Thermal conductive composite film for interface engineering to enhance heat conduction and preparation and application thereof

Abstract

The application discloses a heat-conducting composite film for interface engineering to enhance heat conduction and preparation and application thereof. The application uses conjugated liquid crystal as an interface modifier to modify the surface of boron nitride, and then modifies the boron nitride and aramid nanofiber through a self-assembly process to obtain the heat-conducting composite film. The prepared composite film has excellent mechanical properties, thermal stability and heat-conducting properties. The liquid crystal interface engineering not only effectively retains the intrinsic lattice structure of the boron nitride, avoids the lattice damage caused by traditional chemical grafting, but also optimizes the filler dispersity, fills the interface gap and constructs a dense continuous phonon transmission network, so that the film has higher thermal conductivity and tensile strength. The heat-conducting composite film has wide application prospects in LED heat dissipation, circuit heat dissipation and waste heat recovery.

Description

Technical Field

[0001] This invention belongs to the field of thermal interface material preparation technology, and relates to a thermally conductive thin film, specifically a thermally conductive composite thin film with interface engineering to enhance thermal conductivity, and its preparation and application. Background Technology

[0002] With the continuous miniaturization, integration, and power density increases of electronic devices, efficient thermal management has become crucial for ensuring stable device operation. Polymer-based thermally conductive composite materials have become a core research area in electronic thermal management due to their advantages of low cost, light weight, and ease of processing. Aramid fibers possess excellent thermal stability, mechanical strength, and intrinsic liquid crystal order, which can effectively reduce phonon scattering, making them an ideal matrix for high thermal conductivity composite materials. Boron nitride (BN) has ultra-high thermal conductivity, good electrical insulation, and an intrinsic π-π interaction with aramid fibers, making it a preferred thermally conductive filler for aramid matrices. However, the phonon spectrum mismatch between BN and the aramid matrix can lead to strong interfacial phonon scattering and high interfacial thermal resistance. Existing BN modification methods such as physical coating and chemical bonding can optimize interfacial bonding, but they are difficult to balance the intrinsic high thermal conductivity of BN with low interfacial scattering.

[0003] Liquid crystal modification of boron nitride (BN) is an efficient molecular interface engineering strategy. Liquid crystal molecules can reduce the surface energy of BN, inhibit filler aggregation, and improve its dispersibility in the aramid matrix. Its long-range ordered structure is highly compatible with the liquid crystal order of aramid, and during hot pressing, the liquid crystal can flow to fill interfacial defects, constructing continuous and dense thermally conductive channels. However, currently, there is a lack of a universal thermally conductive filler and high thermal conductivity polymer product that achieves uniform modification of the BN surface by liquid crystal through non-covalent anchoring, and where the liquid crystal-modified BN filler possesses both excellent dispersibility and interfacial compatibility with the polymer matrix. Summary of the Invention

[0004] One of the objectives of this invention is to provide a liquid crystal modified boron nitride thermally conductive filler. This filler is non-covalently anchored on the surface of BN by conjugated liquid crystal, which improves its dispersion in the polymer matrix and its interfacial compatibility with the polymer matrix while retaining the intrinsic lattice structure and high thermal conductivity of BN, and fills interfacial defects.

[0005] The second objective of this invention is to provide a method for preparing a thermally conductive composite thin film with enhanced thermal conductivity through interface engineering of boron nitride modified with liquid crystal.

[0006] The third objective of this invention is to provide a liquid crystal modified boron nitride aramid nanofiber thermally conductive composite film prepared by the above preparation method, which has excellent high thermal conductivity, mechanical strength, thermal stability and flame retardancy.

[0007] A fourth objective of this invention is to provide the application of the aforementioned thermally conductive composite film in electronic devices, circuit thermal management, and waste heat recovery. To achieve the above objective, this invention adopts the following technical solution: The first aspect of this invention provides a method for preparing a thermally conductive composite thin film with enhanced thermal conductivity through interface engineering, comprising the following steps: (1) A liquid crystal compound was prepared by sequentially subjecting acyl chloride, esterification, and recrystallization to 4-butenylbenzoic acid, thionyl chloride, and 4,4'-dihydroxybiphenyl as raw materials; the molecular structure of the liquid crystal compound is as follows: ; (2) The boron nitride was ultrasonically dispersed in ethanol, and the liquid crystal compound ethanol solution obtained in step (1) was added and ultrasonically mixed. The liquid crystal modified boron nitride suspension was obtained by rotary drying and secondary dispersion. (3) Aramid nanofibers with a mass ratio of 3:2 and solid potassium hydroxide were placed in dimethyl sulfoxide for deprotonation reaction, and then dispersed and purified by ethanol / water mixed solvent to obtain aramid nanofiber dispersion. (4) The liquid crystal modified boron nitride suspension and the aramid nanofiber dispersion were blended, and then vacuum filtered and hot-pressed to obtain a thermally conductive composite film with enhanced thermal conductivity through interface engineering.

