CN111234502A - Efficient and uniform heat conduction polymer-based heat conduction material and preparation method thereof - Google Patents
Efficient and uniform heat conduction polymer-based heat conduction material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a polymer-based heat conduction material with high efficiency and uniform heat conduction and a preparation method thereof. The heat conduction material is composed of a polymer matrix material and heat conduction fillers, wherein the heat conduction fillers are in a multi-orientation network structure, the multi-orientation network structure is that the heat conduction fillers are vertically oriented along a longitudinal axis in the vertical direction, the heat conduction fillers are radially oriented in the horizontal direction, namely, the heat conduction fillers are oriented from the periphery to the center, precursor slurry prepared by the heat conduction fillers and adhesives is placed in a specific multi-orientation mold for freeze casting, a filler framework with a multi-orientation structure is obtained through freeze drying, and finally the filler framework is placed in a polymer melt or a precursor and is prepared through vacuum impregnation. The polymer-based conductive material has a multi-orientation network structure, and can realize high thermal conductivity in the in-plane and out-of-plane directions at the same time under low filling content.
Description
Technical Field
The invention belongs to the technical field of heat management materials, and relates to a polymer-based heat conduction material with high-efficiency and uniform heat conduction and a preparation method thereof.
Background
With the trend of high power and miniaturization of electronic devices, these devices generate a large amount of heat during use, and if the heat cannot be dissipated effectively in time, the temperature rise of the devices not only causes the performance reduction, but also accelerates the aging and even failure of the components. Packaging thermal management materials and electronic devices simultaneously with high heat transfer capability is an effective solution to this problem.
The polymer-based heat management material has good development potential due to the characteristics of good insulation, easy processing, low cost and the like, but is limited by the lower thermal conductivity coefficient. In order to improve the thermal management properties of polymer-based materials, it is a very effective strategy to design oriented networks built up from anisotropic fillers. Because anisotropic fillers, particularly those having a two-dimensional structure, such as Boron Nitride (BN), graphite, graphene, etc., have thermal conductivities in the in-plane directions of up to several hundred W/m · K, while the thermal conductivities in the out-of-plane directions are typically two or more orders of magnitude lower than in-plane directions. Therefore, by the orientation of the filler, the thermal management properties of the polymer in the direction of orientation can be greatly improved by utilizing the anisotropy of the filler. However, the presently reported orientation structures generally only achieve orientation of the filler in one direction, such as perpendicular orientation or parallel orientation (ACSAppl. Mater. Inter.2017,9, 22977-. While the increase in thermal conductivity along the direction of orientation always inevitably leads to a large decrease in thermal conductivity perpendicular to the direction of orientation (composite. sci. technol.,2015,122:42-49.), resulting in uneven conduction of heat within the material. Therefore, designing a filler network structure which can not only utilize the anisotropy of the filler to the maximum extent, but also realize the uniform conduction of heat in the polymer has very important significance for the application of the polymer-based thermal management material in the fields of electronic packaging and the like.
Disclosure of Invention
The invention aims to provide a polymer-based heat conduction material with high efficiency and uniform heat conduction and a preparation method thereof. The invention is inspired by the water delivery structure in natural coniferous trees (such as larch, yew and the like), and the filler in the polymer-based heat conduction material is designed to have a multi-orientation network structure, namely, in the vertical direction, the filler is vertically oriented along the longitudinal axis; in the horizontal direction, the filler is oriented radially, i.e. from the periphery towards the centre. Through the multi-orientation network structure, the vibration and the collision of phonons can be ensured to be mainly carried out along the inner direction of the filler surface, and the heat can be ensured to be transferred towards all directions simultaneously, so that the rapid and uniform heat conduction is realized simultaneously, and the heat management performance of the polymer matrix composite material is greatly improved.
The technical scheme for realizing the purpose of the invention is as follows:
the polymer-based heat conduction material with high-efficiency and uniform heat conduction is composed of a polymer matrix material and a heat conduction filler, wherein the heat conduction filler is in a multi-orientation network structure; the multi-orientation network structure is characterized in that the heat-conducting fillers are vertically oriented along the longitudinal axis in the vertical direction, and the heat-conducting fillers are radially oriented in the horizontal direction, namely, oriented from the periphery to the center.
The polymer-based heat conductive material having high efficiency and uniform heat conduction is prepared by a method conventionally used in the art, for example, an ice template method or a 3D printing method.
