Preparation method of polyimide reinforced graphene aerogel terahertz wave-absorbing material

Abstract

The invention belongs to the field of terahertz wave-absorbing materials, provides a preparation method of a polyimide reinforced graphene aerogel terahertz wave-absorbing material, and aims to solve the problems of high density, poor mechanical property and the like of the existing wave-absorbing material. According to the preparation method, an ice template method is adopted, doping or dipping of other wave absorbing agents with loss capacity is not needed, reduction-oxidation graphene aerogel is obtained through directional freezing on the premise that material components are not changed, the high-strength terahertz wave absorbing material with the porous structure is obtained by dipping polyimide, and the high-strength terahertz wave absorbing material with the porous structure is obtained by utilizing the multi-reflection principle of the porous structure. And the broadband strong absorption performance is realized. The polyimide reinforced graphene aerogel with the high-strength porous structure is successfully prepared, the porous structure can increase the propagation path of terahertz waves, incident electromagnetic waves can be weakened step by step due to multiple reflections, loss electromagnetic waves are effectively absorbed, meanwhile, the combination of high strength and high absorption performance of the aerogel is achieved, and the preparation method is suitable for large-scale popularization and application. The wave-absorbing material has the advantages of excellent wave-absorbing performance, stable structure and the like.

Description

Technical Field

[0001] This invention belongs to the field of terahertz absorbing materials, specifically providing a method for preparing a polyimide-reinforced graphene aerogel terahertz absorbing material. Background Technology

[0002] Terahertz absorbing materials are key foundational materials supporting cutting-edge technologies such as next-generation wireless communication, high-precision imaging, and biosensing. Their technological background is rooted in the unique physical properties of terahertz waves and the urgent application needs. The terahertz band (0.1-10 THz) lies between microwaves and infrared, possessing both the penetrability of microwaves and the fingerprint recognition capabilities of infrared, along with low photon energy and extremely high bandwidth. This makes it show revolutionary potential in fields such as 6G communication, security imaging, non-destructive testing, and medical diagnostics. However, these very characteristics present unprecedented challenges to absorbing materials: traditional microwave ferrites suffer a sharp performance decline due to magnetic loss mechanisms failing in the terahertz band; conventional dielectric materials are too transparent and have weak absorption; and metals become highly reflective. This contradiction has spurred research into materials specifically designed for terahertz waves, with the core objective of achieving efficient and controllable electromagnetic energy dissipation to meet critical requirements such as radar shielding in stealth technology, efficient signal conversion in detectors, and clutter suppression in testing systems. To address these challenges, we must move beyond the limitations of the classic "intrinsic properties of materials" and shift our focus to the active design of micro and nanostructures of materials and the exploration of novel loss mechanisms.

[0003] Against this backdrop, porous microwave absorbing materials have emerged and become a hot research topic. Their technical mechanism lies in achieving a synergistic effect of "loss enhancement and impedance matching" through porous structures: on the one hand, closed pores, open pores, and hierarchical channels within the material can significantly increase the multiple reflection and scattering paths of terahertz waves within the material, extending the propagation distance and thus promoting a more complete conversion of electromagnetic energy into heat loss; on the other hand, the introduction of pores can reduce the material's equivalent dielectric constant and density, decrease the wave impedance difference between the material and air interfaces, improve the electromagnetic wave coupling incident efficiency, and reduce surface reflection. Graphene aerogels, due to their large specific surface area, high porosity, lightweight, and designability, are widely used in microwave absorbing research. However, their mechanical load-bearing capacity is often weak; the compressive strength of unreinforced systems can be in the kPa range, making them prone to collapse or irreversible damage under external loads, assembly compression, and cyclic deformation conditions, thus affecting structural integrity and service stability. With increasing demands for processability, environmental tolerance, and lifespan consistency in application scenarios, the structural strengthening and stabilization design of high-strength and tough aerogel microwave absorbing materials is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing polyimide-reinforced graphene aerogel terahertz absorbing materials. This method yields porous, high-strength absorbing materials, addressing the problems of high density and poor mechanical properties in existing absorbing materials. This invention employs an ice-templating method, eliminating the need for doping or impregnation with other loss-inducing absorbing agents. Reduced graphene oxide aerogel is obtained through directional freezing without altering the material composition. By impregnating polyimide, a high-strength, porous terahertz absorbing material is obtained. Utilizing the multiple reflection principle of the porous structure, broadband strong absorption performance is achieved.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a polyimide-reinforced graphene aerogel terahertz absorbing material, characterized by comprising the following steps:

[0007] Step 1. Preparation of graphene oxide solution: Graphene oxide solution was prepared using the Hummers method;

[0008] Step 2. Preparation of reduced graphene oxide aerogel: Pour graphene oxide solution into a mold, freeze and freeze dry to obtain graphene oxide aerogel block, and then reduce at high temperature of 800℃~1000℃ to obtain loose and porous reduced graphene oxide aerogel block.

