Preparation and application of aramid composite film based on interface engineering synergistically strengthening thermal conductivity and electromagnetic shielding performance

Abstract

The application discloses a preparation and application of an aramid composite film based on interface engineering synergistically enhanced heat conduction and electromagnetic shielding performance. The hydroxylated carbon nanotubes and aramid matrix are compounded. In terms of heat conduction, the hydroxyl modification can reduce the interface thermal resistance of the heat conduction filler and the aramid matrix, and also reduce the surface energy of the heat conduction filler, reduce agglomeration, uniformly disperse in the aramid matrix to form more phonon transport paths, thereby enhancing the heat conduction performance of the composite material. In terms of electromagnetic shielding, the introduced hydroxyl functional group belongs to a dipole, which can significantly enhance the interface polarization and dipole polarization of the aramid composite film, enhance the absorption of electromagnetic waves by the material, the uniform dispersion of OH-CNT in the aramid matrix also forms more electron transport paths, the enhanced conductive loss increases the absorption of electromagnetic waves, and the enhancement of the impedance mismatch with air increases the reflection of electromagnetic waves. The application realizes the synergistic enhancement of the heat conduction performance and electromagnetic shielding of the aramid-based thermal interface material through interface engineering, and ensures the safe and stable operation of electronic devices in a complex thermal and magnetic environment.

Description

Technical Field

[0001] This invention relates to the field of thermal interface materials, specifically to the preparation and application of an aramid composite film with synergistic enhancement of thermal conductivity and electromagnetic shielding performance based on interface engineering. Background Technology

[0002] With the continuous increase in power density of electronic devices and the increasing crosstalk caused by multi-band electromagnetic waves, the development of thermal interface materials (TIMs) that combine high thermal conductivity and efficient electromagnetic shielding capabilities has become crucial. This is of great significance for ensuring the stability and long-term reliability of electronic systems operating in complex thermomagnetic environments. Polymer-based composite materials have been extensively studied in the fields of thermal management and electromagnetic shielding due to their advantages such as lightweight and easy processing. Among them, aramid fibers, with their excellent high-temperature resistance (500℃), low thermal expansion, chemical durability, electrical insulation, and flame retardancy, exhibit irreplaceable advantages in unique application scenarios. Aramid materials are particularly suitable for extreme environments and the construction of multifunctional composite materials. Therefore, aramid fibers are ideal candidate materials for thermal management and electromagnetic interference shielding of electronic devices under extremely complex conditions.

[0003] Although various aramid composite materials with thermal conductivity and electromagnetic shielding have been developed, thermal conductivity exceeding 10 W / m² is still a challenge. -1 K -1 It remains a challenge. Overcoming the bottleneck of low thermal conductivity and synergistically enhancing thermal conductivity and electromagnetic shielding performance is a significant challenge. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing an aramid composite film with synergistic enhancement of thermal conductivity and electromagnetic shielding performance based on interface engineering. The prepared composite film has excellent thermal conductivity, electromagnetic shielding and good flexibility.

[0005] The second objective of this invention is to provide the application of the above-mentioned aramid composite film with enhanced thermal conductivity and electromagnetic shielding performance based on interface engineering in high-temperature thermal management of electronic devices.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing an aramid composite film with enhanced thermal conductivity and electromagnetic shielding performance based on interface engineering, comprising the following steps:

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

[0009] (2) Aramid was dissolved in concentrated sulfuric acid at 10℃~25℃ to obtain liquid crystal solution II;

[0010] (3) Mix dispersion I and liquid crystal solution II thoroughly and uniformly to obtain liquid crystal mixture III of hydroxylated carbon nanotubes@aramid (OH-CNT@aramid). Coat liquid crystal mixture III uniformly onto the substrate by a blade coating method to achieve orderly arrangement of hydroxylated carbon nanotubes along the blade coating direction.