Specifically, the method for preparing the polymer-based heat conduction material with high efficiency and uniform heat conduction by adopting an ice template method comprises the following steps:
step 3, immersing the bottom of the mold into liquid nitrogen, and after the mold is completely frozen, obtaining a filler framework with a multi-orientation structure through freeze drying;
and 4, placing the filler framework in a polymer melt or a precursor, and performing vacuum impregnation to obtain the polymer-based heat conduction material with the multi-orientation filler network structure.
In step 1, the heat conductive filler is a heat conductive filler conventionally used in the art, such as boron nitride, graphene, graphite, carbon nanotubes, and the like.
In step 1, the binder is a binder conventionally used in the art, such as graphene oxide, polyvinyl alcohol, cellulose nanocrystals, regenerated cellulose, and the like.
In the embodiment of the invention, the mold in step 2 is a copper rod 25 cm long and 3 cm in diameter, and has a groove 2.54cm in diameter and 1.5 cm in depth on the top and silicone rubber 1cm thick on the bottom of the groove. When the mould is used for freezing casting, the bottom of the copper rod is arranged in the cold groove, the temperature gradient can be vertically and upwardly transmitted along the copper rod, the temperature transmission of the bottom of the groove is slower than that of the peripheral walls due to the layer of silicon rubber in the groove, the freezing speed in the radial direction is slightly higher than that in the vertical direction when liquid is frozen and cast, so that ice crystals can grow in the radial direction (from outside to inside) and the vertical direction at the same time, and the detailed freezing process is shown in figure 2.
Preferably, in the step 3, the temperature of the freeze drying is-80 ℃ to-50 ℃, the pressure is 2Pa to 10Pa, and the freeze drying time is 24h to 56 h.
Preferably, in step 4, the polymer is a polymer conventionally used in the art, such as epoxy resin, polydimethylsiloxane, polyethylene glycol, and the like.
Preferably, in the step 4, the vacuum impregnation is performed under a negative pressure of not less than 5MPa for 4-15 h.
Compared with the prior art, the invention has the following advantages:
the polymer-based conductive material with the multi-orientation network structure can realize high thermal conductivity in the in-plane and out-of-plane directions at the same time under low filling content. Compared with the existing polymer-based heat conduction material only having single-direction orientation, the composite material with the multi-orientation network structure can realize faster and more uniform heat transfer without local overheating even if the composite material is placed under a point heat source, and has potential application prospect in the field of heat management.
Drawings
Fig. 1(a) is an SEM sectional view along the longitudinal axis in a needle tree branch, and fig. 1(b) is an SEM image of a cross section in a needle tree branch.
FIG. 2(a) is a schematic diagram of the preparation process of the GO-BN framework with the multidirectional orientation structure in example 1, FIG. 2(b) is the Raman spectrum of GO, BN and GO-BN hybrid filler, FIG. 2(c-d) is the SEM image of the cross section of pure GO and GO-BN obtained by preparation, and FIG. 2(e) is the digital diagram of the GO-BN three-dimensional framework.
Fig. 3(a) is a schematic view of a mold for multi-directional freeze casting in example 1, fig. 3(b) is a schematic view of ice crystal growth during freeze casting, and fig. 3(c) is a digital view of different times during freeze casting in example 1.
Fig. 4(a) is a schematic view of BN arrangement in the GO-BN framework obtained in example 1, fig. 4(b) is an SEM image of a part of the upper surface in the framework in example 1, fig. 4(c) is a schematic view of a longitudinal section in the GO-BN framework obtained in example 1, fig. 4(d) is an SEM image of a longitudinal interface of the GO-BN framework in example 1, fig. 4(e) is a graph of XRD analysis results of the GO-BN framework obtained in example 1 and comparative example 1, fig. 4(f) is a schematic view of PEG/BN composite material of example 1, and fig. 4(g) and (h) are SEM images of longitudinal and transverse sections of the PEG/BN composite heat conductive material obtained in example 1.
FIG. 5(a) is a schematic view of a mold used for freeze casting in comparative example 1, FIG. 5(b) is a schematic view of ice crystal growth in comparative example 1, FIG. 5(c) is a digital view of GO-BN skeleton obtained in comparative example 1, and FIG. 5(d-e) is an SEM image of cross section and longitudinal section of GO-BN skeleton obtained in comparative example 1.
