A wave-absorbing and heat-conducting flexible composite film and its preparation method

Abstract

The present invention belongs to the technical field of wave-absorbing and heat-conducting composite materials, and relates to a wave-absorbing and heat-conducting flexible composite film and its preparation method. In the composite film, polydimethylsiloxane serves as a matrix, and flaky carbonyl iron and silver nanowires serve as fillers. The flaky carbonyl iron is perpendicular to the matrix and arranged neatly along the radial direction of the matrix, and the silver nanowires connect adjacent flaky carbonyl iron. The preparation method is as follows: dispersing the silver nanowires in a mixed solvent to obtain a dispersion; adding flaky carbonyl iron powder to the dispersion and heating it to obtain a composite filler; adding polydimethylsiloxane to n-hexane and then adding a curing agent to obtain a precursor solution; adding the composite filler to the precursor solution to form a homogeneous state to obtain a mixed solution; vacuum degassing the mixed solution, applying a uniform magnetic field and heating it to obtain a wave-absorbing and heat-conducting flexible composite film. The composite film has significant dual functional properties of broadband wave absorption and high thermal conductivity, which greatly enhances the huge potential of the film in practical applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of wave-absorbing and heat-conducting composite materials, and in particular relates to a wave-absorbing and heat-conducting flexible composite film and a preparation method thereof. Background Art

[0002] The increasing power density and integration of electronic devices has led to an exacerbation of electromagnetic interference (EMI) issues. Common electronic devices such as mobile phones, wireless routers, Bluetooth devices, and microwave ovens typically operate in the 2-6 GHz frequency range. At low frequencies, traditional absorbing materials such as ferrites and carbon-based composites suffer from issues such as excessive thickness, high density, and impedance mismatch at low frequencies, making them difficult to meet the demands for lightweight and efficient absorption at low frequencies. Furthermore, the heat generated by high-power devices during operation, if not dissipated promptly, can severely impact device stability and lifespan.

[0003] However, traditional thermally conductive materials (such as metals and ceramics) often have high electromagnetic wave reflection properties, which can exacerbate electromagnetic pollution. Meanwhile, single absorbing materials generally lack sufficient thermal conductivity. Improving absorbing performance reduces thermal conductivity, and vice versa, increasing thermal conductivity reduces absorbing performance, creating a conflict between absorbing and conducting materials.

[0004] Therefore, it is difficult for electronic packaging materials to achieve effective compatibility between broadband wave absorption and high thermal conductivity, which greatly reduces the working performance of smart electronic devices. Summary of the Invention

[0005] The purpose of the present invention is to provide a wave-absorbing and heat-conducting flexible composite film and a preparation method thereof, which solves the problem that electronic packaging materials are difficult to achieve effective compatibility between broadband wave absorption and high thermal conductivity.

[0006] The present invention is achieved through the following technical solutions:

[0007] The present invention discloses a wave-absorbing and heat-conducting flexible composite film. In the wave-absorbing and heat-conducting flexible composite film, polydimethylsiloxane is used as a matrix, and flaky carbonyl iron and silver nanowires are used as fillers. The flaky carbonyl iron is perpendicular to the matrix and arranged neatly along the radial direction of the matrix, and the silver nanowires connect adjacent flaky carbonyl iron.

[0008] Furthermore, in the wave-absorbing and heat-conducting flexible composite film, the mass fraction of the flaky carbonyl iron is 56%-65%; the mass fraction of the silver nanowire is 4.6%-12.71%, and the rest is the matrix.

[0009] Furthermore, the vertical thermal conductivity of the wave-absorbing and heat-conducting flexible composite film is higher than 1.3 W / mK, and the tensile strength is greater than 1.0 MPa.

[0010] Furthermore, the wave-absorbing response frequency band of the wave-absorbing and heat-conducting flexible composite film covers the S band, C band, X band and Ku band;

[0011] The wave-absorbing and heat-conducting flexible composite film has a reflection loss of less than or equal to -5 dB in a wave-absorbing response frequency band of 2.0 to 18.0 GHz.