[0011] (4) The substrate coated with liquid crystal mixture III is quickly placed into the reverse solvent deionized water, and after phase separation for 1.5 to 2 hours, it is dried and hot-pressed to obtain an OH-CNT@aramid composite film with high thermal conductivity and electromagnetic shielding performance.

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

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

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

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

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

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

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

[0019] Secondly, the present invention also provides the application of the above-mentioned thermally conductive and electromagnetically shielded synergistically enhanced OH-CNT@aramid composite film in the thermal management of electronic devices, especially in LED integrated lamps.

[0020] The OH-CNT@aramid composite film provided by this invention has high thermal conductivity (11.4~33.7 W / m²). -1 K -1 It features high electromagnetic shielding (6–21.7 dB) and good flexibility, which can meet the thermal management application requirements of electronic devices at high temperatures.

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

[0022] 1. The OH-CNT@aramid composite film of the present invention has high thermal conductivity, with a maximum surface thermal conductivity of 33.7 W / m. -1 K -1 The enhanced thermal conductivity stems from two main factors: firstly, the π-π stacking interaction between OH-CNTs and the aramid matrix, and the hydrogen bonding between the -OH functional groups and the carbonyl C=O groups in the aramid, which increases the phonon transmittance at the interface and directly reduces the interfacial thermal resistance (ITR); secondly, the -OH functional groups lower the surface energy of the carbon nanotubes, inhibiting the aggregation of OH-CNTs and allowing the hydroxylated carbon nanotubes to be uniformly dispersed in the aramid matrix, forming more thermal conductivity pathways. These two aspects improve the thermal conductivity of the aramid composite film.

[0023] 2. The OH-CNT@aramid composite film of the present invention also possesses high electromagnetic shielding performance, with a maximum electromagnetic shielding effectiveness of 21.7 dB. The enhanced electromagnetic shielding performance is due to two factors: firstly, the dipole polarization of the -OH functional groups on the carbon nanotubes and the interfacial polarization formed by hydrogen bonding between the -OH groups and the aramid matrix; secondly, the -OH functional groups reduce the surface energy of the carbon nanotubes, inhibiting OH-CNT aggregation and allowing the hydroxylated carbon nanotubes to be uniformly dispersed in the aramid matrix, thus creating more electron transport paths and increasing conductive loss and impedance mismatch with air. These factors—dipole polarization, interfacial polarization, and enhanced conductive loss—enhance the absorption of electromagnetic waves, while the impedance mismatch with air increases the reflection of electromagnetic waves, thereby enhancing the electromagnetic shielding performance.

[0024] 3. When the OH-CNT@aramid composite film of the present invention is applied to the thermal management of LED integrated lamps, when a 4cm×4cm OH-CNT@aramid composite film (OH-CNT-40%) containing 40wt% thermally conductive filler is applied, the stable operating temperature of the electronic device is about 169℃, which is 13℃ lower than that of the CNT@aramid composite film (CNT-40%) containing 40wt% thermally conductive filler. It has broad application prospects in the thermal management of electronic devices. Attached Figure Description

[0025] Figure 1 The schematic diagrams are as follows: (a) Hydrogen bonding and π-π stacking at the interfaces of OH-CNT / aramid and OH-CNT / OH-CNT; (b) Hydroxyl dipole polarization of the OH-CNT surface and interfacial polarization between OH-CNT and aramid under the action of hydrogen bonding; (c) Schematic diagram of interface engineering enhancing phonon transmission and increasing phonon transport paths; (d) Schematic diagram of electromagnetic absorption and electromagnetic reflection; (e) Schematic diagram of OH-CNT uniformly dispersed and forming more phonon transport paths due to the reduction of surface energy; (f) Schematic diagram of OH-CNT uniformly dispersed, forming more electron transport paths, increasing conductivity loss and reflection loss.

[0026] Figure 2 High-resolution transmission electron microscopy (HRTEM) images (a, c) of CNTs and OH-CNTs used in Examples 1-4; higher-magnification HRTEM and inverse Fourier transform (IFT) images (b, d) of CNTs and OH-CNTs; XRD characterization of CNTs, OH-CNTs, aramid fibers and their complexes (e, f).