Fig. 6(a) is a thermal conductivity of the composite materials obtained in example 1 and comparative examples 1 and 2 measured by hot plate method (hot disk), and fig. 6(b) is a thermal conductivity in vertical and horizontal directions, respectively, of the composite materials obtained in example 1, comparative examples 1 and 2 at a filler content of 11.65 vol% (20.00 wt%).
Fig. 7 is a graph showing the results of infrared thermal imaging of the composite heat conductive materials prepared in example 1, comparative example 1 and comparative example 2 when they were placed under a point heat source.
Detailed Description
The present invention will be described in more detail with reference to the following examples and the accompanying drawings.
Reference is made to the preparation of moulds [ Wang C, Chen X, Wang B, et al, Freeze-Casting Process Graphene Oxide with a Radial and central symmetry Structure [ J ]. ACSNano,2018,12(6). 5816-.
In the following examples, a 25 cm long, 3 cm diameter copper bar was used as the mold, with a 2.54cm diameter and 1.5 cm deep groove on the top, and 1cm thick silicone rubber padded on the bottom of the groove.
Example 1: preparation of polyethylene glycol/boron nitride (PEG/BN) composite heat conduction material with multi-orientation structure:
step 1: preparation of Graphene Oxide (GO)
2g of graphite powder and 1g of sodium nitrate were added to a 500ml beaker, and 50ml of concentrated sulfuric acid was added thereto in an ice bath (0 ℃ C.) and mixed uniformly. Under magnetic stirring, 6g of potassium permanganate is added into the mixed system for 6 times in 1 hour, and the reaction is carried out for 2 hours at 0 ℃. After the reaction is finished, the ice-water bath is removed, the temperature of the system is gradually raised to 35 ℃, and the reaction is carried out for 30 min. Then, 100ml of deionized water was slowly added, and after no violent heat release, the temperature was gradually raised to 98 ℃ and the reaction was carried out for 3 hours. After the reaction was completed, when the temperature of the system was lowered to room temperature, 50ml of 30 wt% hydrogen peroxide solution was added. Then, the excess acid and salt are removed by repeated washing by a centrifugal method until the reaction product is neutral. And finally, carrying out ultrasonic treatment on the system for 30min to obtain a uniformly dispersed GO water suspension.
Step 2: preparation of GO-BN slurry
Uniformly mixing 6g of BN powder with 20ml of GO solution with the concentration of 10mg/ml, placing the mixture in a planetary ball mill at room temperature, carrying out ball milling for 2 hours, specifically, carrying out ball milling for 30min at intervals of 5min, and carrying out ball milling for 2 hours in total to obtain GO-BN slurry.
And step 3: preparation of GO-BN three-dimensional framework
Pouring the GO-BN slurry into a special mold for multi-orientation freezing casting, immersing the bottom of the mold into liquid nitrogen, keeping low temperature freezing for 30min, and after the slurry is completely frozen, carrying out freeze drying for 48 hours under the conditions that the temperature is-80 ℃ and the pressure is 5Pa to obtain the GO-BN three-dimensional framework with the multi-orientation structure.
And 4, step 4: preparation of PEG/BN composite material
PEG was placed in a 50ml petri dish and heated in a vacuum oven (90 ℃) to melt and fill the container. And (3) placing the GO-BN three-dimensional framework in a polymer melt, and injecting the polymer into the gaps of the framework through repeated air extraction-air release processes for 5-8 hours. And cooling to obtain the PEG/BN composite heat conduction material with the multidirectional orientation structure.
Example 2: preparing a polyethylene glycol/Graphene (PEG/Graphene) composite heat conduction material with a multi-orientation structure:
step 1: preparation of Graphene Oxide (GO)
2g of graphite powder and 1g of sodium nitrate were added to a 500ml beaker, and 50ml of concentrated sulfuric acid was added thereto in an ice bath (0 ℃ C.) and mixed uniformly. Under magnetic stirring, 6g of potassium permanganate is added into the mixed system for 6 times in 1 hour, and the reaction is carried out for 2 hours at 0 ℃. After the reaction is finished, the ice-water bath is removed, the temperature of the system is gradually raised to 35 ℃, and the reaction is carried out for 30 min. Then, 100ml of deionized water was slowly added, and after no violent heat release, the temperature was gradually raised to 98 ℃ and the reaction was carried out for 3 hours. After the reaction was completed, when the temperature of the system was lowered to room temperature, 50ml of 30 wt% hydrogen peroxide solution was added. Then, the excess acid and salt are removed by repeated washing by a centrifugal method until the reaction product is neutral. And finally, carrying out ultrasonic treatment on the system for 30min to obtain a uniformly dispersed GO water suspension.
