CN112165849B - Broadband adjustable graphene electromagnetic wave absorption material and preparation method thereof - Google Patents

Broadband adjustable graphene electromagnetic wave absorption material and preparation method thereof Download PDF

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CN112165849B
CN112165849B CN202011095278.3A CN202011095278A CN112165849B CN 112165849 B CN112165849 B CN 112165849B CN 202011095278 A CN202011095278 A CN 202011095278A CN 112165849 B CN112165849 B CN 112165849B
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graphene
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electromagnetic wave
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CN112165849A (en
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黄毅
蔡志灏
马文乐
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Nankai University
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    • H05K9/0071—Active shielding
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H01Q17/007—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems with means for controlling the absorption
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    • H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
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Abstract

The invention relates to a broadband adjustable graphene electromagnetic wave absorption material and a preparation method thereof. The preparation steps are as follows: preparing four single-layer graphene oxides with different sizes, and reducing the graphene oxides. Attaching the reduced graphene oxide to a conductive medium to form a first electromagnetic wave absorption interlayer; preparing a graphene film as a surface electrode by adopting a chemical vapor deposition method, preparing an oxide film as a medium layer on the graphene film by adopting an electron beam evaporation coating method, and forming a second wave-absorbing interlayer structure; a third wave-absorbing interlayer structure is formed by fusing semiconductor oxide and conductive polymer; and forming a three-dimensional structure graphene oxide wave-absorbing material as a fourth layer wave-absorbing structure through a hydrothermal reaction. Different voltages are applied to the top layer graphene and the bottom layer graphene, so that the absorption performance of the electromagnetic wave is regulated. The invention aims to prepare the efficient, stable and adjustable electromagnetic wave absorbing material by a simple method, and achieve the purpose of active adjustment for different environments.

Description

Broadband adjustable graphene electromagnetic wave absorption material and preparation method thereof
Technical Field
The invention relates to a broadband adjustable graphene electromagnetic wave absorption material and a preparation method thereof, in particular to an adjustable electromagnetic wave absorption structure.
Background
The rapid development of modern radio technology and radar detection technology greatly improves the target searching and tracking capacity of an aircraft detection system. The traditional combat weapon system is more and more seriously threatened, and the stealth technology becomes an effective means for improving the survival and defense capability of weapons, particularly the deep striking capability. The adjustable electromagnetic wave absorption material is particularly important for the ever-changing environment on the battlefield, and the electromagnetic wave absorption strength and the absorption frequency band can be adjusted according to different environments, so that the activity can be mastered on the battlefield.
The electromagnetic characteristic active regulation and control technology takes a structural composite material as a carrier, is compounded with an electromagnetic characteristic adjustable functional film layer, and controls the impedance characteristic of the film layer through an electric signal, thereby realizing the control of electromagnetic scattering/radiation. The technology can realize the control of the characteristic frequency band and the intensity of the scattering/radiation, thereby changing the RCS characteristics of the target. The technology has the functions of bearing, protecting and the like, can be directly applied to weaponry as a structural material, realizes the combination of ordinary-time high RCS and wartime low RCS of the equipment, avoids the model identification of enemies by changing the electromagnetic scattering and radiation frequency spectrum characteristics of the equipment, and can regulate and control the scattering/radiation characteristics of the equipment according to the scattering/radiation characteristics of background radars so as to ensure that the scattering/radiation characteristics of the equipment are consistent with the background.
Chinese patent CN107072128A discloses a broadband wave-absorbing material based on a polyaniline graphene three-dimensional porous structure. The absorbing material has a remarkable absorbing effect on incident electromagnetic waves in a frequency band of 4-18 GHz.
CN 109121375a discloses a composite microwave absorber of dielectric material filled with magnetic metal and its preparation method. The absorber takes a semiconductor material as a dielectric material outside the cladding structure, and is filled with metal nano particles. The semiconductor material is one of multi-walled carbon nanotubes, zinc oxide, graphene and silicon carbide; the metal nano particles are one or more of Fe, Co and Ni.