[0008] Preferably, in step (1), the acyl chloride reaction temperature is 75°C and the reflux time is 6h; the esterification reaction temperature is 80°C and the reflux time is 8h.

[0009] Preferably, the boron nitride in step (2) has a purity > 99.5 wt%, a particle size of 2~4 μm, and a sheet thickness of 40~60 nm.

[0010] Preferably, the mass ratio of the liquid crystal compound to boron nitride added in step (2) is 1:5.

[0011] Preferably, the aramid nanofibers in step (3) are fully para-polyaramids synthesized by condensation polymerization of p-phenylenediamine and terephthaloyl chloride.

[0012] Preferably, the deprotonation reaction temperature in step (3) is 30°C and the reaction time is 7 days.

[0013] Preferably, the hot pressing temperature in step (4) is 200°C and the hot pressing time is 8h; the mass fraction of liquid crystal modified boron nitride in the composite film is 10wt%~50wt%.

[0014] A second aspect of the present invention provides a thermally conductive composite film with enhanced thermal conductivity through interface engineering, prepared by the above-described method.

[0015] This invention utilizes liquid crystal-modified boron nitride interface engineering to enhance thermal conductivity in a thermally conductive composite film. Liquid crystal molecules form hydrogen bonds and π-π stacking interactions with boron nitride and aramid nanofibers, constructing a continuous and dense phonon transport network. This results in a thermally conductive film possessing high in-plane thermal conductivity, excellent mechanical and thermal stability, and flame retardancy. Atomic-scale theoretical calculations further confirm that liquid crystal modification reduces the interfacial binding energy, enhances interfacial phonon vibrational coupling, and lowers interfacial thermal resistance, thus supporting the enhanced thermal conductivity at the microscopic level.

[0016] Thirdly, the present invention also provides the application of the above-mentioned thermally conductive composite film in electronic devices, circuit thermal management and waste heat recovery.

[0017] Preferably, the thermal management application includes heat dissipation materials used as LED devices and circuit elements.

[0018] Preferably, the waste heat recovery application includes using the composite film in thermoelectric devices to achieve waste heat recovery through thermoelectric power generation.

[0019] The liquid crystal modified boron nitride aramid nanofiber thermally conductive composite film provided by this invention has high thermal conductivity and excellent mechanical properties, thermal stability and flame retardancy. It is suitable for the application requirements of thermal management of highly integrated and high power density electronic devices, and can also be used as an efficient waste heat collection interface layer in the field of waste heat recovery.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a liquid crystal modified boron nitride thermally conductive filler. By non-covalently anchoring the conjugated liquid crystal on the surface of boron nitride, the interfacial compatibility and dispersibility between the filler and the polymer matrix are significantly improved while fully preserving the intrinsic lattice structure and high thermal conductivity of boron nitride. This effectively avoids the damage to the lattice caused by traditional chemical grafting and can be promoted as a general-purpose high-performance thermally conductive filler to various polymer systems.

[0021] 2. The liquid crystal-modified boron nitride aramid nanofiber composite film of the present invention exhibits excellent thermal conductivity, with an in-plane thermal conductivity reaching up to 22.0 W·m. -1 ·K -1 The thermal conductivity was improved by 809.1% compared to pure aramid nanofiber films. This enhanced thermal conductivity is attributed to a synergistic effect of two mechanisms: firstly, liquid crystal modification reduces the surface energy of BN, inhibiting aggregation and improving its dispersibility in the aramid matrix; secondly, aramid possesses an ordered liquid crystal structure, exhibiting good intrinsic compatibility with the ordered structure of liquid crystal compounds. Furthermore, during hot pressing, the fluidity of the liquid crystal allows it to slide to the interface defects between BN and the matrix. Since the ordered structure of the liquid crystal is beneficial for heat conduction, this ordered interface filling reduces phonon scattering centers, forming dense, continuous, low-defect heat conduction channels.

[0022] 3. The liquid crystal-modified boron nitride aramid nanofiber composite film of the present invention possesses excellent mechanical properties, thermal stability, and flame retardancy. The composite film has a tensile strength up to 103 MPa, a rapid thermal decomposition initiation temperature above 580°C, and can quickly self-extinguish after the removal of the ignition source. The enhanced properties stem from two aspects: the three-dimensional interwoven network of aramid nanofibers provides a high-strength framework; the strong interfacial interaction between the liquid crystal, boron nitride, and aramid further improves the structural stability of the film; and the liquid crystal modification optimizes the interfacial bonding, ensuring the overall mechanical properties of the film. Simultaneously, the high thermal stability of boron nitride and aramid itself endows the composite film with excellent heat resistance and flame retardancy.