Step 2: preparation of GO-Graphene slurry
Uniformly mixing 2.66g of Graphene powder with 20ml of GO solution with the concentration of 10mg/ml, placing the mixture in a planetary ball mill at room temperature, carrying out ball milling for 2 hours, specifically, carrying out ball milling for 2 hours at an interval of 5min every 30min, and carrying out ball milling for 2 hours in total to obtain GO-Graphene slurry.
And step 3: preparation of GO-Graphene three-dimensional framework
And pouring the GO-Graphene slurry into a special mold for multi-orientation freezing casting, immersing the bottom of the mold into liquid nitrogen, keeping the mold at a low temperature for freezing for 30min, and after the slurry is completely frozen, carrying out freeze drying for 48 hours under the conditions that the temperature is-80 ℃ and the pressure is 5Pa to obtain the GO-Graphene three-dimensional framework with the multi-orientation structure.
And 4, step 4: preparation of PEG/Graphene composite material
PEG was placed in a 50ml petri dish and heated in a vacuum oven (90 ℃) to melt and fill the container. And then placing the GO-Graphene three-dimensional framework in a polymer melt, and injecting the polymer into the gaps of the framework by repeatedly pumping and deflating for 5-8 hours. And cooling to obtain the PEG/Graphene composite heat conduction material with the multidirectional orientation structure.
Example 3: preparing a polyethylene glycol/Graphite (PEG/Graphite) composite heat conduction material with a multi-orientation structure:
step 1: preparation of Graphene Oxide (GO)
2g of graphite powder and 1g of sodium nitrate were added to a 500ml beaker, and 50ml of concentrated sulfuric acid was added thereto in an ice bath (0 ℃ C.) and mixed uniformly. Under magnetic stirring, 6g of potassium permanganate is added into the mixed system for 6 times in 1 hour, and the reaction is carried out for 2 hours at 0 ℃. After the reaction is finished, the ice-water bath is removed, the temperature of the system is gradually raised to 35 ℃, and the reaction is carried out for 30 min. Then, 100ml of deionized water was slowly added, and after no violent heat release, the temperature was gradually raised to 98 ℃ and the reaction was carried out for 3 hours. After the reaction was completed, when the temperature of the system was lowered to room temperature, 50ml of 30 wt% hydrogen peroxide solution was added. Then, the excess acid and salt are removed by repeated washing by a centrifugal method until the reaction product is neutral. And finally, carrying out ultrasonic treatment on the system for 30min to obtain a uniformly dispersed GO water suspension.
Step 2: preparation of GO-Graphite slurry
Uniformly mixing 2.66g of Graphite powder with 20ml of GO solution with the concentration of 10mg/ml, placing the mixture in a planetary ball mill at room temperature, carrying out ball milling for 2 hours, specifically, carrying out ball milling for 2 hours at an interval of 5min every 30min, and carrying out ball milling for 2 hours in total to obtain GO-Graphite slurry.
And step 3: preparing a GO-Graphite three-dimensional framework:
and pouring the GO-Graphite slurry into a special mould for multi-orientation freezing casting, immersing the bottom of the mould into liquid nitrogen, keeping the temperature for freezing for 30min, and after the slurry is completely frozen, carrying out freeze drying for 48 hours under the conditions that the temperature is-80 ℃ and the pressure is 5Pa to obtain the GO-Graphite three-dimensional framework with the multi-direction orientation structure.
And 4, step 4: preparing a PEG/Graphite composite material:
PEG was placed in a 50ml petri dish and heated in a vacuum oven (90 ℃) to melt and fill the container. And then placing the GO-Graphite three-dimensional framework in a polymer melt, and injecting the polymer into the gaps of the framework by repeatedly pumping and deflating for 5-8 hours. And cooling to obtain the PEG/Graphite composite heat conduction material with the multidirectional orientation structure.