CN109294519A discloses a preparation method of a broadband graphene wave-absorbing material with a multilayer structure and a concentration gradient design, which comprises the following steps: step one, obtaining reduced graphene oxide hydrogel by adopting a hydrothermal chemical self-assembly method; step two, preparing porous graphene sponge; step three, preparing graphene sponges with different densities; filling the graphene sponge into honeycomb holes of the periodic aramid fiber honeycomb, and stacking the graphene sponge from top to bottom according to the sequence of the small concentration to the large concentration of the graphene sponge; and fifthly, a single-layer quartz fiber reinforced resin matrix composite material is adopted between the honeycomb layers as a connecting layer, and quartz fiber reinforced resin matrix composite material skins and carbon fiber reinforced resin matrix composite material skins are respectively covered on the upper side and the lower side of the spliced honeycomb to obtain the broadband graphene wave-absorbing material with the multi-layer structure and the concentration gradient design.
None of the above prior art can well satisfy the active adjustable electromagnetic wave absorption performance, so the application range is limited, the development can well satisfy the active adjustable requirement, and the adjustment of the electromagnetic wave absorption frequency in the X band is necessary.
Disclosure of Invention
The invention aims to provide a broadband adjustable graphene electromagnetic wave absorption material and a preparation method thereof. The material is a multilayer broadband adjustable graphene electromagnetic wave absorption material, can realize the functions of amplitude modulation and frequency modulation of electromagnetic wave absorption, and achieves the purpose of controlling the transmittance and reflectivity of electromagnetic waves by controlling the voltage loaded at two ends of the electromagnetic wave absorption material. The electrolyte/graphene layer assembled composite material is ultrathin, high in electromagnetic wave absorption performance and high in stability, has excellent comprehensive performance, has wide prospects in the field of electromagnetic wave absorption of microelectronic devices and flexible electronic equipment, can be particularly applied to wearable devices, and can regulate the absorption of electromagnetic waves through voltage regulation and control according to the requirements of the environment in the using process.
The multilayer broadband adjustable graphene electromagnetic wave absorption material provided by the invention is adjusted by a voltage of 0-20V in a wave band of 8-40GHz, and the adjustable electromagnetic wave absorption strength ranges from-3 dB to-25 dB, and the preparation method comprises the following steps:
1) preparing a graphene oxide film from freshly prepared graphene oxide by suction filtration or spin coating, and reducing to obtain reduced graphene oxide.
2) Dissolving the conductive medium and the polymer in a solvent, heating in a vacuum oven at 60-100 ℃ for 12-48h, and completely curing the conductive medium.
3) And (3) transferring the graphene film obtained in the step 1) to two ends of the conductive medium solidified in the step 2), and attaching the graphene film to a polymer substrate to form a first wave-absorbing interlayer structure.
4) In the step 3), the top layer graphene and the bottom layer graphene of the sandwich structure are convenient to apply voltage to the graphene sandwich structure by adding the metal gasket.
5) And preparing a graphene film as a surface electrode by adopting a chemical vapor deposition method, and preparing an oxide film as a medium layer on the graphene film by adopting an electron beam evaporation coating method to form a second wave-absorbing interlayer structure.
6) And (3) attaching the second wave-absorbing interlayer structure in the step 5) with the first wave-absorbing interlayer structure in the step 3).
7) A third wave-absorbing interlayer structure is formed by fusing semiconductor oxide and conductive polymer; and (4) attaching the second wave-absorbing interlayer structure in the step 6).
8) Forming a three-dimensional graphene oxide wave-absorbing material as a fourth layer of wave-absorbing structure through a hydrothermal reaction; and (3) attaching the third wave-absorbing interlayer structure in the step 7) to form an integral broadband adjustable graphene electromagnetic wave absorption material.
9) The whole wave-absorbing sandwich structure is packaged, so that the whole wave-absorbing material is prevented from absorbing moisture and influencing the electromagnetic wave absorption effect.