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

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

[0029] Figure 5 The thermal conductivity and applications of the composite films prepared in Examples 1-4 are described. (a) In-plane thermal diffusivity α of pressed pure CNT and OH-CNT sheets. / / and normal thermal diffusivity α ⊥ (b) In-plane thermal conductivity λ of pressed CNT and OH-CNT sheets / / and normal thermal conductivity λ ⊥ (c) In-plane thermal diffusivity α of CNT@aramid composite film and OH-CNT@aramid composite film / / (d) In-plane thermal conductivity λ of CNT@aramid composite film and OH-CNT@aramid composite film / / (e) Compared with pure aramid membranes, the in-plane thermal conductivity λ of CNT@aramid composite membranes and OH-CNT@aramid composite membranes / / Enhancement; (f) Infrared thermal images and time-temperature curves of LED lamp surfaces with CNT-40% and OH-CNT-40% as TIMs, respectively.

[0030] Figure 6 This is a SEM cross-sectional view of the CNT@aramid composite membranes prepared in Comparative Examples 1-4 and the OH-CNT@aramid composite membranes 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 thermally conductive hydroxylated carbon nanotubes was weighed and uniformly dispersed in 10 g of concentrated sulfuric acid under ultrasonic conditions to obtain dispersion I. Then, 0.621 g of aramid was dissolved in 10 g of concentrated sulfuric acid at 10℃~25℃ to obtain liquid crystal solution II. Dispersion I and liquid crystal solution II were thoroughly and uniformly mixed to obtain liquid crystal mixture III of hydroxylated carbon nanotubes@aramid. Liquid crystal mixture III was uniformly coated onto a glass substrate using a blade coating method. The glass substrate coated with liquid crystal mixture III was then rapidly immersed in deionized water for reverse phase separation for 1.5~2 hours. After drying and hot pressing (hot pressing temperature 30~40℃, hot pressing pressure 4~5 kPa, hot pressing time 8~10 h), a film with a thickness of 235 μm was formed.

[0039] The prepared OH-CNT-10% composite film achieved a thermal conductivity of 11.4 W / m². -1 K -1 The electromagnetic shielding effectiveness is 6.0 dB, and the electromagnetic shielding efficiency reaches 74.7%.

[0040] Example 2

[0041] A hydroxylated carbon nanotube@aramid composite film (OH-CNT-20%), wherein the thermally conductive filler carbon nanotubes are distributed along the plane of the coating.

[0042] The mass ratio of hydroxylated carbon nanotubes to aramid fibers is 2:8, meaning the mass fraction of the thermally conductive filler hydroxylated carbon nanotubes is 20 wt%.

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

[0044] The prepared OH-CNT-20% composite film has a thickness of 255 μm and a thermal conductivity of 21.6 W / m². -1 K -1 The electromagnetic shielding effectiveness is 9.6 dB, and the electromagnetic shielding efficiency reaches 89.1%.

[0045] Example 3

[0046] A hydroxylated carbon nanotube@aramid composite film (OH-CNT-30%), wherein the thermally conductive filler carbon nanotubes are distributed along the plane of the coating.

[0047] The mass ratio of hydroxylated carbon nanotubes to aramid fibers is 3:7, meaning the mass fraction of the thermally conductive filler hydroxylated carbon nanotubes is 30 wt%.

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

[0049] The prepared OH-CNT-30% composite film has a thickness of 315 μm and a thermal conductivity of 29.3 W / m². -1 K -1 The electromagnetic shielding effectiveness is 16.4 dB, and the electromagnetic shielding efficiency reaches 97.7%.

[0050] Example 4

[0051] A hydroxylated carbon nanotube@aramid composite film (OH-CNT-40%), wherein the thermally conductive filler carbon nanotubes are distributed along the plane of the coating.

