Liquid metal-based flexible multilayer electromagnetic shielding composite film and preparation method thereof

Abstract

The application discloses a flexible multilayer electromagnetic shielding composite film based on liquid metal and a preparation method thereof. Firstly, Kevlar fiber and polyvinyl alcohol form a mutual entanglement double network structure through hydrogen bonding, so that the flexibility and mechanical strength of the film are improved; secondly, the liquid metal with high conductivity is doped to endow the composite film with excellent conductive performance, and further improve the electromagnetic shielding performance of the film. By designing a multilayer structure, interface reflection loss is introduced to improve the absorption capacity of the material to electromagnetic waves and the mechanical properties. The single-layer and multilayer composite films are prepared by the solution blending and filtration method. Through the multilayer comparison, it is found that when the three-layer composite film has a thickness of 0.4 mm, the electromagnetic shielding effectiveness of the three-layer composite film to the X wave band (8.2-12.4 GHz) reaches 57-78 dB. The film preparation cycle is short, the operation is simple, and the film is safe and controllable, so that the film has potential electromagnetic shielding applications in portable and wearable smart electronic products.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electromagnetic shielding materials, in particular to a flexible multilayer electromagnetic shielding composite film based on liquid metal and a preparation method thereof. BACKGROUND

[0002] With the continuous improvement of integrated circuit scale, electronic devices are becoming smaller and more powerful. However, the resulting electromagnetic radiation pollution and interference are also becoming more and more serious, which is particularly prominent in the fields of aerospace, military, artificial intelligence, 5G communication and wearable electronic devices. At this time, electromagnetic shielding (EMS) materials are crucial for the reliable operation of precision electronic devices, information security and human health.

[0003] Electromagnetic shielding is to use shielding materials to reflect and attenuate electromagnetic waves so that they cannot enter the shielding protection area. The loss modes of shielding materials are usually divided into three types: (1) reflection loss (SE R ). Due to the mismatch of the characteristic impedance of the conductive path formed on the surface of the material and the air, a part of the electromagnetic wave is directly reflected on the surface of the material to form a reflection loss. The reflection loss is related to the magnetic permeability (μ r ) of the material relative to the vacuum and the electrical conductivity (σ r ) of the material. Generally, the greater the electrical conductivity and the smaller the magnetic permeability of the shielding material, the greater the proportion of electromagnetic waves through reflection loss. (2) Absorption loss (SE A ). After the electromagnetic wave enters the shielding material, the electromagnetic wave can gradually be depleted in the material in cooperation with dielectric loss (multiple heterogeneous interface polarization, dipole polarization and conduction loss) and magnetic loss (magnetic resonance, magnetic coupling effect, eddy current loss, etc.), converting the electromagnetic wave energy incident into the interior into heat energy and being absorbed, thereby reducing the radiation effect of the source electromagnetic field. The absorption loss is related to the electrical conductivity (σ r ) of the material and the magnetic permeability (μ r ) of the material relative to the vacuum. Generally, the greater the electrical conductivity and the greater the magnetic permeability of the shielding material, the greater the proportion of electromagnetic waves through absorption loss. (3) Internal multiple reflection loss (SE M ). The multiple reflection loss of the electromagnetic wave is caused by the increased reflection times of the electromagnetic wave due to the existence of multiple interfaces in the material. The electromagnetic shielding efficiency of the electromagnetic shielding material can be effectively improved in the following ways: first, improve the electrical conductivity of the electromagnetic shielding material to increase the absorption loss and the reflection loss; second, further introduce magnetic fillers to improve the magnetic permeability of the electromagnetic shielding material to increase the absorption loss; third, design a porous and multilayer material structure to improve the multiple reflection loss of the electromagnetic wave in the interior.

[0004] Although traditional metal electromagnetic shielding materials have excellent electrical conductivity, electromagnetic shielding and thermal management performance, their high density, poor flexibility, poor chemical corrosion resistance, and difficulty in processing have seriously restricted their application. Compared with traditional metal materials, conductive polymer composites composed of polymer matrix and conductive fillers (such as graphene, multi-walled carbon nanotubes, MXenes, metal nanoparticles and nanowires, and their hybrids) have attracted much attention in electromagnetic shielding applications due to their light weight, strong corrosion resistance, good flexibility, good processability, and low cost. However, polymer composites usually require high filler content and large thickness to achieve ideal electrical conductivity and electromagnetic shielding performance. Although the emergence of conductive polymers overcomes the shortcomings of metal electromagnetic shielding materials, there are still some problems, such as the large contact resistance between adjacent carbon nanotubes or graphene reducing electrical conductivity; MXenes have poor chemical stability and are easily oxidized in humid air or water, greatly limiting their practical application; and electromagnetic shielding materials with high filler content have poor mechanical properties.

