Shape memory electromagnetic shielding polyimide multilayer film composite and preparation method thereof

Abstract

This invention provides a shape memory electromagnetic shielding polyimide multilayer thin film composite material and its preparation method, relating to the field of electromagnetic shielding materials technology. The polyimide multilayer thin film composite material provided by this invention includes a polyimide film layer and silver film layers composited on both sides of the polyimide film layer; the polyimide film layer includes a polyimide matrix and carbon functional fillers dispersed in the polyimide matrix, the carbon functional fillers including reduced graphene oxide and carbon nanofibers. This invention uses polyimide as the material matrix, introducing reduced graphene oxide and carbon nanofibers therein. These two carbon functional fillers are mixed and stacked on a small scale to form a π-π conjugated effect, and the reduced graphene oxide is grafted onto the polyimide, thus giving it good dispersibility; in addition, the combination of the surface-composite silver film layer with the shape memory properties of PI and the electromagnetic wave dissipation capability of the conductive fillers gives the material an intelligently regulated electromagnetic shielding function.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic shielding materials technology, and in particular to a shape memory electromagnetic shielding polyimide multilayer thin film composite material and its preparation method. Background Technology

[0002] Polyimide is an engineering plastic that is resistant to high and cold temperatures, has excellent mechanical properties, is corrosion-resistant, radiation-resistant, and has good shape memory properties. Making polyimide into electromagnetic shielding materials can combine shape memory properties and electromagnetic shielding properties.

[0003] Electromagnetic shielding effectiveness has always been controlled through material structure and filler modification, with filler performance largely determining the shielding effectiveness. However, polyimide electromagnetic shielding film composites still face numerous challenges. For example, the strong electrostatic interactions and intermolecular forces of fillers lead to poor compatibility with solvents or matrices, affecting their dispersibility in polyamic acid and causing filler agglomeration within the material, thus compromising the surface smoothness of the film. Furthermore, the volume shrinkage caused by polyamic acid dehydration during thermal imidization, the competition of nanofillers with molecular chains, hardening and embrittlement, and film curling and deformation due to excessively long heat treatment times all severely impact the shape memory properties and electromagnetic shielding performance of polyimide electromagnetic shielding film composites. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a shape memory electromagnetic shielding polyimide multilayer film composite material and its preparation method. The shape memory electromagnetic shielding polyimide multilayer film composite material provided by this invention has strong shape memory properties and electromagnetic shielding properties.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a shape memory electromagnetic shielding polyimide multilayer film composite material, comprising a polyimide film layer and a silver film layer composited on both sides of the polyimide film layer;

[0007] The polyimide film layer includes a polyimide matrix and carbon functional fillers dispersed in the polyimide matrix. The carbon functional fillers include reduced graphene oxide and carbon nanofibers. The reduced graphene oxide is grafted onto the polyimide matrix. The mass of the reduced graphene oxide and the carbon nanofibers are 1-4% and 0-4% of the mass of the polyimide matrix, respectively.

[0008] Preferably, the thickness of the polyimide layer is 0.1 to 0.4 mm.

[0009] Preferably, the thickness of the silver film layer is 1–5 μm.

[0010] This invention provides a method for preparing the shape memory electromagnetic shielding polyimide multilayer thin film composite material described above, comprising the following steps:

[0011] Diamine, dianhydride, aminated graphene oxide, carbon nanofibers, and solvent are mixed and polymerized to obtain a polyamic acid reaction solution; the mass of the aminated graphene oxide and carbon nanofibers is 1-4% and 0-4% of the total mass of the diamine and dianhydride, respectively.

[0012] After the polyamic acid reaction solution is laid into a film, the solvent is removed and the film is cured to obtain a polyamic acid composite film;

[0013] The polyamic acid composite film is thermally imidized to obtain a polyimide film layer;

[0014] Using a silver target as the target material, a silver film layer is deposited by magnetron sputtering on both sides of the polyimide film layer to obtain the shape memory electromagnetic shielding polyimide multilayer thin film composite material.