[0012] The present invention discloses a method for preparing a wave-absorbing and heat-conducting flexible composite film, comprising the following steps:

[0013] S1. Dispersing silver nanowires in a mixed solvent of ethanol and n-hexane to obtain a dispersion; adding flaky carbonyl iron powder to the dispersion, stirring until uniform, and heating to obtain a composite filler;

[0014] Add polydimethylsiloxane to n-hexane, stir evenly, then add curing agent, continue stirring to obtain a precursor solution;

[0015] S2. Add the composite filler to the precursor solution and continue stirring until the solution is in a homogeneous state to obtain a mixed solution;

[0016] S3. After vacuum degassing the mixed liquid, a uniform magnetic field is applied and the temperature is increased to solidify it, thereby obtaining a wave-absorbing and heat-conducting flexible composite film.

[0017] Furthermore, in S1, the mass ratio of silver nanowires to flaky carbonyl iron powder is (0.07~0.21):1.

[0018] Furthermore, in the mixed solvent, the volume ratio of ethanol to n-hexane is 1:(10-15).

[0019] Furthermore, in S2, when the composite filler is added to the precursor solution, the mass ratio of the added composite filler to the polydimethylsiloxane is (2~2.83):1.

[0020] Furthermore, in S3, the vacuum degassing conditions are: vacuum degree of -0.1 MPa, time of 30 to 60 min;

[0021] The conditions for the temperature-raising curing are: a curing temperature of 70-90° C. and a curing time of 2-4 hours.

[0022] Furthermore, in S3, the magnetic field direction of the uniform magnetic field is perpendicular to the surface of the mixed liquid, the magnetic field intensity is 50-70 mT, and the magnetic field uniformity is 94%-96%.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] The present invention discloses a wave-absorbing and heat-conducting flexible composite film, which uses a composite of flaky carbonyl iron and silver nanowires as a filler and polydimethylsiloxane as a matrix. The flaky carbonyl iron is neatly arranged radially along the matrix, and the silver nanowires connect adjacent flaky carbonyl irons. The flaky carbonyl iron has excellent dielectric loss and magnetic loss properties, and the orderly arrangement perpendicular to the matrix can effectively increase the resonant loss of electromagnetic waves. At the same time, the silver nanowires have excellent electrical conductivity loss, which can enhance low-frequency loss. The interface polarization between the filler and the matrix further enhances the loss of electromagnetic wave energy, effectively broadening the wave-absorbing response frequency band. At the same time, the silver nanowires connect adjacent flaky carbonyl irons to construct multiple phonon / electron conduction channels. The radial orderly arrangement accelerates the phonon / electron conduction rate, effectively improving the thermal conductivity of the composite film.

[0025] The present invention also discloses a method for preparing the wave-absorbing and heat-conducting flexible composite film. The method includes first preparing a composite filler using silver nanowires and flaky carbonyl iron powder, then preparing a polydimethylsiloxane precursor solution. The composite filler is added to the precursor solution and continuously stirred until the solution becomes homogeneous, resulting in a mixed solution. In the mixed solution, the PVP on the surface of the silver nanowires weakly interacts with the carbonyl groups on the surface of the flaky carbonyl iron. A uniform magnetic field-induced assembly technique is used to manipulate the composite filler into an orderly radial arrangement, indirectly assembling the silver nanowires and preventing agglomeration of the composite filler in the matrix. Simultaneously, the polydimethylsiloxane encapsulates the ordered structure, resulting in the wave-absorbing and heat-conducting flexible composite film. Silver nanowires are introduced as a multifunctional reinforcing phase, achieving performance breakthroughs through the following synergistic mechanisms: silver nanowires, with their ultra-high intrinsic thermal conductivity and high aspect ratio, construct a three-dimensional continuous thermal conductive network in the matrix, significantly improving the overall thermal diffusion efficiency of the film; the high electrical conductivity of silver nanowires can induce interfacial polarization and conductivity loss, effectively compensating for the magnetic loss attenuation caused by the skin effect in the low-frequency band; the axial co-orientation design of silver nanowires and flake carbonyl iron reduces the interfacial thermal resistance between fillers and inhibits agglomeration under high load.