[0009] Step 3. Preparation of polyimide-reinforced graphene aerogel: Subsequently, polyimide is used to impregnate reduced graphene oxide bulk material to obtain polyimide-reinforced graphene aerogel terahertz absorbing material.

[0010] Furthermore, in step 1, the concentration of the prepared graphene oxide solution is 6 mg / ml to 8 mg / ml.

[0011] Furthermore, in step 2, the graphene oxide solution is frozen at -20℃ to -30℃ for 1h to 2h, the freeze-drying temperature is -70℃ to -80℃ for 24h to 28h, and the high-temperature reduction time is 1h to 1.5h.

[0012] Furthermore, in step 3, the polyimide used is first heated in an oil bath at 60℃~80℃ to obtain a polyimide solution. Then, the polyimide is poured into a mold containing reduced graphene oxide, submerging the reduced graphene oxide block. The mold is then evacuated in a vacuum drying oven at 60℃~70℃ and 0.15MPa~0.2MPa for 0.5 h~1 h.

[0013] Furthermore, in step 3, the sample after vacuuming is placed in an oven and pre-cured at 160℃~180℃ for 0.5 h~1 h, and then fully cured at 220℃~240℃ for 1 h~1.5 h to obtain polyimide-reinforced graphene aerogel terahertz absorbing material.

[0014] In terms of working principle:

[0015] Graphene, due to its large specific surface area, possesses advantages in lightweight and designability; polyimide, with its unique molecular structure (containing an imide ring), exhibits a variety of superior properties, demonstrating irreplaceable advantages in extreme environments such as high temperature and high stress. Therefore, this invention employs an ice template method, without doping or impregnating with other loss-inducing absorbing agents, to directionally freeze reduced graphene oxide aerogel without altering the material composition. By impregnating with polyimide, a high-strength, porous terahertz absorbing material is obtained. Unlike other simple graphene aerogels, polyimide-reinforced graphene aerogel not only effectively absorbs electromagnetic waves in the terahertz band by subjecting incident electromagnetic waves to multiple reflections and scattering, increasing the propagation path and reducing losses, thus achieving broadband and strong absorption performance, but also enhances the strength of the aerogel itself and significantly improves its compressibility, meeting the requirements of thinness, lightness, width, and strength.

[0016] In summary, the beneficial effects of the present invention are as follows:

[0017] This invention proposes a method for preparing polyimide-reinforced graphene aerogel terahertz absorbing materials. Graphene-polyimide aerogels are prepared without doping or impregnating with other absorbing agents or altering the material composition. The porous structure significantly increases the propagation path of terahertz waves, and the incident electromagnetic waves gradually weaken due to multiple reflections, effectively absorbing and reducing electromagnetic waves—a terahertz absorbing effect through multiple reflections / scattering. Furthermore, this invention combines the high strength and high absorption performance of the aerogel, exhibiting advantages such as excellent absorption performance and structural stability. Attached Figure Description

[0018] Figure 1 This is a SEM image of the polyimide-reinforced graphene aerogel in an embodiment of the present invention.

[0019] Figure 2 This is a reflection loss diagram of polyimide-reinforced graphene aerogel in an embodiment of the present invention.

[0020] Figure 3 This is a diagram showing the compressive strength of polyimide-reinforced graphene aerogel in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] This embodiment provides a method for preparing a polyimide-reinforced graphene aerogel terahertz absorbing material. The method involves directional freezing using an ice template to obtain reduced graphene oxide aerogel, followed by impregnation with polyimide to obtain a high-strength, porous terahertz absorbing material. Polyimide (PI) is a high-performance polymer material with various superior properties due to its unique molecular structure (containing an imide ring), exhibiting irreplaceable advantages in extreme environments such as high temperature and high stress. Based on this, graphene, which has electromagnetic loss capability, is used as a component of the aerogel. After thorough bonding with polyimide, a porous polyimide-reinforced graphene aerogel is formed.

[0023] Specifically, the preparation method of the polyimide-reinforced graphene aerogel includes the following steps:

[0024] Step 1. Preparation of graphene oxide solution: Graphene oxide solution was prepared using a modified Hummers method, with a concentration of 6 mg / ml.

