CN113896428B - Nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film, preparation method thereof and application thereof in electronic device heat management - Google Patents

Abstract

The invention discloses a nematic liquid crystal oriented Kevlar/silicon carbide composite heat conduction film and its preparation method and application in thermal management of electronic devices. Firstly, the silicon carbide nanowire heat conduction filler is uniformly mixed with the Kevlar solute liquid crystal , realize the consistent nematic liquid crystal orientation structure formed by silicon carbide nanowires and Kevlar solute liquid crystals by scraping, and then prepare the Kevlar/silicon carbide composite with nematic liquid crystal orientation through liquid-solid phase separation and hot pressing Thermal film. The composite heat conducting film prepared by the invention has good flexibility, thermal stability, tensile strength, hydrophobicity and flame retardancy; the uniform nematic liquid crystal orientation structure of silicon carbide nanowire and Kevlar matrix effectively inhibits The phonon scattering generated by the interface thermal resistance between the matrix and the contact thermal resistance between the thermally conductive fillers builds a good thermal conduction path and endows the composite thermally conductive film with high thermal conductivity. The application prospect is broad.

Description

A kind of nematic liquid crystal alignment Kevlar/silicon carbide composite heat conduction film and preparation method thereof Method and application in thermal management of electronic devices

technical field

The invention belongs to the technical field of preparation of thermal interface materials, and in particular relates to a nematic liquid crystal oriented Kevlar/silicon carbide composite heat conduction film, a preparation method thereof, and an application in thermal management of electronic devices.

Background technique

With the miniaturization of electronic devices and the continuous increase of power density, thermal management has become an urgent and important research field for scientists today. Among numerous thermal management strategies, designing and fabricating thermal interface materials with excellent thermal conductivity and flame retardancy is an effective strategy to maintain the reliability of electronic devices and extend their service life. In the thermal management of electronic devices, flexible polymer materials are widely used due to their good processability, light weight and low cost. Among various polymers, Kevlar is one of the best candidate materials due to its excellent high strength, high modulus, thermal stability, electrical insulation and flame retardancy. However, due to the unsatisfactory thermal conductivity of Kevlar, its further application in the field of thermal management is limited.

From the point of view of heat conduction, thermally conductive filler is the main heat transfer medium, which can form the heat transfer path. Thermally conductive fillers include carbon-based fillers (graphene, carbon nanotubes, carbon fibers, carbon black, expanded graphite), metals (copper, silver), ceramics (boron nitride, silicon carbide, aluminum nitride, alumina) and their mixed thermal conductivity Fillers are widely used to improve the thermal conductivity of polymers. Insulating ceramics are the preferred fillers for improving thermal conductivity of Kevlar in electronic device applications. However, theoretically, ceramics (1-2000W m ^-1 K ^-1 ) have lower thermal conductivity than carbon-based fillers such as graphene (5300W m ^-1 K ^-1 ) and carbon nanotubes (3500W m ^-1 K -1 ) ^{. 1} ) etc. Therefore, it is also necessary to adjust the microstructure of the ceramic thermally conductive filler to obtain excellent thermal conductivity. Kevlar is a main chain liquid crystal polymer, and the arrangement of its molecular chain segments is ordered. When the ceramic thermally conductive filler has a nematic liquid crystal orientation structure consistent with Kevlar, the interface thermal resistance between the filler and the polymer matrix and the contact thermal resistance between the filler and the filler can be effectively reduced, thereby improving thermal conductivity. Silicon carbide has high thermal conductivity, flame retardancy and superhydrophobic properties, and is an excellent ceramic thermal conductive filler. Therefore, using silicon carbide as a thermally conductive filler to adjust the orientation distribution of silicon carbide so that it has a consistent nematic liquid crystal orientation with the Kevlar matrix, it is expected to construct a high thermal conductivity composite film material to achieve high integration and high power. Thermal management applications in electronics.

Contents of the invention

One of the objectives of the present invention is to provide a method for preparing a nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting film, which has simple steps and is convenient to operate.

The second object of the present invention is to provide the nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film prepared by the above-mentioned preparation method. The silicon carbide heat-conducting filler and the Kevlar matrix have a consistent nematic liquid crystal orientation and have excellent thermal conductivity.

