A flexible electromagnetic shielding material and a preparation method and application thereof

Abstract

The application relates to the technical field of electromagnetic shielding, in particular to a flexible electromagnetic shielding material and a preparation method and application thereof. The application provides a flexible electromagnetic shielding material which comprises a Ni-Fe3O4 film and a shape memory polymer film which are stacked in sequence; the Ni-Fe3O4 is prepared by a hydrothermal method; and the shape memory polymer is prepared from polytetrahydrofuran, diphenylmethane-4,4' diisocyanate, poly(dimethylsiloxane), bis(3-aminopropyl) end-capping and 1,4-butanediol. Thanks to the synergistic cooperation of the above-mentioned materials, the flexible electromagnetic shielding material has excellent comprehensive performance, and has excellent shape memory characteristics, flexibility and good electromagnetic shielding capacity, and has high practical application value and popularization prospect.

Description

Technical Field

[0001] This application relates to the field of electromagnetic shielding technology, and in particular to a flexible electromagnetic shielding material, its preparation method, and its application. Background Technology

[0002] Electromagnetic shielding materials are a class of core functional materials that can suppress electromagnetic wave transmission through reflection, absorption, and attenuation, effectively isolating electromagnetic interference and avoiding the hazards of electromagnetic radiation. They are key basic materials for ensuring the stable operation of electronic equipment, maintaining electromagnetic environment safety, and protecting human physical and mental health, and are widely used in many fields such as electronic communication, precision instruments, aerospace, and biomedicine. In recent years, the rapid development of emerging technologies such as wearable smart electronics, flexible smart devices, implantable medical devices, and deployable communication equipment has driven the transformation of electromagnetic shielding scenarios towards flexibility, dynamism, intelligence, and biocompatibility, and has also placed higher demands on the comprehensive performance of materials. New application scenarios not only require materials to have efficient and stable electromagnetic shielding performance, but also to have excellent deformation recovery ability and shape self-adaptation characteristics to adapt to complex curved surfaces, dynamic deformation, programmable shaping and other working conditions (Bisht, N., Vishwakarma, J., Jaiswal, S. et al. Synergizing chemistry: unlocking the potential of hybrid fillers for enhanced performance in shapememory polymers. Adv Compos Hybrid Mater 8, 7 (2025).).

[0003] Currently, the mainstream traditional electromagnetic shielding materials are mainly metal sheets, metal foams, and cured polymer-based shielding composite materials. These materials possess excellent and stable electromagnetic shielding performance due to their superior electrical and magnetic conductivity, meeting the shielding requirements of conventional static equipment. However, they have significant performance defects. They are hard, lack flexibility, and are brittle, unable to withstand large deformations such as stretching, bending, and torsion. Furthermore, they lack programmable shape control capabilities, making them unsuitable for adapting to novel dynamic scenarios such as dynamic bending of flexible devices, reconfigurable structural deformation, and irregular curved surface covering, resulting in significant application limitations.

[0004] To address these issues, existing research has developed several flexible electromagnetic shielding materials. These materials are mostly prepared using cross-linked elastomers as the matrix and composite functional fillers, exhibiting good flexibility and the ability to achieve basic deformation, making them suitable for simple and flexible applications. However, these materials only support passive deformation and lack shape memory and programmable controllable deformation functions. They cannot actively adjust their shape according to usage requirements or accurately restore the preset structure, making it difficult to meet the core integrated requirements of "controllable shape and stable performance" in high-end applications such as intelligent electronic devices, deployable communication antennas, and adaptive shielding protection systems. This greatly restricts the implementation and development of intelligent electromagnetic shielding technology (Ge H, Gao D, Zhang SD, et al. Regulating the Conductive Network of Graphene / Ni Composite Films toward Tunable Electromagnetic Shielding Efficiency[J]. ACS Applied Materials & Interfaces, 2024, 16(49):68144-68153.).

[0005] Therefore, there is an urgent need to develop a new type of flexible electromagnetic shielding material that combines excellent shape memory properties, superior flexibility, and efficient and stable electromagnetic shielding capabilities to meet the high-end application needs of multiple fields such as biomedicine, wearable electronics, and intelligent communication equipment, and to promote the further development of intelligent electromagnetic shielding technology. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of existing flexible electromagnetic shielding materials that cannot simultaneously achieve excellent shape memory characteristics, flexibility and electromagnetic shielding ability, and to provide a flexible electromagnetic shielding material.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned flexible electromagnetic shielding material.

[0008] Another object of the present invention is to provide the application of the above-mentioned flexible electromagnetic shielding material in the fields of 5G communication, flexible smart electronics or minimally invasive medical treatment.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution: This invention protects a flexible electromagnetic shielding material, which comprises a Ni-Fe3O4 thin film and a shape memory polymer thin film stacked sequentially. The Ni-Fe3O4 in the Ni-Fe3O4 thin film was prepared by a hydrothermal method; The method for preparing the shape memory polymer in the shape memory polymer film includes the following steps: S1. Polytetrahydrofuran, diphenylmethane-4,4'-diisocyanate and organic solvent are mixed and subjected to polymerization reaction to obtain prepolymer; S2. Poly(dimethylsiloxane), bis(3-aminopropyl) end-capped polymer is added to the prepolymer obtained in step S1 and diphenylmethane-4,4' diisocyanate to carry out a polycondensation reaction to obtain a polycondensation polymer containing urea bonds; S3. Add 1,4-butanediol and diphenylmethane-4,4'-diisocyanate to the urea-containing condensate obtained in step S2, carry out chain extension reaction, and post-process to obtain shape memory polymer; Wherein, the number-average molecular weight of the polytetrahydrofuran is 2500~10000 g / mol; the number-average molecular weight of the poly(dimethylsiloxane), bis(3-aminopropyl)-terminated is 800~6000 g / mol; and the number-average molecular weight of the shape memory polymer is 40000~200000 g / mol. The thickness of the Ni-Fe3O4 film is 2.2~4 mm, and the thickness of the shape memory polymer film is 2.2~4 mm.

[0010] The flexible electromagnetic shielding material of this application is composed of a Ni-Fe3O4 thin film and a shape memory polymer thin film. The shape memory polymer achieves precise design of the soft segments by controlling the molecular weight of PDMS, and selects MDI of a specific molecular weight to react with the terminal amino and BD hydroxyl groups of PDMS to generate urea bonds and urethane bonds, respectively, completing the controllable construction of the hard segment structure. The soft and hard segments within the polymer work synergistically, endowing the material with excellent shape memory properties and flexibility. The Ni-Fe3O4 thin film possesses excellent electromagnetic shielding capabilities. The complementary and synergistic effects of the two films enable the composite material to stably complete deformation and shape recovery, adapting to various complex deformation conditions. Relying on the excellent mechanical properties of the shape memory polymer, the overall material structure is stable and highly flexible, meeting the stress requirements under conventional service conditions. Simultaneously, by controlling the thickness of the flexible electromagnetic shielding material, electromagnetic energy can be effectively dissipated, exhibiting good absorption and shielding effects in the Ku band (12~18 GHz). The various properties of this material are mutually compatible and synergistic, possessing high practical application value and promising prospects for widespread application.

[0011] Furthermore, the hydrothermal method includes the following steps: Iron source, nickel source, alkaline regulator, chelating agent and organic solvent are mixed and subjected to hydrothermal reaction, followed by post-treatment to obtain Ni-Fe3O4.

[0012] Furthermore, the iron source includes one or more of ferrous chloride, ferrous sulfate heptahydrate, and ferric citrate.