[0023] 4. The thermally conductive composite film of this invention exhibits excellent heat dissipation capabilities in the thermal management of electronic devices. When the composite film containing 40wt% thermally conductive filler is used as an interface heat dissipation material for LED chips, the stable operating temperature is approximately 20°C lower than that of commercial thermal pads; it exhibits no localized overheating when applied to circuit heat dissipation, and has broad application prospects in the field of heat dissipation.

[0024] 5. The thermally conductive composite film of the present invention also has important application value in the field of waste heat recovery. Its excellent thermal conductivity can be used as a waste heat collection interface layer for thermoelectric devices, efficiently collecting waste heat and converting it into electrical energy, thereby realizing energy recovery and reuse. Attached Figure Description

[0025] Figure 1 A schematic diagram of the preparation process of a thermally conductive composite thin film. Figure 1 b. Schematic diagram of the interfacial interaction of the thermally conductive composite thin film. Figure 1 A schematic diagram of defect filling between c-aramid and boron nitride. Figure 1 d. A schematic diagram of a dense, low-defect, low-scattering, and continuous heat conduction path.

[0026] Figure 2 Image a is a transmission electron microscope (TEM) image of aramid nanofibers (ANF). Figure 2 b is an atomic force microscopy image of the BN structure and its thickness. Figure 2 c represents the molecular structure and infrared spectrum of liquid crystal (LC). Figure 2 d is the differential scanning calorimetry curve of LC. Figure 2 e is a polarizing microscope image of LC. Figure 2 f is the X-ray diffraction (XRD) pattern of liquid crystal modified boron nitride (BN-LC). Figure 2 g is a polarizing microscope image of BN-LC (LC content 10wt%, 20wt%, 30wt%). Figure 2 h is a scanning electron microscope image of BN-LC and its elemental distribution map. Figure 2i is the X-ray photoelectron spectroscopy (XPS) of BN-LC, BN, and LC. Figure 2 j is the C1s energy spectrum of LC and BN-LC.

[0027] Figure 3 a is the XRD pattern of the composite film (LC-ABN) prepared by liquid crystal modified boron nitride and aramid nanofibers. Figure 3 b, Figure 3 c, Figure 3 e, Figure 3 f represents the cross-sectional scanning electron microscope (SEM) morphology of ANF, LC-ABN3, LC-ABN4, and LC-ABN5, respectively. Figure 3 d is XPS for LC-ABN3 and ANF. Figure 3 g is the C1s energy spectrum of LC-ABN3 and ANF. Figure 3 h is the N1s energy spectrum of LC-ABN3 and ANF. Figure 3 i is the B1s energy spectrum of LC-ABN3 and BN. Figure 3 j is the stress-strain curve of the LC-ABN series composite thin film. Figure 3 k is the thermogravimetric analysis (TGA) curve of the LC-ABN series composite thin films. Figure 3 Photographs of the flame retardancy of LC-ABN4 composite films under different burning times are shown in image 1.

[0028] Figure 4 a is the thermal diffusivity of the composite film. Figure 4 b is the thermal conductivity of the composite film. Figure 4 c represents the percentage increase in thermal conductivity of the composite film. Figure 4 d is the bonding energy at the interface between BN and aramid (BN-A) and BN and liquid crystal (BN-LC). Figure 4 ef is a molecular dynamics simulation model of the interface between unmodified BN and aramid (BN-A) and liquid crystal modified boron nitride and aramid (BNLC-A). Figure 4 g is a comparison of the interfacial thermal resistance of BN-A and BNLC-A. Figure 4 hi is the normalized vibrational dynamic density (VDOS) of the unmodified BN / aramid composite system and the liquid crystal modified boron nitride / aramid composite system.

[0029] Figure 5 A is an infrared thermal imaging comparison of LC-ABN4 composite film and commercial thermal pads in LED chip heat dissipation applications. Figure 5 b is a comparison of the surface temperature of LEDs using LC-ABN4 composite film and commercial thermal pads as heat dissipation materials. Figure 5 c represents infrared thermal imaging of the LC-ABN4 composite film in circuit heat dissipation applications. Figure 5 d is a schematic diagram of a thermoelectric power generation system. Figure 5ef is the current evolution of a thermoelectric power generation system when commercial thermal pads and LC-ABN5 composite films are used as waste heat conduction layers, respectively. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained through commercial channels. No requirements are made regarding their brand origin.