The third object of the present invention is to provide the application of the above-mentioned nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting film in thermal management of electronic devices.

To achieve the above object, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a method for preparing a nematic liquid crystal oriented Kevlar/silicon carbide composite thermally conductive film, comprising the following steps:

(1) According to the mass ratio of Kevlar fibers, silicon carbide nanowires and concentrated sulfuric acid of 30:3 to 12:1000, weigh the Kevlar raw materials, silicon carbide nanowires and concentrated sulfuric acid respectively. In concentrated sulfuric acid, ultrasonically disperse evenly, and then dissolve Kevlar fibers in it under heating conditions to obtain a solute liquid crystal mixture of Kevlar/silicon carbide;

(2) uniformly coating the solute liquid crystal mixture obtained in step (1) on a glass plate by scraping, inducing and realizing the formation of a consistent nematic liquid crystal alignment structure of Kevlar and silicon carbide nanowires;

(3) Put the glass plate coated with the Kevlar/SiC solute liquid crystal mixture into water quickly, and undergo several times of liquid-solid phase separation to form a Kevlar/SiC composite film with a nematic liquid crystal orientation ;

(4) A dry nematic liquid crystal oriented Kevlar/silicon carbide composite film is obtained by hot pressing.

Preferably, the step of liquid-solid phase separation in step (3) is: performing liquid-solid phase separation in replaced deionized water for 3 to 5 times.

Preferably, the step of hot-pressing in step (4) is: hot-pressing in a vacuum oven, the temperature of hot-pressing is 40°C-60°C, the pressure is 7-9kPa, and the hot-pressing time is 6-7 hours.

Preferably, the heating condition in step (1) is 50°C to 60°C.

Preferably, the Kevlar fiber in step (1) is Kevlar 49 fiber.

Preferably, the silicon carbide nanowires in step (1) have a diameter of 100nm-600nm and a length of 50μm-100μm.

Preferably, the mass fraction of the concentrated sulfuric acid in step (1) is 98%.

In the second aspect, the present invention also provides a nematic liquid crystal oriented Kevlar/silicon carbide composite thermally conductive film prepared by the above preparation method.

In the nematic liquid crystal oriented Kevlar/silicon carbide composite thermally conductive film of the present invention, the thermally conductive filler and the Kevlar matrix have a consistent nematic liquid crystal orientation, which significantly reduces the interface thermal resistance between the thermally conductive filler-matrix and the filler- The contact thermal resistance between the fillers makes the heat conduction film of the present invention have higher lateral thermal conductivity in the in-plane direction.

In the third aspect, the present invention also provides the application of the above-mentioned nematic liquid crystal oriented Kevlar/silicon carbide composite heat conduction film in thermal management of electronic devices such as LED integrated lamps and thermoelectric power generation devices.

The nematic liquid crystal oriented Kevlar/silicon carbide composite heat conduction film material provided by the invention has excellent thermal conductivity, flexibility, thermal stability, hydrophobicity, mechanical strength and flame retardancy, and is suitable for high integration and high power Application requirements for thermal management of electronic devices.

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

(1) The composite thermal conductive film of the present invention includes Kevlar and silicon carbide nanowires, which have good flexibility, thermal stability, tensile strength, hydrophobicity and flame retardancy on the one hand; on the other hand, the thermal conductive filler silicon carbide nanowires The wire and the Kevlar matrix have a consistent nematic liquid crystal orientation structure, which effectively reduces the thermal resistance, so that the composite thermal conductive film of the present invention has better in-plane thermal conductivity at a lower filling density.

(2) The thermal conductivity of the thermally conductive composite film of the present invention can reach up to 10.16W m ^-1 K ^-1 , which is higher than that of commercial thermally conductive silica gel sheets, and has broad application prospects in the field of thermal management of electronic devices.

Description of drawings

Fig. 1 is a flow chart of the present invention for preparing a nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting film.

Fig. 2 is the nematic liquid crystal orientation KSM-1～KSM-4 and the pure Kevlar film KM of the nematic liquid crystal orientation KSM-1～KSM-4 that embodiment 1-4 makes: Fig. 2 (a) has Tyndall effect The Kevlar nematic lyotropic liquid crystal colloid; Figure 2(b) is the Kevlar/SiC mixed nematic lyotropic liquid crystal with different silicon carbide mass fractions; Figure 2(c) is the flexible pure Kevlar film KM and KSM-1～KSM-4 of nematic liquid crystal oriented Kevlar/SiC composite heat conduction films with different SiC contents.

