid in a 1:3 molar ratio and maintained at 60°C for 72 hours. The solution was then washed with copious amounts of acetone and deionized water, filtered, and dried in a vacuum oven at 75°C for 12 hours. Three grams of the treated MWCNTs were then added to 500 ml of deionized water, along with 4.8 grams of FeCl₃·6H₂O and 2.4 grams of FeCl₂·4H₂O, and stirred for 30 minutes. Once dissolved, ammonia was injected to adjust the pH to 12, and the solution was reacted in an oil bath at 60°C for 2 hours. After the reaction was complete, the solution was repeatedly washed with deionized water until the supernatant was clear, filtered, and dried to yield Fe₃O₄ nanoparticle-modified MWCNTs. Fe3O4 nanoparticle-modified MWCNT and PDMS were mixed into 9 uniform composite slurries with a mass fraction of 1 to 9 wt% of Fe3O4 nanoparticle-modified MWCNT. After removing bubbles in a vacuum environment, the slurries were transferred to a 75°C oven for curing to obtain 9 composite materials with different concentrations and a thickness of about 1 mm.

[0035] Example 2

[0036] MWCNTs were immersed in a solution of hydrochloric acid and nitric acid in a 1:3 molar ratio and maintained at 60°C for 72 hours. The mixture was then washed with copious amounts of acetone and deionized water, filtered, and dried in a vacuum oven at 75°C for 12 hours. 3g of the treated MWCNTs were dissolved in 500ml of deionized water, and 4.8g of FeCl3·6H2O and 2.4g of FeCl2·4H2O were added and stirred for 30 minutes. Once dissolved, ammonia was injected to adjust the pH to 12, and the mixture was reacted in an oil bath at 60°C for 2 hours. After completion of the reaction, the mixture was repeatedly washed with deionized water until the supernatant was clear, filtered, and dried to obtain Fe3O4 nanoparticle-modified MWCNTs. The Fe3O4 nanoparticle-modified MWCNTs and PDMS were mixed to form a uniform composite slurry with a mass fraction of 5wt% Fe3O4 nanoparticle-modified MWCNTs. This slurry was then diluted with an equal volume of toluene and set aside. A 70 vol% volume fraction of granulated sugar (300-500 μm in particle size) was mixed with the diluted conductive composite material, then transferred to a petri dish and cast flat. The surface and bottom of the dish were covered with a permalloy soft magnetic sheet, and a permanent magnet with a surface magnetic field of approximately 5000 Oe was placed at the bottom. After standing at room temperature for 48 hours, the conductive composite skeleton was fully solidified. The composite was then peeled off and transferred to a 100°C water bath to dissolve the granulated sugar. Finally, the foam was rinsed with deionized water and dried naturally to produce a terahertz absorbing foam based on magnetically induced gradient carbon nanotubes with a thickness of approximately 3 mm.

[0037] Then, a portion of Fe3O4 nanoparticle-modified MWCNT and PDMS was mixed into a 5wt% uniform composite slurry. After removing bubbles in a vacuum environment, it was transferred to a 75°C oven for curing to obtain a non-porous structure and gradient distribution composite material with a thickness of about 3mm as a comparison group.

[0038] Figure 1 The dielectric parameter frequency domain spectra of the composite materials modified with MWCNTs of different Fe3O4 nanoparticle concentrations in Example 1; Figure 1 It can be seen that with the increase of the concentration of MWCNT modified by Fe3O4 nanoparticles, the dielectric real part and loss tangent of the composite material increase simultaneously, which improves the overall absorption performance to a certain extent.

[0039] Figure 2 The scanning electron photographs of four longitudinal regions of the terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes in Example 2 are shown; Figure 2 It can be seen that under the guidance of the magnetic field, MWCNTs move in a directional manner, and the concentration of MWCNTs modified with Fe3O4 nanoparticles gradually increases from the foam surface to the background.