[0005] Therefore, it is still a great challenge to develop high-efficiency electromagnetic shielding materials with super flexibility and excellent mechanical properties. Many factors need to be considered when designing and developing any electromagnetic shielding material.

[0006] With the development of information technology, higher requirements are put forward for shielding materials, and new shielding materials should meet the characteristics of "thin, light, wide, strong", i.e. under the same conditions, the shielding material is thin, light, wide, and strong. Therefore, scientifically designing and manufacturing high-performance electromagnetic shielding materials with the characteristics of "light, thin, wide, and strong" (light weight, thin thickness, wide absorption frequency, and strong absorption) has become one of the key research directions at this stage.

[0007] Document 1 "Yao B, Hong W, Chen T, et al. Highly Stretchable Polymer Composite with Strain-Enhanced Electromagnetic Interference Shielding Effectiveness [J]. Advanced Materials, 2020, 32(14): 1907499." reports a highly stretchable polydimethylsiloxane (PDMS) composite embedded with a three-dimensional (3D) liquid metal (LM) network. When the volume fraction of LM particles is 30%, the electromagnetic shielding performance of the composite material with a thickness of 1.6 mm reaches more than 40 dB.

[0008] Document 2“Dong J, Luo S, Ning S, et al. MXene-Coated Wrinkled Fabrics for Stretchable and Multifunctional Electromagnetic Interference Shielding and Electro / Photo-Thermal Conversion Applications [J]. ACS Applied Materials & Interfaces, 2021, 13(50): 60478-60488.” reports a stretchable MXene-coated thermoplastic polyurethane (TPU) fabric, in which TPU is used as the substrate, and a MXene conductive layer is deposited on the surface of TPU by spraying method, so that the fabric has good shielding efficiency, and the total shielding efficiency reaches 35 dB.

[0009] Document 3“Cai Z, Su L, Wang H, et al. Alternating multilayered Si3N4 / SiC aerogels for broadband and high-temperature electromagnetic wave absorption up to 1000℃ [J]. ACS Applied Materials & Interfaces, 2021, 13(14): 16704-16712.” reports a high-performance electromagnetic wave absorbing ceramic aerogel composed of alternating multilayer wave-transparent Si3N4(N) layers and wave-absorbing SiC(C) layers, in which the (N6 / C6) aerogel with 6 layers of wave-transparent and wave-absorbing layers has a total shielding efficiency of 45 dB for electromagnetic waves with a frequency of 8.2-12.4 GHz.

[0010] Document 4 "Wang Z, Xia X, Zhu M, et al. Rational Assembly of Liquid Metal / Elastomer Lattice Conductors for High-Performance and Strain-Invariant Stretchable Electronics [J]. Advanced Functional Materials, 2021: 2108336." reports the use of 3D printing technology to rationally assemble liquid metal (LM) and polydimethylsiloxane (PDMS) into elastomers. The highly ordered and robust polydimethylsiloxane lattice skeleton provides support for the three-dimensionally interconnected deformable liquid conductive network. Among them, LM has significant shielding performance, for example, when the LM content is 50wt%, the total shielding effectiveness of the 3mm thick PDMS / LM elastomer to the electromagnetic wave with a frequency of 8.2-12.4GHz reaches 72dB, which has good shielding performance.

[0011] The above documents report some preparation methods of electromagnetic shielding materials for electromagnetic interference shielding field, but all have certain defects to varying degrees, for example: in document 1, the PDMS-LM composite material has poor mechanical strength, which limits its further application; in document 2, the interface adhesion between the substrate and the MXene conductive layer is poor; in document 3, the experimental steps are complex, and the preparation of the composite material is difficult; in document 4, the thickness of the composite material is large, which does not meet the requirement of thin thickness of electromagnetic shielding. SUMMARY

[0012] The purpose of the present application is to provide a flexible multilayer electromagnetic shielding composite film based on liquid metal and a preparation method thereof, to realize the target performance of low thickness, high shielding and high strength.