[0025] Step 2. Preparation of reduced graphene oxide aerogel: Pour the graphene oxide solution into a silicone mold and freeze at -20℃ for 2 hours. After freezing, freeze-dry to obtain graphene oxide aerogel blocks. The freeze-drying temperature is -80℃ and the time is 24 hours. Then, reduce at 1000℃ for 1 hour to obtain loose and porous reduced graphene oxide aerogel blocks.

[0026] Step 3. Preparation of polyimide-reinforced graphene aerogel: Polyimide was heated in an oil bath at 80°C to obtain a polyimide solution. Then, the polyimide was poured into a mold containing reduced graphene oxide, ensuring the reduced graphene oxide was completely submerged, thus completing the casting process. The sample was then vacuumed in a vacuum drying oven at 60°C and 0.15 MPa for 0.5 hours to defoam. After defoaming, the sample was placed in an oven for pre-curing at 160°C for 0.5 hours and then fully cured at 220°C for 1 hour to obtain a polyimide-reinforced graphene aerogel terahertz absorbing material.

[0027] like Figure 1 The image shown is an SEM image of the polyimide-reinforced graphene aerogel prepared in this embodiment. Reduced graphene oxide aerogel was obtained by directional freezing using the ice template method. By impregnating polyimide, a high-strength porous terahertz absorbing material was obtained. Compared with it, pure graphene aerogel is obviously more loose.

[0028] Furthermore, such as Figure 2The figure shows the reflection loss diagram of the polyimide-reinforced graphene aerogel prepared in this embodiment. As can be seen from the figure, the maximum reflection loss of the polyimide-reinforced graphene aerogel can reach -35dB in the frequency band of 0.2THz~1.2THz, indicating that the polyimide-reinforced graphene aerogel has excellent terahertz absorption performance.

[0029] like Figure 3 The figure shown is a compressive strength diagram of the polyimide-reinforced graphene aerogel prepared in this embodiment. Figure 1 As can be seen from the structural comparison, the high-strength porous terahertz absorbing material prepared in this embodiment maintains excellent absorbing performance while greatly improving the compressibility of graphene aerogel.

[0030] In summary, this invention successfully prepared a polyimide-reinforced graphene aerogel using the ice template method and freeze-drying method. This microwave absorbing material has advantages such as being lightweight, having strong support, and being structurally stable.

[0031] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A method for preparing a polyimide-reinforced graphene aerogel terahertz absorbing material, characterized in that, Includes the following steps: Step 1. Preparation of graphene oxide solution: Graphene oxide solution was prepared using the Hummers method; Step 2. Preparation of reduced graphene oxide aerogel: Pour graphene oxide solution into a mold, freeze and then freeze-dry to obtain graphene oxide aerogel block, and then reduce it at high temperature to obtain loose and porous reduced graphene oxide aerogel block. Step 3. Preparation of polyimide-reinforced graphene aerogel: Polyimide is used to impregnate reduced graphene oxide aerogel blocks to obtain polyimide-reinforced graphene aerogel terahertz absorbing materials.

2. The preparation method of the polyimide-reinforced graphene aerogel terahertz absorbing material according to claim 1, characterized in that, In step 1, the concentration of the graphene oxide solution is 6 mg / ml to 8 mg / ml.

3. The method for preparing the polyimide-reinforced graphene aerogel terahertz absorbing material according to claim 1, characterized in that, In step 2, the graphene oxide solution is frozen at -20℃ to -30℃ for 1h to 2h, and the freeze-drying temperature is -70℃ to -80℃ for 24h to 28h.

4. The preparation method of the polyimide-reinforced graphene aerogel terahertz absorbing material according to claim 1, characterized in that, The high-temperature reduction is carried out at a temperature of 800℃~1000℃ for 1h~1.5h.

5. The method for preparing the polyimide-reinforced graphene aerogel terahertz absorbing material according to claim 1, characterized in that, In step 3, the specific impregnation process is as follows: the polyimide is heated in an oil bath at 60℃~80℃ to obtain a polyimide solution, and then the polyimide solution is poured into a mold containing reduced graphene oxide aerogel blocks, submerging the reduced graphene oxide aerogel blocks, and then vacuumed in a vacuum drying oven at 60℃~70℃ and 0.15MPa~0.2MPa for 0.5 h~1 h.

6. The method for preparing the polyimide-reinforced graphene aerogel terahertz absorbing material according to claim 5, characterized in that, In step 3, the impregnated sample is placed in an oven and pre-cured at 160℃~180℃ for 0.5h~1h, and then fully cured at 220℃~240℃ for 1h~1.5h to obtain polyimide-reinforced graphene aerogel terahertz absorbing material.

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