[0026] Furthermore, the composite film has a vertical thermal conductivity exceeding 1.3 W / mK, and a reflection loss of less than or equal to -5 dB within the 2.0-18.0 GHz absorption response band. This fully covers the S, C, X, and Ku bands, demonstrating both strong low-frequency absorption and effective broadband absorption, effectively complementing the existing electronic packaging materials' compatibility between broadband absorption and high thermal conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The following are photos of the wave-absorbing and heat-conducting flexible composite film prepared by the present invention; Figure a is a photo of the film in a flat state; Figure b is a photo of the film after being folded once; and Figure c is a photo of the film after being folded twice.

[0028] Figure 2This is a reflection loss curve of the wave-absorbing and heat-conducting flexible composite film prepared in Example 1;

[0029] Figure 3 This is a reflection loss curve of the wave-absorbing and heat-conducting flexible composite film prepared in Example 2;

[0030] Figure 4 This is a reflection loss curve of the wave-absorbing and heat-conducting flexible composite film prepared in Example 3;

[0031] Figure 5 This is a reflection loss curve of the wave-absorbing and heat-conducting flexible composite film prepared in Example 4;

[0032] Figure 6 This is a reflection loss curve of the wave-absorbing and heat-conducting flexible composite film prepared in Example 5;

[0033] Figure 7 This is a SEM image of the cross section of the wave-absorbing and heat-conducting flexible composite film prepared in the present invention;

[0034] Figure 8 Schematic diagram of the microstructure of the cross section of the wave-absorbing and heat-conducting flexible composite film prepared by the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clear, the following is a further detailed description with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. That is, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments.

[0036] The detailed description of the embodiment of the present invention provided in the following figures is not intended to limit the scope of the claimed invention, but merely represents a selected embodiment of the present invention. All other embodiments derived by those skilled in the art based on the figures and embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0037] The present invention discloses a method for preparing a wave-absorbing and heat-conducting flexible composite film, comprising the following steps:

[0038] S1. Dispersing silver nanowires in a mixed solvent of ethanol and n-hexane to obtain a dispersion; adding flaky carbonyl iron powder to the dispersion, stirring until uniform, and heating to obtain a composite filler;

[0039] Add polydimethylsiloxane to n-hexane, stir evenly, then add curing agent, continue stirring to obtain a precursor solution;

[0040] S2. Add the composite filler to the precursor solution and continue stirring until the solution is in a homogeneous state to obtain a mixed solution;

[0041] S3. After vacuum degassing the mixed liquid, a uniform magnetic field is applied and the temperature is increased to solidify it, thereby obtaining a wave-absorbing and heat-conducting flexible composite film.

[0042] The size of the flake-shaped carbonyl iron used in the present invention is 1-5 μm, and the diameter of the silver nanowire is usually 10 nm to 200 nm.

[0043] The curing agent used in the present invention is Dow Corning DC184 curing agent, and the core component of Dow Corning DC184 curing agent is usually a silicon-containing cross-linking agent.

[0044] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0045] Example 1

[0046] The present invention discloses a method for preparing a wave-absorbing and heat-conducting flexible composite film, comprising the following steps:

[0047] (1) Disperse 1.0 g of silver nanowires (AgNWs) in a mixed solvent of 1 mL of ethanol and 10 mL of n-hexane to obtain a dispersion;

[0048] 14 g of flake carbonyl iron (FCI) powder was added to the dispersion, mechanically stirred until uniform, and heated to 70°C to remove the solvent to obtain the AgNWs / FCI composite filler.

