Preparation and application of aramid fiber composite film based on interface engineering synergistic reinforcement of heat conduction and electromagnetic shielding performance

Abstract

The invention discloses preparation and application of an aramid fiber composite film with heat conduction and electromagnetic shielding performance synergistically enhanced based on interface engineering. Heat-conducting filler hydroxylated carbon nanotubes are compounded with an aramid fiber matrix. In the aspect of heat conduction, hydroxyl modification can reduce the interface thermal resistance of the heat-conducting filler and the aramid fiber matrix, the surface energy of the heat-conducting filler is reduced, agglomeration is reduced, and the heat-conducting filler is uniformly dispersed in the aramid fiber matrix to form more phonon transport paths, so that the heat-conducting property of the composite material is enhanced. In the aspect of electromagnetic shielding, an introduced hydroxyl functional group belongs to a dipole, interface polarization and dipole polarization of an aramid fiber composite film can be remarkably enhanced, absorption of electromagnetic waves by the material is enhanced, more electron transport paths are formed by uniform dispersion of OH-CNT in an aramid fiber matrix, absorption of the electromagnetic waves is increased due to enhanced conductive loss, and the electromagnetic shielding performance is improved. The enhancement of air impedance mismatch increases the reflection of electromagnetic waves. The heat-conducting property and electromagnetic shielding of the aramid-based thermal interface material are synergistically enhanced through interface engineering, and safe and stable operation of an electronic device in a complex thermomagnetic environment is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of thermal interface materials, in particular to a preparation and application of aramid composite film based on interface engineering for synergistically enhancing thermal conductivity and electromagnetic shielding performance. BACKGROUND

[0002] With the continuous increase of power density of electronic devices and the increasing signal crosstalk caused by multi-band electromagnetic waves, it is essential to develop thermal interface materials (TIMs) with high thermal conductivity and high electromagnetic shielding ability, which is of great significance to ensure the stability and long-term reliability of electronic systems operating in complex thermal-magnetic environments. Polymer-based composites have been widely studied in the field of thermal management and electromagnetic shielding due to their lightweight and easy processing. Among them, aramid has unique advantages in extreme application scenarios due to its excellent high-temperature resistance (500℃), low thermal expansion, chemical durability, electrical insulation and flame retardance. Aramid materials are particularly suitable for extreme environments and the construction of multifunctional composites. Therefore, aramid is an ideal candidate material for thermal management and electromagnetic interference shielding of electronic devices in extreme and complex conditions.

[0003] Although various aramid composites with thermal conductivity and electromagnetic shielding have been developed, it is still a challenge to have a thermal conductivity exceeding 10 Wm -1 K -1 To break through the bottleneck of low thermal conductivity and synergistically enhance thermal conductivity and electromagnetic shielding performance is an important challenge. SUMMARY

[0004] One of the purposes of the present application is to provide a preparation method of aramid composite film based on interface engineering for synergistically enhancing thermal conductivity and electromagnetic shielding performance, and the prepared composite film has excellent thermal conductivity, electromagnetic shielding performance and good flexibility.

[0005] The second purpose of the present application is to provide the application of the above-mentioned aramid composite film based on interface engineering for synergistically enhancing thermal conductivity and electromagnetic shielding performance in high-temperature thermal management of electronic devices.

[0006] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0007] In the first aspect, the present application provides a preparation method of aramid composite film based on interface engineering for synergistically enhancing thermal conductivity and electromagnetic shielding performance, comprising the following steps:

[0008] (1) Weigh the thermal conductive filler hydroxylated carbon nanotube (OH-CNT) and uniformly disperse it in concentrated sulfuric acid under ultrasonic conditions to obtain dispersion liquid I;

[0009] (2) Dissolve aramid in concentrated sulfuric acid at 10℃-25℃ to obtain liquid crystal solution II;

[0010] (3) mixing the dispersion liquid I and the liquid crystal solution II evenly to obtain a liquid crystal mixture III of hydroxylated carbon nanotube@aramid (OH-CNT@aramid), and coating the liquid crystal mixture III on a substrate by using a doctor blade method to realize the ordered arrangement of the hydroxylated carbon nanotube along the direction of the doctor blade method;

[0011] (4) rapidly placing the substrate coated with the liquid crystal mixture III into a reverse solvent deionized water, and performing reverse phase separation for 1.5-2 hours, and then drying and hot pressing to obtain an OH-CNT@aramid composite film with high thermal conductivity and electromagnetic shielding performance.

[0012] Preferably, the purity of the hydroxylated carbon nanotube in step (1) is ≥98%, the diameter is 5-20 nm, the length is 10-30 μm, and the mass fraction of the hydroxyl functional group in the filler structure is 5.43 wt%.

[0013] Preferably, the mass ratio of the thermal conductive filler and concentrated sulfuric acid in step (1) is 1-4:40-100.