[0052] The mass ratio of hydroxylated carbon nanotubes to aramid fibers is 4:6, meaning the mass fraction of the thermally conductive filler hydroxylated carbon nanotubes is 40 wt%.

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

[0054] The prepared OH-CNT-40% composite film has a thickness of 265 μm and a thermal conductivity of 33.7 W / m². -1 K -1 The electromagnetic shielding effectiveness is 21.7 dB, and the electromagnetic shielding efficiency reaches 99.3%.

[0055] Comparative Example 1

[0056] A carbon nanotube@aramid composite film (CNT-10%), wherein the thermally conductive filler carbon nanotubes are distributed along the plane of the coating.

[0057] The mass ratio of carbon nanotubes to aramid fibers is 1:9, meaning the mass fraction of thermally conductive filler carbon nanotubes is 10 wt%.

[0058] The prepared composite film has a thickness of 240 μm and a thermal conductivity of 9.6 W / m². -1 K -1 The electromagnetic shielding effectiveness is 5.8dB, and the electromagnetic shielding efficiency reaches 73.6%.

[0059] Comparative Example 2

[0060] A carbon nanotube@aramid composite film (CNT-20%), wherein the thermally conductive filler carbon nanotubes are distributed along the plane of the coating.

[0061] The mass ratio of carbon nanotubes to aramid fibers is 2:8, meaning the mass fraction of thermally conductive filler carbon nanotubes is 20 wt%.

[0062] The prepared composite film has a thickness of 250 μm and a thermal conductivity of 14.2 W / m². -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%), wherein the thermally conductive filler carbon nanotubes are distributed along the plane of the coating.

[0065] The mass ratio of carbon nanotubes to aramid fibers is 3:7, meaning the mass fraction of thermally conductive carbon nanotubes is 30 wt%.

[0066] The prepared composite film has a thickness of 305 μm and a thermal conductivity of 20.2 W / m². -1 K -1 The electromagnetic shielding effectiveness is 15.2dB, and the electromagnetic shielding efficiency reaches 97%.

[0067] Comparative Example 4

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

[0069] The mass ratio of carbon nanotubes to aramid fibers is 4:6, meaning the mass fraction of thermally conductive carbon nanotubes is 40 wt%.

[0070] The prepared composite film has a thickness of 285 μm and a thermal conductivity of 23.8 W / m². -1 K -1 The electromagnetic shielding effectiveness is 19.6 dB, and the electromagnetic shielding efficiency reaches 98.9%.

[0071] Figure 1 This is a schematic diagram of an aramid composite film based on interface engineering. This invention utilizes an interface engineering strategy based on hydroxyl-modified carbon nanotubes (OH-CNTs) to develop aramid-based TIMs with superior thermal conductivity and EMI shielding performance, achieving synergistic enhancement of thermal conductivity and electromagnetic shielding. Firstly, the strong π-π stacking between OH-CNTs and aramid originates from the delocalized π-electron cloud. Furthermore, the hydrogen bonds formed between the -OH groups and the -CO- in the aramid enhance phonon interfacial transmission (PMI). Figure 1 (a), Figure 1 (c) This reduces the ITR. The hydrogen bonding interaction between OH-CNT and aramid strengthens the differential charge density distribution and enhances interfacial polarization; the -OH group, acting as a dipole, polarizes in the electric field, introducing additional dipole polarization. Both interfacial polarization and dipole polarization enhance the absorption of electromagnetic waves, thereby improving electromagnetic interference shielding. Figure 1 (b) Furthermore, compared to CNTs, the reduced surface energy of OH-CNTs inhibited aggregation, improved the dispersion of nanofillers within the matrix, and created additional phonon transport pathways. Figure 1 (e)- Figure 1 (f) enhances thermal conductivity; it also creates additional electron transport paths, increasing conductive losses and reflection losses caused by impedance mismatch with air, thus enhancing electromagnetic shielding performance. Figure 1 (c)- Figure 1 (d)).