[0032] The aramid used in the following examples was manufactured by DuPont and is a fully para-polyaramid produced by the condensation polymerization of p-phenylenediamine and terephthaloyl chloride.

[0033] The liquid crystal-modified boron nitride thermally conductive filler used in the following examples was prepared through the following steps: 4-Butenylbenzoic acid, thionyl chloride, and 4,4'-dihydroxybiphenyl were used as raw materials, and the liquid crystal compound 4-butenylbenzoic acid biphenol monoester was obtained through acyl chloride reaction (75℃, reflux for 6 h), esterification reaction (80℃, reflux for 8 h), and recrystallization. Boron nitride (purity > 99.5 wt%, particle size 2~4 μm, sheet thickness 40~60 nm) was ultrasonically dispersed in ethanol, and the above liquid crystal compound ethanol solution was added and ultrasonically mixed. The mass ratio of liquid crystal to boron nitride was 1:5, i.e., the liquid crystal accounted for 20 wt% of the boron nitride mass fraction. When the liquid crystal accounts for 10 wt% of boron nitride, the surface modification effect of the liquid crystal on boron nitride is low, and boron nitride cannot be well dispersed. When the liquid crystal accounts for 20 wt% of boron nitride, the surface modification effect of the liquid crystal on boron nitride is more ideal, and the distribution on the boron nitride surface is more uniform, achieving good dispersion of boron nitride. When the liquid crystal accounts for 30 wt% of boron nitride, local aggregation of liquid crystal occurs. Therefore, a mass ratio of liquid crystal to boron nitride of 1:5 was selected, i.e., the liquid crystal accounts for 20 wt% of boron nitride. After rotary drying and secondary dispersion with ethanol / deionized water (volume ratio 1:5), a liquid crystal modified boron nitride suspension was obtained. After drying, the liquid crystal modified boron nitride thermally conductive filler was obtained.

[0034] The reaction equation for liquid crystal preparation is as follows: .

[0035] This conjugated liquid crystal, through non-covalent anchoring modification of the boron nitride surface, fully preserves the intrinsic lattice structure of boron nitride, while improving the interfacial compatibility between boron nitride and the polymer matrix. Furthermore, during hot pressing, the fluidity of the liquid crystal can fill interfacial defects through molecular slippage, making it an ideal interfacial modification strategy.

[0036] Example 1 A thermally conductive composite film (LC-ABN1) with enhanced thermal conductivity through interface engineering by modifying boron nitride with liquid crystal, wherein the thermally conductive filler modified with liquid crystal boron nitride is uniformly distributed along the plane of the composite film.

[0037] The mass ratio of liquid crystal modified boron nitride to aramid nanofiber is 1:9, that is, the mass fraction of thermally conductive filler is 10wt%.

[0038] The specific implementation process is as follows: First, an aramid nanofiber dispersion was prepared using an alkaline deprotonation method. 1.5g of aramid nanofiber and 1g of solid potassium hydroxide were placed in 850mL of dimethyl sulfoxide and reacted at 30℃ for 7 days. The dispersion was then purified by dispersing in 340mL of a mixed solvent of ethanol / deionized water (volume ratio 1:5) for 1 hour. Second, the liquid crystal modified boron nitride suspension was thoroughly mixed with the aramid nanofiber dispersion and mechanically stirred for 30 minutes. The wet composite membrane was obtained by vacuum filtration and then hot-pressed at 200℃ for 8 hours to form a film.

[0039] The prepared LC-ABN1 composite film achieved a thermal conductivity of 9.8 W·m. - ¹·K - ¹, with a tensile strength of 103 MPa, and rapid thermal decomposition begins at 586℃.

[0040] Example 2 A thermally conductive composite film (LC-ABN2) with enhanced thermal conductivity through interface engineering by modifying boron nitride with liquid crystal, wherein the thermally conductive filler modified with liquid crystal boron nitride is uniformly distributed along the plane of the composite film.

[0041] The mass ratio of liquid crystal modified boron nitride to aramid nanofibers is 2:8, that is, the mass fraction of thermally conductive filler is 20wt%.

[0042] The preparation method is the same as in Example 1.

[0043] The prepared LC-ABN2 composite film has a thermal conductivity of 12.2 W·m. - ¹·K - ¹, with a tensile strength of 98 MPa, and begins to rapidly thermally decompose at 584 °C.