[0049] (2) Add 6 g of n-hexane to 6 g of polydimethylsiloxane (PDMS), stir magnetically until evenly mixed, then add 0.6 g of curing agent, and continue magnetic stirring to obtain a precursor solution;

[0050] (3) Add 15.0 g of AgNWs / FCI composite filler to the precursor solution and continue stirring until the solution is homogeneous to obtain a mixed solution;

[0051] (4) The mixed liquid was placed in a mold and transferred to the sample stage in the center of the Helmholtz coil. A 50 mT uniform magnetic field was applied and vacuum degassing was performed for 30 min at a vacuum degree of -0.1 MPa. The temperature was then raised to 70 °C and kept at this temperature for 4 h to obtain an AgNWs / FCI / PDMS composite film.

[0052] In the AgNWs / FCI / PDMS composite film prepared in this example, the mass fraction of the flaky carbonyl iron is 64.8%; and the mass fraction of the silver nanowires is 4.6%.

[0053] As shown in Table 1, the water contact angle test of the AgNWs / FCI / PDMS composite film prepared in this example was conducted, and the contact angle was 112°.

[0054] As shown in Table 1, when the AgNWs / FCI / PDMS composite film prepared in this example was heated from the bottom, the surface temperature reached 20° C. within 30 seconds, indicating that the film has good thermal conductivity.

[0055] As shown in Table 1, the vertical thermal conductivity of the AgNWs / FCI / PDMS composite film prepared in this example is 1.37 W / mK.

[0056] The tensile strength of the AgNWs / FCI / PDMS composite film prepared in Example 1 was tested, and the tensile strength was 1.37 MPa.

[0057] like Figure 2 As shown, the wave absorption response band of the AgNWs / FCI / PDMS composite film prepared in this embodiment completely covers the S band, C band, X band, and Ku band.

[0058] At 3.9 GHz in the S-band, the minimum return loss value is -24.42 dB.

[0059] At the C-band frequency of 5.1 GHz, the minimum reflection loss value is -42.34 dB, which means that the absorption capacity is the strongest at this frequency.

[0060] At 9.0 GHz in the X-band, the minimum return loss value is -19.41 dB.

[0061] At the Ku-band frequency of 13.8 GHz, the minimum return loss value is -14.26 dB.

[0062] The S, C, X, and Ku bands mentioned in this invention refer to electromagnetic wave bands in different frequency ranges, as follows:

[0063] S-band: The frequency range is typically 2-4 GHz. The S-band is common in radar applications. For example, weather radar often uses the S-band to detect meteorological phenomena such as precipitation. This is because electromagnetic waves in this band are relatively less affected by weather when propagating through the atmosphere and can effectively penetrate clouds and raindrops, providing more accurate weather information.

[0064] C-band: The frequency range generally covers 4-8 GHz. The C-band is widely used in satellite communications and radar detection. In satellite communications, the C-band leverages its frequency characteristics to achieve stable signal transmission and has relatively little interference with other communication bands. In the radar field, C-band radar has certain advantages in target detection and recognition, providing high resolution and detection accuracy.

[0065] X-band: The frequency range is approximately 8-12 GHz. The X-band is widely used in military radar, civil aviation radar, and some high-precision weather radars. In the military, X-band radar can be used for precise target tracking and identification. Its higher frequency enables a narrower beamwidth, improving angular resolution and more accurately determining the target's position and shape. In civil aviation, X-band radar is used for approach and landing guidance at airports, providing aircraft with precise navigation information.

[0066] Ku-band: The frequency range is typically 12-18 GHz. The Ku-band is primarily used in satellite communications and radar systems. In satellite communications, the Ku-band offers high transmission rates and strong anti-interference capabilities, making it widely used in television signal transmission, data communications, and other fields. Many live satellite television systems utilize the Ku-band to transmit television program signals to users. In radar, Ku-band radar excels in specific application scenarios, such as low-altitude target detection and tracking, as its higher frequency provides better resolution and the ability to detect small targets.

[0067] Example 2

[0068] The present invention discloses a method for preparing a wave-absorbing and heat-conducting flexible composite film, comprising the following steps:

[0069] (1) Disperse 2.0 g of AgNWs in a mixed solvent of 1 mL of ethanol and 12 mL of n-hexane to obtain a dispersion;

[0070] 14 g of FCI powder was added to the dispersion, mechanically stirred until uniform, and heated to 75°C to remove the solvent to obtain AgNWs / FCI composite filler.