[0015] Preferably, the diamine is 4,4'-diaminodiphenyl ether, and the dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride or 4,4'-hydroxydiphenylcarboxylic anhydride; the molar ratio of the diamine to the dianhydride is (10-20):(10-20).

[0016] Preferably, the aminated graphene oxide is graphene oxide grafted with dodecyl dimethylamine oxide.

[0017] Preferably, the solvent is N-methylpyrrolidone.

[0018] Preferably, the polymerization reaction is carried out at a temperature of 0–25°C for 12–24 hours.

[0019] Preferably, the thermal imidization includes a first stage, a second stage, a third stage, and a fourth stage performed sequentially; the temperature of the first stage is 120–140°C, and the holding time is 1–1.5 h; the temperature of the second stage is 180–200°C, and the holding time is 1–1.5 h; the temperature of the third stage is 220–250°C, and the holding time is 1–1.5 h; the temperature of the fourth stage is 280–320°C, and the holding time is 1–1.5 h.

[0020] Preferably, the conditions for the magnetron sputtering include: a vacuum degree of 1.0 × 10⁻⁶. -3 ~3.0×10 -3 Pa; Argon gas is introduced at a pressure of 0.8–1.5 Pa; sputtering power is 100–300 W, and sputtering rate is 68.6 nm / min.

[0021] This invention provides a shape memory electromagnetic shielding polyimide multilayer film composite material, comprising a polyimide film layer and silver film layers composited on both sides of the polyimide film layer; the polyimide film layer comprises a polyimide matrix and carbon functional fillers dispersed in the polyimide matrix, the carbon functional fillers comprising reduced graphene oxide and carbon nanofibers, wherein the reduced graphene oxide is grafted onto the polyimide matrix. This invention uses polyimide as the material matrix and introduces reduced graphene oxide and carbon nanofibers into it. These two carbon functional fillers are mixed and stacked on a small scale to form a π-π conjugation effect, and the reduced graphene oxide is grafted onto the polyimide, thereby giving the reduced graphene oxide and carbon nanofibers good dispersibility in the polyimide matrix material. Furthermore, the reduced graphene oxide has excellent mechanical properties and dispersibility, and the carbon nanofibers have excellent electrical and thermal conductivity. The addition of both can share some of the stress when the material is under stress, greatly enhancing the mechanical and electromagnetic shielding properties of the material. On this basis, this invention composites a silver film layer on both sides of the material, which improves the conductivity, increases the reflection efficiency, increases the absorption efficiency, and enhances the overall electromagnetic shielding efficiency, forming a good shield. The polyimide multilayer film composite material provided by this invention has a sandwich multilayer structure, forming an incident layer (Ag), a loss layer (PI / rGO / CNF), and an absorption layer (Ag), exhibiting strong electromagnetic shielding performance. Simultaneously, the reduced graphene oxide and carbon nanofibers, two nano-functional fillers, possess high conductivity and energy conversion efficiency, which also improve the shape recovery rate of the polyimide material. Therefore, the shape memory electromagnetic shielding polyimide multilayer film composite material provided by this invention possesses strong shape memory and electromagnetic shielding properties. Attached Figure Description

[0022] Figure 1 The storage modulus and loss factor curves are shown for the polyimide film (CGPI44) obtained in Example 1 and the polyimide film (PI) obtained in Comparative Example 1.

[0023] Figure 2 The total shielding effectiveness SE of CGPI44 in Example 1, Ag-CGPI-Ag (1μmAg) in Example 3, and Ag-CGPI-Ag (5μmAg) in Example 7 is shown. T Line graph;

[0024] Figure 3 These are shape recovery demonstration diagrams for CGPI in Example 1 and Ag-CGPI-Ag in Example 3. Figure 3 (a) shows CGPI in near-infrared light (808nm, 1.5W·cm⁻¹). -2(a) is the shape recovery process under irradiation, (b) is the shape recovery process of Ag-CGPI-Ag under 3000W power magnetic induction heating, and (c) is the shape recovery process of Ag-CGPI-Ag under 10V DC voltage. Detailed Implementation

[0025] This invention provides a shape memory electromagnetic shielding polyimide multilayer film composite material, comprising a polyimide film layer and a silver film layer composited on both sides of the polyimide film layer;

[0026] The polyimide film layer comprises a polyimide (PI) matrix and carbon functional fillers dispersed in the polyimide matrix. The carbon functional fillers include reduced graphene oxide (rGO) and carbon nanofibers (CNF), wherein the reduced graphene oxide is grafted onto the polyimide matrix. The mass of the reduced graphene oxide and the carbon nanofibers are 1-4% and 0-4% of the mass of the polyimide matrix, respectively.