[0014] Preferably, the aramid used in step (2) is a para-aramid formed by condensation polymerization of p-phenylenediamine and terephthalic acid.

[0015] Preferably, the mass ratio of the aramid and concentrated sulfuric acid in step (2) is 6-9:100-120.

[0016] Preferably, the mass ratio of the thermal conductive filler and aramid in the liquid crystal mixture III in step (3) is 1-4:6-9.

[0017] Preferably, in step (4), the temperature of the hot pressing is 30-40℃, the pressure of the hot pressing is 4-5 kPa, and the time of the hot pressing is 8-10 h.

[0018] Preferably, the thickness of the OH-CNT@aramid composite film in step (4) is 60-320 μm.

[0019] In a second aspect, the application further provides the application of the OH-CNT@aramid composite film with the synergistically enhanced thermal conductivity and electromagnetic shielding in the thermal management of electronic devices, in particular, in the application of LED integrated lamps.

[0020] The OH-CNT@aramid composite film provided by the application has high thermal conductivity (11.4-33.7 Wm -1 K -1 ), high electromagnetic shielding (6-21.7 dB) and good flexibility, and can meet the application requirements of the thermal management of electronic devices under high temperature.

[0021] Compared with the prior art, the application has the following beneficial effects:

[0022] 1.The OH-CNT@aramid composite film of the present application has high thermal conductivity, and the highest thermal conductivity can reach 33.7Wm -1 K -1 The enhancement of thermal conductivity is due to the π-π stacking between OH-CNT and aramid matrix and the hydrogen bonding between the -OH functional group and the carbonyl group C=O in aramid, which improves the phonon transmission rate at the interface and directly reduces the interface thermal resistance (ITR). On the other hand, the -OH functional group can reduce the surface energy of carbon nanotubes, inhibit the agglomeration of OH-CNT, and make the hydroxylated carbon nanotubes uniformly dispersed in the aramid matrix to form more thermal conduction paths. The above two aspects improve the thermal conductivity of the aramid composite film.

[0023] 2.The OH-CNT@aramid composite film of the present application has high electromagnetic shielding performance, and the highest electromagnetic shielding effectiveness can reach 21.7dB. The enhancement of electromagnetic shielding performance is due to the dipole polarization of the -OH functional group on the carbon nanotube and the hydrogen bonding between the -OH functional group on the carbon nanotube and the aramid matrix to form interface polarization; on the other hand, the -OH functional group can reduce the surface energy of carbon nanotubes, inhibit the agglomeration of OH-CNT, and make the hydroxylated carbon nanotubes uniformly dispersed in the aramid matrix to also form more electron transport paths, thereby increasing the conductive loss and impedance mismatch with air. The above dipole polarization, interface polarization and conductive loss enhance the absorption of electromagnetic waves, and the impedance mismatch with air improves the reflection of electromagnetic waves, thereby enhancing the electromagnetic shielding performance.

[0024] 3.When the OH-CNT@aramid composite film containing 40wt% thermal conductive filler (OH-CNT-40%) of 4cm×4cm is applied to the thermal management of LED integrated lamp, the electronic device operates stably at a temperature of about 169℃, which is reduced by 13℃ compared with the CNT@aramid composite film containing 40wt% thermal conductive filler (CNT-40%), and has a broad application prospect in electronic device thermal management. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the principle diagram of aramid composite film based on interface engineering: (a) OH-CNT / aramid and OH-CNT / OH-CNT interface hydrogen bonding and π-π stacking; (b) hydroxyl dipole polarization on the surface of OH-CNT and interface polarization of OH-CNT and aramid under hydrogen bonding; (c) schematic diagram of interface engineering enhancing phonon transmission and increasing phonon transmission path; (d) electromagnetic absorption and electromagnetic reflection schematic diagram; (e) OH-CNT uniformly dispersed due to the reduction of surface energy and forming more phonon transport paths; (f) OH-CNT uniformly dispersed, forming more electron transport paths, increasing conductive loss and reflection loss.

[0026] Figure 2 are high-resolution transmission electron microscope images (HRTEM) of CNT, OH-CNT used in Examples 1-4 (a, c); higher magnification HRTEM and inverse Fourier transform (IFT) images of CNT, OH-CNT (b, d); XRD characterization of CNT, OH-CNT, aramid and its composites (e, f).

[0027] Figure 3 are surface scanning electron microscope images (SEM) and energy dispersive spectroscopy (EDS) of aramid composite films containing 30 wt% CNT (CNT-30%), aramid composite films containing 40 wt% CNT (CNT-40%), aramid composite films containing 30 wt% OH-CNT (OH-CNT-30%), aramid composite films containing 40 wt% OH-CNT (OH-CNT-40%) prepared in Examples 1-4.