[0013] Furthermore, the nickel source includes one or both of elemental nickel and nickel nanowires.

[0014] Furthermore, the nickel source is nickel nanowires.

[0015] Furthermore, the molar ratio of iron in the iron source to nickel in the nickel source is 1:(1.5~3).

[0016] Furthermore, the alkalinity regulator includes one or more of sodium hydroxide, potassium hydroxide, and ammonia water.

[0017] Furthermore, the mass ratio of the iron source to the alkaline regulator is 1:(1~2).

[0018] Furthermore, the chelating agent includes one or more of sodium citrate, ethylenediaminetetraacetic acid, and polyvinylpyrrolidone.

[0019] Furthermore, the mass ratio of the iron source to the chelating agent is 1:(2~4).

[0020] Furthermore, the organic solvent includes one or more of ethylene glycol, propylene glycol, and diethylene glycol.

[0021] Furthermore, the mass-to-volume ratio of the iron source to the organic solvent is 1 g: (80~120) mL.

[0022] Furthermore, the temperature of the hydrothermal reaction is 180~220 ℃.

[0023] Furthermore, the hydrothermal reaction takes 8 to 16 hours.

[0024] Furthermore, the post-processing includes cooling, centrifugation, washing, and drying.

[0025] Furthermore, the cooling refers to cooling the reaction solution to room temperature.

[0026] Furthermore, the centrifugation involves centrifuging the cooled reaction liquid to separate and collect the solids.

[0027] Furthermore, the washing process involves washing the collected solids with ethanol.

[0028] Furthermore, the drying process involves drying the washed solid.

[0029] Furthermore, the number-average molecular weight of the polytetrahydrofuran is 3000~5000 g / mol.

[0030] Further, in step S1, the molar ratio of the polytetrahydrofuran and diphenylmethane-4,4' diisocyanate is 1:(0.5~4).

[0031] Furthermore, the organic solvent includes one or more of dimethylformamide (DMF), tetrahydrofuran (THF), and dimethyl sulfoxide (DMSO).

[0032] Furthermore, the organic solvent is DMF.

[0033] Furthermore, the mass-to-volume ratio of the polytetrahydrofuran to the organic solvent is 1 g: (0.5~3) mL.

[0034] Furthermore, the polymerization reaction is carried out at a temperature of 70-90 °C.

[0035] Furthermore, the polymerization reaction takes 0.5 to 3 hours.

[0036] Furthermore, the polymerization reaction is carried out at a speed of 300-500 rpm.

[0037] Furthermore, the poly(dimethylsiloxane) with bis(3-aminopropyl) end caps has a number-average molecular weight of 900~5000 g / mol.

[0038] Preferably, the poly(dimethylsiloxane) with bis(3-aminopropyl) end caps has a number-average molecular weight of 1000~3000 g / mol.

[0039] More preferably, the poly(dimethylsiloxane) with bis(3-aminopropyl) end caps has a number-average molecular weight of 1000 g / mol.

[0040] Furthermore, as a preferred method, the poly(dimethylsiloxane), bis(3-aminopropyl)-terminated ...

[0041] Furthermore, the preparation method of the poly(dimethylsiloxane), bis(3-aminopropyl) capped solution includes the following steps: Dissolve poly(dimethylsiloxane), bis(3-aminopropyl)-terminated ...

[0042] Furthermore, the organic solvent includes one or more of dimethylformamide (DMF), tetrahydrofuran (THF), and dimethyl sulfoxide (DMSO).

[0043] Furthermore, the mass-to-volume ratio of the poly(dimethylsiloxane), bis(3-aminopropyl) end-capped compound, and organic solvent is 1 g: (1~5) mL.

[0044] Furthermore, the molar ratio of the polytetrahydrofuran and poly(dimethylsiloxane) with bis(3-aminopropyl) end caps is 1:(1~3).

[0045] Furthermore, the molar ratio of the poly(dimethylsiloxane), bis(3-aminopropyl)-terminated and diphenylmethane-4,4'-diisocyanate is 1:(0.05~1).

[0046] Furthermore, the temperature of the polycondensation reaction is 70~90 °C.

[0047] Furthermore, the polycondensation reaction takes 0.5 to 2 hours.

[0048] Furthermore, the molar ratio of the polytetrahydrofuran to 1,4-butanediol is 1:(0.1~1).

[0049] Furthermore, the molar ratio of 1,4-butanediol and diphenylmethane-4,4'-diisocyanate is 1:(0.3~2).

[0050] Further, in steps S1 to S3, the total molar ratio of the polytetrahydrofuran and diphenylmethane-4,4' diisocyanate is 1:(2~5).

[0051] Furthermore, the chain extension reaction is carried out at a temperature of 60~100 °C.

[0052] Furthermore, the chain extension reaction takes 3-4 hours.

[0053] Furthermore, the post-processing includes dilution, molding, and drying.

[0054] Furthermore, the dilution involves raising the temperature of the reaction solution to 90-95 °C, adding an organic solvent, and mixing thoroughly to obtain the diluted reaction solution.

[0055] Furthermore, the casting process involves pouring the diluted reaction solution into a mold and casting it into a film.

[0056] Furthermore, the drying process is vacuum drying.

[0057] Preferably, the vacuum drying temperature is 50~70 ℃.

[0058] Furthermore, the structural formula of the shape memory polymer in the shape memory polymer film is as follows: ; The values ​​of m are 30 to 100, n is 5 to 200, j is 1 to 50, and k is 1 to 50.

[0059] In this invention, the values ​​of m and n are determined based on the number-average molecular weight specifications of PTMEG and PDMS, corresponding to the chain length design of the polymer soft segments and intermediate blocks to ensure the flexibility and heat resistance of the material. The values ​​of j and k are determined according to the mild polymerization and chain extension reaction conditions of this invention. Due to reaction kinetic limitations, the stepwise polymerization reaction of isocyanate and hydroxyl / amino groups is difficult to form hard segments with higher polymerization degrees. Therefore, they are limited to this range, which not only adapts to the process conditions but also ensures the role of hard segments as physical crosslinking points, achieving a synergistic balance between material properties and prepareability.

[0060] Furthermore, the structural formula of the shape memory polymer in the shape memory polymer film is as follows: ; The values ​​of m are 40 to 70, n is 10 to 100, j is 1 to 50, and k is 1 to 50.

[0061] Furthermore, the mass ratio of Ni-Fe3O4 in the Ni-Fe3O4 film to the shape memory polymer in the shape memory polymer film is 1:(3~30).

[0062] Furthermore, the mass ratio of Ni-Fe3O4 in the Ni-Fe3O4 film to the shape memory polymer in the shape memory polymer film is 1:(5~20).

[0063] Furthermore, the thickness of the Ni-Fe3O4 film is 2.25~3 mm.

[0064] Furthermore, the thickness of the shape memory polymer film is 2.25~3 mm.

[0065] This invention protects a method for preparing the aforementioned flexible electromagnetic shielding material, comprising the following steps: The Ni-Fe3O4 dispersion was poured into a mold and dried to obtain a Ni-Fe3O4 film; then the shape memory polymer dilution was poured onto the surface of the aforementioned Ni-Fe3O4 film and dried to obtain the flexible electromagnetic shielding material.

[0066] Furthermore, the preparation method of the Ni-Fe3O4 dispersion includes the following steps: The Ni-Fe3O4 obtained above was added to water and dispersed to obtain the Ni-Fe3O4 dispersion.

[0067] Furthermore, the mass-to-volume ratio of Ni-Fe3O4 to water is 1 g: (5~50) mL.

[0068] Furthermore, the dispersion is ultrasonic dispersion.