[0044] Example 3 A thermally conductive composite film (LC-ABN3) with enhanced thermal conductivity through interface engineering by modifying boron nitride with liquid crystal is disclosed. The thermally conductive filler BN-LC has a mass fraction of 30 wt%, and the liquid crystal-modified boron nitride is uniformly distributed along the plane of the composite film.

[0045] The mass ratio of liquid crystal modified boron nitride to aramid nanofibers is 3:7, that is, the mass fraction of thermally conductive filler is 30wt%.

[0046] The preparation method is the same as in Example 1.

[0047] The prepared LC-ABN3 composite film achieved a thermal conductivity of 16.6 W·m. - ¹·K - ¹, with a tensile strength of 90 MPa, and rapid thermal decomposition begins at 586℃.

[0048] Example 4 A thermally conductive composite film (LC-ABN4) with enhanced thermal conductivity through interface engineering by modifying boron nitride with liquid crystal, wherein the thermally conductive filler modified with liquid crystal boron nitride is uniformly distributed along the plane of the composite film.

[0049] The mass ratio of liquid crystal modified boron nitride to aramid nanofibers is 4:6, that is, the mass fraction of thermally conductive filler is 40wt%.

[0050] The preparation method is the same as in Example 1.

[0051] The prepared LC-ABN4 composite film achieved a thermal conductivity of 18.2 W·m. - ¹·K - ¹, with a tensile strength of 52 MPa, and rapid thermal decomposition begins at 581℃.

[0052] Example 5 A thermally conductive composite film (LC-ABN5) with enhanced thermal conductivity through interface engineering by modifying boron nitride with liquid crystal, wherein the thermally conductive filler modified with liquid crystal boron nitride is uniformly distributed along the plane of the composite film.

[0053] The mass ratio of liquid crystal modified boron nitride to aramid nanofiber is 5:5, that is, the mass fraction of thermally conductive filler is 50wt%.

[0054] The preparation method is the same as in Example 1.

[0055] The prepared LC-ABN5 composite film achieved a thermal conductivity of 22.0 W·m. - ¹·K - ¹, with a tensile strength of 35 MPa, it begins to rapidly thermally decompose at 586℃. It possesses optimal thermal conductivity.

[0056] Application Example 1: Thermal Management Applications of LED Devices The LC-ABN4 composite film prepared in Example 4 was used as the thermal interface material for LED chips, and compared with the use of commercial thermal pads as the thermal interface material for LED chips. After 150 seconds of operation, the surface temperature of the LED chips using the LC-ABN4 composite film as the thermal interface material was reduced by approximately 10.4°C compared with the LED chips using commercial thermal pads as the thermal interface material, with no local heat accumulation and excellent heat dissipation effect.

[0057] Application Example 2: Circuit Heat Dissipation Using the LC-ABN4 composite film prepared in Example 4 as a substrate, a silver paste circuit was drawn on the surface and a voltage of 0.4V was applied. During continuous heating, the temperature of the heated area of ​​the composite film silver circuit was uniform, with no local overheating, which can efficiently conduct the heat of the circuit and avoid thermal accumulation failure of electronic components.

[0058] Application Example 3: Waste Heat Recovery Application The LC-ABN5 composite membrane prepared in Example 5 was used as a waste heat collection interface layer and attached to the hot end of a thermoelectric device. The composite membrane was used to achieve a heat recovery rate of 22.0 W·m. - ¹·K - ¹ Its ultra-high in-plane thermal conductivity enables efficient collection of waste heat generated by electronic devices and conduction to the cold end of thermoelectric devices, establishing a stable temperature difference between the hot and cold ends of thermoelectric devices, realizing the conversion of waste heat into electrical energy, and achieving the purpose of energy recovery and reuse.

[0059] Theoretical verification of the thermal conductivity enhancement mechanism To further verify the mechanism by which liquid crystal interface engineering enhances thermal conductivity, this invention combines density functional theory (DFT) and molecular dynamics (MD) simulations to conduct an atomic-scale theoretical analysis from three levels: interface binding energy, interface thermal resistance, and phonon vibrational coupling.

[0060] DFT calculations show that the binding energy between unmodified boron nitride and aramid monomers is 0.66 eV, while the binding energy between boron nitride and liquid crystal molecules decreases to 0.13 eV after the introduction of liquid crystal. This reduction of approximately 80% indicates that liquid crystal molecules have a higher thermodynamic affinity for the boron nitride surface, preferentially anchoring to it, reducing its surface energy, and promoting uniform dispersion, thus creating the preconditions for constructing a continuous thermally conductive network.