Fig. 3 is the infrared spectrum (a), the XRD spectrum of the nematic phase liquid crystal alignment Kevlar/silicon carbide composite heat-conducting film KSM-1～KSM-4, pure Kevlar film KM and SiC that embodiment 1-4 makes (b), hydrophilic and hydrophobic analysis (c), thermogravimetric analysis (d), tensile strength analysis (e) and fire resistance analysis of KSM-4 (f).

Fig. 4 is the polarizing texture of the nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting films KSM-1-KSM-4 and the pure Kevlar film KM prepared in Examples 1-4.

Fig. 5 is a surface topography diagram of the nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting films KSM-1-KSM-4 and the pure Kevlar film KM prepared in Examples 1-4 under a scanning electron microscope.

Fig. 6 is the comparison and thermal conduction mechanism of the nematic phase liquid crystal oriented Kevlar/silicon carbide composite heat conduction film KSM-4 and the pure Kevlar film KM thermal conductivity obtained in Example 4: Fig. 6 (a) is the KSM- 4 and KM are placed on a 60°C hot stage at the same time as the infrared thermal image; Figure 6(b) is the change of the average temperature in the film over time when KSM-4 and KM are placed on a 60°C hot stage at the same time; Figure 6(c) is the thermal diffusivity, specific heat capacity, density and thermal conductivity values of KSM-4 and KM; Figure 6(d) is a schematic diagram of the heat conduction mechanism of KM and KSM-4.

Figure 7 is the thermal management application of Example 4 as a thermal interface material in an LED integrated lamp: Figure 7(a) is a schematic diagram of using a thermally conductive silica gel sheet as a thermal interface material for thermal management of an LED integrated lamp; Figure 7(b) is A schematic diagram of KSM-4 used as a thermal interface material for thermal management of LED integrated lamps; Figure 7(c) is the surface temperature of two different thermal interface materials LED integrated lamps continuously collected by the DAQ970A data acquisition system; Figure 7(d) is KSM- 4 is the infrared thermal image of the LED integrated lamp with thermal interface material and the LED integrated lamp with commercial silica gel as thermal interface material after lighting for 400 seconds.

Figure 8 is the thermal management application of Example 4 as a thermal interface material in a thermoelectric power generation device: Figure 8(a) is a schematic structural diagram of an assembled thermoelectric power generation device; Figure 8(b) is the operation process of an LED integrated lamp in a thermoelectric power generation device power generation situation.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

In the following examples, unless otherwise specified, the raw materials and reagents used are commercially available.

Example 1

A nematic liquid crystal oriented Kevlar/silicon carbide composite thermally conductive film KSM-1, the thermally conductive filler silicon carbide nanowire and Kevlar matrix have a consistent nematic liquid crystal oriented structure.

Among them, the raw material of Kevlar is Kevlar 49 fiber produced by DuPont. The diameter of silicon carbide nanowires is 100nm-600nm, the length is 50μm-100μm, the purity is 98%, and the mass fraction of concentrated sulfuric acid is 98%. The mass ratio of Kevlar 49, silicon carbide nanowires and concentrated sulfuric acid is 30:3:1000, that is, the mass fraction of the thermally conductive filler silicon carbide is 10%.

Prepare according to the flow process shown in Figure 1, the specific steps are as follows:

(1) According to the preferred mass ratio of Kevlar, silicon carbide nanowires and concentrated sulfuric acid of 30:3:1000, weigh Kevlar, silicon carbide nanowires and concentrated sulfuric acid respectively, and place the silicon carbide nanowires in In concentrated sulfuric acid, ultrasonically disperse evenly, and then dissolve Kevlar in it under heating conditions of 50-60°C to obtain a solute liquid crystal mixture of Kevlar/silicon carbide;

(2) The solute liquid crystal mixture is uniformly coated on the glass plate by scraping, so as to induce the formation of a consistent nematic liquid crystal alignment structure of Kevlar and silicon carbide nanowires;

(3) Put the glass plate coated with Kevlar/silicon carbide solute liquid crystal mixture into deionized water quickly, and perform liquid-solid phase separation in deionized water for 3 to 5 times to form Kevlar with nematic liquid crystal orientation. Pull/silicon carbide composite film;

(4) Carry out hot pressing in a vacuum drying oven. The hot pressing temperature is 60°C, the pressure is 7.84*10 ³ Pa, and the hot pressing time is 6 hours, and the dry nematic liquid crystal oriented Kevlar/silicon carbide can be obtained Composite film.