[0013] The technical solution to achieve the purpose of the present application is:

[0014] The flexible multilayer electromagnetic shielding composite film based on liquid metal is obtained by adding polyvinyl alcohol-Kevlar fiber suspension to the liquid metal aqueous dispersion, filtering, drying, packaging and tabletting to obtain a single-layer composite film.

[0015] The flexible multilayer electromagnetic shielding composite film based on liquid metal, the first layer and the third layer are polyvinyl alcohol-Kevlar fiber film, and the middle layer is polyvinyl alcohol-Kevlar fiber-liquid metal film.

[0016] The preparation method of the flexible multilayer electromagnetic shielding composite film based on liquid metal comprises the following steps:

[0017] Preparation of Kevlar fiber dispersion and liquid metal aqueous dispersion;

[0018] The polyvinyl alcohol is added into dimethyl sulfoxide to form a polyvinyl alcohol solution; the prepared Kevlar fiber dispersion is added into the polyvinyl alcohol solution, stirred uniformly, and washed to remove dimethyl sulfoxide, so as to obtain a polyvinyl alcohol-Kevlar fiber suspension;

[0019] The liquid metal aqueous dispersion is added into the polyvinyl alcohol-Kevlar fiber suspension, and stirring is performed to form a uniformly mixed polyvinyl alcohol-Kevlar fiber-liquid metal suspension; the polyvinyl alcohol-Kevlar fiber-liquid metal suspension is subjected to suction filtration, drying, packaging and tabletting, so as to obtain a single-layer polyvinyl alcohol-Kevlar fiber-liquid metal composite film.

[0020] The polyvinyl alcohol-Kevlar fiber suspension is divided into three parts, one part of which has a larger volume than the other two parts; the liquid metal aqueous dispersion is added into the polyvinyl alcohol-Kevlar fiber suspension with the largest volume for stirring and mixing, serving as a second layer, and the other two parts of the polyvinyl alcohol-Kevlar fiber suspension serve as a first layer and a third layer, respectively; then, suction filtration, drying, packaging and tabletting are sequentially performed, so as to obtain a three-layer composite film.

[0021] Compared with the prior art, the present application has the following advantages:

[0022] (1) The flexible multi-layer electromagnetic shielding composite film material based on liquid metal provided by the present application ensures the electrical conductivity of the composite film by introducing high-conductivity liquid metal; when the prepared three-layer film has a thickness of 0.4 mm, the electrical conductivity of the three-layer film is 56 S / cm, and the total electromagnetic shielding effectiveness for the X-band frequency can reach 57-78 dB, which is sufficient to resist 99.99999% of electromagnetic wave radiation. The hydrogen bonding between Kevlar fiber (KNF) and polyvinyl alcohol (PVA) can improve the flexibility and mechanical strength of the film; the film has high shielding performance and can also provide a tensile strength of 13.2 MPa, thereby ensuring the mechanical stability of the shielding material. The three-layer film can be used as an excellent electromagnetic shielding material, and the preparation method of the composite electromagnetic shielding film is simple in operation, has good mechanical properties, and has a wide application prospect.

[0023] (2) The Kevlar nanofiber prepared in the present application has a short cycle, while the Kevlar nanofiber prepared in the prior art has a long preparation time. The deprotonation time of Kevlar fiber in the present application is only 2 days, which shortens the synthesis cycle. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 X-ray diffraction (XRD) patterns of the liquid metal dispersion, polyvinyl alcohol-Kevlar fiber film (PK) and polyvinyl alcohol-Kevlar fiber-liquid metal composite film (PKL);

[0025] Figure 2 FTIR spectrum of the polyvinyl alcohol-Kevlar fiber-liquid metal single layer composite electromagnetic shielding film prepared in step (4) of Example 1;

[0026] Figure 3a SEM image of the liquid metal small particles prepared in step (2) of Example 1, Figure 3b size distribution of the metal small particles;

[0027] Fig. 4 is a SEM image of the surface of the polyvinyl alcohol-Kevlar fiber-liquid metal single layer composite electromagnetic shielding film without compression (4a) and with compression (4b);

[0028] Fig. 5 is a SEM image of the cross section of the polyvinyl alcohol-Kevlar fiber-liquid metal single layer composite electromagnetic shielding film without compression (5a)

[0029] and with compression (5b);