The graphene oxide in the step 1) is prepared by using natural crystalline flake graphite as a raw material through an improved Hummer's method, controlling the size of the natural crystalline flake graphite to be 10-300 mu m through controlling the size of the natural crystalline flake graphite, the dosage of an oxidant, the reaction temperature, the oxidation time and a subsequent centrifugation process, and preferably preparing four graphene oxides with different sizes, wherein the four graphene oxides are all single-layered and have the sizes of 10-30 mu m, 40-50 mu m, 80-100 mu m, 120-150 mu m and 150-300 mu m respectively. The thickness of the graphene oxide film in the step 1) is 5-60 μm, preferably 10-20 μm.
The reduction method in the step 1) comprises a thermal reduction method, wherein the reduction temperature is 600-800 ℃ under the protection of argon; there is a chemical reduction method, the reduction reagent is at least one of hydriodic acid, sodium citrate, ammonia water and phosphoric acid.
The conductive medium in the step 2) is bis (trifluoromethyl sulfonyl) lithium amide (LiTFSA), bis (trifluoromethyl sulfonyl) lithium imide (LiTFSI) and lithium perchlorate (LiClO)4) Lithium hexafluorophosphate (LiPF)6) Lithium tetrafluoroborate (LiBF)4) At least one of them.
The polymer in the step 2) is at least one of Polyacrylonitrile (PAN), polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA) and polyvinylidene chloride (PVDC). The thickness of the polymer is 10-500 μm, preferably 100-200 μm.
The solvent in the step 2) is at least one of ethanol, deionized water, Dimethylformamide (DMF), acetonitrile and tetrahydrofuran.
The polymer substrate in the step 3) is at least one of Polyimide (PI), polyvinyl chloride (PVC), Polyethylene (PE), polypropylene (PP), Polystyrene (PS), Polyamide (PA), polyethylene terephthalate (PET) and Polycarbonate (PC).
The metal gasket in the step 4) is at least one of copper, nickel, ruthenium, cobalt, iridium, palladium, platinum and alloy thereof.
The oxide in the step 5) is tungsten trioxide (WO)3) Nickel oxide (NiO), vanadium dioxide (VO)2) Vanadium pentoxide (V)2O5) Titanium dioxide (TiO)2) At least one of (1).
The semiconductor oxide in the step 7) is tin oxide (SnO)2) Zinc oxide (ZnO), cadmium oxide (CdO), ferric oxide (Fe)2O3) Aluminum oxide (Al)2O3) At least one of; the conductive polymer is at least one of polyacetylene, polypyrrole, polythiophene, polyphenylene and polyphenylacetylene.
The temperature of the hydrothermal reaction in the step 8) is 100-200 ℃; the temperature can be selected from 100 ℃, 120 ℃, 150 ℃, 180 ℃ or 200 ℃. Preferably 180 deg.c.
Step 9), the concentration of the hydrothermal reaction graphene oxide ethanol solution is 0.1-1.5 mg/mL; optionally 0.1mg/mL, 0.3mg/mL, 0.5mg/mL, 0.6mg/mL, 0.9mg/mL, 1mg/mL, 1.2mg/mL, or 1.5 mg/mL.
The application of the broadband adjustable graphene electromagnetic wave absorption material provided by the invention comprises the field of electromagnetic wave absorption of microelectronic devices and flexible electronic equipment and the like, and the material can be particularly applied to wearable electromagnetic wave absorption devices.
The invention provides a broadband adjustable graphene electromagnetic wave absorption material. The broadband adjustable graphene electromagnetic wave absorption material has the following characteristics:
1) the multilayer composite material is used as the electromagnetic absorption material with adjustable absorption performance for the first time, and the electromagnetic absorption material shows excellent comprehensive performance.
2) The electromagnetic wave absorbing material has an ultrathin thickness as low as millimeter level, and has wide prospects in applications such as aircrafts, aerospace, wearable electronic devices and portable electronic equipment.