Example 2

A nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting film KSM-2, the heat-conducting filler silicon carbide nanowire and the Kevlar matrix have a consistent nematic liquid crystal oriented structure.

Among them, the raw material of Kevlar is Kevlar 49 fiber produced by DuPont. The diameter of silicon carbide nanowires is 100nm-600nm, the length is 50μm-100μm, the purity is 98%, and the mass fraction of concentrated sulfuric acid is 98%. The mass ratio of Kevlar 49, silicon carbide nanowires and concentrated sulfuric acid is 30:6:1000, that is, the mass fraction of the thermally conductive filler silicon carbide is 20%.

The preparation method is the same as in Example 1.

Example 3

A nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting film KSM-3, the heat-conducting filler silicon carbide nanowire and the Kevlar matrix have a consistent nematic liquid crystal oriented structure.

Among them, the raw material of Kevlar is Kevlar 49 fiber produced by DuPont. The diameter of silicon carbide nanowires is 100nm-600nm, the length is 50μm-100μm, the purity is 98%, and the mass fraction of concentrated sulfuric acid is 98%. The mass ratio of Kevlar 49, silicon carbide nanowires and concentrated sulfuric acid is 30:9:1000, that is, the mass fraction of the thermally conductive filler silicon carbide is 30%.

The preparation method is the same as in Example 1.

Example 4

A nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting film KSM-4, the heat-conducting filler silicon carbide nanowire and the Kevlar matrix have a consistent nematic liquid crystal oriented structure.

Among them, the raw material of Kevlar is Kevlar 49 fiber produced by DuPont Company, the diameter of silicon carbide nanowires is 100nm-600nm, the length is 50μm-100μm, the purity is 98%, and the mass fraction of concentrated sulfuric acid is 98%. The mass ratio of Kevlar 49, silicon carbide nanowires and concentrated sulfuric acid is 30:12:1000, that is, the mass fraction of the thermally conductive filler silicon carbide is 40%.

The preparation method is the same as in Example 1.

Fig. 2 is a physical picture of the nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting films KSM-1-KSM-4 and the pure Kevlar film KM prepared in Examples 1-4. Specifically, Figure 2(a) is a Kevlar nematic lyotropic liquid crystal colloid with Tyndall effect, and Figure 2(b) is a Kevlar/SiC mixed nematic lyotropic liquid crystal with different silicon carbide mass fractions , Figure 2(c) is the flexible pure Kevlar film KM and the nematic liquid crystal orientation Kevlar/silicon carbide composite thermally conductive film KSM-1～KSM-4 with different silicon carbide content.

Fig. 3(a) is the infrared spectrum of the nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting films KSM-1-KSM-4, pure Kevlar films KM and SiC prepared in Examples 1-4. It can be seen from Fig. 3(a) that the peaks of SiC at 927cm ^-1 and 801cm ^-1 are attributed to the vibration absorption peaks of Si-C single bond. The 3312cm ^-1 and 1545cm ^-1 vibrational absorption peaks are attributed to the NH single bond in the Kevlar membrane KM, the 1400cm ^-1 vibrational absorption peak is attributed to the CN single bond in KM, and the 1651cm ^-1 vibrational absorption peak is attributed to the C in KM ＝O single bond, 1606cm ^-1 and 1513cm ^-1 vibrational absorption peaks belong to Ar- in KM. The above-mentioned characteristic peaks of SiC and KM all appear in the infrared spectra of KSM-1-KSM-4, which proves that KSM-1-KSM-4 of Examples 1-4 conform to the design.