[0069] Furthermore, the material of the mold is not specifically limited, as long as it can fix the shape.

[0070] Furthermore, as a preferred embodiment, the mold is a polytetrafluoroethylene mold.

[0071] Furthermore, the drying temperature is 60~100 ℃.

[0072] Furthermore, the drying time is 10 to 60 minutes.

[0073] Furthermore, the preparation method of the shape memory polymer diluent includes the following steps: The shape memory polymer and organic solvent are mixed to obtain a diluted shape memory polymer solution.

[0074] Furthermore, the organic solvent includes one or more of dimethylformamide, tetrahydrofuran, and dimethyl sulfoxide.

[0075] Furthermore, the mass-to-volume ratio of the shape memory polymer to the organic solvent is 1 g: (0.5~2) mL.

[0076] Furthermore, the drying temperature is 60~100 ℃.

[0077] Furthermore, the drying time is 8 to 16 hours.

[0078] This invention protects the application of the aforementioned flexible electromagnetic shielding material in the fields of 5G communication, flexible smart electronics, or minimally invasive medical care.

[0079] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a flexible electromagnetic shielding material comprising sequentially stacked Ni-Fe3O4 films and shape memory polymer films. The Ni-Fe3O4 film is prepared via a hydrothermal method. The shape memory polymer is prepared from polytetrahydrofuran, diphenylmethane-4,4'-diisocyanate, poly(dimethylsiloxane), bis(3-aminopropyl)-terminated, and 1,4-butanediol. Thanks to the synergistic effect of these materials, this flexible electromagnetic shielding material exhibits excellent comprehensive performance, possessing superior shape memory properties, reliable mechanical properties, and good electromagnetic shielding capabilities, thus demonstrating high practical application value and promising prospects for widespread adoption. Attached Figure Description

[0080] Figure 1 The images are scanning electron microscope (SEM) images of the Ni-Fe3O4 nanowires in Example 1 at different magnifications.

[0081] Figure 2The images are scanning electron microscope (SEM) images of Ni-Fe3O4 nanowires in Comparative Example 1 at different magnifications.

[0082] Figure 3 The images are scanning electron microscope (SEM) images of Ni-Fe3O4 nanowires in Comparative Example 2 at different magnifications.

[0083] Figure 4 The X-ray diffraction patterns are for Ni-Fe3O4 nanowires in Example 1 and Comparative Examples 1-2.

[0084] Figure 5 The image shows the 1H NMR spectrum of the shape memory polymer in Example 1.

[0085] Figure 6 The infrared spectra of the shape memory polymers in Examples 1-3 are shown.

[0086] Figure 7 The thermogravimetric analysis diagrams of the shape memory polymers in Examples 1-3 are shown.

[0087] Figure 8 The image shows the DSC exothermic peak curves of the shape memory polymers in Examples 1-3.

[0088] Figure 9 The image shows the DSC melt endothermic peak curves of the shape memory polymers in Examples 1-3.

[0089] Figure 10 The figures shown are (a) a morphological dimension diagram and (b) a flexible test diagram of the flexible electromagnetic shielding material in Example 1.

[0090] Figure 11 The images are scanning electron microscope (SEM) images of the surface of the flexible electromagnetic shielding material in Example 1 at different magnifications.

[0091] Figure 12 The images show scanning electron microscope (SEM) images of the cross-section of the flexible electromagnetic shielding material in Example 1 at different magnifications.

[0092] Figure 13 The image shows the EDS elemental energy spectrum analysis of the flexible electromagnetic shielding material in Example 1.

[0093] Figure 14 This is an EDS elemental distribution diagram of the flexible electromagnetic shielding material in Example 1.

[0094] Figure 15 The stress-strain curves of the shape memory polymers in Examples 1-3 are shown.

[0095] Figure 16 Figures (a) to (f) show the deformation recovery process of the shape memory polymer in Example 1.

[0096] Figure 17The electromagnetic absorption performance of flexible electromagnetic shielding materials of different thicknesses in Examples 1, 4 and Comparative Examples 3-8 is shown in the figure. Detailed Implementation

[0097] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0098] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0099] Figure 1 (a) represents Figure 1 Figure (a) in the middle, Figure 1 (b) represents Figure 1 The order of the other figures follows the same pattern as in figure (b).

[0100] Poly(dimethylsiloxane), bis(3-aminopropyl) capped: number average molecular weight 1000 g / mol, purchased from Adamas-beta; 4-4'-Methylenebis(phenyl isocyanate) was purchased from Aladdin.

[0101] Example 1: Preparation of a flexible electromagnetic shielding material 1. Preparation of Ni-Fe3O4 nanowires Accurately weigh 0.81 g ferrous chloride (6.39 mmol), 2.0 g sodium citrate, 1.0 g sodium hydroxide, and 0.8 g nickel nanowires (13.63 mmol). Add these raw materials sequentially to 80 mL ethylene glycol and stir thoroughly until the system is homogeneous. Transfer the prepared solution to a 100 mL hydrothermal reactor, seal the reactor, and place it in a drying oven. Maintain the reaction temperature at 200 °C for 12 h. After the reaction is complete, cool the reaction system to room temperature, centrifuge, wash with ethanol, and dry to obtain Ni-Fe3O4 nanowires.

[0102] 2. Preparation of shape memory polymers S1. Preparation of prepolymer 10 g of polytetrahydrofuran (PTMEG, number average molecular weight 3000 g / mol, 3.33 mmol) and 10 mL of DMF were added to a three-necked flask and stirred at 60 °C and 250 rpm until dissolved. Then the temperature was raised to 80 °C, and 1 g of diphenylmethane-4,4' diisocyanate (MDI, 4.0 mmol) was added. The polymerization reaction was carried out at 80 °C and 400 rpm for 1 h. The remaining 1 g of MDI (4.0 mmol) was added, and the reaction was continued for 0.5 h to obtain the prepolymer. S2. Preparation of condensation polymers containing urea bonds 5 g of poly(dimethylsiloxane), bis(3-aminopropyl)-terminated (PDMS, number average molecular weight of 1000 g / mol, 5 mmol) was mixed with 10 mL of DMF and slowly added dropwise to the prepolymer obtained in step S1. Then 0.4 g of MDI (1.6 mmol) was added and polycondensed at 80 °C for 1 h to obtain a condensation polymer containing urea bonds. S3. Preparation of shape memory polymers 0.2 mL of 1,4-butanediol (BD, 2.2 mmol) was added to the urea-containing condensate obtained in step S2. After stirring for 5 min, 0.4 g of MDI (1.6 mmol) was added, and the chain extension reaction was carried out at 80 °C for 3 h. Then, the temperature of the reaction solution was raised to 95 °C, 5 mL of DMF was added, and the mixture was stirred for 5 min. While still hot, the reaction solution was poured into a polytetrafluoroethylene mold preheated to 80 °C for casting. The film was then dried in a vacuum environment at 60 °C for 24 h to remove residual solvent, yielding a shape memory polymer with a number average molecular weight of 122281 g / mol, denoted as PTSI-1.

[0103] The synthetic route for shape memory polymers is as follows: ; Wherein, m = 30~100, n = 5~200, j = 1~50, and k = 1~50.