[0028] Figure 4 are sheet resistance of CNT@aramid composite films, OH-CNT@aramid composite films prepared in Examples 1-4 (a); XPS spectra of aramid, CNT, OH-CNT, aramid composite films containing 20 wt% CNT (CNT-20%) and aramid composite films containing 20 wt% OH-CNT (OH-CNT-20%) (b); C1s and N1s spectral analysis of aramid, CNT-20% and OH-CNT-20% composite films (c, d).

[0029] Figure 5 are thermal conductivity properties and applications of composite films prepared in Examples 1-4. (a) In-plane thermal diffusivity a / / and normal thermal diffusivity a ⊥ of pressed pure CNT and OH-CNT sheets; (b) In-plane thermal conductivity l / / and normal thermal conductivity l ⊥ of pressed CNT and OH-CNT sheets; (c) In-plane thermal diffusivity a / / of CNT@aramid composite films and OH-CNT@aramid composite films; (d) In-plane thermal conductivity l / / of CNT@aramid composite films and OH-CNT@aramid composite films; (e) In-plane thermal conductivity l / / enhancement of CNT@aramid composite films and OH-CNT@aramid composite films compared with pure aramid films; (f) Surface infrared thermal images and time-temperature curves of LED lamps with CNT-40% and OH-CNT-40% as TIMs, respectively.

[0030] Figure 6 are SEM cross-section images of CNT@aramid composite films prepared in Comparative Examples 1-4, OH-CNT@aramid composite films prepared in Examples 1-4.

[0031] Figure 7 Electromagnetic interference shielding and mechanical properties of CNT@aramid composite films prepared in Examples 1-4 and OH-CNT@aramid composite films prepared in Examples 1-4: (ab) Electromagnetic shielding effectiveness (EMI SE) of CNT@aramid composite films and OH-CNT@aramid composite films in the X-band (8.2-12.4GHz); (c) Electromagnetic shielding effectiveness per unit thickness (EMI SSE) of CNT@aramid composite films and OH-CNT@aramid composite films; (d) Electromagnetic shielding efficiency of CNT@aramid composite films and OH-CNT@aramid composite films; (ef) Total EMI SE (SE) of CNT@aramid composite films and OH-CNT@aramid composite films. T ), reflection loss (SE) R ) and absorption loss (SE) A (g) Comparison of EMI SSE and in-plane thermal conductivity λ of CNT@aramid composite film and OH-CNT@aramid composite film; (h) Stress-strain curve of OH-CNT@aramid composite film; (i) Bending diagram of OH-CNT-40% film. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0033] Unless otherwise specified, all raw materials and reagents used in the following examples and comparative examples are commercially available products. The aramid fiber was manufactured by DuPont and is a fully para-aramid fiber synthesized by the condensation polymerization of p-phenylenediamine and terephthalic acid; the hydroxylated carbon nanotubes had a diameter of 5–20 nm, a length of 10–30 μm, a purity ≥98%, and a hydroxylation ratio of 5.43 wt% in the structure; the concentrated sulfuric acid had a mass fraction of 98%.

[0034] Example 1

[0035] A hydroxylated carbon nanotube@aramid composite film (OH-CNT-10%), wherein the thermally conductive filler carbon nanotubes are distributed along the plane of the coating.

[0036] The mass ratio of hydroxylated carbon nanotubes to aramid fibers is 1:9, meaning the mass fraction of the thermally conductive filler hydroxylated carbon nanotubes is 10 wt%.

[0037] The specific implementation process is as follows:

[0038] First, 0.069 g of heat-conducting filler hydroxylated carbon nanotube is uniformly dispersed in 10 g of concentrated sulfuric acid under ultrasonic conditions to obtain dispersion liquid I. Then, 0.621 g of aramid is dissolved in 10 g of concentrated sulfuric acid at 10-25 °C to obtain liquid crystal solution II. The dispersion liquid I and the liquid crystal solution II are uniformly mixed to obtain a liquid crystal mixture III of hydroxylated carbon nanotube and aramid, and the liquid crystal mixture III is uniformly coated on a glass substrate by means of scraping. The glass substrate coated with the liquid crystal mixture III is quickly placed in deionized water for reverse phase separation for 1.5-2 hours, and then is dried, hot-pressed (hot-pressing temperature: 30-40 °C, hot-pressing pressure: 4-5 kPa, hot-pressing time: 8-10 h) to form a film with a thickness of 235 μm.

[0039] The prepared OH-CNT-10% composite film has a thermal conductivity of 11.4 Wm -1 K -1 , an electromagnetic shielding effectiveness of 6.0 dB, and an electromagnetic shielding efficiency of 74.7%.

[0040] Example 2

[0041] A hydroxylated carbon nanotube and aramid composite film (OH-CNT-20%) in which heat-conducting filler carbon nanotube is distributed along the plane direction of scraping.