[0027] In this invention, the mass of the reduced graphene oxide is preferably 4% of the mass of the polyimide matrix, and the mass of the carbon nanofibers is preferably 1-3% of the mass of the polyimide matrix. In this invention, the thickness of the polyimide layer is preferably 0.1-0.4 mm, and the thickness of the silver film layer is preferably 1-5 μm, specifically 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm.

[0028] Polyimide is an engineering plastic with excellent high-temperature resistance, cold resistance, mechanical properties, corrosion resistance, radiation resistance, and good shape memory properties. This invention uses it as a matrix material, introducing reduced graphene oxide and carbon nanofibers. Graphene oxide has excellent mechanical properties and dispersibility, while carbon nanofibers have excellent electrical and thermal conductivity. The addition of these two materials can share some of the stress when the material is under pressure, greatly enhancing the material's mechanical and electromagnetic shielding properties. Furthermore, this invention composites a silver film on the surface of the polyimide material, forming an Ag-(PI / rGO / CNF)-Ag sandwich multilayer structure, creating an incident layer (Ag), a loss layer (PI / rGO / CNF), and an absorption layer (Ag). This effectively improves internal reflection efficiency and reduces the dielectric loss, conductive loss, and magnetic loss of high specific surface area materials against electromagnetic waves. Simultaneously, the well-dispersed filler forms a multi-interface, strong network structure within the material, effectively bearing stress and strain, thus exhibiting strong shape memory and electromagnetic shielding properties. This invention improves the electromagnetic shielding performance of polyimide materials while retaining their radiation resistance and lightweight characteristics, and at the same time saves costs and material consumption.

[0029] Compared to pure polyimide, polyimide composites with added carbon functional fillers exhibit superior mechanical properties and heat resistance. Furthermore, the combination of the surface-coated silver film layer with the shape memory properties of polyimide and the electromagnetic wave dissipation capability of conductive fillers enables the material to intelligently regulate electromagnetic shielding, achieving high electromagnetic shielding effectiveness under conditions of low filler ratio and low metal film thickness.

[0030] This invention provides a method for preparing the shape memory electromagnetic shielding polyimide multilayer thin film composite material described above, comprising the following steps:

[0031] Diamine, dianhydride, aminated graphene oxide, carbon nanofibers, and solvent are mixed and polymerized to obtain a polyamic acid reaction solution; the mass of the aminated graphene oxide and carbon nanofibers is 1-4% and 0-4% of the total mass of the diamine and dianhydride, respectively.

[0032] After the polyamic acid reaction solution is laid into a film, the solvent is removed and the film is cured to obtain a polyamic acid composite film;

[0033] The polyamic acid composite film is thermally imidized to obtain a polyimide film layer;

[0034] Using a silver target as the target material, a silver film layer is deposited by magnetron sputtering on both sides of the polyimide film layer to obtain the shape memory electromagnetic shielding polyimide multilayer thin film composite material.

[0035] Unless otherwise specified, all raw materials involved in this invention are commercially available products well known to those skilled in the art.