[0030] Figure 6a SE of the reflection loss, SE of the absorption loss and SE of the total shielding effectiveness of the electromagnetic wave in the X band frequency range of the polyvinyl alcohol-Kevlar fiber-liquid metal single layer composite electromagnetic shielding film without encapsulation R A T ; Figure 6b SE of the total shielding effectiveness, SE of the reflection loss and SE of the absorption loss of the electromagnetic wave in the X band frequency range of the polyvinyl alcohol-Kevlar fiber-liquid metal single layer, three layer and five layer composite electromagnetic shielding films T R A ;

[0031] Figure 7a stress-strain diagram of the polyvinyl alcohol-Kevlar fiber (PK) film in Example 4; Figure 7b stress-strain diagram of the polyvinyl alcohol-Kevlar fiber-liquid metal single layer composite film in Example 1 and the Kevlar fiber-liquid metal composite electromagnetic shielding film in Example 5; Figure 7c stress-strain diagram of the polyvinyl alcohol-Kevlar fiber-liquid metal single layer, three layer and five layer composite films. DETAILED DESCRIPTION

[0032] ​​​​The following examples are only a part of the embodiments of the present application, rather than all the embodiments. Therefore, the detailed description of the embodiments of the present application provided below is not intended to limit the scope of the claimed application, but merely represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of the present application. The specific conditions not indicated in the examples are carried out under the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not indicated by the manufacturer are all conventional products that can be commercially available.

[0033] In the following examples, the ultrasonic cell crusher used is JY96-IIN from Ningbo Xinzhi Biotechnology Co., Ltd., with a maximum output power of 100 W. During use, the output power is controlled by setting the percentage of the output power. Too small output power will affect the dispersion of liquid metal. In the embodiments of the present application, the output ratio is set to 80%.

[0034] Example 1

[0035] The preparation method of the flexible multilayer electromagnetic shielding composite film based on liquid metal in this embodiment specifically comprises the following steps:

[0036] (1) Preparation of Kevlar fiber:

[0037] First, the Kevlar fiber is deprotonated: weigh 2.5 g of potassium hydroxide, then weigh 3 g of Kevlar fiber, cut into about 2 cm long with scissors, and add to a beaker; finally, add 120 mL of dimethyl sulfoxide to the beaker, and magnetically stir under an oil bath at 35°C for 2 days, until the Kevlar fiber is completely dissolved, finally obtaining a uniform and viscous dark red Kevlar fiber dispersion with a concentration of 25 mg / mL.

[0038] (2) Preparation of liquid metal dispersion by ultrasonic assistance:

[0039] Take 6 mL of deionized water and add it to a 20 mL sample bottle, then add 3 g of liquid metal (in this embodiment, a gallium-based eutectic alloy with electrical conductivity greater than 10 6 S / m at room temperature), and use an ultrasonic cell crusher for ultrasonic treatment, with a power setting of 80%, a working time of 5 min, a rest time of 3 min, and then a working time of 5 min, for a total working time of 15 min.

[0040] (3) Preparation of polyvinyl alcohol solution:

[0041] Take 25 mg of polyvinyl alcohol (type 1799) into a 50 mL beaker, and then add 25 mL of dimethyl sulfoxide as a solvent. Stir magnetically in a water bath at 80°C for 30 min until the polyvinyl alcohol is completely dissolved. Take 1 g of polyvinyl alcohol into a 20 mL sample bottle, and then add 9 mL of deionized water. Stir magnetically in a water bath at 80°C for 60 min until the polyvinyl alcohol is completely dissolved to form a polyvinyl alcohol aqueous solution, which is used as the encapsulating liquid metal.

[0042] (4) Preparation of a polyvinyl alcohol-Kevlar fiber-liquid metal (PKL) single-layer flexible composite electromagnetic shielding film:

[0043] First, take 2 mL of the Kevlar fiber dispersion in step (1) into the polyethylene solution in step (3), and stir with a homogenizer to form a uniformly dispersed solution. Wash with a large amount of deionized water until the solution changes from dark red to light yellow and forms fiber floc. Then add the liquid metal aqueous dispersion obtained in step (2) into the beaker, and stir with a homogenizer to obtain a uniformly dispersed polyvinyl alcohol-Kevlar fiber-liquid metal mixture. Then perform suction filtration to obtain a polyvinyl alcohol-Kevlar fiber-liquid metal film, which is then placed in a vacuum drying oven at 105°C for drying for 1-2 h to obtain a polyvinyl alcohol-Kevlar fiber-liquid metal composite film. Then uniformly coat the surface and periphery of the film with a polyvinyl alcohol aqueous solution, and then perform drying. Then use a tablet press, set the pressure to 1-2 MPa, and press for 3 min to finally obtain an encapsulated polyvinyl alcohol-Kevlar fiber-liquid metal composite electromagnetic shielding film with a thickness of 0.5 mm. Without encapsulation with polyvinyl alcohol, the film can be directly pressed after drying to obtain an unencapsulated polyvinyl alcohol-Kevlar fiber-liquid metal composite electromagnetic shielding film with a thickness of 0.43 mm.

[0044] Example 2

[0045] Example 2

[0046] Example 3

[0047] Example 3 is the preparation of flexible polyvinyl alcohol-Kevlar fiber-liquid metal five-layer composite electromagnetic shielding film: same as Example 2, the polyvinyl alcohol-Kevlar fiber suspension is divided into two parts according to the volume ratio of 3:4. The liquid metal dispersion is added to the polyvinyl alcohol-Kevlar fiber suspension with a proportion of 4 / 7, and then divided into two parts after stirring, which are used as the second layer and the fourth layer, respectively. The polyvinyl alcohol-Kevlar fiber suspension with a proportion of 3 / 7 is divided into three parts as the first, third and fifth layers, and then filtered in sequence to obtain a five-layer film. Place it in a vacuum drying oven at 105°C for 1-2h. Then evenly coat the film with polyvinyl alcohol solution for packaging, and then dry for 10min. Then use a tablet press, set the pressure to 1-2MPa, and press for 3min to obtain a five-layer film.

[0048] Example 4

[0049] Example 4 is the preparation of flexible polyvinyl alcohol-Kevlar fiber film (PK). The specific steps are the same as steps (1), (3) and (4) of Example 1. In step (4), after obtaining the polyvinyl alcohol-Kevlar fiber flocculation, use a homogenizer to stir at 5000rpm for 5min without adding liquid metal aqueous dispersion. The obtained polyvinyl alcohol-Kevlar fiber mixture is then filtered, placed in a vacuum drying oven at 105°C for 1-2h to obtain a flexible polyvinyl alcohol-Kevlar fiber film.

[0050] Example 5

[0051] The present example is the preparation of flexible Kevlar fiber-liquid metal composite film (KL), the specific steps are the same as steps (1) and (2) of Example 1. Take 2 mL of Kevlar fiber dispersion in step (1) and 25 mL of DMSO solution into a 50 mL beaker, and stir with a homogenizer to form a uniform dispersion solution. After washing with a large amount of deionized water, the solution changes from dark red to light yellow, and fiber flocculation is formed. Add the liquid metal aqueous dispersion obtained in step (2) of Example 1 to the beaker, and stir with a homogenizer to obtain a uniformly dispersed Kevlar fiber-liquid metal mixture. Perform filtration, drying, tabletting and packaging operations, and the specific process is the same as Example 1.

[0052] The liquid metal, polyvinyl alcohol-Kevlar fiber and polyvinyl alcohol-Kevlar fiber-liquid metal composite electromagnetic shielding film prepared in the above preparation process were characterized, and the results are as follows:

[0053] Figure 1 The XRD patterns of liquid metal (GaIn alloy), polyvinyl alcohol-Kevlar fiber (PK) and polyvinyl alcohol-Kevlar fiber-liquid metal composite film, and the three characteristic diffraction peaks of (110), (200) and (021) in the figure. The two characteristic diffraction peaks of PVA-KNF-LM at (110) and (200), i.e. at 2θ angles of 19.6° and 23.2°, correspond to the diffraction peaks of PVA-KNF, and the characteristic diffraction peak of (021) at 2θ angle of 35° corresponds to the main peak of GaIn alloy, proving the existence of PVA, KNF and LM in the composite film.

[0054] Figure 2 The infrared spectrum of the prepared polyvinyl alcohol-Kevlar fiber-liquid metal single-layer composite film.3317 cm -1 N-H / O-H vibration; 2940 cm -1 and 2905 cm -1 Stretching vibration of -CH2 and -CH groups on PVA chain; 1640 cm -1 C=O stretching vibration; 1544 cm -1 N-H deformation and C-N stretching vibration; 1401 cm -1 Ga-O stretching vibration; 1309 cm -1 Ph-N vibration; 1012 cm -1 Coupling of C-H in-plane stretching vibration. After consulting the literature, it is found that there are amide bond, benzene ring, hydroxyl group and gallium oxide characteristic peaks, proving that the composite film contains PVA, KNF and LM.