[0042] The mass ratio of the hydroxylated carbon nanotube and the aramid is 2:8, i.e., the mass fraction of the heat-conducting filler hydroxylated carbon nanotube is 20 wt%.

[0043] The preparation method is the same as that in Example 1 (wherein the hydroxylated carbon nanotube in the dispersion liquid I is 0.1553 g, and the concentrated sulfuric acid is 10 g. The amount of the aramid and the concentrated sulfuric acid in the liquid crystal solution II is unchanged).

[0044] The prepared OH-CNT-20% composite film has a thickness of 255 μm and a thermal conductivity of 21.6 Wm -1 K -1 , an electromagnetic shielding effectiveness of 9.6 dB, and an electromagnetic shielding efficiency of 89.1%.

[0045] Example 3

[0046] A hydroxylated carbon nanotube and aramid composite film (OH-CNT-30%) in which heat-conducting filler carbon nanotube is distributed along the plane direction of scraping.

[0047] The mass ratio of the hydroxylated carbon nanotube and the aramid is 3:7, i.e., the mass fraction of the heat-conducting filler hydroxylated carbon nanotube is 30 wt%.

[0048] The preparation method is the same as that in Example 1 (wherein the hydroxylated carbon nanotube in the dispersion liquid I is 0.2661 g, and the concentrated sulfuric acid is 10 g. The amount of the aramid and the concentrated sulfuric acid in the liquid crystal solution II is unchanged).

[0049] The prepared OH-CNT-30% composite film has a thickness of 315 μm and a thermal conductivity of 29.3 Wm -1 K -1 , an electromagnetic shielding effectiveness of 16.4 dB, and an electromagnetic shielding efficiency of 97.7%.

[0050] Example 4

[0051] A hydroxylated carbon nanotube@aramid composite film (OH-CNT-40%) in which the heat-conducting filler carbon nanotubes are distributed along the plane direction of the coating.

[0052] The mass ratio of the hydroxylated carbon nanotubes and aramid is 4:6, i.e., the mass fraction of the heat-conducting filler hydroxylated carbon nanotubes is 40 wt%.

[0053] The preparation method is the same as that in Example 1 (wherein the amount of hydroxylated carbon nanotubes in dispersion I is 0.414 g, and the amount of concentrated sulfuric acid is 10 g. The amounts of aramid and concentrated sulfuric acid in liquid crystal solution II are unchanged).

[0054] The prepared OH-CNT-40% composite film has a thickness of 265 μm and a thermal conductivity of 33.7 Wm -1 K -1 , an electromagnetic shielding effectiveness of 21.7 dB, and an electromagnetic shielding efficiency of 99.3%.

[0055] Comparative Example 1

[0056] A carbon nanotube@aramid composite film (CNT-10%) in which the heat-conducting filler carbon nanotubes are distributed along the plane direction of the coating.

[0057] The mass ratio of the carbon nanotubes and aramid is 1:9, i.e., the mass fraction of the heat-conducting filler carbon nanotubes is 10 wt%.

[0058] The prepared composite film has a thickness of 240 μm and a thermal conductivity of 9.6 Wm -1 K -1 , an electromagnetic shielding effectiveness of 5.8 dB, and an electromagnetic shielding efficiency of 73.6%.

[0059] Comparative Example 2

[0060] A carbon nanotube@aramid composite film (CNT-20%) in which the heat-conducting filler carbon nanotubes are distributed along the plane direction of the coating.

[0061] The mass ratio of the carbon nanotubes and aramid is 2:8, i.e., the mass fraction of the heat-conducting filler carbon nanotubes is 20 wt%.

[0062] The prepared composite film has a thickness of 250 μm and a thermal conductivity of 14.2 Wm -1 K-1 The electromagnetic shielding effectiveness is 7.9 dB, and the electromagnetic shielding efficiency reaches 83.6%.

[0063] Comparative Example 3

[0064] A carbon nanotube@aramid composite film (CNT-30%) in which the thermally conductive filler carbon nanotubes are distributed along the plane direction of the blade coating.

[0065] The mass ratio of the carbon nanotubes and the aramid is 3:7, that is, the mass fraction of the thermally conductive filler carbon nanotubes is 30wt%.

[0066] The prepared composite film has a thickness of 305μm, and the thermal conductivity reaches 20.2Wm -1 K -1 The electromagnetic shielding effectiveness is 15.2 dB, and the electromagnetic shielding efficiency reaches 97%.

[0067] Comparative Example 4

[0068] A carbon nanotube@aramid composite film (CNT-40%) in which the thermally conductive filler carbon nanotubes are distributed along the plane direction of the blade coating.

[0069] The mass ratio of the carbon nanotubes and the aramid is 4:6, that is, the mass fraction of the thermally conductive filler carbon nanotubes is 40wt%.