3) The electromagnetic wave absorption material has high absorption efficiency, the electromagnetic wave absorption performance is adjusted by the voltage of 0-20V in the wave band of 8-40GHz, the absorption intensity of the adjustable electromagnetic wave ranges from-3 dB to-25 dB, and the requirement of active adjustment can be well met. The adjustment of the absorption frequency of the electromagnetic wave in the X wave band can be achieved by changing the voltage loaded at two ends of the third wave-absorbing interlayer structure.
4) The electromagnetic wave absorbing material has high oxidation resistance. The graphene has good impermeability, thermal stability and chemical stability, so that the oxidation of the graphene is slowed down to a great extent, and the stability of the whole absorption performance of the graphene is ensured.
5) The invention can realize the regulation and control of the absorption performance through the regulation of low voltage, has a large space on the application prospect, and can regulate and control the absorption rate of electromagnetic waves according to different environments and requirements. The average absorption performance of the whole electromagnetic wave absorption material at 8-40GHz is-3 dB when the voltage is 0V, the whole material can meet the electromagnetic wave absorption of-8 dB at 8-40GHz when the voltage is increased to 5V, the highest absorption performance of the electromagnetic wave of the material is further improved to-15 dB when the voltage is increased to 10V, the electromagnetic wave absorption performance is best when the voltage reaches 15V, the highest absorption strength reaches-25 dB, the absorption performance of the electromagnetic wave is weakened when the voltage is increased again, and the average absorption performance of the electromagnetic wave absorption is only-13 dB when the voltage is 20V. And for the third layer wave-absorbing sandwich structure, different voltages are loaded, the resistance of the semiconductor oxide layer is correspondingly changed, so that the requirement of adjusting the absorption frequency is met in an X wave band, when the voltage loaded at two ends is 0V, the absorption frequency is about 12GHz, when the voltage is slowly increased to 3V, the absorption peak gradually moves to low frequency, when the voltage is 1.3V, the position of the absorption peak is about 10GHz, and when the voltage reaches 3V, the position of the absorption peak further moves to low frequency, and the position is about 8 GHz. The broadband adjustable performance is well met, and the electromagnetic wave absorption efficiency is different for different electromagnetic wave band regulation and control voltages. The invention provides a new way for researching the electromagnetic wave absorption, reflection and transmissivity of the material.
In a word, the electrolyte/graphene layer combined composite material is ultrathin, high in electromagnetic wave absorption performance and high in stability, has excellent comprehensive performance, has wide prospects in the field of electromagnetic wave absorption of microelectronic devices and flexible electronic equipment, is particularly applicable to wearable devices, and can adjust the absorption of electromagnetic waves through voltage regulation and control according to the requirements of the environment in the using process.
Drawings
Fig. 1 is an SEM photograph of the broadband-tunable graphene electromagnetic wave absorbing material of the four-layer wave absorbing structure prepared in example 1.
FIG. 2 is a schematic view of a four-layer wave-absorbing material structure prepared in example 1.
FIG. 3 is a wave-absorbing 8-40GHz electromagnetic wave reflectivity curve of the four-layer wave-absorbing material structure prepared in example 1.
FIG. 4 is a reflection curve of the integral material of electromagnetic wave of X-band integral material, when the voltage applied to the two ends of the integral wave-absorbing material is 15V, the highest absorption intensity of the electromagnetic wave reaches-18 dB, the corresponding absorption frequency is 12GHz, the reflection loss at 8.2-12.4GHz is lower than-13 dB, and the excellent broadband absorption effect is shown.
FIG. 5 is a reflection curve of the integral material of electromagnetic wave of X-band integral material, when the voltage applied to the two ends of the integral wave-absorbing material is 20V, the highest absorption intensity of the electromagnetic wave reaches-21 dB, the corresponding absorption frequency is 12.3GHz, and the reflection loss at 8.2-12.4GHz is lower than-12 dB, showing excellent broadband absorption effect.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.
The experimental methods in the examples, in which specific conditions are not specified, are generally performed under the conditions described in the manual and the conventional conditions, or under the conditions recommended by the manufacturer; the equipment, materials, reagents and the like used are commercially available unless otherwise specified.