Example 4: preparing a polyethylene glycol/expanded graphite (PEG/EG) composite heat conduction material with a multi-orientation structure:
step 1: preparation of Graphene Oxide (GO)
2g of graphite powder and 1g of sodium nitrate were added to a 500ml beaker, and 50ml of concentrated sulfuric acid was added thereto in an ice bath (0 ℃ C.) and mixed uniformly. Under magnetic stirring, 6g of potassium permanganate is added into the mixed system in 6 times in 1h and reacted for 2h at 0 ℃. After the reaction is finished, the ice-water bath is removed, the temperature of the system is gradually raised to 35 ℃, and the reaction is carried out for 30 min. Then, 100ml of deionized water was slowly added, and after no violent heat release, the temperature was gradually raised to 98 ℃ and the reaction was carried out for 3 hours. After the reaction was completed, 50ml of 30 wt% hydrogen peroxide solution was added after the temperature of the system was lowered to room temperature. Then, the excess acid and salt are removed by repeated washing by a centrifugal method until the reaction product is neutral. And finally, carrying out ultrasonic treatment on the system for 30min to obtain a uniformly dispersed GO water suspension.
Step 2: preparation of GO-EG slurry
Uniformly mixing 2.66g of EG powder with 20ml of GO solution with the concentration of 10mg/ml, placing the mixture in a planetary ball mill at room temperature, carrying out ball milling for 2 hours, specifically, carrying out ball milling for 2 hours at an interval of 5min every 30min, and carrying out ball milling for 2 hours in total to obtain GO-EG slurry.
And step 3: preparation of GO-EG three-dimensional framework
Pouring the GO-EG slurry into a special mold for multi-orientation freezing casting, immersing the bottom of the mold into liquid nitrogen, keeping the mold at a low temperature for freezing for 30min, and after the slurry is completely frozen, carrying out freeze drying for 48 hours under the conditions that the temperature is-80 ℃ and the pressure is 5Pa to obtain the GO-EG three-dimensional framework with the multi-orientation structure.
And 4, step 4: preparation of PEG/EG composite material
PEG was placed in a 50ml petri dish and heated in a vacuum oven (90 ℃) to melt and fill the container. And then placing the GO-EG three-dimensional framework in a polymer melt, and injecting the polymer into the gaps of the framework by repeatedly pumping and deflating for 5-8 hours. And cooling to obtain the PEG/EG composite heat conduction material with the multidirectional orientation structure.
Example 5: preparation of polyethylene glycol/carbon nanotube (PEG/MWCNT) composite heat conduction material with multi-orientation structure:
step 1: preparation of Cellulose Nanofibers (CNF)
First, 10g of microfibrillated cellulose (MFC) was added to 1000ml of deionized water and swelled under stirring for 24 hours. Then shearing and emulsifying for 15min at 7000-8000rpm by using an emulsifying machine. Then 0.32g TEMPO and 2g NaBr were added to the treated MFC slurry separately and stirred until dissolved. After that, NaClO was slowly added to the pretreated MFC slurry (5mmol/g MFC) to initiate the reaction, during which the pH of the adjusted system was kept at around 10.5 for 4 hours. After completion of the reaction, 10ml of anhydrous ethanol was added to terminate the reaction. Subsequently, the cellulose pulp obtained above was washed to neutrality by repeated suction filtration through deionized water. And finally, centrifuging the cellulose mixed solution at 8000rpm for 15min to collect an upper solution, namely the CNF stable water dispersion.
Step 2: preparation of RC-MWCNT paste
2.66g of MWCNT and 20ml of CNF solution with the concentration of 10mg/ml are uniformly mixed, and the mixture is placed in a planetary ball mill at room temperature for ball milling for 2 hours, specifically, ball milling is carried out for 2 hours at intervals of 5min every 30min, so that RC-MWCNT slurry can be obtained.
And step 3: preparation of RC-MWCNT three-dimensional framework
And mixing the RC-MWCNT slurry with 0.2g of epoxy chloropropane, pouring into a special mould for multi-orientation freezing casting, immersing the bottom of the mould into liquid nitrogen, keeping low-temperature freezing for 30min, and after the slurry is completely frozen, carrying out freeze drying for 48 hours at the temperature of-80 ℃ and under the pressure of 5Pa to obtain the RC-MWCNT three-dimensional framework with the multi-direction orientation structure.