[0061] MD simulation results show that the average interfacial thermal resistance (ITR) of the unmodified boron nitride-aramid interface is (2.99±0.03)×10⁻⁶. -9 m²·K·W - ¹, After liquid crystal modification, the value decreased to (2.82±0.03)×10 -9 m²·K·W - ¹ This directly confirms that the liquid crystal interface layer effectively reduces the thermal resistance barrier between the filler and the substrate.

[0062] Vibrational dynamic density of motion (VDOS) analysis further revealed the underlying mechanism: in the unmodified system, there is a significant phonon spectrum mismatch between the high-frequency lattice vibrations of boron nitride and the low-frequency segmental vibrations of aramid, leading to interfacial phonon scattering. After liquid crystal modification, the liquid crystal molecules, through the combination of a rigid conjugated framework and flexible segments, act as vibrational mediators between boron nitride and aramid, increasing the phonon spectrum overlap integral S of the low-frequency vibrational modes on both sides of the interface from 0.54 to 0.58. This enhanced vibrational coupling effect reduces the interfacial phonon impedance mismatch, elucidating the intrinsic mechanism of reduced interfacial thermal resistance from a microscopic vibrational perspective.

[0063] like Figure 1 As shown in a, this application uses aramid nanofibers (ANF) as the polymer matrix, employs conjugated liquid crystals to perform surface anchoring modification on boron nitride (BN), and then constructs an aramid-based thermally conductive composite film through self-assembly. Figure 1 bd further revealed that the liquid crystal tightly coats the surface of BN and forms hydrogen bonds and π-π stacking interactions with ANF, which can fill the defects between aramid and BN and construct a continuous phonon transport path.

[0064] Figure 2 Transmission electron microscopy (TEM) Figure 2 a) It shows that one-dimensional linear ANFs have been successfully fabricated, possessing micrometer-scale lengths, 10-30 nm diameters, and large aspect ratios, interwoven to form a three-dimensional network framework; atomic force microscopy (AFM) Figure 2 b) indicates that BN is a typical two-dimensional sheet-like structure, with a diameter of 2-4 μm and a thickness of 40-60 nm, exhibiting a high specific surface area. Infrared spectroscopy ( Figure 2 c) The molecular structure of the conjugated liquid crystal (LC) was verified (–OH, –C=O– and characteristic peaks of the benzene ring). In the FT-IR spectrum, 3440 cm⁻¹... - The characteristic peak at ¹ is attributed to the –OH stretching vibration, 1704 cm⁻¹ - The strong absorption peak at ¹ corresponds to the stretching vibration of –C=O–, while at 1600 cm⁻¹… - The peak at position ¹ is attributed to the stretching vibrations of the benzene ring skeleton. Differential scanning calorimetry (DSC) Figure 2 d) This indicates that the LC is a reversible thermotropic liquid crystal with a melting point of 178.8°C and a clearing point of 232.0°C. During the heating process, its liquid crystal range is 178.8°C-232.0°C. Within this liquid crystal range, it can flow orderly and fill interface defects under hot pressing. Polarizing microscope (…) Figure 2 e) Typical texture of the nematic phase was observed, exhibiting a marbled texture when heated to 225°C and a black cross-shaped texture when cooled to 236°C. XRD patterns clearly show the crystal structure characteristics of LC and BN-LC. Figure 2f). LC exhibits characteristic diffraction peaks at 2θ = 20.3° and 22.8°, corresponding to its (001) and (100) crystal planes, respectively. BN exhibits characteristic diffraction peaks at 2θ = 26.7°, 41.6°, 43.9°, 50.2°, and 55.2°, corresponding to its (002), (100), (101), (102), and (004) crystal planes, respectively. BN-LC not only exhibits typical characteristic diffraction peaks of LC at 2θ ≈ 20.3° and 22.8°, but also retains obvious characteristic diffraction peaks of BN, confirming the successful modification of BN by LC, and that BN still maintains its hexagonal crystal phase structure. Orthogonally polarized light images ( Figure 2 g) shows that when the liquid crystal accounts for 10 wt% of boron nitride, the surface modification effect of the liquid crystal on boron nitride is low, and boron nitride cannot be well dispersed; when the liquid crystal accounts for 20 wt% of boron nitride, the surface modification effect of the liquid crystal on boron nitride is more ideal, and the distribution on the boron nitride surface is more uniform, achieving good dispersion of boron nitride; when the liquid crystal accounts for 30 wt% of boron nitride, local aggregation of liquid crystal occurs. Therefore, a liquid crystal content of 20 wt% of boron nitride was selected for modification. Scanning electron microscopy and elemental analysis (SEM and elemental analysis) Figure 2 h) The modified BN retains a two-dimensional lamellar morphology with uniform C distribution, confirming that LC is uniformly coated on the boron nitride surface. XPS spectra show the surface elemental composition and chemical state of LC, BN, and BN-LC, such as... Figure 2 As shown in Figure ij, LC exhibits C1s and O1s spectral peaks, while BN shows B1s and N1s spectral peaks. BN-LC simultaneously displays B1s, N1s, C1s, and O1s spectral peaks, confirming the successful modification of LC. The C1s spectrum of LC can be resolved to correspond to the peak positions of C–O (285.66 eV) and C=O (288.9 eV). Compared to pure LC, the binding energies of C–O and C=O in BN-LC increase to 286.2 eV and 289.1 eV, respectively (shifted by +0.54 eV and +0.20 eV, respectively), and the peak areas change significantly. This indicates a strong non-covalent interfacial interaction between LC and BN, rather than a simple physical mixing. This interfacial modification and strong interaction are beneficial for efficient phonon transport, providing a key foundation for constructing thermally conductive composite materials.