Example 1:
1) by an improved Hummer's method, natural crystalline flake graphite is used as a raw material, and the size is controlled by controlling the size of the natural crystalline flake graphite, the using amount of an oxidant, the reaction temperature, the oxidation time and the subsequent centrifugation process, so that the small piece of graphene oxide (SGO) is prepared, wherein the size of the small piece of graphene oxide is 40-50 mu m (SGO).
2) Firstly, 250 mg of graphene oxide is dissolved in ethanol, then a square polytetrafluoroethylene die with the thickness of 18cm x 18cm is prepared, the graphene oxide dispersion liquid is slowly dripped into the die, the graphene oxide dispersion liquid is uniformly distributed in the die in a spin coating mode, the thickness of the graphene oxide film is about 15 mu m, then the graphene oxide film is placed into an oven for drying treatment at 60 ℃, and two graphene oxide films are prepared by the same method.
3) Lithium perchlorate (LiClO)4) Adding the mixture and polymethyl methacrylate (PMMA) into an acetonitrile solvent, heating to 50 ℃, uniformly mixing, pouring the mixed solution into a 18 cm-18 cm mould, and heating and drying in a glove box at 60 ℃.
4) Placing the graphene oxide film in hydriodic acid (HI), soaking for 20min, placing the film in deionized water and ethanol in sequence, washing off residual hydriodic acid on the surface, drying at room temperature to obtain a reduced graphene oxide film, and transferring the reduced graphene oxide film to a polyvinyl chloride (PVC) substrate.
5) Two graphene films are attached to an electrolyte (lithium perchlorate), and two metal copper gaskets are respectively connected from the upper surface of the top graphene layer and the lower surface of the bottom graphene layer to serve as electrodes, so that a first wave-absorbing interlayer structure is formed. The voltage is conveniently added, different voltages are applied to two ends of the graphene through a direct-current stabilized voltage supply, and the regulation and control of the sandwich structure on the absorption of electromagnetic waves are measured through a waveguide method and an arc method of a vector network analyzer. The test parameters are conventional.
6) Preparing a graphene film as a surface electrode by adopting a chemical vapor deposition method, and preparing oxide VO on the graphene film by adopting an electron beam evaporation coating method2The film is used as a medium layer to form a second wave-absorbing interlayer structure.
7) And (3) attaching the second wave-absorbing interlayer structure in the step 6) with the first wave-absorbing interlayer structure in the step 5).
8) Using semiconductor oxide SnO2And dissolving conductive high-molecular polyacetylene in an acetonitrile solution for fusion, and then putting the fused material into a vacuum drying oven for drying at 60 ℃ for 12 hours to form a third wave-absorbing interlayer structure. Attaching the second wave-absorbing sandwich structure in the step 7)。
9) Graphene oxide ethanol solution with the concentration of 0.6mg/mL is put into a hydrothermal reaction kettle to carry out hydrothermal reaction at 180 ℃ to form a three-dimensional graphene oxide wave-absorbing material as a fourth-layer wave-absorbing structure. And (3) attaching the third wave-absorbing interlayer structure in the step 8) to form an integral broadband adjustable graphene electromagnetic wave absorption material. And packaging the whole wave-absorbing interlayer structure, and putting the whole material into a polyvinyl chloride (PVC) square box by stacking layer by layer.
Fig. 1 is an SEM photograph of the prepared broadband adjustable graphene electromagnetic wave absorbing material with the four-layer wave absorbing structure.
FIG. 2 is a schematic view of a four-layer wave-absorbing material structure prepared. The four-layer wave-absorbing material structure body is formed by mutually attaching a first wave-absorbing interlayer structure, a second wave-absorbing interlayer structure, a third wave-absorbing interlayer structure and a fourth wave-absorbing structure.
