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
Nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film, preparation method thereof and application thereof in electronic device heat management Download PDFInfo
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Abstract
The invention discloses a nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting film, a preparation method thereof and application thereof in electronic device heat management. The composite heat-conducting film prepared by the invention has good flexibility, thermal stability, tensile strength, hydrophobicity and flame retardance; the consistent nematic liquid crystal orientation structure of the silicon carbide nanowires and the Kevlar matrix effectively inhibits phonon scattering generated by interface thermal resistance between the heat-conducting filler and the matrix and contact thermal resistance between the heat-conducting filler, constructs a good heat-conducting path, endows the composite heat-conducting film with higher heat conductivity, and has wide application prospect in the aspect of heat dissipation of high-power and high-integration-degree electronic devices.
Description
Technical Field
The invention belongs to the technical field of thermal interface material preparation, and particularly relates to a nematic liquid crystal oriented Kevlar/silicon carbide composite heat-conducting film, a preparation method thereof and application thereof in electronic device thermal management.
Background
With the miniaturization of electronic device volumes and the ever-increasing power density, thermal management is an urgent and important area of research for today's scientists. Among the numerous thermal management strategies, the design and fabrication of thermal interface materials with excellent thermal conductivity and flame retardancy is an effective strategy to maintain the reliability and extend the useful life of electronic devices. In the heat management of electronic devices, flexible polymer materials are widely used because of their good processability, light weight and low cost. Among various polymers, kevlar has excellent high strength, high modulus, thermal stability, electrical insulation and flame retardancy, and is one of the best candidate materials. However, since the thermal conductivity of kevlar has been less than ideal, it has limited further applications in the field of thermal management.
From the perspective of heat conduction, the heat conductive filler is the main heat conductive medium and can form a heat transfer path. The heat-conducting filler comprises carbon-based fillers (graphene, carbon nanotubes, carbon fibers, carbon black, expanded graphite), metals (copper, silver), ceramics (boron nitride, silicon carbide, aluminum nitride, aluminum oxide) and mixed heat-conducting fillers thereof, and is widely used for improving the heat-conducting property of polymers. In electronic applications, insulating ceramics are the preferred filler to improve kevlar thermal conductivity. However, in theory, ceramics (1-2000W m) -1 K -1 ) Has a thermal conductivity lower than that of carbon-based fillers such as graphene (5300W m) -1 K -1 ) And carbon nanotubes (3500W m) -1 K -1 ) Etc., therefore, it is also required to adjust the microstructure of the ceramic heat conductive filler to obtain excellent heat conductive properties. Kevlar is a backbone liquid crystalline polymer whose molecular segments are aligned in an orderly fashion. When the ceramic heat-conducting filler has a nematic liquid crystal orientation structure consistent with Kevlar, the interface thermal resistance between the filler and a polymer matrix and the contact thermal resistance between the filler and the filler can be effectively reduced, so that the heat-conducting property is improved. The silicon carbide has high thermal conductivity, flame retardant property and super-hydrophobic property, and is an excellent ceramic heat-conducting filler. Therefore, the silicon carbide is used as the heat-conducting filler, the orientation distribution of the silicon carbide is adjusted, the silicon carbide and the Kevlar matrix have the consistent nematic liquid crystal orientation, and the high-heat-conducting composite film material is expected to be constructed, so that the heat management application of the silicon carbide in high-integration and high-power electronic devices is realized.
Disclosure of Invention
One of the purposes of the invention is to provide a preparation method of a nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film, which has simple steps and convenient operation.
The second purpose of the invention is to provide the nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film prepared by the preparation method, and the silicon carbide heat-conducting filler and the Kevlar matrix have the consistent nematic liquid crystal orientation and excellent heat-conducting performance.
The invention also aims to provide the application of the nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film in the heat management of electronic devices.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a preparation method of a nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film, which comprises the following steps:
(1) Respectively weighing a Kevlar raw material, a silicon carbide nanowire and concentrated sulfuric acid according to the mass ratio of 30-12 of the Kevlar fiber to the silicon carbide nanowire to 1000, placing the silicon carbide nanowire in the concentrated sulfuric acid, uniformly dispersing the silicon carbide nanowire in an ultrasonic mode, and dissolving the Kevlar fiber in the concentrated sulfuric acid under a heating condition to obtain a Kevlar/silicon carbide solute liquid crystal mixture;
(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 the Kevlar and the silicon carbide nanowires to 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 film with nematic liquid crystal orientation;
(4) And (3) obtaining the dry nematic liquid crystal orientation Kevlar/silicon carbide composite film by adopting a hot pressing method.