[0070] The prepared composite film has a thickness of 285μm, and the thermal conductivity reaches 23.8Wm -1 K -1 The electromagnetic shielding effectiveness is 19.6 dB, and the electromagnetic shielding efficiency reaches 98.9%.

[0071] Figure 1 The schematic diagram of the aramid composite film based on interface engineering. The aramid-based TIMs with superior thermal conductivity and EMI shielding performance are developed based on the interface engineering strategy of hydroxyl-modified carbon nanotubes (OH-CNT) in the embodiment of the application, and the synergistic enhancement of heat conduction and electromagnetic shielding is realized. First, the strong π-π stacking between OH-CNT and aramid is derived from the delocalized π-electron cloud, and the hydrogen bond formed by the -OH group and the -CO- in the aramid improves the phonon interface transmission Figure 1 (a), Figure 1 (c)), thereby reducing the ITR. The hydrogen bond interaction between OH-CNT and aramid strengthens the differential charge density distribution, and enhances the interface polarization; the -OH group as a dipole is polarized in the electric field, and introduces additional dipole polarization. The interface polarization and the dipole polarization both enhance the absorption of electromagnetic waves, thereby improving the electromagnetic interference shielding Figure 1 (b)). In addition, compared with CNT, the reduction of the surface energy of OH-CNT inhibits the agglomeration, improves the dispersion of the nanofiller in the matrix, and forms additional phonon transport pathsFigure 1 (e)- Figure 1 (f)),enhanced thermal conductivity; while also forming additional electron transport paths, which enhance the electrical conduction loss, reflection loss caused by impedance mismatch with air, so that the electromagnetic shielding performance is enhanced Figure 1 (c)- Figure 1 (d)).

[0072] Figure 2 (a)- Figure 2 (d) is the morphology and microstructure of CNT, OH-CNT are characterized by HRTEM. Figure 2 (a), Figure 2 (c) presents the HRTEM images of CNT, OH-CNT, which reveals their concentric cylindrical multi-layer graphene structure, and directly shows the stacking morphology of multiple tube walls. Figure 2 (b), Figure 2 (d) is a higher magnification HRTEM image, which directly shows the lattice fringes of CNT and OH-CNT, and their interlayer spacing is about 0.34 nm, corresponding to the (002) crystal plane, showing good crystallinity. The inverse Fourier transform (IFT) image clearly shows the layered arrangement, further verifying the excellent crystallinity of CNT and OH-CNT. Aramid shows a (200) crystal plane diffraction peak at 24.8°, CNT shows (002) and (100) crystal plane diffraction peaks at 26.1° and 43°, and OH-CNT shows (002) and (100) crystal plane diffraction peaks at 26.1° and 43.3°, which proves that the hydroxyl functionalization does not significantly change the crystal structure of carbon nanotubes; OH-CNT and CNT series composites all show the characteristic peaks of aramid and its fillers Figure 2 (e), Figure 2 (f)). With the increase of CNT or OH-CNT content, the diffraction peak intensity of CNT or OH-CNT in CNT@aramid composite film and OH-CNT@aramid composite film gradually increases, but its original sharp characteristic peak is covered and broadened, indicating that CNT or OH-CNT is coated by aramid molecules.

[0073] Scanning electron microscopy (SEM) imaging and energy dispersive spectroscopy (EDS) tests show that there is a uniform aramid polymer coating on the surface of OH-CNT and CNT Figure 3 ). EDS shows that there is a clear nitrogen (N) and oxygen (O) signal along OH-CNT, which is closely overlapped with the carbon (C) signal. This provides direct evidence for the coating of OH-CNT by aramid molecules through interfacial interactions (hydrogen bonding and π-π stacking), and the -NH-CO- group in aramid provides N and O elements to cover the surface of the filler, indicating that both CNT and OH-CNT are coated by aramid molecules.