[0071] (2) Add 6 g of PDMS to 6 g of n-hexane, stir magnetically, then add 0.6 g of curing agent and continue magnetic stirring to obtain a precursor solution;

[0072] (3) Add 16.0 g of AgNWs / FCI composite filler to the precursor solution and continue stirring until the solution is homogeneous to obtain a mixed solution;

[0073] (4) The mixed liquid was placed in a mold and transferred to the sample stage in the center of the Helmholtz coil. A 60 mT uniform magnetic field was applied and vacuum degassing was performed for 40 min at a vacuum degree of -0.1 MPa. The temperature was then raised to 75 °C and kept at this temperature for 4 h to obtain an AgNWs / FCI / PDMS composite film.

[0074] In the AgNWs / FCI / PDMS composite film prepared in this example, the mass fraction of the flaky carbonyl iron is 61.95%; and the mass fraction of the silver nanowires is 8.85%.

[0075] As shown in Table 1, the water contact angle test of the AgNWs / FCI / PDMS composite film prepared in this example was conducted, and the contact angle was 116°.

[0076] As shown in Table 1, when the AgNWs / FCI / PDMS composite film prepared in this example was heated from the bottom, the surface temperature reached 29° C. within 30 seconds, indicating that the film has good thermal conductivity.

[0077] As shown in Table 1, the vertical thermal conductivity of the AgNWs / FCI / PDMS composite film prepared in this example is 1.49 W / mK.

[0078] The tensile strength of the AgNWs / FCI / PDMS composite film prepared in Example 1 was tested, and the tensile strength was 3.38 MPa.

[0079] like Figure 3 As shown in FIG, the Ag NWs / FCI / PDMS composite film prepared in this embodiment completely covers the S band, C band, X band, and Ku band.

[0080] At 3.8 GHz in the S-band, the minimum return loss value is -26.73 dB.

[0081] At the 4.2 GHz frequency in the C band, the minimum reflection loss value is -47.20 dB, which means that the absorption capacity is the strongest at this frequency.

[0082] At 8.2 GHz in the X-band, the minimum return loss value is -14.86 dB.

[0083] At 12.1 GHz in the Ku band, the minimum return loss value is -10.35 dB.

[0084] Example 3

[0085] The present invention discloses a method for preparing a wave-absorbing and heat-conducting flexible composite film, comprising the following steps:

[0086] (1) Disperse 3.0 g of AgNWs in a mixed solvent of 1 mL of ethanol and 15 mL of n-hexane to obtain a dispersion;

[0087] 14 g of FCI powder was added to the dispersion, mechanically stirred until uniform, and heated to 70°C to remove the solvent to obtain AgNWs / FCI composite filler.

[0088] (2) Add 6 g of PDMS to 6 g of n-hexane, stir magnetically, then add 0.6 g of curing agent and continue magnetic stirring to obtain a precursor solution;

[0089] (3) Add 17.0 g of AgNWs / FCI composite filler to the precursor solution and continue stirring until the solution is homogeneous;

[0090] (4) The mixed liquid was placed in a mold and transferred to the sample stage in the center of the Helmholtz coil. A 70 mT uniform magnetic field was applied and vacuum degassing was performed for 60 min at a vacuum degree of -0.1 MPa. The temperature was then raised to 85 °C and kept at this temperature for 4 h to obtain an AgNWs / FCI / PDMS composite film.

[0091] In the AgNWs / FCI / PDMS composite film prepared in this example, the mass fraction of the flaky carbonyl iron is 59.3%; and the mass fraction of the silver nanowires is 12.71%.

[0092] As shown in Table 1, the water contact angle test of the AgNWs / FCI / PDMS composite film prepared in this example was conducted, and the contact angle was 118°.