[0036] This invention involves mixing a diamine, a dianhydride, aminated graphene oxide, carbon nanofibers, and a solvent to perform a polymerization reaction, yielding a polyamic acid reaction solution. In this invention, the diamine is preferably 4,4'-diaminodiphenyl ether (ODA, structure shown in formula a), and the dianhydride is preferably 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA, structure shown in formula b) or 4,4'-dioxydiphenylcarboxylic anhydride (ODPA, structure shown in formula c); the molar ratio of the diamine to the dianhydride is preferably (10-20):(10-20), more preferably 10:10. In this invention, the aminated graphene oxide is preferably graphene oxide grafted with dodecyl dimethylamine oxide (DDAO). This invention does not have particular requirements regarding the source of the dodecyl dimethylamine oxide graphene oxide; it can be prepared using commercially available products or methods well-known to those skilled in the art. In this invention, the preferred mass percentages of the aminated graphene oxide and carbon nanofibers are 1-4% and 0-4% of the total mass of the diamine and dianhydride, respectively, and the preferred mass percentage of the carbon nanofibers is 1-3% of the total mass of the diamine and dianhydride. In this invention, the preferred solvent is N-methylpyrrolidone (NMP). The use of N-methylpyrrolidone as a solvent in this invention enables the reduced graphene oxide and carbon nanofibers to exhibit excellent dispersibility.

[0037]

[0038] In this invention, the preferred mixing method is as follows: the aminated graphene oxide and carbon nanofibers are added to a solvent, and then stirred and ultrasonically dispersed sequentially to obtain a filler dispersion; diamine and dianhydride are then added sequentially to the filler dispersion. In this invention, the stirring time is preferably 30 min, the ultrasonic dispersion power is preferably 800 W, and the time is preferably 30 min; the temperature of the dispersion is preferably 0°C when the dianhydride is added, and the dianhydride is preferably added within 1 hour. In this invention, the solid content of the resulting mixture is preferably 8-10%.

[0039] In this invention, the polymerization reaction temperature is preferably 0–25°C, more preferably 0–10°C, and the reaction time is preferably 12–24 h, more preferably 12–15 h; the polymerization reaction time is calculated from the point when the dianhydride is completely added; the polymerization reaction is preferably carried out under stirring conditions. During the polymerization reaction, the diamine reacts with the dianhydride to generate polyamic acid, and graphene oxide, because it has amino groups, can also be grafted onto the polyamic acid. Finally, the two fillers, graphene oxide and carbon nanofibers, are uniformly dispersed in the polyimide, forming a network structure with the polyimide.

[0040] After obtaining the polyamic acid reaction solution, the present invention lays the polyamic acid reaction solution into a film and then removes the solvent and cures it to obtain a polyamic acid composite film. Preferably, the polyamic acid reaction solution is poured onto a flat glass plate for film laying. After film laying, the present invention further preferably removes air bubbles from the obtained liquid film under vacuum. The vacuuming and degassing is preferably carried out in a vacuum drying oven, and the vacuuming and degassing temperature is preferably 60–80°C, with a preferred time of 1 hour. In the present invention, the solvent removal curing temperature is preferably the same as the vacuuming and degassing temperature, and the solvent removal curing time is preferably 12 hours.

[0041] After obtaining the polyamic acid composite film, the present invention performs thermal imidization on the polyamic acid composite film to obtain a polyimide film layer. In the present invention, the thermal imidization preferably includes a first stage, a second stage, a third stage, and a fourth stage performed sequentially; the temperature of the first stage is preferably 120–140°C, and the holding time is preferably 1–1.5 h; the temperature of the second stage is preferably 180–200°C, and the holding time is preferably 1–1.5 h; the temperature of the third stage is preferably 220–250°C, and the holding time is preferably 1–1.5 h; the temperature of the fourth stage is preferably 280–320°C, and the holding time is preferably 1–1.5 h. In the present invention, cooling is performed after the fourth stage, preferably from the temperature of the fourth stage to 40°C, and the cooling time is preferably 1 h. After the thermal imidization, the polyamic acid in the polyamic acid composite film is converted into polyimide, and the oxygen-containing groups in the graphene oxide are also reduced to reduced graphene oxide. After demolding from the glass plate surface (after soaking in water at 100°C for 1 hour to demold), a PI / rGO / CNF composite film with a smooth surface and a thickness between 0.1 and 0.4 mm is obtained, which is the polyimide film layer.