[0074] Due to the encapsulation of fillers by aramid molecules, all composites have certain insulating properties Figure 4 (a). Figure 4 (a) shows the sheet resistance values and standard deviations. Although hydroxyl groups usually destroy the sp 2 conjugation of carbon nanotubes, thereby reducing their intrinsic electrical conductivity, the sheet resistance of OH-CNT series films (1.03-3.2 kQ / sq) is significantly lower than that of carbon nanotube series films (4.51-75.00 kQ / sq). This is mainly due to the improved dispersibility of OH-CNT in the aramid matrix, which helps to form a more dense conductive network, ultimately outweighing the loss of intrinsic conductivity. In this study, changes in the elemental binding energies were observed by X-ray photoelectron spectroscopy (XPS), demonstrating the hydrogen bonding and π-π stacking interactions between the aramid matrix and the fillers. Representative XPS spectra of aramid, CNT, OH-CNT, CNT-20%, and OH-CNT-20% are shown in Figure 4 (b). Figure 4 (d). Both CNT-20% and OH-CNT-20% exhibit characteristic peaks corresponding to O1s, N1s, and C1s binding energies. The O1s / C1s intensity ratio in CNT-20% and OH-CNT-20% composite films significantly increased compared to CNT and OH-CNT, confirming the successful attachment of aramid molecules to the fillers. The corresponding peaks of CNT-20% and OH-CNT-20% shifted to lower binding energies (287.95 eV and 287.84 eV) relative to the C=O peak of C1s in aramid (288.08 eV). For C-N of C1s in aramid (285.37 eV), CNT-20% and OH-CNT-20% exhibited higher binding energies (286.37 eV and 286.32 eV). In addition, N-H of N1s in aramid (400.04 eV) shifted to higher binding energies in the composite films (400.13 eV for CNT-20% and 400.09 eV for OH-CNT-20%). These changes in binding energies clearly demonstrate changes in the chemical environment of C=O, C-N, and N-H, confirming the formation of hydrogen bonding and π-π stacking interactions between aramid and fillers.

[0075] To elucidate the effect of interfacial modification on the thermal conductivity of fillers, the in-plane thermal diffusivity (a / / ) and normal thermal diffusivity (a ⊥ ) of pressed CNT and OH-CNT flakes were measured. As shown in Figure 5 (a). Figure 5 (b), the average a / / of CNT and OH-CNT flakes were 2.58 mm 2 / s and 3.95 mm 2 / s, respectively, and the average a⊥ Their respective velocity ranges are 0.73 mm² / s and 1.25 mm² / s. Correspondingly, their λ... / / 10.7W m -1 K -1 and 12.4W m -1 K -1 Their normal thermal conductivity (λ) ⊥ ) respectively 3.0W m -1 K -1 and 3.9W m -1 K -1 α / / and λ / / The average α value is greater than that in the normal direction. This is partly because during tableting, the fillers are mainly arranged in the in-plane direction, resulting in anisotropy; and partly because the high phonon transmittance and low ITR between OH-CNT fillers, along with the reduced surface energy of OH-CNTs, reduce agglomeration and create more thermal conductivity paths. The beneficial effects of hydroxylation interface engineering outweigh the reduction in inherent thermal conductivity, ultimately leading to an enhanced apparent thermal conductivity of the OH-CNT sheets. The influence of interface engineering on the thermal conductivity of aramid composite films was further investigated. / / Values ​​such as Figure 5 As shown in (c), with the increase of filler content, α / / The value gradually increases. At the same content, the α value of the OH-CNT@aramid composite film... / / (6.3~17.96mm 2 Both ( / s) are superior to the α of CNT@aramid composite film. / / (4.48~13.37mm 2 / s). Similarly, λ was observed. / / Significantly enhanced ( Figure 5 (d)). When the filler content increases from 10 wt% to 40 wt%, the average λ of the CNT@aramid composite film... / / From 9.6W m -1 K -1 Increased to 23.8W m -1 K -1 The average λ of OH-CNT@aramid composite film / / From 11.4W m -1 K -1 Increased to 33.7W m -1 K -1 Hydroxylation modification leads to the maximum λ of the OH-CNT-40% composite membrane. / / The enhancement is approximately 42%. The λ of CNT@aramid composite films and OH-CNT@aramid composite films relative to pure aramid films... / / The percentage of enhancement is as follows Figure 5(e) shown. Compared to pure aramid, the λ / / enhanced by 1291.67%. When the filler content is 20wt%, the λ / / enhanced most obviously, and the enhancement ratio decreased when the concentration was over this value. The α / / and λ / / values of OH-CNT@aramid composite films were higher than those of CNT@aramid composite films with the same filler loading. These performance advantages come from two synergistic mechanisms: first, the hydroxylation reduces the ITR between filler and filler, and between filler and aramid matrix. Second, the hydroxylation reduces the surface energy of the filler, promoting the uniform dispersion of OH-CNT in the aramid matrix, and OH-CNT can establish more effective thermal conduction paths in the aramid matrix. In this study, the thermal management performance of CNT-40% and OH-CNT-40% as TIMs was evaluated (f)). They were placed between an LED lamp (20W) and an aluminum heat sink, respectively. An infrared camera (emissivity ε = 0.98) captured the infrared thermal images, and a data acquisition system recorded the working temperature of the LED lamp surface. The steady-state surface temperature of CNT-40% stabilized at 174°C, and that of OH-CNT-40% stabilized at 161°C, resulting in a temperature difference of 13°C, confirming the superior heat dissipation ability of OH-CNT-40%. Figure 5