[0065] XRD ( Figure 3 a) The results show that all LC-ABN films exhibit characteristic peaks of the aramid liquid crystal structure at 2θ≈20°, corresponding to the (002) and (004) crystal planes of BN at 26.91° and 55.25°, respectively. The BN peak intensity increases with increasing BN content, confirming successful film preparation. (SEM cross-section after liquid nitrogen fracture) Figure 3(b, c, e, f) shows that the pure ANF film has a one-dimensional interwoven nanofiber structure; in LC-ABN4 and LC-ABN5, the two-dimensional BN nanosheets are uniformly dispersed, oriented, and without agglomeration. LC, as an interface modifier, effectively fills the defects between ANF and BN, improves interfacial compatibility, and forms a continuous thermally conductive pathway. XPS spectra ( Figure 3 d, Figure 3 (gi) Analysis of interfacial interactions: LC-ABN3 simultaneously exhibits C, O, N, and B signals; compared to pure ANF, C–N (285.60 eV) and C=O (288.03 eV) in C1s shift towards higher energies, N–H (399.98 eV) in N1s shifts towards lower energies and N–B bond energy (398.17 eV) appears, and B–N (190.66 eV) in B1s shifts towards higher energies, confirming a significant non-covalent interfacial interaction between ANF and LC-BN. Uniaxial tensile testing ( Figure 3 j) indicates that the tensile strength of the thermally conductive filler is 90–103 MPa when the BN-LC content is ≤30 wt.%, and it remains between 35–52 MPa when the BN-LC content is 40–50 wt.%, demonstrating good mechanical properties. Thermogravimetric analysis (TGA) Figure 3 k) shows that the thermal decomposition temperatures (with 5% mass loss) of all films are between 450–520°C, with the fastest thermal decomposition temperature between 580–586°C, attributed to the high thermal stability of ANF and BN. Flame combustion test ( Figure 3 l) Taking LC-ABN4 as an example, it quickly self-extinguishes after being removed from the fire, with no melting drips and only surface carbonization, exhibiting excellent flame retardancy.

[0066] Figure 4 The thermal diffusivity of the composite film increased from 4.549 mm²·s⁻¹ as the filler loading increased from 10 wt% to 50 wt%. - ¹Increased to 8.365 mm²·s - ¹( Figure 4 a) Thermal conductivity (λ) from 9.8 W·m at 10 wt% - ¹·K - ¹22.0 W·m³ at 50 wt% - ¹·K - ¹, the percentage increase (η) compared to pure aramid nanofiber membranes reached 809.1% ( Figure 4 b–c). To elucidate the mechanism of liquid crystal interface engineering, density functional theory (DFT) calculations were performed. Figure 4d) shows that the binding energy between unmodified BN and aramid (BN-A) is 0.66 eV, while the binding energy between BN and LC molecules (BN-LC) is 0.13 eV, a reduction of 80%. This indicates that LC lowers the interfacial energy barrier and improves the thermodynamic affinity for the BN surface. Molecular dynamics (MD) simulations constructed interface models of unmodified and liquid crystal-modified BN with aramid (BN-A and BNLC-A). Figure 4 e–f), non-equilibrium molecular dynamics (NEMD) calculation of interfacial thermal resistance (ITR), Figure 4 The g–i) results show that the unmodified BN-A interface has a higher thermal resistance, while the liquid crystal-modified BNLC-A interface has a lower thermal resistance, confirming that LC interface engineering effectively promotes microscopic heat transfer.