[0072] Figure 2 (a)- Figure 2 (d) The morphology and microstructure of CNT and OH-CNT were characterized using HRTEM. Figure 2 (a) Figure 2 (c) HRTEM images of CNT and OH-CNT reveal their concentric cylindrical multilayer graphene structures, visually demonstrating the stacking morphology of multiple tube walls. Figure 2 (b) Figure 2 (d) is a higher magnification HRTEM image, directly showing the lattice fringes of CNTs and OH-CNTs, with interlayer spacing of approximately 0.34 nm, corresponding to the (002) crystal plane, exhibiting good crystallinity. The inverse Fourier transform (IFT) image clearly shows the layered arrangement, further verifying the excellent crystallinity of CNTs and OH-CNTs. Aramids show a (200) crystal plane diffraction peak at 24.8°, CNTs show (002) and (100) crystal plane diffraction peaks at 26.1° and 43°, and OH-CNTs show (002) and (100) crystal plane diffraction peaks at 26.1° and 43.3°, proving that hydroxyl functionalization did not significantly change the crystal structure of carbon nanotubes; both OH-CNT and CNT series composites exhibit characteristic peaks of aramids and their 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 their original sharp characteristic peaks are 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 showed that both OH-CNT and CNT surfaces had a uniform aramid polymer coating. Figure 3 EDS analysis revealed distinct nitrogen (N) and oxygen (O) signals along the OH-CNT line, with their spatial distribution closely overlapping with the carbon (C) signal. This provides direct evidence that aramid molecules coat OH-CNTs through interfacial interactions (hydrogen bonding and π-π stacking). The -NH-CO- groups in the aramid provide N and O elements to cover the filler surface, indicating that both CNTs and OH-CNTs are coated by aramid molecules.

[0074] Because the filler is encapsulated by aramid molecules, all composite materials possess certain insulating properties. Figure 4 (a)). Figure 4 (a) shows the sheet resistance values ​​and standard deviation. Although hydroxyl groups typically disrupt the sp... 2 The conjugated structure reduces the inherent conductivity, but the sheet resistance of the OH-CNT series films (1.03–3.2 kΩ / sq) is significantly lower than that of the carbon nanotube series films (4.51–75.00 kΩ / sq). This is mainly due to the improved dispersion of OH-CNT in the aramid matrix, which helps to form a denser conductive network, ultimately overcoming the loss of inherent conductivity. In this study, changes in elemental binding energy were observed by X-ray photoelectron spectroscopy (XPS), demonstrating the hydrogen bonding and π-π stacking interactions between the aramid matrix and the filler. The XPS spectra of aramid, CNT, OH-CNT, CNT-20%, and OH-CNT-20% are representative examples. Figure 4 (b)- Figure 4 As shown in (d), both CNT-20% and OH-CNT-20% exhibit characteristic peaks corresponding to the binding energies of O1s, N1s, and C1s. Compared to CNT and OH-CNT, the O1s / C1s intensity ratio in the CNT-20% and OH-CNT-20% composite films is significantly increased, confirming the successful attachment of aramid molecules to the filler. The corresponding peaks of CNT-20% and OH-CNT-20% shift to lower binding energies (287.95 eV and 287.84 eV) relative to the C=O peak (288.08 eV) of C1s in aramid. For the CN peak (285.37 eV) of C1s in aramid, CNT-20% and OH-CNT-20% exhibit higher binding energies (286.37 eV and 286.32 eV). Furthermore, the NH in N1s of the aramid (400.04 eV) is transferred to a higher binding energy in the composite film (400.13 eV for CNT-20% and 400.09 eV for OH-CNT-20%). These changes in binding energy clearly demonstrate a change in the chemical environment of C=O, CN, and NH, confirming the formation of hydrogen bonds and π-π stacking interactions between the aramid and the filler.