[0042] After obtaining the polyimide film, this invention uses a silver target as the target material to deposit silver films on both sides of the polyimide film by magnetron sputtering, thereby obtaining the shape memory electromagnetic shielding polyimide multilayer thin film composite material. In this invention, the preferred conditions for the magnetron sputtering include: a vacuum degree of 1.0 × 10⁻⁶. -3 ~3.0×10 -3Pa; Argon gas is introduced at a pressure of 0.8–1.5 Pa; sputtering power is 100–300 W, and sputtering rate is 68.6 nm / min. Preferably, before magnetron sputtering, the magnetron sputtering instrument is evacuated to the specified vacuum level, and argon gas is introduced to maintain the argon gas pressure within the specified range, thereby ensuring good adhesion of silver to the substrate. The magnetron sputtering instrument is preferably a vacuum magnetron sputtering machine, and the evacuation time is preferably 4 hours. In this invention, the magnetron sputtering time depends on the thickness of the silver film. In this embodiment, the relationship between the thickness of the silver film and the magnetron sputtering time, calculated based on the sputtering rate, is as follows: 1 μm = 14.57 min, 2 μm = 29.15 min, 3 μm = 43.73 min, 4 μm = 58.33 min, 5 μm = 72.9 min.

[0043] The preparation method provided by this invention is simple, easy to operate, and suitable for large-scale production.

[0044] To further illustrate the present invention, the shape memory electromagnetic shielding polyimide multilayer thin film composite material and its preparation method provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] With the aid of mechanical stirring, excess dodecyl dimethylamine oxide (DDAO) was slowly added to the graphene oxide (GO) suspension. The GO then rapidly flocculated and deposited. Finally, the DDAO-grafted graphene oxide was washed by vacuum filtration and dried at 60°C for 24 hours.

[0047] Weigh 0.20 g of aminated graphene oxide (the above-mentioned DDAO-grafted graphene oxide) and 0.20 g of carbon nanofibers and place them in a 500 mL plastic cup. Then add 45 g of N-methylpyrrolidone, stir at high speed with a magnetic stirrer for 0.5 h, and sonicate in an 800 W ultrasonic cleaner for 0.5 h to complete the preparation of the dispersion.

[0048] 10 mmol of diamine (4,4'-diaminodiphenyl ether) and the above dispersion were added to a flask. 10 mmol of dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride) was added to the solution and dissolved over 1 hour. The two monomers and the filler were mixed evenly under 0°C and mechanical stirring for 24 hours to obtain a polyamic acid reaction solution.

[0049] Pour the polyamic acid reaction solution onto a flat glass plate, vacuum it at 80°C for 1 hour to remove air bubbles, and then depressurize and cure it at 80°C for 12 hours to remove the solvent.

[0050] The cured polyamic acid film was subjected to thermal imidization in a forced-air drying oven with the temperature program set as follows: (140℃ / 1h, 200℃ / 1h, 250℃ / 1h, 280℃ / 1h, followed by a 1h cooling down from 280℃ to 40℃).

[0051] A glass plate covered with a polyimide film was immersed in a 100°C hot water bath for 1 hour, then the film was removed and dried to obtain a PI / rGO / CNF composite film (polyimide film layer), named CGPI44, for later use.

[0052] Example 2

[0053] The mass of carbon nanofibers in Example 1 was changed to 0g, 0.05g, 0.1g, and 0.15g, respectively, while the rest remained the same as in Example 1. PI / rGO / CNF composite films (polyimide film layers) were obtained and named CGPI04, CGPI14, CGPI24, and CGPI34, respectively.

[0054] Comparative Example 1

[0055] First, add 45g of N-methylpyrrolidone to the flask, then add 2.0024g of 4'4-diaminodiphenyl ether (ODA) to the flask, and then add 2.9422g of dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride) to the solution in 1-hour increments. Under 0°C and mechanical stirring conditions, the two monomers are mixed evenly for 24 hours to obtain a polyamic acid reaction solution.

[0056] Pour the polyamic acid reaction solution onto a flat glass plate, vacuum it at 80°C for 1 hour to remove air bubbles, and then depressurize and cure it at 80°C for 12 hours to remove the solvent.

[0057] The cured polyamic acid film was subjected to thermal imidization in a forced-air drying oven with the temperature program set as follows: (140℃ / 1h, 200℃ / 1h, 250℃ / 1h, 280℃ / 1h, followed by a 1h cooling down from 280℃ to 40℃).