[0067] To evaluate the thermal management performance of the composite film, the LC-ABN4 composite film was used as a heat dissipation material for LED chips and compared with commercial thermal pads as the heat dissipation material. Infrared thermal imaging (…) Figure 5 a) shows that the surface temperature of LED beads using LC-ABN4 composite film as heat dissipation material is consistently lower than that of LED beads using commercial thermal pads as heat dissipation material; the temperature difference reaches 10.4°C after 150 seconds of operation. Figure 5 (b) indicates that LC-ABN4 can effectively suppress heat accumulation and has excellent heat dissipation performance. Further, a silver circuit was fabricated on its surface and a voltage of 0.4V was applied ( Figure 5 c) During the continuous power-on period of 410 seconds, there was no local overheating in the circuit heating area and the surface temperature remained stable, indicating that LC-ABN4 can effectively conduct the heat generated by the circuit operation, avoid heat accumulation, and ensure the safe use of electronic components.

[0068] In addition, the LC-ABN5 composite membrane is applied to thermoelectric power generation (TEG) systems for waste heat recovery. Figure 5 d): The system consists of LED lights, a thermoelectric generator, an LC-ABN5 or commercial thermal pad, and an aluminum heat sink. When using the commercial thermal pad, the maximum current reaches 351.2 mA in 241.6 seconds and stabilizes at 338.4 mA after 603.7 seconds, generating a charge of 219.7 C. Figure 5 e); However, when using LC-ABN5, due to its superior thermal conductivity, the maximum current reaches 391.7 mA in 240.0 seconds and stabilizes at 386.7 mA after 600 seconds, generating a charge of 240.1 C ( Figure 5 (f) is 9.3% higher than that of commercial thermal pads. The results show that the highly thermally conductive LC-ABN5 composite membrane has great potential for waste heat recovery in thermoelectric power generation.

[0069] 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 a thermally conductive composite thin film with enhanced thermal conductivity through interface engineering, characterized in that, Includes the following steps: (1) A liquid crystal compound was prepared by sequentially subjecting acyl chloride, esterification, and recrystallization to 4-butenylbenzoic acid, thionyl chloride, and 4,4'-dihydroxybiphenyl as raw materials; the molecular structure of the liquid crystal compound is as follows: ； (2) The boron nitride was ultrasonically dispersed in ethanol, and the liquid crystal compound ethanol solution obtained in step (1) was added and ultrasonically mixed. The liquid crystal modified boron nitride suspension was obtained by rotary drying and secondary dispersion. (3) Aramid nanofibers with a mass ratio of 3:2 and solid potassium hydroxide were placed in dimethyl sulfoxide for deprotonation reaction, and then dispersed and purified by ethanol / water mixed solvent to obtain aramid nanofiber dispersion. (4) The liquid crystal modified boron nitride suspension and the aramid nanofiber dispersion were blended, and then vacuum filtered and hot-pressed to obtain a thermally conductive composite film with enhanced thermal conductivity through interface engineering.

2. The method for preparing a thermally conductive composite thin film with enhanced thermal conductivity through interface engineering according to claim 1, characterized in that, In step (1), the acyl chloride reaction temperature is 75℃ and the reflux time is 6h; the esterification reaction temperature is 80℃ and the reflux time is 8h.

3. The method for preparing a thermally conductive composite thin film with enhanced thermal conductivity through interface engineering according to claim 1, characterized in that, The boron nitride mentioned in step (2) has a purity of >99.5wt%, a particle size of 2~4μm, and a sheet thickness of 40~60nm.

4. The method for preparing a thermally conductive composite thin film with enhanced thermal conductivity through interface engineering according to claim 1, characterized in that, The mass ratio of the liquid crystal compound to boron nitride added in step (2) is 1:

5.

5. The method for preparing a thermally conductive composite thin film with enhanced thermal conductivity through interface engineering according to claim 1, characterized in that, The aramid nanofibers mentioned in step (3) are fully para-polyaramids synthesized by condensation polymerization of p-phenylenediamine and terephthaloyl chloride.

6. The method for preparing a thermally conductive composite thin film with enhanced thermal conductivity through interface engineering according to claim 1, characterized in that, The deprotonation reaction in step (3) is carried out at a temperature of 30°C for 7 days.

7. The method for preparing a thermally conductive composite thin film with enhanced thermal conductivity through interface engineering according to claim 1, characterized in that, In step (4), the hot pressing temperature is 200℃ and the hot pressing time is 8h; the mass fraction of liquid crystal modified boron nitride in the composite film is 10wt%~50wt%.

8. A thermally conductive composite thin film with enhanced thermal conductivity through interface engineering, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the interface-engineered thermally conductive composite film with enhanced thermal conductivity as described in claim 8 in the thermal management and waste heat recovery of electronic devices.

Images