[0093] As shown in Table 1, when the AgNWs / FCI / PDMS composite film prepared in this example was heated from the bottom, the surface temperature reached 38° C. within 30 seconds, indicating that the film has good thermal conductivity.

[0094] As shown in Table 1, the vertical thermal conductivity of the AgNWs / FCI / PDMS composite film prepared in this example is 3.37 W / mK.

[0095] The tensile strength of the AgNWs / FCI / PDMS composite film prepared in Example 1 was tested, and the tensile strength was 4.95 MPa.

[0096] like Figure 3 As shown, the Ag NWs / FCI / PDMS composite film prepared in this embodiment completely covers the S band, C band, X band, and Ku band.

[0097] At 3.9 GHz in the S-band, the minimum return loss value is -33.79 dB.

[0098] At the 4.2 GHz frequency in the C band, the minimum reflection loss value is -43.35 dB, which means that the absorption capacity is the strongest at this frequency.

[0099] At 8.1 GHz in the X-band, the minimum return loss value is -15.35 dB.

[0100] Example 4

[0101] The present invention discloses a method for preparing a wave-absorbing and heat-conducting flexible composite film, comprising the following steps:

[0102] (1) Disperse 2.0 g of AgNWs in a mixed solvent of 1 mL of ethanol and 12 mL of n-hexane to obtain a dispersion;

[0103] 14 g of FCI powder was added to the dispersion, mechanically stirred until uniform, and heated to 70°C to remove the solvent to obtain AgNWs / FCI composite filler.

[0104] (2) Add 7 g of PDMS to 7 g of n-hexane, stir magnetically, then add 0.7 g of curing agent, and continue magnetic stirring to obtain a precursor solution;

[0105] (3) Add 16.0 g of AgNWs / FCI composite filler to the precursor solution and continue stirring until the solution is homogeneous to obtain a mixed solution;

[0106] (4) The mixed liquid was placed in a mold and transferred to the sample stage in the center of the Helmholtz coil. A 60 mT uniform magnetic field was applied and vacuum degassing was performed for 60 min at a vacuum degree of -0.1 MPa. The temperature was then raised to 80 °C and kept at this temperature for 3 h to obtain the AgNWs / FCI / PDMS composite film.

[0107] In the AgNWs / FCI / PDMS composite film prepared in this example, the mass fraction of the flaky carbonyl iron is 59.07%; and the mass fraction of the silver nanowires is 8.4%.

[0108] As shown in Table 1, the water contact angle test of the AgNWs / FCI / PDMS composite film prepared in this example was conducted, and the contact angle was 118°.

[0109] As shown in Table 1, when the AgNWs / FCI / PDMS composite film prepared in this example was heated from the bottom, the surface temperature reached 26° C. within 30 seconds, indicating that the film has good thermal conductivity.

[0110] As shown in Table 1, the vertical thermal conductivity of the AgNWs / FCI / PDMS composite film prepared in this example is 2.85 W / mK.

[0111] The tensile strength of the AgNWs / FCI / PDMS composite film prepared in Example 1 was tested, and the tensile strength was 3.82 MPa.

[0112] like Figure 3 As shown, the AgNWs / FCI / PDMS composite film prepared in this embodiment completely covers the S band, C band, X band, and Ku band.

[0113] At 3.9 GHz in the S-band, the minimum return loss value is -22.14 dB.

[0114] At the 5.5 GHz frequency in the C band, the minimum reflection loss value is -54.45 dB, which means that the absorption capacity is the strongest at this frequency.

[0115] At 8.1 GHz in the X-band, the minimum return loss value is -23.68 dB.

[0116] At the Ku-band frequency of 14.0 GHz, the minimum return loss value is -16.36 dB.

[0117] Example 5

[0118] The present invention discloses a method for preparing a wave-absorbing and heat-conducting flexible composite film, comprising the following steps:

[0119] (1) Preparation of Ag NWs / FCI composite filler: 2.0 g of Ag NWs was dispersed in a mixed solvent of 1 mL of ethanol and 12 mL of n-hexane to obtain a dispersion;

[0120] 14 g of flaky carbonyl iron powder was added to the dispersion, mechanically stirred until uniform, and the solvent was removed by heating to obtain Ag NWs / FCI composite filler.