[0058] A glass plate coated with a polyimide film was immersed in a 100°C hot water bath for 1 hour, then the film was removed, dried, and stored for later use to obtain a pure PI film.

[0059] The polyimide films obtained in Examples 1-2 and Comparative Example 1 were subjected to tensile property tests according to standard ISO 527-2 / 1BB. The test results are shown in Table 1.

[0060] Table 1. Tensile properties of the polyimide films obtained in Examples 1-2 and Comparative Example 1

[0061] polyimide film Tensile strength (MPa) Elongation at break (%) PI 137.74±2.80 43.81±0.72 CGPI04 103.81±0.34 15.87±2.72 CGPI14 143.19±2.36 20.12±3.06 CGPI24 127.91±12.68 25.19±6.03 CGPI34 131.70±13.13 25.98±8.56 CGPI44 142.61±1.23 30.73±5.60

[0062] Table 1 compares the tensile properties of pure PI and CGPI. When only graphene oxide is added, the stress and strain of the material both decrease significantly due to the formation of interfacial effects or defects in the graphene oxide caused by high-temperature imidization. When a certain amount of carbon nanofibers is added, the stress and strain of the material both increase significantly. Further addition does not significantly enhance the tensile strength, but the elongation at break continues to increase. The comparison shows that carbon nanofibers enhance the mechanical properties of the material. However, because graphene oxide lacks toughness, which carbon nanofibers can compensate for, the tendency for brittle fracture initially decreases and then increases.

[0063] Dynamic mechanical analysis was performed on the polyimide films obtained in Example 1 and Comparative Example 1. Figure 1 The graphs show the storage modulus and loss factor curves of the polyimide film (CGPI44) obtained in Example 1 and the polyimide film (PI) obtained in Comparative Example 1. Comparing the storage modulus and loss factor curves of PI and CGPI44, it is found that PI exhibits a loss factor peak at 259℃, while CGPI44 requires 312℃ to show a corresponding peak. This indicates that the glass transition temperatures of PI and CGPI44 are 259℃ and 312℃, respectively. This is determined by the high heat resistance of the network bonds formed by polyimide and graphene oxide / carbon nanofibers, as well as the filler.

[0064] From Table 1 and Figure 1 It can be seen that the polyimide composite material with uniformly dispersed filler has certain mechanical properties and a higher glass transition temperature compared to pure polyimide without filler.

[0065] Example 3

[0066] Weigh 0.20 g of aminated graphene oxide (graphene oxide grafted with dodecyl dimethylamine oxide in Example 1) and 0.20 g of carbon nanofibers and place them in a 500 mL plastic cup. Then add 45 g of N-methylpyrrolidone, stir at high speed with a magnetic stirrer for 0.5 h, and sonicate in an 800 W ultrasonic cleaner for 0.5 h to complete the preparation of the dispersion.

[0067] 10 mmol of diamine (4,4'-diaminodiphenyl ether) and the above dispersion were added to a flask. 10 mmol of dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride) was added to the solution and dissolved over 1 hour. The two monomers and fillers were mixed evenly under 0°C and mechanical stirring for 24 hours to obtain a polyamic acid reaction solution.

[0068] Pour the polyamic acid reaction solution onto a flat glass plate, vacuum it at 80°C for 1 hour to remove air bubbles, and then depressurize and cure it at 80°C for 12 hours to remove the solvent.

[0069] The cured polyamic acid film was subjected to thermal imidization in a forced-air drying oven with the temperature program set as follows: (140℃ / 1h, 200℃ / 1h, 250℃ / 1h, 280℃ / 1h, followed by a 1h cooling down from 280℃ to 40℃).

[0070] A glass plate with a polyimide film is immersed in a 100°C hot water bath for 1 hour, then the film is removed and dried to obtain a PI / rGO / CNF composite film (polyimide film layer) for later use.