Attaching the reduced graphene oxide to a conductive medium to form a first electromagnetic wave absorption interlayer; preparing a graphene film as a surface electrode by adopting a chemical vapor deposition method, preparing an oxide film as a medium layer on the graphene film by adopting an electron beam evaporation coating method, and forming a second wave-absorbing interlayer structure; a third wave-absorbing interlayer structure is formed by fusing semiconductor oxide and conductive polymer; and forming a three-dimensional structure graphene oxide wave-absorbing material through hydrothermal reaction to serve as a fourth layer of wave-absorbing structure, and packaging the whole wave-absorbing sandwich structure.
FIG. 3 is a wave-absorbing 8-40GHz electromagnetic wave reflectivity curve of the prepared four-layer wave-absorbing material structure.
When the voltage applied to the two ends of the integral wave-absorbing material is 15V, the highest absorption intensity of electromagnetic waves reaches-25 dB, the corresponding absorption frequency is 37.2GHz, the reflection loss at 26.5-40GHz is lower than-12 dB, and the excellent broadband absorption effect is displayed.
Example 2:
1) by an improved Hummer's method, natural crystalline flake graphite is used as a raw material, and the size is controlled by controlling the size of the natural crystalline flake graphite, the using amount of an oxidant, the reaction temperature, the oxidation time and the subsequent centrifugation process, so that the small piece of graphene oxide (SGO) is prepared, wherein the size of the small piece of graphene oxide is 40-50 mu m (SGO).
2) Firstly, 400 mg of graphene oxide is dissolved in ethanol, then a square polytetrafluoroethylene die with the thickness of 18cm x 18cm is prepared, the graphene oxide dispersion liquid is slowly dripped into the die, the graphene oxide dispersion liquid is uniformly distributed in the die in a spin coating mode, the thickness of the graphene oxide film is about 30 mu m, then the graphene oxide film is placed into an oven for drying treatment at 60 ℃, and two graphene oxide films are prepared by the same method.
3) Adding lithium bistrifluoromethylsulfonyl amide (LiTSFI) and polyethylene oxide (PEO) into an acetonitrile solvent, heating to 50 ℃, uniformly mixing, pouring the mixed solution into a 18 cm-18 cm mould, and heating and drying in a glove box at 60 ℃.
4) And (2) placing the graphene oxide film in a tubular furnace for reduction treatment, raising the temperature in the furnace to 700 ℃ under the protection of argon, wherein the time is 60min, obtaining the reduced graphene oxide film, and transferring the reduced graphene oxide film to a polyvinyl chloride (PVC) substrate.
5) Two graphene films are attached to an electrolyte (bis (trifluoromethyl sulfonyl) lithium amide), and two metal copper gaskets are respectively connected from the upper surface of the top graphene and the lower surface of the bottom graphene to serve as electrodes, so that a first wave-absorbing interlayer structure is formed. The voltage is conveniently added, different voltages are applied to two ends of the graphene through a direct-current stabilized voltage supply, and the regulation and control of the sandwich structure on the absorption of electromagnetic waves are measured through a waveguide method and an arc method of a vector network analyzer.
6) Preparing a graphene film as a surface electrode by adopting a chemical vapor deposition method, and preparing oxide NiO on the graphene film by adopting an electron beam evaporation coating method3The film is used as a medium layer to form a second wave-absorbing interlayer structure.
7) And (3) attaching the second wave-absorbing interlayer structure in the step 6) with the first wave-absorbing interlayer structure in the step 5).
8) The third layer of wave-absorbing interlayer structure is formed by dissolving semiconductor oxide ZnO and conductive high-molecular polythiophene into acetonitrile solution for fusion, and then putting the mixture into a vacuum drying oven for drying at 60 ℃ for 12 hours. And (4) attaching the second wave-absorbing interlayer structure in the step (7).
9) Graphene oxide ethanol solution with the concentration of 0.9mg/mL is put into a hydrothermal reaction kettle to carry out hydrothermal reaction at 180 ℃ to form a three-dimensional graphene oxide wave-absorbing material serving as a fourth layer of wave-absorbing structure. And (3) attaching the third layer of wave-absorbing interlayer structure in the step 8). An integral broadband adjustable graphene electromagnetic wave absorption material is formed.