Preferably, the step of liquid-solid phase separation in step (3) is: liquid-solid phase separation is carried out 3-5 times in the replaced deionized water.
Preferably, the step of hot pressing of step (4) is: hot pressing in a vacuum drying oven at 40-60 deg.c and 7-9 kPa for 6-7 hr.
Preferably, the heating in step (1) is carried out at a temperature of 50 ℃ to 60 ℃.
Preferably, kevlar 49 fiber is adopted as the Kevlar fiber in the step (1).
Preferably, the diameter of the silicon carbide nanowire in the step (1) is 100nm to 600nm, and the length is 50 μm to 100 μm.
Preferably, the mass fraction of the concentrated sulfuric acid in the step (1) is 98%.
In a second aspect, the invention further provides the nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film prepared by the preparation method.
In the nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film, the heat-conducting filler and the Kevlar matrix have consistent nematic liquid crystal orientation, so that the interface thermal resistance between the heat-conducting filler and the matrix and the contact thermal resistance between the filler and the filler are obviously reduced, and the heat-conducting film has higher transverse heat conductivity in the in-plane direction.
In a third aspect, the invention also provides application of the nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film in heat management of electronic devices such as LED integrated lamps and thermoelectric power generation devices.
The nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film material provided by the invention has excellent heat-conducting property, flexibility, thermal stability, hydrophobicity, mechanical strength and flame retardance, and is suitable for the application requirements of high-integration-level and high-power electronic device heat management.
Compared with the prior art, the invention has the following beneficial effects:
(1) The composite heat-conducting film comprises Kevlar and silicon carbide nanowires, and has good flexibility, thermal stability, tensile strength, hydrophobicity and flame retardance on one hand; on the other hand, the heat-conducting filler silicon carbide nanowires and the Kevlar matrix have the consistent nematic liquid crystal orientation structure, so that the thermal resistance is effectively reduced, and the composite heat-conducting film disclosed by the invention has better in-plane heat-conducting property under the condition of lower filling density.
(2) The heat conductivity of the heat-conducting composite film can reach 10.16W m at most -1 K -1 Higher than commercial heat-conducting silica gel sheet, in electricityThe method has wide application prospect in the field of heat management of the sub-devices.
Drawings
FIG. 1 is a flow chart of the present invention for preparing a nematic liquid crystal orientation Kevlar/silicon carbide composite heat-conducting film.
FIG. 2 shows the nematic liquid crystal alignment Kevlar/silicon carbide composite heat conductive films KSM-1 to KSM-4 and pure Kevlar films KM prepared in examples 1 to 4: FIG. 2 (a) is a Kevlar nematic lyotropic liquid crystal gel having the Tyndall effect; FIG. 2 (b) is a Kevlar/silicon carbide mixed nematic phase lyotropic liquid crystal of different silicon carbide mass fractions; FIG. 2 (c) shows a flexible pure Kevlar film KM and nematic phase liquid crystal orientation Kevlar/silicon carbide composite heat-conductive films KSM-1 to KSM-4 with different silicon carbide contents.
FIG. 3 shows IR spectra (a), XRD spectra (b), hydrophilicity/hydrophobicity analyses (c), thermogravimetric analyses (d), tensile strength analyses (e), and fire resistance analyses (f) of the nematic liquid crystal alignment Kevlar/silicon carbide composite heat conductive films KSM-1 to KSM-4, pure Kevlar films KM and SiC obtained in examples 1 to 4.
FIG. 4 shows the polarization textures of the nematic liquid crystal oriented Kevlar/silicon carbide composite heat conductive films KSM-1 to KSM-4 and the pure Kevlar film KM obtained in examples 1 to 4.
FIG. 5 is a surface topography under a scanning electron microscope of nematic liquid crystal orientation Kevlar/silicon carbide composite heat conductive films KSM-1 to KSM-4 and pure Kevlar films KM prepared in examples 1 to 4.