[0104] 3. Preparation of flexible electromagnetic shielding materials 0.3 g of the Ni-Fe3O4 nanowires obtained in step 1 were added to 10 mL of deionized water and ultrasonically dispersed using an ultrasonic cleaner. The uniformly dispersed suspension was poured evenly into a 6 cm × 6 cm polytetrafluoroethylene mold and transferred to an electrically heated constant-temperature drying oven. The mixture was dried at 80 °C for 30 min to form a uniform and dense Ni-Fe3O4 nanowire film with a thickness of 2.25 mm. At a volume ratio of 1:1, 3 g of the shape memory polymer obtained in step 2 was mixed with 3 mL of DMF solvent to prepare a polymer dilution with good flowability. The polymer dilution was poured evenly onto the surface of the formed Ni-Fe3O4 nanowire film and then dried continuously at 80 °C for 12 h to form a 2.25 mm thick shape memory polymer film on the surface of the Ni-Fe3O4 nanowire film. After drying, a flexible electromagnetic shielding material with a total thickness of 4.5 mm was obtained.

[0105] Example 2: Preparation of a flexible electromagnetic shielding material The difference from Example 1 is that in the preparation step of the shape memory polymer, the number-average molecular weight of poly(dimethylsiloxane), bis(3-aminopropyl) end capping is replaced from 1000 g / mol to 3000 g / mol, and the number-average molecular weight of the resulting shape memory polymer is 114451 g / mol, denoted as PTSI-2.

[0106] The other steps and conditions are the same as in Example 1.

[0107] Example 3: Preparation of a flexible electromagnetic shielding material The difference from Example 1 is that in the preparation step of the shape memory polymer, the number-average molecular weight of poly(dimethylsiloxane), bis(3-aminopropyl) end capping is replaced from 1000 g / mol to 5000 g / mol, and the number-average molecular weight of the resulting shape memory polymer is 53452 g / mol, denoted as PTSI-3.

[0108] The other steps and conditions are the same as in Example 1.

[0109] Example 4: Preparation of a Flexible Electromagnetic Shielding Material The difference from Example 1 is that in the preparation steps of the flexible electromagnetic shielding material, the thickness of both the Ni-Fe3O4 nanowire film and the shape memory polymer film is adjusted from 2.25 mm to 2.5 mm, that is, the thickness of the flexible electromagnetic shielding material is 5 mm.

[0110] The other steps and conditions are the same as in Example 1.

[0111] Comparative Example 1: Preparation of a Flexible Electromagnetic Shielding Material The difference from Example 1 is that the hydrothermal method is replaced with the glucose reduction method in the preparation steps of Ni-Fe3O4 nanowires.

[0112] The specific steps are as follows: Preparation of 0.05 mol / L Fe 3+ Prepare a solution, bring the volume to 50 mL; prepare a 0.2 mol / L glucose solution, bringing the volume to 50 mL. Adjust the Fe content using NaOH. 3+ Adjust the pH of the solution to 11.5. Then add the Fe solution with the adjusted pH. 3+ The solution and glucose solution were sequentially transferred to a three-necked flask, and 0.2 g of nickel nanowires were added. A mechanical stirrer was started at 2000 rpm, and the reaction temperature was kept constant at 60 °C for 5 h. After the reaction was complete, heating and stirring were stopped, and the reaction system was allowed to cool naturally to room temperature. The solid-liquid mixture was separated by centrifugation. The precipitate was washed four times sequentially with deionized water and anhydrous ethanol. The washed precipitate was then dried in a 40 °C oven for 12 h to obtain Ni-Fe3O4 nanowires.

[0113] The other steps and conditions are the same as in Example 1.

[0114] Comparative Example 2: Preparation of a Flexible Electromagnetic Shielding Material The difference from Example 1 is that the hydrothermal method is replaced with the co-deposition method in the preparation steps of Ni-Fe3O4 nanowires.

[0115] The specific steps are as follows: Accurately weigh 0.162 g of ferrous chloride tetrahydrate and 0.27 g of anhydrous ferric chloride, dissolve the two salts in 100 mL of deoxygenated deionized water; then add 0.4 g of nickel nanowires, and ultrasonically disperse to obtain a precursor mixture. Measure 200 mL of 1 mol / L NaOH solution and add it to a 500 mL three-necked flask, continuously purging with nitrogen and allowing it to stand to purge oxygen. Under nitrogen protection, slowly add the precursor mixture dropwise to the three-necked flask through a needle. After the addition is complete, mechanically stir at 2500 rpm at room temperature for 1 h. After the reaction is complete, stop the aeration and stirring, and allow the system to cool naturally to room temperature. Separate the solid product by high-speed centrifugation, and wash the precipitate three times alternately with deoxygenated deionized water and anhydrous ethanol. Dry the washed precipitate in a 40 ℃ constant temperature oven for 12 h to obtain Ni-Fe3O4 nanowires.

[0116] The other steps and conditions are the same as in Example 1.

[0117] Comparative Example 3: Preparation of a Flexible Electromagnetic Shielding Material The difference from Example 1 is that in the preparation steps of the flexible electromagnetic shielding material, the thickness of both the Ni-Fe3O4 nanowire film and the shape memory polymer film is adjusted from 2.25 mm to 0.5 mm, that is, the thickness of the flexible electromagnetic shielding material is 1 mm.

[0118] The other steps and conditions are the same as in Example 1.

[0119] Comparative Example 4: Preparation of a Flexible Electromagnetic Shielding Material The difference from Example 1 is that in the preparation steps of the flexible electromagnetic shielding material, the thickness of both the Ni-Fe3O4 nanowire film and the shape memory polymer film is adjusted from 2.25 mm to 0.75 mm, that is, the thickness of the flexible electromagnetic shielding material is 1.5 mm.

[0120] The other steps and conditions are the same as in Example 1.

[0121] Comparative Example 5: Preparation of a Flexible Electromagnetic Shielding Material The difference from Example 1 is that in the preparation steps of the flexible electromagnetic shielding material, the thickness of both the Ni-Fe3O4 nanowire film and the shape memory polymer film is adjusted from 2.25 mm to 1 mm, that is, the thickness of the flexible electromagnetic shielding material is 2 mm.

[0122] The other steps and conditions are the same as in Example 1.

[0123] Comparative Example 6: Preparation of a Flexible Electromagnetic Shielding Material The difference from Example 1 is that in the preparation steps of the flexible electromagnetic shielding material, the thickness of both the Ni-Fe3O4 nanowire film and the shape memory polymer film is adjusted from 2.25 mm to 1.25 mm, that is, the thickness of the flexible electromagnetic shielding material is 2.5 mm.

[0124] The other steps and conditions are the same as in Example 1.

[0125] Comparative Example 7: Preparation of a Flexible Electromagnetic Shielding Material The difference from Example 1 is that in the preparation steps of the flexible electromagnetic shielding material, the thickness of both the Ni-Fe3O4 nanowire film and the shape memory polymer film is adjusted from 2.25 mm to 1.5 mm, that is, the thickness of the flexible electromagnetic shielding material is 3 mm.

[0126] The other steps and conditions are the same as in Example 1.

[0127] Comparative Example 8: Preparation of a Flexible Electromagnetic Shielding Material The difference from Example 1 is that in the preparation steps of the flexible electromagnetic shielding material, the thickness of both the Ni-Fe3O4 nanowire film and the shape memory polymer film is adjusted from 2.25 mm to 2 mm, that is, the thickness of the flexible electromagnetic shielding material is 4 mm.

[0128] The other steps and conditions are the same as in Example 1.

[0129] Experimental Example 1: Structural Characterization of a Flexible Electromagnetic Shielding Material I. Structural Characterization of Ni-Fe3O4 Nanowires 1. Scanning electron microscopy characterization (1) Experimental methods The microstructure of Ni-Fe3O4 nanowires in Example 1 and Comparative Examples 1-2 was observed using a field emission scanning electron microscope (Regulus 8220, manufactured by Hitachi, Japan).