[0075] To clarify the effect of interface modification on the thermal conductivity of fillers, the in-plane thermal diffusivity (α) of pressed CNT and OH-CNT sheets was measured. / / ) and normal thermal diffusivity (α) ⊥ ).like Figure 5 (a)- Figure 5 As shown in (b), the average α of CNT and OH-CNT films / / They are 2.58mm respectively. 2 / s and 3.95mm 2 / s, average α⊥ 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 5As shown in (e). Compared to pure aramid, OH-CNT-40% λ / / It increased by 1291.67%. When the filler content is 20wt%, λ / / The enhancement is most pronounced above this concentration; beyond this concentration, the enhancement rate decreases. The α-coating of OH-CNT@aramid composite membranes... / / and λ / / The values ​​were all higher than those of CNT@aramid composite films with the same filler content. These performance advantages stem from two synergistic mechanisms: First, hydroxylation reduces the ITR between fillers and between the filler and the aramid matrix. Second, hydroxylation reduces the surface energy of the filler, promoting the uniform dispersion of OH-CNTs within the aramid matrix, allowing OH-CNTs to establish more efficient thermal conduction pathways within the aramid matrix. This study evaluated the thermal management performance of CNT-40% and OH-CNT-40% as TIMs (Thermal Management Indicators). Figure 5 (f)). They were placed between the LED lamp (20W) and the aluminum heat sink, respectively. An infrared camera (emissivity ε = 0.98) captured infrared thermal images, and a data acquisition system recorded the operating temperature of the LED lamp surface. The steady-state surface temperature of CNT-40% stabilized at 174℃, while that of OH-CNT-40% stabilized at 161℃, resulting in a temperature difference of 13℃, which confirms the superior heat dissipation capability of OH-CNT-40%.

[0076] SEM cross-sectional images of the CNT@aramid composite films prepared in Comparative Examples 1-4 and the OH-CNT@aramid composite films prepared in Examples 1-4 are shown below. Figure 6 As shown, OH-CNTs exhibit uniform dispersion in the aramid matrix, which is attributed to the reduction in surface energy. Conversely, as indicated by the marked areas in the image, the CNT-30% and CNT-40% films show significant agglomeration. When the filler content exceeds 30 wt%, unmodified CNTs agglomerate in the aramid matrix.

[0077] Figure 7 (a)- Figure 7(b) shows the EMI SE of aramid composite films containing CNTs and OH-CNTs 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 film exhibiting significantly higher electromagnetic shielding effectiveness than the CNT@aramid composite film. The EMI SE values ​​of the CNT@aramid composite film ranged from 5.8 to 19.6 dB, while those of the OH-CNT@aramid composite film ranged from 6.0 to 21.7 dB. The OH-CNT-40% film (265 μm) achieved an EMI SE of 21.7 dB, exceeding the typical commercial requirement (20 dB) for electromagnetic shielding applications. Thickness is an important parameter for evaluating electromagnetic shielding performance. Shielding effectiveness per unit thickness (SSE) is defined as the ratio of shielding effectiveness to thickness (SSE = SE / t), providing insight into the contribution of thickness to overall shielding effectiveness. SSE value of OH-CNT@aramid composite film (255dB cm⁻¹) -1 376dB cm -1 520dB cm -1 819dB cm -1 ) higher than CNT@aramid composite film (242dB cm) -1 316dB cm -1 498dBcm -1 688dB cm -1 ()( Figure 7 (c) The maximum SSE value of the OH-CNT-40% film is 19% higher than that of the CNT-40% film. Therefore, the OH-CNT@aramid composite film has a higher electromagnetic shielding efficiency. Electromagnetic shielding efficiency represents the percentage of incident electromagnetic waves blocked and is calculated using the following formula: 100 - (1 / 10) SE / 10 The shielding efficiency increases with increasing filler content (×100). OH-CNT@aramid composite film consistently exhibits higher shielding efficiency than CNT@aramid composite film. The maximum shielding efficiency of OH-CNT-40% film is 99.3%. Figure 7 (d) indicates that it can effectively block almost all incident electromagnetic waves (EMW).