FIG. 6 shows the comparison of thermal conductivity between the nematic liquid crystal oriented Kevlar/silicon carbide composite thermal conductive film KSM-4 and pure Kevlar film KM prepared in example 4 and the thermal conductivity mechanism: FIG. 6 (a) is an infrared thermal image of KSM-4 and KM simultaneously placed on a 60 ℃ hot stage as a function of time; FIG. 6 (b) is a graph showing the average temperature in films as a function of time when KSM-4 and KM are placed on a 60 ℃ hot stage at the same time; FIG. 6 (c) is the values of thermal diffusivity, specific heat capacity, density and thermal conductivity for KSM-4 and KM; FIG. 6 (d) is a schematic diagram of the heat transfer mechanism of KM and KSM-4.
Fig. 7 is a thermal management application of example 4 as a thermal interface material in an LED integrated lamp: FIG. 7 (a) is a schematic diagram of a thermally conductive silicone sheet as a thermal interface material for LED integrated lamp thermal management; FIG. 7 (b) is a schematic illustration of KSM-4 as a thermal interface material for thermal management of an LED integrated lamp; FIG. 7 (c) shows that the DAQ970A data acquisition system continuously acquires the surface temperatures of two different thermal interface material LED integrated lamps; FIG. 7 (d) is an infrared thermography of an LED integrated lamp with KSM-4 as a thermal interface material and an LED integrated lamp with commercial silica gel as a thermal interface material after 400 seconds of illumination.
Fig. 8 is the thermal management application of example 4 as a thermal interface material in a thermoelectric device: fig. 8 (a) is a schematic structural view of an assembled thermoelectric power generating device; fig. 8 (b) is a power generation amount situation during the operation of the LED integrated lamp in the thermoelectric generation device.
Detailed Description
The invention is described in further detail below with reference to the figures and the specific embodiments.
In the following examples, the starting materials and reagents used were all commercially available products unless otherwise specified.
Example 1
A Kevlar/silicon carbide composite heat-conducting film KSM-1 with nematic liquid crystal orientation is disclosed, wherein the heat-conducting filler silicon carbide nano-wires and the Kevlar matrix have a consistent nematic liquid crystal orientation structure.
Wherein, the Kevlar 49 fiber produced by DuPont is used as the Kevlar raw material, the diameter of the silicon carbide nanowire is 100 nm-600 nm, the length is 50 μm-100 μm, the purity is 98%, and the mass fraction of the concentrated sulfuric acid is 98%. The mass ratio of the Kevlar 49 to the silicon carbide nanowires to the concentrated sulfuric acid is 30.
The preparation is carried out according to the flow shown in figure 1, and the specific steps are as follows:
(1) Respectively weighing Kevlar, silicon carbide nanowires and concentrated sulfuric acid according to the preferable mass ratio of 30;
(2) Uniformly coating the solute liquid crystal mixture on a glass plate by adopting a blade coating method so as to induce the Kevlar and the silicon carbide nanowires to 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 deionized water, and carrying out liquid-solid phase separation in the deionized water for 3-5 times to form a Kevlar/silicon carbide composite membrane with nematic liquid crystal orientation;
(4) Hot pressing in a vacuum drying oven at 60 deg.C under 7.84 × 10 3 Pa, and the hot pressing time is 6 hours, thus obtaining the dry nematic liquid crystal orientation Kevlar/silicon carbide composite film.
Example 2
A nematic liquid crystal orientation Kevlar/silicon carbide composite heat conduction film KSM-2 is provided, wherein the heat conduction filler silicon carbide nano wire and the Kevlar matrix have a consistent nematic liquid crystal orientation structure.
Wherein, the Kevlar 49 fiber produced by DuPont is used as the Kevlar raw material, the diameter of the silicon carbide nanowire is 100 nm-600 nm, the length is 50 μm-100 μm, the purity is 98%, and the mass fraction of the concentrated sulfuric acid is 98%. The mass ratio of the Kevlar 49 to the silicon carbide nanowires to the concentrated sulfuric acid is 30.
The preparation method is the same as example 1.
Example 3
A nematic liquid crystal orientation Kevlar/silicon carbide composite heat conduction film KSM-3 is provided, wherein the heat conduction filler silicon carbide nano wire and the Kevlar matrix have a consistent nematic liquid crystal orientation structure.
Wherein, the Kevlar raw material is Kevlar 49 fiber produced by DuPont, the diameter of the silicon carbide nanowire is 100 nm-600 nm, the length is 50 μm-100 μm, the purity is 98%, and the mass fraction of the concentrated sulfuric acid is 98%. The mass ratio of the Kevlar 49 to the silicon carbide nanowires to the concentrated sulfuric acid is 30.
The preparation method is the same as example 1.