[0130] (2) Experimental results Microscopic characterization results at different magnifications are as follows Figures 1-3 The results show that the sample prepared by the hydrothermal method in Example 1 has the best microstructure. The high temperature and high pressure environment of the hydrothermal system can precisely control the crystal nucleation process. Under low magnification, the overall linear skeleton of the sample can be observed to be complete and regular, without obvious breakage or damage. Under high magnification, Fe3O4 nanoparticles can be clearly seen to be uniformly and densely attached to the surface of the nickel nanowire matrix, with no obvious agglomeration of particles. The overall linear structure is complete and regular, and the interface is tightly bonded, making it easy to construct a continuous and stable electromagnetic response network, which can ensure the stable performance of the material's electromagnetic shielding performance. Figure 1 (a) ~ Figure 1 (d)). In contrast, the glucose reduction method in Comparative Example 1 (…) Figure 2 (a) ~ Figure 2 (d) and the co-deposition method of Comparative Example 2 ( Figure 3 (a) ~ Figure 3 (d) The reaction process is difficult to control, and the growth rate of crystal nuclei varies greatly: Low-magnification observation reveals that the Ni-Fe3O4 composite nanowires form a continuous linear framework structure, with localized agglomeration of the Fe3O4 nanoparticles loaded on their surface. Furthermore, the surface coating formed by the particles is discontinuous and lacks integrity. High-magnification observation shows that the exposed nickel nanowire substrate surface is relatively smooth, indicating that the amount of Fe3O4 particles attached to most areas of the substrate is low. Based on these morphological characteristics, it can be concluded that the distribution uniformity of Fe3O4 nanoparticles on the substrate surface is poor. Such defective structures can disrupt the internal electromagnetic conduction pathways, significantly weakening the material's electromagnetic wave loss capability and magnetic response.

[0131] 2. X-ray diffraction characterization (1) Experimental methods The phase structure of the Ni-Fe3O4 nanowires prepared in Example 1 and Comparative Examples 1 and 2 was characterized using an X-ray diffractometer (Ultima IV-285E, manufactured by Rigaku, Japan). The testing conditions were: Cu Kα target (λ = 0.15406 nm), tube voltage 40 kV, tube current 40 mA; continuous scanning mode, 2θ scan range 10°–80°, step size 0.02°, scan speed 4° / min.

[0132] (2) Experimental results XRD results are as follows Figure 4 As shown, the Ni-Fe3O4 prepared by the hydrothermal method in Example 1 exhibits excellent crystallinity with a stable baseline and sharp, high-intensity diffraction peaks. The characteristic peaks of Ni-Fe3O4 at 2θ≈18.3°, 30.1°, 35.5°, 43.1°, 57.0°, 62.6°, and 74.0° correspond to the (111), (220), (311), (511), (400), (440), and (533) crystal planes of Fe3O4, respectively (PDF#19-0629). Meanwhile, the diffraction peaks at 2θ≈44.5° and 51.8° match the (111) and (200) crystal planes of face-centered cubic metallic Ni (PDF#04-0850). All diffraction peaks showed no significant broadening or shift, and no impurity phases such as NiO and Fe2O3 were detected, indicating that the hydrothermal method can successfully prepare Ni-Fe3O4 composite structures with high crystallinity and pure phases.

[0133] The Ni-Fe3O4 sample prepared by the glucose reduction method in Comparative Example 1 exhibited poor overall diffraction peak performance, with significantly reduced peak intensity, broadened peak shape, and prominent baseline noise. Its overall crystallinity was far lower than that of Example 1. Although characteristic diffraction signals of Fe3O4 could be detected, the peaks were diffuse and weak, indicating incomplete Fe3O4 grain growth and small grain size. Simultaneously, the characteristic peaks of metallic Ni were masked by background noise, making them difficult to identify clearly. This suggests that neither the Ni nor Fe3O4 crystal phases grew sufficiently under this process, resulting in a large amount of amorphous structure and extremely poor crystal integrity.

[0134] The sample prepared by the co-deposition method in Comparative Example 2 exhibited a single phase, with high-intensity, high-sharpness characteristic peaks of metallic Ni appearing only at 2θ≈44.5° and 51.8°, indicating excellent crystallinity of metallic Ni in the sample. However, no obvious characteristic diffraction peaks of Fe3O4 were observed in the spectrum, proving that the co-deposition method is difficult to generate a crystalline Fe3O4 phase, and thus cannot successfully construct a Ni-Fe3O4 composite structure, failing to meet the experimental design requirements.

[0135] A comprehensive comparison reveals that only the Ni-Fe3O4 sample prepared by the hydrothermal method in Example 1 can simultaneously achieve efficient crystallization of both Ni and Fe3O4 phases, possessing both a pure phase and a complete composite structure. Compared to the imperfect crystallization of the glucose reduction method and the inability of the co-precipitation method to effectively generate the Fe3O4 phase, the hydrothermal method has significant advantages in composite phase construction and crystallization performance control, making it the optimal process for preparing high-performance Ni-Fe3O4 nanowires.

[0136] II. Structural Characterization of Shape Memory Polymers 1. Proton NMR spectroscopy (1) Experimental methods The molecular structure of the shape memory polymer prepared in Example 1 was characterized using nuclear magnetic resonance spectroscopy. The test solvent was deuterated chloroform (CDCl3), with tetramethylsilane (TMS) as an internal standard. The test frequency was 400 MHz, and the test temperature was 25 ℃.

[0137] (2) Experimental results The results are as follows Figure 5 As shown, in the ¹H NMR spectrum of the shape memory polymer in Example 1, each characteristic peak precisely corresponds to the target polymer molecular structure: δ7.29 ppm (doublet, d) corresponds to the aryl hydrogen proton on the benzene ring of the diphenylmethane diisocyanate (MDI) unit, verifying the successful introduction of the MDI structural unit; δ3.43 ppm (multiplex, m) is the main signal of the methylene proton (-Ph-CH2-Ph-) of diphenylmethane in the MDI unit, and the shoulder peak is the alkoxymethylene proton connected to the oxygen atom in the soft segment of polytetrahydrofuran (PTMEG); δ1.64 ppm (doublet, dt) corresponds to the middle methylene proton of the alkoxy chain of the PTMEG soft segment, confirming the successful integration of the PTMEG soft segment into the polymer backbone; δ1.28 ppm (doublet, d) corresponds to the middle methylene proton of the propyl linkage at both ends of the aminopropyl-terminated polydimethylsiloxane (PDMS), proving the successful integration of the PDMS linkage into the polymer molecular structure; δ0.11 The ppm (multiplet, m) peak represents the methyl proton in the -Si(CH3)2-O- repeating unit of PDMS, a characteristic peak of PDMS, directly verifying the successful copolymerization of PDMS into the polyurethane backbone. It is evident that each proton characteristic peak closely matches the theoretical molecular structure, indicating that the pre-defined shape memory polymer was successfully synthesized in this invention.

[0138] 2. Fourier transform infrared spectroscopy test (1) Experimental methods The chemical structures and functional groups of the shape memory polymers prepared in Examples 1-3 were characterized using Fourier transform infrared spectroscopy. The test conditions were as follows: spectral scanning range 4000–500 cm⁻¹. -1 The test temperature was room temperature.