Figure 3(b) is the XRD spectrum of KM and KSM-1~KSM-4. From the XRD data in Figure 3(b), it can be seen that KM has a wide absorption peak in the wide-angle region near 2θ=18°, and there is no sharp peak related to smectic liquid crystals in the small-angle region, so KM has a nematic Phase liquid crystal alignment structure. The XRD patterns of KSM-1～KSM-4 not only have obvious SiC diffraction peaks at 35.9°, 60.3° and 72.4°, which correspond to the (111), (220) and (311) crystal planes of SiC, but also have KM Broad absorption peak around 2θ=18°. The above results show that KSM-1 to KSM-4 of Examples 1-4 also have a nematic liquid crystal alignment structure.

Fig. 3(c) is the hydrophilic-hydrophobic analysis of KM and KSM-1-KSM-4. Figure 3(c) shows the contact angle data of water droplets falling on KM and KSM-1~KSM-4. The hydrophobicity of SiC makes the contact angles of KSM-1~KSM-4 larger than KM (CA=90.1°). It shows that KSM-1 to KSM-4 of Examples 1-4 are all hydrophobic.

Fig. 3(d) is the thermogravimetric analysis curves of KM and KSM-1～KSM-4. It can be seen from Fig. 3(d) that the initial decomposition temperature of KSM-1～KSM-4 is higher than that of KM. The pyrolysis of KM mainly occurs at about 490-570 °C, while that of KSM-1~KSM-4 mainly occurs at about 540-620 °C, indicating that SiC nanowires enhance the thermal stability of KSM-1~KSM-4 . Similarly, due to the good thermal stability of SiC, in KSM-1~KSM-4, the residual rate is also proportional to the mass fraction of SiC. Figure 3(d) also plots the temperature at the maximum weight loss rate. The temperature at the maximum weight loss rate of KM is about 547°C, and the temperature at the maximum weight loss rate of KSM-1~KSM-4 is about 600°C, which also shows that SiC has a positive effect on the thermal stability of the composite heat-conducting film. According to the thermogravimetric analysis curve, it can be known that the KSM-1-KSM-4 composite heat-conducting films of Examples 1-4 have good thermal stability.

Figure 3(e) is the stress-strain curves of KM and KSM-1～KSM-4. As shown in the figure, the strains of all the samples are above 55%, and the stresses are around 40-60MPa, indicating that the KSM-1-KSM-4 composite heat-conducting films of Examples 1-4 have good mechanical properties.

Figure 3(f) is an illustration of the flame retardancy of the thermally conductive composite film represented by KSM-4. Ignite KSM-4 with a flame, KSM-4 will be ignited after 0.4s contact with the flame, and KSM-4 will be extinguished immediately when the fire source is withdrawn. Figure 3(f) is the self-extinguishing image of KSM-4 after being ignited for 1s, 2.5s, 3.5s, 4.7s, 5.8s, 7s, and 13s and then evacuated from the fire source. The black part is carbonized Kevlar, flame-retardant The gray part is the SiC skeleton of the thermally conductive filler. It shows that the composite heat conduction film of the present invention has flame retardancy.

Fig. 4 is the polarizing texture of the nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting films KSM-1-KSM-4 and the pure Kevlar film KM prepared in Examples 1-4. It can be seen that the polarizing texture of KM is a typical nematic liquid crystal stripe texture, while the polarizing textures of KSM-1 to KSM-4 in Examples 1-4 are also nematic stripe textures, indicating that the 1-4 have a nematic liquid crystal alignment structure.

Fig. 5 is a surface topography diagram of the nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting films KSM-1-KSM-4 and the pure Kevlar film KM prepared in Examples 1-4 under a scanning electron microscope. It can be seen that the surface morphology of KM is regular and uniform, and the SiC nanowires are uniformly distributed in the Kevlar liquid crystal matrix in Examples 1-4. When the mass fraction of SiC nanowires in Examples 1-4 increases from 10% to 40%, the SiC nanowires in Examples 1-4 all have a consistent liquid crystal orientation.

Fig. 6 is the comparison and thermal conduction mechanism of the nematic liquid crystal oriented Kevlar/silicon carbide composite heat conduction film KSM-4 and the pure Kevlar film KM prepared in Example 4. In order to visually illustrate the difference in thermal conductivity, KM and KSM-4 with the same size (20 mm × 30 mm) were placed on the same hot stage at 60 °C. The in-plane temperature changes of KM and KSM-4 were captured by infrared cameras.