[0076] The cross-sectional SEM images of CNT@aramid composite films prepared in Comparative Examples 1-4 and OH-CNT@aramid composite films prepared in Examples 1-4 are shown in FIGS. 1-4, respectively. The OH-CNTs exhibited uniform dispersion in the aramid matrix, which was attributed to the reduction of surface energy. In contrast, CNT-30% and CNT-40% films showed obvious agglomeration, as shown in the marked areas in the images. When the filler content was over 30wt%, the unmodified CNTs agglomerated in the aramid matrix. Figure 6

[0077] Figure 7 (a)- Figure 7 ​​(b) shows the EMI SE of CNT and OH-CNT containing aramid composite films in the X-band frequency range (8.2-12.4 GHz). The incorporation of both CNTs and OH-CNTs enhanced the EMI SE of the films, with the OH-CNT@aramid composite films exhibiting significantly higher electromagnetic shielding effectiveness than the CNT@aramid composite films. The EMI SE values of the CNT@aramid composite films ranged from 5.8 to 19.6 dB, while the EMI SE values of the OH-CNT@aramid composite films ranged from 6.0 to 21.7 dB. The OH-CNT-40% film (265 pm) achieved an EMI SE of 21.7 dB, exceeding the typical commercial requirement for electromagnetic shielding applications (20 dB). Thickness is an important parameter in evaluating electromagnetic shielding performance. The specific shielding effectiveness (SSE) is defined as the ratio of the shielding effectiveness to the thickness (SSE = SE / t) and can provide insight into the contribution of thickness to the overall shielding effectiveness. The SSE values of the OH-CNT@aramid composite films (255 dB cm -1 , 376 dB cm -1 , 520 dB cm -1 , 819 dB cm -1 ) were higher than those of the CNT@aramid composite films (242 dB cm -1 , 316 dB cm -1 , 498 dB cm -1 , 688 dB cm -1 ) Figure 7 (c)). The maximum SSE value of the OH-CNT-40% film was 19% higher than that of the CNT-40% film. Therefore, the OH-CNT@aramid composite films exhibited higher electromagnetic shielding efficiency. Electromagnetic shielding efficiency represents the percentage of incident electromagnetic waves that are blocked and was calculated using the following equation: 100 - (1 / 10 SE / 10 ) x 100. The shielding efficiency increased with increasing filler content. The OH-CNT@aramid composite films consistently exhibited higher shielding efficiency than the CNT@aramid composite films. The maximum shielding efficiency of the OH-CNT-40% film was 99.3% ( Figure 7 (d)), indicating that it could effectively block almost all incident electromagnetic waves (EMWs).

[0078] To elucidate the electromagnetic shielding enhancement mechanism in the OH-CNT series of films, the total electromagnetic shielding effectiveness EMI SE (SE T ), which mainly includes the reflection loss (SE R ) and the absorption loss (SE A ) Figure 7 (e)- Figure 7 (f)), was investigated. Both SE A and SE R exhibited a similar trend as SE TThe same trend occurs, increasing with increasing filler content. All SE A The values ​​all exceeded the corresponding SE. R The values ​​indicate that both CNT@aramid composite films and OH-CNT@aramid composite films possess strong electromagnetic absorption capabilities. The SE values ​​for OH-CNT@aramid composite films (OH-CNT-10%~OH-CNT-40%)... A The values ​​were 4.4 dB, 6.0 dB, 10.0 dB, and 13.7 dB, respectively, all higher than those of CNT@aramid composite films (3.9 dB, 5.9 dB, 9.1 dB, and 11.9 dB). Absorption loss mainly originates from the interaction between mobile carriers, dipoles, and electromagnetic waves within the composite film, typically including ohmic loss caused by carrier migration and dielectric loss caused by interface and dipole polarization. In OH-CNT@aramid composite films, the hydroxyl functional groups introduce additional hydroxyl dipoles and enhance interfacial polarization through hydrogen bonding. Furthermore, the improved surface energy of OH-CNTs helps form more electron transport paths, thereby increasing ohmic loss. Therefore, OH-CNT@aramid composite films exhibit superior electromagnetic absorption capabilities. Additionally, the SE values ​​of OH-CNT-20% to OH-CNT-40% are significantly higher. R SE values ​​higher than CNT-20% to CNT-40% R Value. Reflection loss is caused by impedance mismatch between free space (such as air) and the shielding material, which, according to plane wave theory, is positively correlated with conductivity. When the filler content is ≥20wt%, the OH-CNT@aramid composite film, due to the formation of more electron transport paths within the aramid matrix, exhibits significantly lower sheet resistance than the CNT@aramid composite film, thus reducing SE. R The value is higher. However, CNT-10% SE R The value is slightly higher than OH-CNT-10% SE R This value is due to the fact that a sufficient number of continuous electron transport paths have not yet been formed, SE R The electromagnetic shielding efficiency is primarily governed by the inherent conductivity of CNTs. When electromagnetic waves strike the film surface, due to the increased impedance mismatch between the air and the OH-CNT@aramid composite film, some incident waves are directly reflected. Subsequently, most of the electromagnetic waves penetrate the internal structure and interact with electron carriers, leading to ohmic losses. Furthermore, hydroxyl dipoles are polarized under electromagnetic wave excitation, and hydrogen bonds between OH-CNTs and aramid promote interfacial polarization. These two polarization mechanisms contribute to dielectric loss, further dissipating electromagnetic wave energy and thus improving overall electromagnetic shielding efficiency. The EMI, SSE, and λ of the CNT@aramid composite film and the OH-CNT@aramid composite film are also discussed. / / Comparison Figure 7 As shown in (g). With the increase of filler content, λ / / Both EMI SSEs show synergistic enhancement, and OH-CNT@aramid composite films show more obvious improvement. For example, the λ / / = 33.7 W m -1 K -1 , EMI SSE = 819 dB cm -1 , which are 42% and 19% higher than CNT-40% (λ / / = 23.8 W m - 1 K -1 , EMI SSE = 688 dB cm -1 ), respectively. In addition, OH-CNT@aramid composite films have good mechanical strength, flexibility, foldability and self-supporting. As can be seen from the stress-strain curves Figure 7 (h), the tensile strength ranges from 35 to 40 MPa. Even at a filling amount of 40%, the composite film can withstand bending, folding and trimming without breaking Figure 7 (i). These properties make them particularly suitable for thermal management applications of electronic devices in complex thermal-magnetic environments.