[0139] (2) Experimental results The results are as follows Figure 6 As shown, all samples exhibited typical polyurethane / polyurea structural characteristics, with consistent peak shapes, demonstrating the successful synthesis of the target shape memory polymer. Specifically, the peak shapes were observed at 3300-3400 cm⁻¹. -1 The broad absorption peak at 2960 cm⁻¹ is attributed to the NH stretching vibrations of the urethane and urea bonds. The broadened peak shape and lack of sharp splitting indicate the presence of numerous intermolecular hydrogen bonds in the system, providing direct evidence for the construction of a physically cross-linked network. -1 With 2900 cm -1 The nearby absorption peaks correspond to the CH stretching vibrations of the alkyl groups in the PDMS main chain and side chains, reflecting the integrity of the soft segment skeleton; 1720-1730 cm⁻¹ -1 The strong absorption peak at 1600-1640 cm⁻¹ corresponds to the stretching vibration of the C=O bond in the carbamate bond. -1 The characteristic absorption of the urea bond C=O is present nearby, and both confirm the successful reaction of the isocyanate with the amino group to form a hard segment microregion; 1530-1550 cm⁻¹ -1 The absorption peak of amide II at 1000-1100 cm⁻¹ further confirms the formation of the urethane bond with the urea bond; -1 The strong and broad absorption peak at the point is attributed to the Si-O-Si stretching vibration of PDMS, and the peak intensity increases with the increase of PDMS molecular weight, which is consistent with the trend of soft segment content.

[0140] Comparing the spectra of different samples, the NH and C=O peaks were relatively stronger in the low molecular weight PTSI-1~PTSI-2, indicating a higher hydrogen bond density and a denser crosslinking network. This demonstrates that adjusting the molecular weight of PDMS can precisely control the ratio of soft and hard segments and the hydrogen bond density of the polymer, ultimately achieving controllable modification of the crosslinking network morphology and molecular chain segment mobility.

[0141] 3. Thermogravimetric analysis (1) Experimental methods The thermal stability of the shape memory polymers prepared in Examples 1-3 was characterized using a thermogravimetric analyzer (TGA). The test conditions were as follows: under a nitrogen protective atmosphere, 10 mg of each shape memory polymer from Examples 1-3 was weighed and placed in an alumina crucible; the heating rate was set to 20 °C / min; and the test temperature range was 35–600 °C.

[0142] (2) Experimental results Test results are as follows Figure 7The results show that all three polymers exhibit the typical two-step thermal decomposition behavior of polyurethane materials, possessing a good overall heat resistance. However, slight differences exist in the thermal stability and high-temperature carbon residue characteristics among the different polymers. Specifically, using the temperature corresponding to 5% thermal weight loss as the initial thermal decomposition temperature, the initial decomposition temperatures of the three samples were 328 ℃, 340 ℃, and 315 ℃, respectively. This indicates that PTSI-2 exhibits the best initial thermal stability, maintaining structural stability at higher temperatures and demonstrating stronger resistance to high-temperature thermal damage. The thermal decomposition of the material can be divided into two stages: the first thermal decomposition range is 300–400 ℃, where mass loss mainly originates from the thermal breakage of urethane and urea bonds within the polyurethane hard segments; the second main decomposition range is 400–550 ℃, which is also the primary stage of mass loss, corresponding to the thermal decomposition and carbonization processes of the polytetrahydrofuran soft segments and polydimethylsiloxane segments.

[0143] When the test temperature reached 600 °C, the carbon residue rates of the three polymers were 10%, 22%, and 11%, respectively. PTSI-2 exhibited a significantly higher carbon residue rate than the other two groups. This higher carbon residue rate allows for the formation of a dense carbonized barrier layer during heating, inhibiting the transfer of heat and oxygen into the material and further enhancing its high-temperature safety. This indicates that PTSI-2 possesses the optimal high-temperature carbon residue characteristics. Overall, the shape memory polymers in this application demonstrate good comprehensive heat resistance. Initial heat stability and high-temperature heat damage resistance can be optimized by adjusting the formulation. PTSI-2 combines optimal initial thermal stability and high-temperature carbon residue performance, exhibiting the best overall thermal performance among the three groups.

[0144] 4. Differential scanning calorimetry (1) Experimental methods The thermal transition behavior of the shape memory polymers obtained in Examples 1-3 was characterized using differential scanning calorimetry (DSC). A protective nitrogen atmosphere was continuously purged throughout the test. The experiment was conducted using a three-stage temperature control program: first, the temperature was increased from room temperature to 80 °C to eliminate the inherent thermal history of the samples; then, the temperature was decreased from 80 °C to -20 °C at a rate of 10 °C / min; finally, the temperature was increased from -20 °C to 180 °C at a rate of 10 °C / min, with the secondary heating curves collected simultaneously. By analyzing the DSC curves, the glass transition temperature (Tg), crystallization temperature, and melting temperature of the samples could be measured.

[0145] (2) Experimental results The results are as follows Figures 8-9 As shown, all samples exhibited sharp characteristic peaks in the range of -15 to -10 ℃. Figure 8The peak corresponds to the shape memory transition temperature (Tg) of the material. The lower transition temperature allows the polymer to achieve shape memory response at low temperatures, effectively broadening its applicable operating range. Furthermore, all samples exhibited a single, sharp exothermic crystallization peak in the 16–17 °C range. Figure 8 This is attributed to the ordered crystallization process of the soft segment molecular chains of polytetrahydrofuran (PTMEG). The maximum difference in crystallization temperature among the samples was only 0.9 °C, indicating that the molecular weight of PDMS has a weak effect on the crystallization ability of PTMEG soft segments. This crystallization temperature is significantly higher than the glass transition temperature of the material, and crystallization stabilization can be triggered by cooling to below 16-17 °C. Compared with materials with lower crystallization temperatures, the required cooling conditions are more moderate.

[0146] Meanwhile, all three samples exhibited a single, sharp endothermic melting peak at around 176 °C. Figure 9 This corresponds to the melting process of the urea and urethane bonds in the hard segment microregions generated by the reaction of MDI with BD and PDMS. The difference in hard segment melting temperature between samples is less than 1 °C, indicating that the molecular weight of PDMS does not significantly change the chemical composition and crystallinity of the hard segment, and the thermal stability of the hard segment is mainly determined by its own intermolecular hydrogen bonding.

[0147] The low-temperature crystallization peak and the high-temperature melting peak in the DSC curves were completely separated with no overlapping regions, proving that the material has a clear two-phase separation structure, consistent with the classic structural model of shape memory polymers. No shoulder peaks or double peaks appeared in any of the samples, indicating that the stepwise polymerization process used in this experiment achieved uniform incorporation of PDMS segments. Among them, PTSI-3 showed the best symmetry and sharpness in its hard segment melting peak, indicating that its hard segment micro-region structure was the most regular and the phase separation was the most complete.

[0148] III. Structural Characterization of Flexible Electromagnetic Shielding Materials 1. Morphological characteristics (1) Experimental methods The macroscopic dimensions of the flexible electromagnetic shielding material in Example 1 were determined by comparison with a scale, and the flexibility and mechanical plasticity of the sample were visually tested and evaluated by manually pressing and bending it.

[0149] (2) Experimental results The results are as follows Figure 10 As shown, this experiment successfully prepared a flexible electromagnetic shielding material with a complete shape and a smooth surface. The film has a regular size of 6 cm × 6 cm and a uniform thickness. Figure 10 (a) The overall molding effect is good. (From) Figure 10 (b) The bending test results show that the flexible electromagnetic shielding material can be bent and deformed at will, and there is no cracking or falling off during the bending process. It exhibits excellent flexibility and mechanical plasticity, which can meet the deformation requirements of flexible electromagnetic shielding materials.