[0055] Figure 3a The scanning electron micrograph of the liquid metal small particles prepared by the ultrasonic-assisted method, from which it can be seen that the liquid metal is uniformly dispersed into small particles.Figure 3b is the size distribution diagram of liquid metal, the diameter of small particles of liquid metal is 2-4 μm, so it can be uniformly dispersed in the film to form more uniform effective channels.

[0056] Figure 4a is the scanning electron microscope diagram of the surface of the single-layer composite electromagnetic shielding film without tabletting, it can be seen that the liquid metal is uniformly dispersed on the surface of polyvinyl alcohol-Kevlar fiber. Figure 4b is the scanning electron microscope diagram of the surface of the single-layer composite electromagnetic shielding film after tabletting, it can be seen that the oxide shell on the surface of the liquid metal particles is broken under the action of external force after tabletting, forming interconnected liquid metal, which makes the conductive network more perfect, improving the conductivity of the film, and at the same time increasing the SE A and SE R of the composite film.

[0057] Figure 5a is the scanning electron microscope diagram of the cross section of the single-layer composite electromagnetic shielding film without tabletting, it can be seen that the liquid metal is embedded in the polyvinyl alcohol-Kevlar fiber, and the composite film is a layered structure. Figure 5b is the scanning electron microscope diagram of the cross section of the single-layer composite electromagnetic shielding film material after tabletting, it can be seen that the liquid metal also forms a conductive path inside after tabletting, ensuring uniform conductivity, while the porosity decreases and the thickness decreases after tabletting, but it is still a layered structure, which is beneficial to increase the internal reflection loss. The high electromagnetic shielding performance mainly comes from the high conductivity and layered structure of the composite electromagnetic shielding film.

[0058] Figure 6 is a test of the total electromagnetic shielding performance of the composite electromagnetic shielding film, the sample is tested by a vector network analyzer, the waveguide method is adopted, the connected clamp is a waveguide clamp, the sample bin tested by the waveguide is a rectangular clamp with a fixed size, the calibration frequency is X band during calibration, and the absorption loss SE R , the absorption loss SE A and the total shielding effectiveness SE T are calculated by using the data of S11 and S21. The total shielding effectiveness of the electromagnetic shielding material provided by the application includes three shielding mechanisms of absorption loss, absorption loss and interface reflection loss, mainly absorption loss, and reflection loss and interface reflection loss as auxiliary, and the electromagnetic wave in the composite film is dissipated or absorbed in the form of heat. As can be seen from the figure, Figure 6a is the total shielding effectiveness of the single-layer film without packaging for electromagnetic waves with a frequency of X band, which is 98-136 dB, enough to resist 99.9999999% of electromagnetic wave radiation, only 0.0000001% of electromagnetic waves can penetrate the shielding body and continue to propagate. However, since the liquid metal leaks during the compression process of the single-layer film without packaging, it needs to be packaged. Figure 6bThe total shielding effectiveness of the encapsulated single-layer, three-layer and five-layer films to X-band electromagnetic waves is 42-64 dB, 57-78 dB and 53-66 dB respectively, and the three-layer film can resist 99.9999% of electromagnetic wave radiation, and only 0.0001% of electromagnetic waves can continue to propagate through the shielding body. The conductivity of the single-layer film is 72 S / cm before encapsulation, and the conductivity is 40 S / cm after encapsulation. Therefore, the encapsulation affects the effective path in the interior, resulting in a decrease in shielding performance, and subsequent research needs to adjust the encapsulation method. Figure 6c The reflection loss of the single-layer, three-layer and five-layer films to X-band electromagnetic waves is compared, and the increase in the number of interfaces leads to an increase in the reflection loss of the five-layer film. Figure 6d The absorption loss of the single-layer, three-layer and five-layer films to X-band electromagnetic waves is compared. The conductivity of the single-layer film is 40 S / cm, but due to the increase in the number of layers, the thickness of the absorption layer is relatively reduced, and the conductivity is 56 S / cm when the three-layer film is formed, so the absorption loss is the largest. The conductivity of the five-layer film is 38 S / cm, and because the effective path is blocked by the intermediate wave-transparent layer, the conductivity decreases, so the absorption loss decreases.