[0079] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any modification, equivalent replacement and improvement made by those skilled in the art within the technical scope disclosed by the present application, as long as it is within the spirit and principle of the present application, should be covered within the protection scope of the present application.

Claims

1. A method for preparing an aramid composite film based on interface engineering synergistically strengthening the thermal conductivity and electromagnetic shielding performance, characterized in that, It comprises the following steps: (1) Take the heat-conducting filler hydroxylated carbon nanotube, uniformly disperse it in concentrated sulfuric acid under ultrasonic condition to obtain dispersion liquid I; (2) Dissolve aramid in concentrated sulfuric acid at 10-25℃ to obtain liquid crystal solution II; (3) Mix dispersion liquid I and liquid crystal solution II evenly to obtain liquid crystal mixture III of hydroxylated carbon nanotube@aramid, uniformly coat liquid crystal mixture III on the substrate by scraping to realize the ordered arrangement of hydroxylated carbon nanotube along the scraping direction; (4) Put the substrate coated with liquid crystal mixture III into reverse solvent deionized water quickly, separate by reverse phase for 1.5-2 hours, dry and hot-press to obtain hydroxylated carbon nanotube@aramid composite film with high heat conduction and electromagnetic shielding performance.

2. The method for preparing an aramid composite film based on interface engineering synergistically reinforced thermal conductivity and electromagnetic shielding performance according to claim 1, characterized in that, The purity of hydroxylated carbon nanotube in step (1) is ≥98%, the diameter is 5-20 nm, the length is 10-30 μm, and the mass fraction of hydroxyl functional group in the filler structure is 5.43 wt%.

3. The method for preparing an aramid composite film based on interface engineering synergistically enhanced thermal conductivity and electromagnetic shielding performance according to claim 1, characterized in that, The mass ratio of heat-conducting filler and concentrated sulfuric acid in step (1) is 1-4:40-100.

4. The method for preparing an aramid composite film based on interface engineering synergistically enhanced thermal conductivity and electromagnetic shielding performance according to claim 1, characterized in that, The aramid in step (2) is para-aramid obtained by condensation polymerization of p-phenylenediamine and terephthalic acid.

5. The method for preparing an aramid composite film based on interface engineering synergistically enhanced thermal conductivity and electromagnetic shielding performance according to claim 1, characterized in that, The mass ratio of aramid and concentrated sulfuric acid in step (2) is 6-9:100-120.

6. The method for preparing an aramid composite film based on interface engineering synergistically enhanced thermal conductivity and electromagnetic shielding performance according to claim 1, characterized in that, The mass ratio of heat-conducting filler and aramid in liquid crystal mixture III in step (3) is 1-4:6-9.

7. The method of claim 1, wherein the method is characterized by: In step (4), the temperature of hot-pressing is 30-40℃, the pressure of hot-pressing is 4-5 kPa, and the time of hot-pressing is 8-10 h.

8. The method for preparing an aramid composite film based on interface engineering synergistically enhanced thermal conductivity and electromagnetic shielding performance according to claim 1, characterized in that, The thickness of hydroxylated carbon nanotube@aramid composite film in step (3) is 60-320 μm.

9. The application of hydroxylated carbon nanotube@aramid composite film with high heat conduction and electromagnetic shielding performance in the thermal management of electronic devices according to any one of claims 1-8.

10. Use according to claim 9, characterized in that, The electronic device is LED integrated lamp.

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