Example 4
A Kevlar/silicon carbide composite heat-conducting film KSM-4 with nematic liquid crystal orientation is disclosed, wherein the heat-conducting filler silicon carbide nano-wires and the Kevlar matrix have a consistent nematic liquid crystal orientation structure.
Wherein, the Kevlar 49 fiber produced by DuPont is used as the Kevlar raw material, the diameter of the silicon carbide nanowire is 100 nm-600 nm, the length is 50 μm-100 μm, the purity is 98%, and the mass fraction of the concentrated sulfuric acid is 98%. The mass ratio of the Kevlar 49 to the silicon carbide nanowires to the concentrated sulfuric acid is 30.
The preparation method is the same as example 1.
FIG. 2 is a schematic diagram of the nematic liquid crystal alignment Kevlar/silicon carbide composite heat conductive films KSM-1 to KSM-4 and the pure Kevlar film KM obtained in examples 1 to 4. Specifically, FIG. 2 (a) shows a Kevlar nematic phase lyotropic liquid crystal colloid having the Tyndall effect, FIG. 2 (b) shows Kevlar/SiC mixed nematic phase lyotropic liquid crystals having different SiC mass fractions, and FIG. 2 (c) shows a flexible pure Kevlar film KM and nematic phase liquid crystal oriented Kevlar/SiC composite heat conductive films KSM-1 to KSM-4 having different SiC contents.
FIG. 3 (a) is an IR spectrum of a nematic liquid crystal oriented Kevlar/silicon carbide composite heat conductive film KSM-1 to KSM-4, a pure Kevlar film KM and SiC obtained in example 1-4. As can be seen from FIG. 3 (a), siC was 927cm -1 And 801cm -1 The peak at (A) is assigned to the vibration absorption peak of the Si-C single bond. 3312cm -1 ， 1545cm -1 The vibration absorption peak is attributed to the N-H single bond in the Kevlar film KM, 1400cm -1 The vibration absorption peak belongs to the C-N single bond in KM, 1651cm -1 The vibration absorption peak belongs to C = O single bond, 1606cm in KM -1 And 1513cm -1 The vibration absorption peak was ascribed to Ar-in KM. The above characteristic peaks of both SiC and KM appeared in the IR spectra of KSM-1 to KSM-4, confirming that KSM-1 to KSM-4 of example 1-4 were satisfactory in design.
FIG. 3 (b) is an XRD spectrum of KM and KSM-1 to KSM-4. As can be seen from the XRD data in fig. 3 (b), KM has a broad absorption peak in the wide-angle region around 2 θ =18 °, and a sharp peak associated with smectic liquid crystal does not occur in the small-angle region, so KM has a nematic liquid crystal alignment structure. The XRD patterns of KSM-1 to KSM-4 not only have obvious diffraction peaks of SiC at 35.9 degrees, 60.3 degrees and 72.4 degrees, which correspond to the (111), (220) and (311) crystal planes of SiC, but also simultaneously have wide absorption peaks of KM near 2 theta =18 degrees. As a result, KSM-1 to KSM-4 of examples 1 to 4 also had a nematic liquid crystal alignment structure.
FIG. 3 (c) shows the hydropathic/hydrophobic analyses of KM and KSM-1 to KSM-4. In FIG. 3 (c), it can be seen that water drops fall on the contact angle data of KM and KSM-1 to KSM-4, and that the hydrophobicity of SiC is such that the contact angles of KSM-1 to KSM-4 are larger than KM (CA =90.1 °), indicating that KSM-1 to KSM-4 of examples 1 to 4 are all hydrophobic.
FIG. 3 (d) is a thermogravimetric analysis curve of KM and KSM-1 to KSM-4. As can be seen from FIG. 3 (d), KSM-1 to KSM-4 have an initial decomposition temperature higher than KM. The pyrolysis of KM mainly occurs at about 490-570 ℃, and the pyrolysis of KSM-1 to KSM-4 mainly occurs at about 540-620 ℃, which shows that the SiC nanowires enhance the thermal stability of KSM-1 to KSM-4. Similarly, the residual ratio is proportional to the mass fraction of SiC in KSM-1 to KSM-4 because of the good thermal stability of SiC. Fig. 3 (d) also plots the temperature at the maximum rate of weight loss. The temperature under the KM maximum weight loss rate is about 547 ℃, and the temperature under the KSM-1-KSM-4 maximum weight loss rate is about 600 ℃, which also shows that SiC has positive promotion effect on the thermal stability of the composite heat conducting membrane. It can be known from thermogravimetric analysis curves that the KSM-1 to KSM-4 composite heat conductive films of examples 1 to 4 have good thermal stability.