Figure 6(a) is an infrared thermal image of KSM-4 and KM simultaneously placed on a 60°C hot stage and heated for 1s, 15s, 30s, 45s, 60s and 90s.

Fig. 6 (b) is that KSM-4 and KM are placed on 60 ℃ of hot stages simultaneously and are heated 1s, 15s, 30s, 45s, 60s and 90s in-plane mean plane temperature figure, illustrate that the KSM-4 of embodiment 4 has relatively Good thermal conductivity.

Figure 6(c) is the thermal diffusivity, specific heat capacity, density and thermal conductivity values of KSM-4 and KM. It can be seen from Fig. 6(c) that compared with KM, the thermal conductivity and thermal diffusivity of KSM-4 are respectively increased to 10.16W m ^-1 K ^-1 , 7.35×10 ^-6 m ² /s, compared with KM , the thermal conductivity increased nearly 4 times.

Compared with KM, KSM-4 has a higher thermal conductivity, and its mechanism diagram is shown in Figure 6(d). The specific reasons are analyzed as follows. First, KSM-4 forms a SiC-SiC heat conduction path, making the heat flow along the SiC - SiC path transmission, thereby improving thermal conductivity; another reason is that SiC nanowires and Kevlar matrix have a consistent nematic liquid crystal orientation, which can suppress phonon scattering to increase heat transfer and reduce SiC and Kevlar Interfacial thermal resistance between substrates; the third reason is that the silicon carbide nanowires used in the present invention have a higher intrinsic aspect ratio, and there are relatively few contact nodes between the thermally conductive filler and the substrate, so the contact thermal resistance is also relatively Less, thus greatly improving the thermal conductivity of KSM-4.

Application 1: The thermal management application of the composite heat conducting film KSM-4 prepared in Example 4 as a thermal interface material in an LED integrated lamp.

As we all know, electronic equipment generates a lot of heat during operation. Efficient heat dissipation not only ensures the safe and efficient operation of electronic equipment, but also prolongs the service life of electronic equipment. The thermal interface material between the LED integrated lamp and the heat sink is the key medium for transferring the heat generated by the LED integrated lamp to the heat sink. In order to evaluate the application of KSM-4 in thermal management, KSM-4 composite heat conduction film was used as a thermal interface material in LED integrated lamps to investigate its thermal management ability under actual application conditions.

Equipment: LED integrated lamp, model ZZGD-20W, commercial heat-conducting silicone sheet with a thermal conductivity of 4W m ^-1 K ^-1 , and KSM-4 with a thermal conductivity of 10.16W m ^-1 K ^-1 .

Application effect: Place KSM-4 and a commercial silicone sheet of the same lateral size between the LED integrated lamp and the aluminum heat sink respectively. The LED integrated lamp and thermal interface material are fixed on the aluminum heat sink with four screws, as shown in Figure 7(a) and Figure 7(b). LED lights start working at room temperature. The DAQ970A data acquisition system is used to continuously collect the surface temperature of the LED integrated lamp, which visually demonstrates the heat dissipation capability of the KSM-4. The steady-state average temperature of the LED integrated lamp with KSM-4 as the thermal interface material after lighting for 400s is 131°C, and the steady-state average temperature of the LED integrated lamp with commercial heat-conducting silicone sheet as the thermal interface material after lighting for 400s is 140°C , the average temperature difference can reach 9°C, as shown in Figure 7(c). The infrared thermal imaging camera also took the infrared thermal images of the LED integrated lamps with KSM-4 and commercial heat-conducting silica gel sheets as thermal interface materials after lighting for 400s. It can also be clearly seen from the infrared thermal images of the two. Example 4 of the present invention has more excellent thermal conductivity, as shown in FIG. 7( d ).

Application 2: The thermal management application of the composite heat conducting film KSM-4 prepared in Example 4 as a thermal interface material in a thermoelectric power generation device.

In order to further verify the excellent thermal management capability of Example 4 of the present invention, KSM-4 was also used in thermoelectric conversion devices.