[0040] Figure 3 is a comparison curve of the reflection and absorption frequency domain spectra of the terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes in Example 2 and the control group of the composite material without porous structure and gradient distribution; Figure 3 It can be seen that compared with the control group of non-porous structure and gradient distribution composite materials, the reflection suppression ability of the absorbing foam in Example 2 in the 0.2-1.2 THz frequency band is greatly improved, and it shows an average absorption rate higher than 99.99%.

[0041] The above description is only a preferred specific implementation method of the present invention and does not limit the present invention in any other form. Any technician familiar with the profession, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the protection scope of the present invention.

Claims

1. A terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes, characterized in that: It includes a porous skeleton and a wave absorbing agent distributed in the porous skeleton; The porous skeleton is a PDMS matrix with holes, the absorber is MWCNT modified with Fe3O4 nanoparticles, and the mass percentage of the absorber is 3-7wt%.

2. The terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes according to claim 1, characterized in that: In the PDMS substrate with holes, the hole diameter is 50-100 μm, 150-250 μm or 300-500 μm.

3. The terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes according to claim 1, characterized in that: The thickness of the wave-absorbing foam is 2 to 4 mm.

4. The terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes according to claim 1, characterized in that: In the wave-absorbing foam, the concentration of the wave-absorbing agent is distributed in a gradient in the longitudinal direction, decreasing from bottom to top.

5. A method for preparing terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes, characterized in that: The following steps are involved: Step 1. Surface modification of MWCNTs: 1.1 Soak the multi-walled carbon nanotubes in a mixture of hydrochloric acid and nitric acid at a molar ratio of 1:3 at 60°C for at least 72 hours; after washing and filtering, transfer to a vacuum oven at 75°C and dry for at least 12 hours; 1.2 The MWCNTs treated in step 1.1 are added to deionized water to prepare a 0.3-0.9 wt% multi-walled carbon nanotube solution, and then FeCl3·6H2O and FeCl2·4H2O are added to the multi-walled carbon nanotube solution and stirred for 20-40 minutes to obtain a precursor mixed solution; wherein the mass ratio of MWCNT, FeCl3·6H2O and FeCl2·4H2O is (3-7):8:4; 1.3 Add ammonia water to the precursor mixed solution obtained in step 1.2, adjust its pH to above 12, and react in an oil bath at 60°C for 1.5 to 2.5 hours. After the reaction is complete, wash, filter, and dry to obtain Fe3O4 nanoparticle-modified MWCNTs; Step 2. Preparation of conductive composite slurry: Mixing Fe3O4 nanoparticle-modified MWCNTs with PDMS to form a uniform composite slurry, wherein the mass ratio of Fe3O4 nanoparticle-modified MWCNTs to PDMS is (1-4.5):100; adding toluene of the same volume as the composite slurry to dilute the composite slurry and set aside; Step 3. Preparation of porous framework: Mix the white sugar granules and the composite slurry diluted in step 2, and then transfer them to a culture dish and cast them flat; Step 4. Magnetic induced gradient distribution: The surface and bottom of the culture dish obtained in step 3 are covered with permalloy soft magnetic sheets, and a permanent magnet is placed at the bottom; after standing at room temperature for not less than 48 hours, the conductive composite slurry is completely solidified, peeled off and transferred to a water bath at 60-100°C to dissolve white sugar; finally, after rinsing and drying, a terahertz absorbing foam based on magnetically induced gradient distributed carbon nanotubes is obtained.

6. The method for preparing terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes according to claim 5, characterized in that: In step 3, the volume fraction of the white sugar particles is 50-70 vol%; the particle size of the white sugar particles is 50-100 μm, 150-250 μm or 300-500 μm.

7. The method for preparing terahertz absorbing foam based on magnetically induced gradient distribution of carbon nanotubes according to claim 5, characterized in that: In step 4, a magnetic field of not less than 5000 Oe is applied in a direction perpendicular to the surface of the permanent magnet.

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