FIG. 3 (e) is a stress-strain curve of KM, KSM-1 to KSM-4. As shown in the figure, the strain of all samples is over 55 percent, and the stress is about 40-60MPa, which indicates that the KSM-1 to KSM-4 composite heat-conducting film of the embodiment 1-4 has good mechanical property.
FIG. 3 (f) is a diagram illustrating the flame retardancy of a thermally conductive composite film represented by KSM-4. The KSM-4 is ignited by flame, the KSM-4 is ignited after contacting with the flame for 0.4s, and the KSM-4 is immediately extinguished when the fire source is removed. FIG. 3 (f) is a self-extinguishing image of KSM-4 ignited for 1s, 2.5s, 3.5s, 4.7s, 5.8s, 7s, 13s after being removed from the fire source, the black part is carbonized Kevlar, and the flame-retardant gray part is a heat-conducting filler SiC skeleton. The composite heat-conducting film has flame retardance.
FIG. 4 shows the polarization textures of the nematic liquid crystal alignment Kevlar/silicon carbide composite heat conductive films KSM-1 to KSM-4 and the pure Kevlar film KM obtained in examples 1 to 4. It can be seen that the polarization texture of KM is a typical fringe texture of nematic liquid crystal, while the polarization textures of KSM-1 to KSM-4 of examples 1 to 4 are also nematic fringe textures, indicating that examples 1 to 4 have a nematic liquid crystal alignment structure.
FIG. 5 is a surface topography of the nematic liquid crystal oriented Kevlar/silicon carbide composite heat conductive films KSM-1 to KSM-4 and pure Kevlar films KM prepared in examples 1 to 4 under a scanning electron microscope. It can be seen that the surface topography of KM is regular and uniform, and the SiC nanowires in examples 1-4 are uniformly distributed in the kevlar liquid crystal matrix. The SiC nanowires of examples 1-4 all had a consistent liquid crystal orientation when the mass fraction of the SiC nanowires of examples 1-4 was increased from 10% to 40%.
FIG. 6 is a comparison of thermal conductivity between the nematic liquid crystal oriented Kevlar/silicon carbide composite thermal conductive film KSM-4 and a pure Kevlar film KM prepared in example 4 and a thermal conductive mechanism. To visually illustrate the difference in thermal conductivity, KM and KSM-4 having the same size (20 mm. Times.30 mm) were placed on the same hot stage at 60 ℃. And (3) shooting the in-plane temperature change of the KM and the KSM-4 by using an infrared camera.
FIG. 6 (a) is an infrared thermography image of KSM-4 and KM heated on a 60 ℃ hot stage for 1s, 15s, 30s, 45s, 60s and 90s at the same time.
FIG. 6 (b) is an in-plane average planar temperature plot of KSM-4 and KM heated on a 60 ℃ hot stage for 1s, 15s, 30s, 45s, 60s and 90s, illustrating the superior thermal conductivity of KSM-4 of example 4.
FIG. 6 (c) is the values of thermal diffusivity, specific heat capacity, density and thermal conductivity for KSM-4 and KM. As can be seen from FIG. 6 (c), the thermal conductivity and thermal diffusivity of KSM-4 were respectively improved to 10.16W m as compared with KM -1 K -1 ， 7.35×10 -6 m 2 In contrast to KM, the thermal conductivity increased by a factor of approximately 4.
Compared with KM and KSM-4, the heat conductivity is higher, the mechanism diagram is shown in FIG. 6 (d), and the specific reason is analyzed as follows, firstly, the KSM-4 forms a SiC-SiC heat conduction path, so that heat flow is transmitted along the SiC-SiC path, and the heat conductivity is improved; the other reason is that the SiC nanowires and the Kevlar matrix have the same nematic liquid crystal orientation, so that phonon scattering can be inhibited to increase heat transfer, and the interface thermal resistance between the SiC nanowires and the Kevlar matrix is reduced; the third reason is that the silicon carbide nanowires used in the present invention have a high intrinsic aspect ratio, and the contact junction between the thermally conductive filler and the matrix is relatively small, and thus the contact thermal resistance is also relatively small, thereby greatly improving the thermal conductivity of KSM-4.