FIG. 4 is a reflection curve of the integral material of electromagnetic wave of the X-band integral material, when the voltage applied to the two ends of the integral wave-absorbing material is 15V, the highest absorption intensity of the electromagnetic wave reaches-18 dB, the corresponding absorption frequency is 12GHz, and the reflection loss at 8.2-12.4GHz is lower than-13 dB, thus showing excellent broadband absorption effect.
Example 3:
1) by an improved Hummer's method, natural crystalline flake graphite is used as a raw material, and the size is controlled by controlling the size of the natural crystalline flake graphite, the using amount of an oxidant, the reaction temperature, the oxidation time and the subsequent centrifugation process, so that the small piece of graphene oxide (SGO) is prepared, wherein the size of the small piece of graphene oxide is 40-50 mu m (SGO).
2) Firstly, 250 mg of graphene oxide is dissolved in ethanol, then a square polytetrafluoroethylene die with the thickness of 18cm x 18cm is prepared, the graphene oxide dispersion liquid is slowly dripped into the die, the graphene oxide dispersion liquid is uniformly distributed in the die in a spin coating mode, the thickness of the graphene oxide film is about 15 mu m, then the graphene oxide film is placed into an oven for drying treatment at 60 ℃, and two graphene oxide films are prepared by the same method.
3) Adding lithium bistrifluoromethylsulfonyl amide (LiTSFI) and polyethylene oxide (PEO) into an acetonitrile solvent, heating to 50 ℃, uniformly mixing, pouring the mixed solution into a 18 cm-18 cm mould, and heating and drying in a glove box at 60 ℃.
4) And (2) placing the graphene oxide film in a tubular furnace for reduction treatment, raising the temperature in the furnace to 700 ℃ under the protection of argon, wherein the time is 60min, obtaining the reduced graphene oxide film, and transferring the reduced graphene oxide film to a polyvinyl chloride (PVC) substrate.
5) Two graphene films are attached to an electrolyte (bis (trifluoromethyl sulfonyl) lithium amide), and two metal aluminum gaskets are respectively connected from the upper surface of the top graphene and the lower surface of the bottom graphene to serve as electrodes, so that a first wave-absorbing interlayer structure is formed. The voltage is conveniently added, different voltages are applied to two ends of the graphene through a direct-current stabilized voltage supply, and the regulation and control of the sandwich structure on the absorption of electromagnetic waves are measured through a waveguide method and an arc method of a vector network analyzer.
6) Preparing a graphene film as a surface electrode by adopting a chemical vapor deposition method, and preparing an oxide WO on the graphene film by adopting an electron beam evaporation coating method3The film is used as a medium layer to form a second wave-absorbing interlayer structure.
7) And (3) attaching the second wave-absorbing interlayer structure in the step 6) with the first wave-absorbing interlayer structure in the step 5).
8) Using a semiconductor oxide Al2O3And the conductive polymer polythiophene are dissolved in acetonitrile solution to be fused, and then are placed into a vacuum drying oven at 60 ℃ and dried for 12 hours to form a third layer wave-absorbing interlayer structure. And (4) attaching the second wave-absorbing interlayer structure in the step (7).
9) Graphene oxide ethanol solution with the concentration of 1.2mg/mL is put into a hydrothermal reaction kettle to carry out hydrothermal reaction at 180 ℃ to form a three-dimensional graphene oxide wave-absorbing material serving as a fourth layer of wave-absorbing structure. And (3) attaching the third layer of wave-absorbing interlayer structure in the step 8). An integral broadband adjustable graphene electromagnetic wave absorption material is formed.
FIG. 5 is a reflection curve of the integral material of electromagnetic wave of X-band integral material, when the voltage applied to the two ends of the integral wave-absorbing material is 20V, the highest absorption intensity of the electromagnetic wave reaches-21 dB, the corresponding absorption frequency is 12.3GHz, and the reflection loss at 8.2-12.4GHz is lower than-12 dB, showing excellent broadband absorption effect.