[0071] The film was cut into 50×50mm squares and placed in a vacuum magnetron sputtering machine. A silver target (purchased from Guocai Technology Co., Ltd.) was used as the target material, and a vacuum was drawn until the pressure reached 1.5×10⁻⁶. -3 The argon gas pressure was controlled at 1.0 Pa, the sputtering power was 200 W, the sputtering rate was measured to be 68.6 nm / min using an ultra-flat silicon wafer, and the sputtering time was 14.57 min. Then the material was flipped over and sputtered for the same amount of time to obtain a sample with a double-sided Ag film thickness of 1 μm, which is a shape memory electromagnetic shielding polyimide multilayer thin film composite material, denoted as Ag-CGPI-Ag.

[0072] Example 4

[0073] The sputtering time was changed to 29.15 min, and then the material was flipped over and sputtered for the same time. The rest was the same as in Example 3, and a sample with a double-sided Ag film thickness of 2 μm was obtained.

[0074] Example 5

[0075] The sputtering time was changed to 43.73 min, and then the material was flipped over and sputtered for the same time. The rest was the same as in Example 3, and a sample with a double-sided Ag film thickness of 3 μm was obtained.

[0076] Example 6

[0077] The sputtering time was changed to 58.33 min, and then the material was flipped over and sputtered for the same time. The rest was the same as in Example 3, and a sample with a double-sided Ag film thickness of 4 μm was obtained.

[0078] Example 7

[0079] The sputtering time was changed to 72.90 min, and then the material was flipped over and sputtered for the same time. The rest was the same as in Example 3, and a sample with a double-sided Ag film thickness of 5 μm was obtained.

[0080] Electromagnetic shielding effectiveness test:

[0081] The overall shielding effectiveness (SE) of CGPI44 in Example 1 and Ag-CGPI-Ag in Examples 3-7 was measured in the frequency range of 8.2-12.4 GHz. T )test, Figure 2The total shielding effectiveness SE of CGPI44 in Example 1, Ag-CGPI-Ag (1μmAg) in Example 3, and Ag-CGPI-Ag (5μmAg) in Example 7 is shown. T A line graph. (From...) Figure 2 It can be seen that CGPI44's SE T The electromagnetic shielding efficiency is only 0.51 dB, which is extremely low, and the conductivity is also 0. This is because the filler is covered by polyimide, resulting in extremely low surface conductivity, and the shielding efficiency is reduced by internal multiple internal reflection losses and weak dielectric losses. However, after coating both sides with a 1 μm Ag film, the electromagnetic shielding efficiency is significantly improved, reaching a maximum of 93.79 dB, and the change is very small within the frequency range. When the film thickness is further increased, the overall shielding efficiency of the material continues to rise, but only slightly, because the conductive loss reaches its maximum, and the electromagnetic shielding performance is difficult to improve further. In Example 7, when the coating thickness is 5 μm, the highest electromagnetic shielding efficiency is achieved, which is 136.88 dB (conductivity of 2.268 × 10⁻⁶). 4 S / cm).

[0082] Shape memory performance test:

[0083] Dynamic thermomechanical analysis was employed to measure the energy storage modulus and loss factor; the highest temperature for measuring shape memory performance was set at 330℃ (T). g The maximum temperature was 30℃, the minimum temperature was 30℃, the heating rate was 10℃ / min, and the temperature was held for 5 minutes after each maximum or minimum temperature was reached; the maximum strain was 10%, the tensile rate was 2% / min, and after three memory cycles, the shape fixation rate and recovery rate of the CGPI material obtained in Examples 1-2 and the PI material obtained in Comparative Example 1 were calculated. The test results are shown in Table 2.

[0084] Table 2. Material Shape Memory Fixation Rate and Recovery Rate

[0085]

[0086]

[0087] Table 2 shows that CGPI34 has the highest shape retention rate at 97.31%, while CGPI04 has the highest shape recovery rate at 93.73%, demonstrating that CGPI possesses superior shape memory performance. The composite material's numerous grafting points, physical crosslinking points, and network bonds enhance the shape retention rate. During shape recovery, the nano-functional filler exhibits high conductivity and energy conversion efficiency, further improving the shape recovery rate of CGPI.