Application 1: the composite heat conducting film KSM-4 prepared in the example 4 is used as a thermal interface material for thermal management application in an LED integrated lamp.
It is well known that electronic devices generate a large amount of heat during operation. The efficient heat diffusion not only ensures the safe and efficient operation of the electronic equipment, but also prolongs the service life of the electronic equipment. The thermal interface material between the LED integrated lamp and the heat sink is a key medium for transferring heat generated by the LED integrated lamp to the heat sink. In order to evaluate the application of KSM-4 in heat management, the KSM-4 composite heat conducting film is used as a thermal interface material in an LED integrated lamp to examine the heat management capability under the actual application condition.
Equipment: the LED integrated lamp has the model of ZZGD-20W and the thermal conductivity of 4W m -1 K -1 The commercial heat-conducting silica gel sheet has the heat conductivity of 10.16W m -1 K -1 KSM-4 of (1).
The application effect is as follows: KSM-4 and a commercial silicone sheet of the same lateral dimensions were placed between the LED integrated lamp and the aluminum heat sink, respectively. The LED integrated lamp and the thermal interface material were fixed to an aluminum heat sink with four screws, as shown in fig. 7 (a) and 7 (b). The LED lamp starts to operate at room temperature. The DAQ970A data acquisition system is used for continuously acquiring the surface temperature of the LED integrated lamp, and the heat dissipation capacity of the KSM-4 is intuitively displayed. The steady-state average temperature of the LED integrated lamp taking KSM-4 as the thermal interface material after being illuminated for 400s is 131 ℃, the steady-state average temperature of the LED integrated lamp taking the commercial heat-conducting silica gel sheet as the thermal interface material after being illuminated for 400s is 140 ℃, and the average temperature difference can reach 9 ℃, as shown in figure 7 (c). The thermal infrared imager also photographs the infrared thermographs of the LED integrated lamps respectively taking the KSM-4 and the commercial heat-conducting silica gel sheets as thermal interface materials after the LED integrated lamps are illuminated for 400s, and it is also obvious from the infrared thermographs of the KSM-4 and the commercial heat-conducting silica gel sheets that the embodiment 4 of the invention has more excellent heat-conducting capability, as shown in FIG. 7 (d).
Application 2: the composite heat conducting film KSM-4 prepared in the example 4 is used as a thermal interface material for thermal management application in a thermoelectric power generation device.
To further demonstrate the excellent thermal management capabilities of inventive example 4, KSM-4 was also used in thermoelectric conversion devices.
Equipment: a temperature difference generating sheet (TEP 1-142T300, 40mm multiplied by 44 mm), KSM-4, an LED integrated lamp (ZZGD-20W) and an aluminum radiator.
The application effect is as follows: when the two sides of the thermoelectric generation piece generate temperature difference, current can be generated, and the thermoelectric generation piece (TEP 1-142T300, 40mm multiplied by 44 mm), KSM-4, LED integrated lamp (ZZGD-20W) and aluminum radiator are assembled into a thermoelectric generation device according to the working principle of the thermoelectric generation piece, as shown in figure 8 (a). When the LED integrated lamp runs, a large amount of waste heat can be generated, and a high-temperature surface is formed on one side of the thermoelectric generation piece; due to the fact that the KSM-4 has good heat conducting performance, the KSM-4 can transfer heat generated when the LED integrated lamp works to the aluminum radiator, and a low-temperature surface is formed on the other side of the thermoelectric generation sheet. Therefore, ideal temperature difference is formed on two sides of the thermoelectric power generation piece to generate power. Fig. 8 (b) is a power generation amount situation during the operation of the LED integrated lamp in the thermoelectric generation device. The method comprises the following steps: when the LED integrated lamp runs for 8 seconds, the thermoelectric generation piece starts to generate 0.8mA current; the operation is continued for 150 seconds, and the current is stabilized at about 76 mA. By fitting the time and the current, the amount of electricity generated by the LED integrated lamp when the LED integrated lamp runs for 400 seconds can be calculated to be 27.5 coulombs (Q in FIG. 8 b) 1 A region). Due to the fact that KSM-4 has good heat management capacity, after the LED integrated lamp stops operating, the thin film can still transmit waste heat within 260 seconds, and the thermoelectric module can continuously generate 3.0 coulomb of electricity (Q in fig. 8 b) 2 A region). The results show that KSM-4 has outstanding thermal management capabilities.
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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