[0121] (2) Add 8 g of PDMS to 8 g of n-hexane, stir magnetically until evenly mixed, then add 0.8 g of curing agent, and continue magnetic stirring to obtain a precursor solution;

[0122] (3) Add 16.0 g of AgNWs / FCI composite filler to the precursor solution and continue stirring until the solution is homogeneous to obtain a mixed solution;

[0123] (4) The mixed liquid was placed in a mold and transferred to the sample stage in the center of the Helmholtz coil. A 70 mT uniform magnetic field was applied and vacuum degassing was performed for 60 min at a vacuum degree of -0.1 MPa. The temperature was then raised to 90 °C and kept at this temperature for 2 h to obtain an AgNWs / FCI / PDMS composite film.

[0124] In the AgNWs / FCI / PDMS composite film prepared in this example, the mass fraction of the flaky carbonyl iron is 56.45%; and the mass fraction of the silver nanowires is 8.06%.

[0125] As shown in Table 1, the water contact angle test of the AgNWs / FCI / PDMS composite film prepared in this example was conducted, and the contact angle was 114°.

[0126] As shown in Table 1, when the AgNWs / FCI / PDMS composite film prepared in this example was heated from the bottom, the surface temperature reached 24° C. within 30 seconds, indicating that the film has good thermal conductivity.

[0127] As shown in Table 1, the vertical thermal conductivity of the AgNWs / FCI / PDMS composite film prepared in this example is 2.43 W / mK.

[0128] The tensile strength of the AgNWs / FCI / PDMS composite film prepared in Example 1 was tested, and the tensile strength was 3.20 MPa.

[0129] like Figure 3 As shown, the Ag NWs / FCI / PDMS composite film prepared in this embodiment completely covers the S band, C band, X band, and Ku band.

[0130] At 3.8 GHz in the S-band, the minimum return loss value is -30.07 dB.

[0131] At the 4.1 GHz frequency in the C band, the minimum reflection loss value is -42.28 dB, which means that the absorption capacity is the strongest at this frequency.

[0132] At 8.0 GHz in the X-band, the minimum return loss value is -12.23 dB.

[0133] In summary, the AgNWs / FCI / PDMS composite film prepared by the present invention has a reflection loss value of ≤ -5 dB (absorbing 68% of electromagnetic waves) and an absorption response band of 2.0-18.0 GHz. The vertical thermal conductivity of the film is higher than 1.3 W / mK. It has strong low-frequency response, wide absorption bandwidth, excellent thermal conductivity, high mechanical strength, and superhydrophobicity, further expanding the practical application range of the composite film.

[0134] Table 1

[0135]

[0136] like Figure 1 The following are photos of the wave-absorbing and heat-conducting flexible composite film prepared according to the present invention: Figure a shows the film in a flat state; Figure b shows the film after being folded once; and Figure c shows the film after being folded twice. This demonstrates that the wave-absorbing and heat-conducting flexible composite film prepared according to the present invention has good flexibility and can be folded multiple times.

[0137] like Figure 7 and Figure 8As shown, in the wave-absorbing and heat-conducting flexible composite film prepared by the present invention, polydimethylsiloxane is used as a matrix, and flaky carbonyl iron and silver nanowires are used as fillers. The flaky carbonyl iron is neatly arranged along the radial direction of the matrix, and the silver nanowires connect adjacent flaky carbonyl iron. Figure 8 The medium green represents sheet-like carbonyl iron, and the purple lines represent silver nanowires.