[0059] Figure 7a The stress-strain diagram of the polyvinyl alcohol-Kevlar fiber film is shown in the figure, and it can be seen from the figure that the tensile strength of the polyvinyl alcohol-Kevlar fiber film is 122.7 MPa. The mechanical properties support the design of the multilayer film. Figure 7b The stress-strain diagram of the Kevlar fiber-liquid metal film (KL) and the polyvinyl alcohol-Kevlar fiber-liquid metal single-layer film (PKL) is shown in the figure, and it can be seen from the figure that the introduction of polyvinyl alcohol can increase the mechanical strength of the PKL from 9.5 MPa to 13.2 MPa; Figure 7c The stress-strain diagram of the polyvinyl alcohol-Kevlar fiber-liquid metal single-layer, three-layer and five-layer composite film is shown in the figure, and the tensile strength is 13.2 MPa, 19.8 MPa and 15.5 MPa respectively. When the three-layer film is formed, the first layer and the third layer PVA-KNF film provide mechanical support, so that the tensile strength of the entire three-layer film is increased by 50% compared with the single-layer film. However, due to the relatively reduced thickness of the absorption layer (PKL layer) and the relatively large content of LM, the tensile strength is affected. Therefore, the tensile strength of the five-layer film is decreased, so the tensile strength of the three-layer film is the best.

[0060] The above only describes the preferred embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent transformation or direct or indirect application in other related technical fields based on the content of the specification and the drawings is also included in the patent protection scope of the present application.

Claims

1. A method for preparing a flexible multilayer electromagnetic shielding composite film based on liquid metal, characterized in that, Includes the following steps: Preparation of Kevlar fiber dispersion and aqueous dispersion of liquid metal; wherein the liquid metal is a gallium-based alloy; Polyvinyl alcohol is added to dimethyl sulfoxide to form a polyvinyl alcohol solution; The prepared Kevlar fiber dispersion was added to a polyvinyl alcohol solution, stirred until homogeneous, and washed to remove dimethyl sulfoxide, resulting in a polyvinyl alcohol-Kevlar fiber suspension. A liquid metal aqueous dispersion was added to a polyvinyl alcohol-Kevlar fiber suspension and stirred to form a uniformly mixed polyvinyl alcohol-Kevlar fiber-liquid metal suspension. A single-layer polyvinyl alcohol-Kevlar fiber-liquid metal composite film was obtained by filtration, drying, encapsulation and tableting of a polyvinyl alcohol-Kevlar fiber-liquid metal suspension. The obtained polyvinyl alcohol-Kevlar fiber suspension is divided into three parts, one of which has a larger volume than the other two. The liquid metal aqueous dispersion is added to the polyvinyl alcohol-Kevlar fiber suspension with the largest volume and stirred to form the second layer. The other two polyvinyl alcohol-Kevlar fiber suspensions are used as the first and third layers, respectively. Then, the three-layer composite film is obtained by sequentially filtering, drying, encapsulating and pressing.

2. The method for preparing a flexible multilayer electromagnetic shielding composite film based on liquid metal according to claim 1, characterized in that, The polyvinyl alcohol-Kevlar fiber suspension was divided into three portions at a volume ratio of 1:2:

1.

3. The method for preparing a flexible multilayer electromagnetic shielding composite film based on liquid metal according to claim 1, characterized in that, The thickness of the polyvinyl alcohol-Kevlar fiber-liquid metal membrane is greater than that of the polyvinyl alcohol-Kevlar fiber membrane.

4. The method for preparing a flexible multilayer electromagnetic shielding composite film based on liquid metal according to claim 1, characterized in that, The conductivity of the gallium-based alloy is greater than 10. 6 S / m.

5. The method for preparing a flexible multilayer electromagnetic shielding composite film based on liquid metal according to claim 1, characterized in that, The mass ratio of polyvinyl alcohol to Kevlar fiber in the polyvinyl alcohol-Kevlar fiber suspension is 1:

2.

6. The method for preparing a flexible multilayer electromagnetic shielding composite film based on liquid metal according to claim 1, characterized in that, The encapsulation process involves uniformly coating a three-layer composite film with a polyvinyl alcohol aqueous solution.

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