[0150] 2. Scanning electron microscopy characterization (1) Experimental methods The microstructure of the flexible electromagnetic shielding material was characterized using a field emission scanning electron microscope (Regulus 8220, manufactured by Hitachi, Japan).

[0151] (2) Experimental results Figure 11 (a) ~ Figure 11 (d) shows the surface microstructure of the flexible electromagnetic shielding material at different magnifications. As can be seen from the figure, the original surface of the polymer matrix is ​​smooth and flat; Ni-Fe3O4 nanowires are uniformly attached to the matrix surface in an interlaced stacking manner, forming a large number of dense, fine protrusions in the loaded region. These protrusions exhibit granular or short rod-like morphologies, corresponding to the loaded Ni-Fe3O4 nanowires. The nanowires cover the matrix surface continuously and are regularly distributed, forming a significant morphological difference from the smooth substrate; the measured nanowire diameter is 170~180 nm.

[0152] Further observation of the cross-sectional microstructure of the flexible electromagnetic shielding material yielded the following results: Figure 12 As shown. Among them. Figure 12 (a) ~ Figure 12 (b) It can clearly show the overall outline of the two layers of the flexible electromagnetic shielding material; Figure 12 (c) A two-phase layered structure is clearly distinguishable. The upper layer is a continuous and dense polymer matrix, exhibiting the wavy, smooth cross-section characteristic of flexible materials; the lower layer is a Ni-Fe3O4 nanowire functional layer, exhibiting a rough, stacked, continuous morphology, forming a clear boundary with the matrix layer. The nanowires are interwoven and stacked, resulting in a distinct network of pores within the functional layer; magnified from the interface... Figure 12 (d) It can be seen that the interface between the polymer matrix and the nanowires is tightly connected and the combination effect is excellent, which fully demonstrates that the Ni-Fe3O4 nanowires are stably loaded on the surface of the polymer substrate and the composite structure is well formed.

[0153] 3. EDS elemental analysis and characterization (1) Experimental methods The flexible electromagnetic shielding material of Example 1 was tested using energy-dispersive X-ray spectroscopy (EDS) to analyze the composition and distribution characteristics of elements such as C, N, O, Si, Fe, and Ni on the sample surface.

[0154] (2) Experimental results The results are as follows Figures 13-14 As shown, the test spectrum can detect six elements: C, N, O, Si, Fe, and Ni. Each element corresponds to the polymer matrix and the Ni-Fe3O4 nanowire component, respectively. Figure 13This demonstrates that the magnetic filler Ni-Fe3O4 nanowires have been successfully incorporated into the polymer matrix. EDS elemental surface scan results ( Figure 14 The results show that the matrix-related elements are uniformly distributed, and the Fe and Ni elements in the Ni-Fe3O4 nanowires do not show local aggregation. They are well dispersed in the matrix, and the two-phase interface is well composited, which further confirms the successful preparation of the target flexible electromagnetic shielding material.

[0155] Experiment Example 2: Performance Testing of Flexible Electromagnetic Shielding Materials I. Mechanical Properties 1. Experimental Methods The flexible electromagnetic shielding material prepared by this invention is a composite structure with shape memory polymer as the substrate and Ni-Fe3O4 functional film loaded on the surface. Since the surface functional layer has little impact on the overall mechanical properties, the mechanical properties of the shape memory polymer substrate can be basically equivalent to the mechanical properties of the flexible electromagnetic shielding composite material.

[0156] Based on the above principles, this invention, referring to GB / T 1040 "Determination of Tensile Properties of Plastics", uses a universal testing machine to test the tensile properties of the shape memory polymers prepared in Examples 1-3. During the test, the equipment applies tensile loads to the PTSI-1 to PTSI-3 samples at a constant rate, continuously collecting data such as tensile force, displacement, stress, and strain until the samples break. Through this test, the tensile strength, elongation at break, and maximum force of PTSI-1 to PTSI-3 can be measured, thereby characterizing the overall mechanical properties of the flexible electromagnetic shielding material.

[0157] 2. Experimental Results Table 1 Mechanical tensile properties of shape memory polymers

[0158] As shown in Table 1, with the decrease in the number-average molecular weight of PDMS from 5000 g / mol to 1000 g / mol, the maximum force of the polymer increased from 0.74 kgf to 0.91 kgf (1 kgf = 9.8 N, stress range 7.252~8.918 N), the tensile strength increased significantly from 18.2 MPa to 111.4 MPa, and the elongation at break increased from 678% to 752%. Figure 15 The above data indicate that the number-average molecular weight of PDMS has a significant regulatory effect on the mechanical properties of polymers.

[0159] As the soft segment of the polymer, the increase in the molecular weight of PDMS directly leads to a decrease in the relative proportion of hard segments formed by urea bonds and urethane bonds generated from the reaction of MDI with amino groups and BD. Hard segments form physical cross-linking points and micro-region structures through intermolecular hydrogen bonds, which are the main source of the polymer's mechanical strength. When the molecular weight of PDMS is 1000 g / mol, the system exhibits the highest hard segment content, the densest synergistic hydrogen bond network formed by urea bonds and silicon-oxygen bonds, continuous and uniform hard segment micro-regions, and a high density of physical cross-linking, thus demonstrating the highest tensile strength. Simultaneously, the moderate soft segment length ensures good flexibility of the molecular chain, allowing it to maintain a high elongation at break, resulting in optimal overall mechanical properties.

[0160] When the molecular weight of PDMS increases to 3000 g / mol and 5000 g / mol, the length of the soft segment increases significantly, the relative content of the hard segment decreases, and the hydrogen bond crosslinking density decreases, leading to a continuous decrease in tensile strength. It is worth noting that, theoretically, a longer soft segment should impart higher elongation to the material. However, due to the progressively worsening compatibility between PDMS and the polyurethane matrix with increasing molecular weight, the degree of phase separation intensifies, the interfacial bonding force between the two phases weakens, and cracks easily initiate at the interface during tensile testing, ultimately resulting in a slight decrease in elongation at break.

[0161] Comprehensive evaluation shows that although the tensile strength of PTSI-2 and PTSI-3 is lower than that of PTSI-1, they still meet the conventional performance requirements of polyurethane-based shape memory polymers, and all three samples exhibit good overall mechanical properties. Furthermore, PTSI-2 to PTSI-3 also demonstrate good performance in other aspects such as thermal stability, resistance to thermal decomposition, and protection against high-temperature carbon residue, making them practically applicable. Among them, PTSI-1 possesses both excellent mechanical strength and flexibility, outstanding structural stability, and can withstand the harsh mechanical conditions of repeated deformation and recovery of shape memory films, exhibiting the best overall performance. Therefore, thanks to the excellent mechanical properties of the matrix polymer itself, the final flexible electromagnetic shielding material also possesses good mechanical properties.

[0162] II. Shape Memory Performance 1. Experimental Methods The flexible electromagnetic shielding material prepared by this invention has a composite structure with a shape memory polymer as the substrate and a Ni-Fe3O4 functional film loaded on the surface. Since the Ni-Fe3O4 functional layer has a weak interference with the deformation recovery characteristics of the material, the shape memory performance of the substrate can basically reflect the actual deformation response level of the flexible electromagnetic shielding material.

[0163] Based on the above principles, this invention employs a thermally triggered deformation recovery experiment to characterize the thermally induced shape memory properties of the shape memory polymer prepared in Example 1. The polymer film was cut into petal-shaped samples, and a temporary morphology was imparted to the samples using rapid cryogenic solidification with liquid nitrogen. Subsequently, the samples were placed in an environment of 110 °C to trigger deformation recovery. The evolution of the sample morphology and the recovery rate were observed throughout the process, and the complete recovery process was recorded. This was used to evaluate the shape memory effect of the polymer and thus characterize the shape memory properties of the flexible electromagnetic shielding material.