[0078] To elucidate the electromagnetic shielding enhancement mechanism in the OH-CNT series thin films, the total electromagnetic shielding effectiveness (EMI SE) was investigated. T ), mainly including reflection loss (SE) R ) and absorption loss (SE) A ()( Figure 7 (e)- Figure 7 (f)). SE A and SE R All showed similarities to 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 and SSE exhibit synergistic enhancement, with OH-CNT@aramid composite films showing a more significant improvement. For example, the λ of OH-CNT-40% film... / / =33.7W m -1 K -1 EMI SSE = 819 dB cm -1 They exceeded CNT-40% (λ) / / =23.8W m - 1 K -1 EMI SSE = 688dB cm -1 42% and 19%. Furthermore, OH-CNT@aramid composite films possess good mechanical strength, flexibility, foldability, and self-supporting properties. From the stress-strain curve ( Figure 7 (h) shows that the tensile strength ranges from 35 to 40 MPa. Even with a 40% filler content, the composite membrane can withstand bending, folding, and trimming without breaking. Figure 7 (i)). These characteristics make them particularly suitable for thermal management applications of electronic devices in complex thermo-magnetic environments.

[0079] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing an aramid composite film with synergistic enhancement of thermal conductivity and electromagnetic shielding performance based on interface engineering, characterized in that, Includes the following steps: (1) Weigh out the thermally conductive filler hydroxylated carbon nanotubes and uniformly disperse them in concentrated sulfuric acid under ultrasonic conditions to obtain dispersion I; the purity of the hydroxylated carbon nanotubes is ≥98%, the diameter is 5 nm~20 nm, the length is 10 μm~30 μm, and the mass fraction of hydroxyl functional groups in the filler structure is 5.43 wt%; (2) Aramid was dissolved in concentrated sulfuric acid at 10℃ ~25℃ to obtain liquid crystal solution II; (3) Mix dispersion I and liquid crystal solution II thoroughly and uniformly to obtain liquid crystal mixture III of hydroxylated carbon nanotubes@aramid. Coat liquid crystal mixture III uniformly onto the substrate by a scraping method to achieve orderly arrangement of hydroxylated carbon nanotubes along the scraping direction; wherein the mass ratio of thermally conductive filler to aramid in liquid crystal mixture III is 1~4:6~9. (4) The substrate coated with liquid crystal mixture III is quickly placed into the reverse solvent deionized water, and after phase separation for 1.5 to 2 hours, it is dried and hot-pressed to obtain a hydroxylated carbon nanotube@aramid composite film with high thermal conductivity and electromagnetic shielding performance.

2. The method for preparing an aramid composite film with synergistic enhancement of thermal conductivity and electromagnetic shielding performance based on interface engineering according to claim 1, characterized in that, In step (1), the mass ratio of thermally conductive filler to concentrated sulfuric acid is 1~4:40~100.

3. The method for preparing an aramid composite film with synergistic enhancement of thermal conductivity and electromagnetic shielding performance based on interface engineering according to claim 1, characterized in that, The aramid used in step (2) is a fully para-aramid formed by the condensation polymerization of p-phenylenediamine and terephthalic acid.

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

5. The method for preparing an aramid composite film with synergistic enhancement of thermal conductivity and electromagnetic shielding performance based on interface engineering according to claim 1, characterized in that, In step (4), the hot pressing temperature is 30~40℃, the hot pressing pressure is 4~5kPa, and the hot pressing time is 8~10h.

6. The method for preparing an aramid composite film with synergistic enhancement of thermal conductivity and electromagnetic shielding performance based on interface engineering according to claim 1, characterized in that, The thickness of the hydroxylated carbon nanotube@aramid composite film in step (4) is 60 μm to 320 μm.

7. The application of the hydroxylated carbon nanotube@aramid composite film with high thermal conductivity and electromagnetic shielding properties prepared by the preparation method according to any one of claims 1 to 6 in the thermal management of electronic devices.

8. The application according to claim 7, characterized in that, The electronic device is an integrated LED lamp.

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