Claims (10)

1. A preparation method of a broadband adjustable graphene electromagnetic wave absorption material for a wearable device is characterized in that the material is adjusted by a voltage of 0-20V in a wave band of 8-40GHz, and the adjustable electromagnetic wave absorption intensity is in a range from-3 dB to-25 dB, and the preparation method comprises the following steps:
1) preparing graphene oxide by using natural crystalline flake graphite as a raw material and using an improved Hummer's method; reduced graphene oxide is obtained through reduction treatment; preparing a graphene oxide film with the thickness of 10-20 microns in a spin coating mode;
2) dissolving conductive medium lithium perchlorate or bis-trifluoromethyl sulfonyl amino lithium and polymer polymethyl methacrylate or polyethylene oxide in a solvent, heating in a vacuum oven at 60-100 ℃ for 12-48h, and completely curing the conductive medium;
3) transferring the graphene film in the step 1) to two ends of the conductive medium solidified in the step 2), and attaching the graphene film to a polymer substrate to form a first wave-absorbing interlayer structure;
4) in the step 3), the top layer graphene and the bottom layer graphene of the sandwich structure are convenient to apply voltage to the graphene sandwich structure by adding metal gaskets;
5) preparing a graphene film as a surface electrode by adopting a chemical vapor deposition method, preparing an oxide film as a medium layer on the graphene film by adopting an electron beam evaporation coating method, and forming a second wave-absorbing interlayer structure;
6) attaching the second wave-absorbing interlayer structure in the step 5) to the first wave-absorbing interlayer structure in the step 3);
7) a third wave-absorbing interlayer structure is formed by fusing semiconductor oxide and conductive polymer; attaching the second wave-absorbing interlayer structure in the step 6);
8) forming a three-dimensional graphene oxide wave-absorbing material as a fourth layer of wave-absorbing structure through a hydrothermal reaction; attaching the third layer of wave-absorbing interlayer structure in the step 7) to form an integral broadband adjustable graphene electromagnetic wave absorption material;
9) and packaging the whole wave-absorbing interlayer structure.
2. The method of claim 1, wherein: step 1) controlling the size of 10-300 mu m by controlling the size of natural crystalline flake graphite, the dosage of an oxidant, the reaction temperature, the oxidation time and the subsequent centrifugation process; the reduction method comprises the following steps: a reduction method, namely under the protection of argon, the reduction temperature is 600-800 ℃; or a chemical reduction process wherein the reducing agent is hydroiodic acid.
3. The method according to claim 1, wherein the polymer of step 2) has a thickness of 10 to 500 μm; the solvent is ethanol, deionized water, dimethylformamide, acetonitrile or tetrahydrofuran.
4. The method according to claim 1, wherein the polymer substrate in step 3) is at least one of polyimide, polyvinyl chloride, polyethylene, polypropylene, polystyrene, polyamide, polyethylene terephthalate, and polycarbonate.
5. The method of claim 1, wherein the metal pad of step 4) is copper, nickel, ruthenium, cobalt, iridium, palladium, platinum, or an alloy thereof.
6. The method according to claim 1, wherein the oxide in step 5) is at least one of tungsten trioxide, nickel oxide, vanadium dioxide, vanadium pentoxide, and titanium dioxide.
7. The method according to claim 1, wherein the semiconductor oxide in step 7) is at least one of tin oxide, zinc oxide, cadmium oxide, ferric oxide, and aluminum oxide; the conductive polymer is at least one of polyacetylene, polypyrrole, polythiophene, polyphenylene and polyphenylacetylene.
8. The process according to claim 1, wherein the temperature of the hydrothermal reaction in step 8) is 100-200 ℃.
9. The method according to claim 1, wherein the concentration of the hydrothermal reaction graphene oxide ethanol solution in the step 9) is 0.1 to 1.5 mg/mL.
10. The broadband tunable graphene electromagnetic wave absorbing material obtained by the preparation method of any one of claims 1 to 9.
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