[0164] 2. Experimental Results Based on previous DSC tests, it was found that room temperature (approximately 25 °C) is higher than the crystallization temperature of the PTMEG soft segment (16~17 °C), which cannot meet the temperature requirements for sufficient polymer crystallization and shaping. Therefore, this invention uses liquid nitrogen for rapid cooling to temporarily fix the shape of the sample. Using the PTSI-1 sample as the test object, the petal-shaped sample was folded and placed in liquid nitrogen for isothermal shaping for 20 seconds. Figure 16 (a) After removal, place in a room temperature environment ( Figure 16 (b) ), then transferred to a 110 ℃ heating stage for thermally triggered shape recovery. Combined with Figure 16 (c)~ Figure 16 (e) The changes in the morphology of the sample are visible. The sample can be completely restored to its initial flat state. The overall shape recovery process takes about 2 minutes, and the thermal recovery effect is excellent.

[0165] To further verify the shape memory properties of the material, the folded, original petal-shaped sample was directly immersed in liquid nitrogen for cryogenic treatment. After removal, obvious plasticization marks remained on the sample surface, such as... Figure 16 As shown in (f). This phenomenon fully demonstrates that the shape memory polymer of the present invention possesses excellent thermally induced shape memory properties. Therefore, thanks to the excellent shape memory characteristics of the matrix polymer itself, the final flexible electromagnetic shielding material also possesses excellent shape memory properties.

[0166] III. Electromagnetic shielding performance 1. Experimental Methods Electromagnetic absorption performance was tested using an Agilent N5244A vector network analyzer via waveguide and coaxial methods. The test objects were the flexible electromagnetic shielding materials from Examples 1, 4, and Comparative Examples 3-8; the test electromagnetic wave frequency band was set to 2–18 GHz.

[0167] 2. Experimental Results Test results are as follows Figure 17As shown, when the thickness of the flexible electromagnetic shielding material in Comparative Examples 3-8 is in the range of 1.0-4.0 mm, the maximum reflection loss of the samples does not exceed -10 dB, and the electromagnetic wave absorption efficiency is less than 90%, indicating poor absorption performance. When the thickness of the flexible electromagnetic shielding material is increased to more than 4 mm, the absorption capability of the flexible electromagnetic shielding material is significantly improved, achieving electromagnetic wave absorption of more than 90%. Specifically, the 4.5 mm flexible electromagnetic shielding material in Example 1 has the best overall absorption performance, with a maximum reflection loss of -17.5 dB at 14.0 GHz and an effective bandwidth of 1.6 GHz, corresponding to a frequency band of 13.2-14.8 GHz. The 5 mm flexible electromagnetic shielding material in Example 4 has a peak loss of approximately -17.0 dB at 12.8 GHz, an effective absorption bandwidth of 1.6 GHz, and a frequency band range of 12.0-13.6 GHz. Overall, this flexible electromagnetic shielding material exhibits excellent electromagnetic wave absorption characteristics in the Ku band (12-18 GHz) with a thickness of 4.5-5 mm. Excellent absorption loss capability can significantly dissipate incident electromagnetic energy and reduce electromagnetic wave transmission. This, combined with the material's own shielding effect, effectively improves the overall electromagnetic shielding performance, giving the material both excellent absorption and electromagnetic shielding performance.

[0168] In summary, the flexible electromagnetic shielding material of this application exhibits excellent comprehensive performance, possessing outstanding shape memory properties, flexibility, and good electromagnetic shielding capabilities. The flexible electromagnetic shielding material can stably achieve deformation and shape recovery, adapting to complex deformation conditions. Based on the excellent mechanical properties of the shape memory polymer film, the flexible electromagnetic shielding material has a stable overall structure and excellent flexibility, meeting the stress requirements of daily service. Furthermore, through thickness control, it can effectively dissipate electromagnetic energy, exhibiting ideal absorption and shielding effects in the Ku band (12~18 GHz). The synergistic adaptation of multiple properties gives it high practical application value and promising prospects for widespread application.

[0169] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A flexible electromagnetic shielding material, characterized in that, The flexible electromagnetic shielding material comprises a Ni-Fe3O4 thin film and a shape memory polymer thin film stacked sequentially. The Ni-Fe3O4 in the Ni-Fe3O4 thin film was prepared by a hydrothermal method; The method for preparing the shape memory polymer in the shape memory polymer film includes the following steps: S1. Polytetrahydrofuran, diphenylmethane-4,4'-diisocyanate and organic solvent are mixed and subjected to polymerization reaction to obtain prepolymer; S2. Poly(dimethylsiloxane), bis(3-aminopropyl) end-capped polymer is added to the prepolymer obtained in step S1 and diphenylmethane-4,4' diisocyanate to carry out a polycondensation reaction to obtain a polycondensation polymer containing urea bonds; S3. Add 1,4-butanediol and diphenylmethane-4,4'-diisocyanate to the urea-containing condensate obtained in step S2, carry out chain extension reaction, and post-process to obtain shape memory polymer; Wherein, the number-average molecular weight of the polytetrahydrofuran is 2500~10000 g / mol; the number-average molecular weight of the poly(dimethylsiloxane), bis(3-aminopropyl)-terminated is 800~6000 g / mol; and the number-average molecular weight of the shape memory polymer is 40000~200000 g / mol. The thickness of the Ni-Fe3O4 film is 2.2~4 mm, and the thickness of the shape memory polymer film is 2.2~4 mm.

2. The flexible electromagnetic shielding material according to claim 1, characterized in that, The mass ratio of Ni-Fe3O4 in the Ni-Fe3O4 film to the shape memory polymer in the shape memory polymer film is 1:(3~30).

3. The flexible electromagnetic shielding material according to claim 1, characterized in that, The molar ratio of the polytetrahydrofuran and poly(dimethylsiloxane) with bis(3-aminopropyl) end caps is 1:(1~3).

4. The flexible electromagnetic shielding material according to claim 1, characterized in that, The molar ratio of polytetrahydrofuran to 1,4-butanediol is 1:(0.1~1).

5. The flexible electromagnetic shielding material according to claim 1, characterized in that, The total molar ratio of the polytetrahydrofuran and diphenylmethane-4,4' diisocyanate is 1:(2~5).

6. The flexible electromagnetic shielding material according to claim 1, characterized in that, The hydrothermal method includes the following steps: Iron source, nickel source, alkaline regulator, chelating agent and organic solvent are mixed and subjected to hydrothermal reaction, followed by post-treatment to obtain Ni-Fe3O4.

7. The flexible electromagnetic shielding material according to claim 6, characterized in that, The iron source includes one or more of ferrous chloride, ferrous sulfate heptahydrate, and ferric citrate.

8. The flexible electromagnetic shielding material according to claim 6, characterized in that, The chelating agent includes one or more of sodium citrate, ethylenediaminetetraacetic acid, and polyvinylpyrrolidone.

9. A method for preparing the flexible electromagnetic shielding material according to any one of claims 1 to 8, characterized in that, The steps include the following: The Ni-Fe3O4 dispersion was poured into a mold and dried to obtain a Ni-Fe3O4 film; then the shape memory polymer dilution was poured onto the surface of the aforementioned Ni-Fe3O4 film and dried to obtain the flexible electromagnetic shielding material.

10. The application of the flexible electromagnetic shielding material according to any one of claims 1 to 8 in the fields of 5G communication, flexible smart electronics, or minimally invasive medical treatment.

Images