[0088] PI itself possesses a thermal stimulus response, and rGO / CNF provides CGPI with high photothermal conversion efficiency and photostimulation response. Building upon this, by depositing an Ag thin film on CGPI, both magnetocaloric and electrothermal conversion efficiencies are improved to very high levels. Therefore, in addition to the original thermal and photostimulation, Ag-CGPI-Ag also exhibits electro- and magnetic stimulation responses, forming a quadruple stimulation response. This allows for stimulation response under conditions requiring one of these stimuli, forming a fixed electromagnetic shielding structure and enhancing electromagnetic shielding effectiveness. Figure 3 The shape recovery diagrams of CGPI (Example 1) and Ag-CGPI-Ag (Example 3) reflecting the above characteristics are shown, where (a) shows the shape recovery of CGPI in near-infrared light (808nm, 1.5W cm⁻¹). -2 (a) is the shape recovery process under irradiation, (b) is the shape recovery process of Ag-CGPI-Ag under 3000W power magnetic induction heating, and (c) is the shape recovery process of Ag-CGPI-Ag under 10V DC voltage.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A shape memory electromagnetic shielding polyimide multilayer film composite material, characterized in that, It includes a polyimide film layer and a silver film layer composited on both sides of the polyimide film layer; The polyimide film layer comprises a polyimide matrix and carbon functional fillers dispersed in the polyimide matrix. The carbon functional fillers include reduced graphene oxide and carbon nanofibers, wherein the reduced graphene oxide is grafted onto the polyimide matrix. The mass percentages of the reduced graphene oxide and carbon nanofibers are 1-4% and 1-4% of the mass of the polyimide matrix, respectively. The thickness of the silver film layer is 1~5μm.

2. The shape memory electromagnetic shielding polyimide multilayer film composite material according to claim 1, characterized in that, The thickness of the polyimide film is 0.1~0.4 mm.

3. The method for preparing the shape memory electromagnetic shielding polyimide multilayer thin film composite material according to any one of claims 1 to 2, characterized in that, Includes the following steps: A polyamic acid reaction solution was obtained by mixing diamine, dianhydride, aminated graphene oxide, carbon nanofibers, and a solvent and carrying out a polymerization reaction; the mass of the aminated graphene oxide and the carbon nanofibers were 1-4% and 1-4% of the total mass of diamine and dianhydride, respectively. After the polyamic acid reaction solution is laid into a film, the solvent is removed and the film is cured to obtain a polyamic acid composite film; The polyamic acid composite film is thermally imidized to obtain a polyimide film layer; Using a silver target as the target material, a silver film layer is deposited by magnetron sputtering on both sides of the polyimide film layer to obtain the shape memory electromagnetic shielding polyimide multilayer thin film composite material.

4. The preparation method according to claim 3, characterized in that, The diamine is 4,4'-diaminodiphenyl ether, and the dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride or 4,4'-hydroxydiphenylcarboxylic anhydride; the molar ratio of the diamine to the dianhydride is (10~20):(10~20).

5. The preparation method according to claim 3, characterized in that, The aminated graphene oxide is graphene oxide grafted with dodecyl dimethylamine oxide.

6. The preparation method according to claim 3, characterized in that, The solvent is N-methylpyrrolidone.

7. The preparation method according to claim 3, characterized in that, The polymerization reaction is carried out at a temperature of 0~25℃ for 12~24h.

8. The preparation method according to claim 3, characterized in that, The thermal imidization includes a first stage, a second stage, a third stage, and a fourth stage performed sequentially; the temperature of the first stage is 120~140℃, and the holding time is 1~1.5h; the temperature of the second stage is 180~200℃, and the holding time is 1~1.5h; the temperature of the third stage is 220~250℃, and the holding time is 1~1.5h; the temperature of the fourth stage is 280~320℃, and the holding time is 1~1.5h.

9. The preparation method according to claim 3, characterized in that, The conditions for the magnetron sputtering include: a vacuum level of 1.0 × 10⁻⁶. -3 ~3.0×10 -3 Pa; Argon gas is introduced at a pressure of 0.8~1.5 Pa; sputtering power is 100~300 W, and sputtering rate is 68.6 nm / min.

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