[0138] The present invention selects flaky carbonyl iron as a magnetic loss material, utilizes its high saturation magnetization intensity for loss, and then uses PDMS for encapsulation. At the same time, the orientation of carbonyl iron is regulated by a magnetic field, the magnetic anisotropy is optimized, the magnetic coupling is improved, and the loss capacity is further improved. The antenna-like structure generated by the longitudinally oriented array structure is conducive to the introduction of electromagnetic waves and optimizes the impedance matching of the material. However, the electrical conductivity of carbonyl iron itself is not high, and the loss form is single. At the same time, in the dielectric loss of the low-frequency band, the conductivity loss occupies a dominant position. Therefore, by compounding AgNWs, a three-dimensional conductive network is formed to improve the dielectric loss of the material, enrich the loss form, and improve the low-frequency wave absorption ability and thermal conductivity of the material.

[0139] In summary, the present invention uses FCI as a magnetic loss material, induces a longitudinally oriented FCI array structure through a magnetic field, and uses PDMS as a packaging material. AgNWs are then added to increase the material's electrical conductivity, optimizing its microwave absorption and thermal conductivity at low frequencies.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a wave-absorbing and heat-conducting flexible composite film, characterized in that: The following steps are involved: S1. Dispersing silver nanowires in a mixed solvent of ethanol and n-hexane to obtain a dispersion; adding flaky carbonyl iron powder to the dispersion, stirring until uniform, and heating to obtain a composite filler; Add polydimethylsiloxane to n-hexane, stir evenly, then add curing agent, continue stirring to obtain a precursor solution; S2. Add the composite filler to the precursor solution and continue stirring until the solution is in a homogeneous state to obtain a mixed solution; S3. After vacuum degassing the mixed liquid, a uniform magnetic field is applied and the temperature is increased to solidify it, thereby obtaining a wave-absorbing and heat-conducting flexible composite film.

2. The method for preparing the wave-absorbing and heat-conducting flexible composite film according to claim 1, characterized in that: In S1, the mass ratio of silver nanowires to flaky carbonyl iron powder is (0.07~0.21):

1.

3. The method for preparing the wave-absorbing and heat-conducting flexible composite film according to claim 1, characterized in that: In S1, the volume ratio of ethanol to n-hexane in the mixed solvent is 1:(10-15).

4. The method for preparing a wave-absorbing and heat-conducting flexible composite film according to claim 1, wherein: In S2, when the composite filler is added to the precursor solution, the mass ratio of the added composite filler to the polydimethylsiloxane is (2~2.83):

1.

5. The method for preparing the wave-absorbing and heat-conducting flexible composite film according to claim 1, wherein: In S3, the vacuum degassing conditions are: vacuum degree of -0.1 MPa, time of 30 to 60 minutes; The conditions for the temperature-raising curing are: a curing temperature of 70-90° C. and a curing time of 2-4 hours.

6. The method for preparing a wave-absorbing and heat-conducting flexible composite film according to claim 1, wherein: In S3, the magnetic field direction of the uniform magnetic field is perpendicular to the surface of the mixed liquid, the magnetic field intensity is 50-70 mT, and the magnetic field uniformity is 94%-96%.

7. A wave-absorbing and heat-conducting flexible composite film prepared by the preparation method according to any one of claims 1 to 6.

8. The wave-absorbing and heat-conducting flexible composite film according to claim 7, characterized in that: In terms of mass percentage, in the wave-absorbing and heat-conducting flexible composite film, the mass fraction of the flaky carbonyl iron is 56%-65%; the mass fraction of the silver nanowire is 4.6%-12.71%, and the rest is the matrix.

9. The wave-absorbing and heat-conducting flexible composite film according to claim 7, characterized in that: The vertical thermal conductivity of the wave-absorbing and heat-conducting flexible composite film is higher than 1.3 W / mK, and the tensile strength is greater than 1.0 MPa.

10. The wave-absorbing and heat-conducting flexible composite film according to claim 7, characterized in that: The wave-absorbing response frequency band of the wave-absorbing and heat-conducting flexible composite film covers the S band, C band, X band and Ku band; The wave-absorbing and heat-conducting flexible composite film has a reflection loss of less than or equal to -5 dB in a wave-absorbing response frequency band of 2.0 to 18.0 GHz.

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