Equipment: temperature difference generator (TEP1-142T300, 40mm×44mm), KSM-4, LED integrated lamp (ZZGD-20W), aluminum radiator.

Application effect: When there is a temperature difference between the two sides of the thermoelectric generator, current can be generated. Based on the working principle of the thermoelectric generator, the temperature difference generator (TEP1-142T300, 40mm×44mm), KSM-4, and LED integrated lamp (ZZGD -20W), aluminum heat sink assembled into a thermoelectric power generation device, as shown in Figure 8(a). When the LED integrated lamp is running, a large amount of waste heat will be generated, forming a high-temperature surface on one side of the thermoelectric power sheet; due to the good thermal conductivity of KSM-4, KSM-4 can transfer the heat generated by the LED integrated lamp to the aluminum In the radiator, a low-temperature surface is formed on the other side of the thermoelectric sheet. Therefore, an ideal temperature difference is formed on both sides of the thermoelectric power sheet to generate electricity. Figure 8(b) shows the power generation of the LED integrated lamp in the thermoelectric power generation device during operation. Specifically: when the LED integrated lamp runs for 8 seconds, the thermoelectric generator starts to generate a current of 0.8mA; when it continues to run for 150 seconds, the current stabilizes at about 76mA. By fitting time and current, it can be calculated that the LED integrated lamp generates 27.5 coulombs of electricity (Q ₁ area in Figure 8b) when it runs for 400 seconds. Because KSM-4 has good thermal management ability, after the LED integrated lamp stops running, the film can still transfer waste heat within 260 seconds, so that the thermoelectric module continues to generate 3.0 coulombs of electricity (Q ₂ area in Figure 8b). The results show that KSM-4 has outstanding thermal management ability.

Claims (8)

1. A preparation method of a nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film is characterized by comprising the following steps:

(1) Respectively weighing the Kevlar fiber, the silicon carbide nanowire and concentrated sulfuric acid according to the mass ratio of 30:3 to 12:1000 of the Kevlar fiber, the silicon carbide nanowire and the concentrated sulfuric acid, firstly placing the silicon carbide nanowire in the concentrated sulfuric acid, uniformly dispersing the silicon carbide nanowire in an ultrasonic mode, and then dissolving the Kevlar fiber in the concentrated sulfuric acid under a heating condition to obtain a solute liquid crystal mixture of Kevlar/silicon carbide; the diameter of the silicon carbide nanowire is 100nm to 600nm, and the length of the silicon carbide nanowire is 50 mu m to 100 mu m;

(2) Uniformly coating the solute liquid crystal mixture obtained in the step (1) on a glass plate by adopting a blade coating method, and inducing to realize that the Kevlar fiber and the silicon carbide nanowire form a consistent nematic liquid crystal orientation structure;

(3) Quickly putting the glass plate coated with the Kevlar/silicon carbide solute liquid crystal mixture into water, and performing liquid-solid phase separation for multiple times to form a Kevlar/silicon carbide composite heat-conducting film with nematic phase liquid crystal orientation;

(4) Obtaining a dry nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film by adopting a hot-pressing method; the hot pressing comprises the following steps: hot pressing in a vacuum drying oven at a temperature of 40 deg.C ^o C~60 ^o C, the pressure is 7 to 9kPa, and the hot pressing time is 6 to 7 hours.

2. The method for preparing a nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film according to claim 1, wherein the liquid-solid phase separation in the step (3) comprises the following steps: and performing liquid-solid phase separation in the replaced deionized water for 3 to 5 times.

3. The method for preparing a nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film according to claim 1, wherein the heating condition in the step (1) is 50 ^o C~60 ^o C。

4. The method for preparing the nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film according to claim 1, wherein Kevlar 49 fiber is adopted as the Kevlar fiber in the step (1).

5. The method for preparing a nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film according to claim 1, wherein the mass fraction of the concentrated sulfuric acid in the step (1) is 98%.

6. The nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film prepared by the preparation method of any one of claims 1 to 5.

7. Use of a nematic liquid crystal oriented kevlar/silicon carbide composite heat conductive film as defined in claim 6 in the thermal management of electronic devices.

8. Use according to claim 7, wherein the electronic device is an LED integrated lamp or a thermoelectric device.

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