And 4, step 4: preparation of PEG/MWCNT composite material
PEG was placed in a 50ml petri dish and heated in a vacuum oven (90 ℃) to melt and fill the container. The RC-MWCNT three-dimensional framework is then placed in a polymer melt and the polymer is injected into the voids of the framework by repeated pump-off processes for 5-8 hours. And cooling to obtain the PEG/MWCNT composite heat conduction material with the multidirectional orientation structure.
Example 6: preparation of polydimethylsiloxane/boron nitride (PEG/BN) composite heat conduction material with multi-orientation structure:
step 1: dissolution of polyvinyl alcohol (PVA)
10.2g of PVA powder was added to 500ml of deionized water, and vigorously stirred in a water bath at 90 ℃ for 30min until PVA was completely dissolved, to obtain a 2 wt% aqueous solution of PVA.
Step 2: preparation of PVA-BN slurry
Uniformly mixing 6g of BN powder with 20ml of PVA solution with the concentration of 2 wt%, placing the mixture in a planetary ball mill at room temperature, carrying out ball milling for 2 hours, specifically, carrying out ball milling for 2 hours at an interval of 5min every 30min, and carrying out ball milling for 2 hours in total to obtain PVA/BN slurry.
And step 3: preparation of PVA-BN three-dimensional framework
Pouring the PVA/BN slurry into a special mold for multi-orientation freezing casting, immersing the bottom of the mold into liquid nitrogen, keeping low temperature for freezing for 30min, and after the slurry is completely frozen, carrying out freeze drying for 48 hours under the conditions that the temperature is-80 ℃ and the pressure is 5Pa to obtain the PVA-BN three-dimensional framework with the multi-orientation structure.
And 4, step 4: preparation of PEG/BN composite material
PEG was placed in a 50ml petri dish and heated in a vacuum oven (90 ℃) to melt and fill the container. Then the PVA-BN three-dimensional framework is placed in the polymer melt, and the polymer is injected into the gaps of the framework through repeated air suction-air release processes for 5-8 hours. And cooling to obtain the PEG/BN composite heat conduction material with the multidirectional orientation structure.
Example 7: preparation of polydimethylsiloxane/boron nitride (PDMS/BN) composite heat-conducting material with multi-orientation structure:
10.2g of PVA powder was added to 500ml of deionized water, and vigorously stirred in a water bath at 90 ℃ for 30min until PVA was completely dissolved, to obtain a 2 wt% aqueous solution of PVA.
Step 2: preparation of PVA-BN slurry
Uniformly mixing 6g of BN powder with 20ml of 2 wt% PVA solution, placing the mixture in a planetary ball mill at room temperature, carrying out ball milling for 2 hours, specifically, carrying out ball milling for 30min at intervals of 5min, and carrying out ball milling for 2 hours in total to obtain PVA-BN slurry.
And step 3: preparation of PVA-BN three-dimensional framework
Pouring the PVA-BN slurry into a special mold for multi-orientation freezing casting, immersing the bottom of the mold into liquid nitrogen, keeping low temperature for freezing for 30min, and after the slurry is completely frozen, carrying out freeze drying for 48 hours under the conditions that the temperature is-80 ℃ and the pressure is 5Pa to obtain the PVA-BN three-dimensional framework with the multi-orientation structure.
And 4, step 4: preparation of PDMS/BN composite
Mixing polydimethylsiloxane monomer and cross-linking agent in a ratio of 10: 1 part by weight and placed in a 25ml petri dish. Then, the PVA-BN three-dimensional framework is placed in a polymer melt, and a mixed system of a polymer monomer and a cross-linking agent is injected into the gaps of the framework through repeated air extraction-air release processes for 5-8 hours. And finally, raising the temperature of the system to 60 ℃, keeping the temperature for 30 minutes, and realizing the curing of the polymer matrix, thereby obtaining the PDMS/BN composite heat conduction material with the multidirectional orientation structure.
Comparative example 1
This comparative example is essentially the same as example 1, except that the casting mold is a plastic cylinder, with only the bottom made of copper, which when immersed in the cold bath forms only a vertically upward temperature gradient, such that the resulting filler network is oriented vertically along the longitudinal axis, producing a composite heat conductive material with only a vertical orientation.
Comparative example 2
Step 1: mixing of PEG and BN
6g of BN powder and 24g of PEG were simultaneously added to a 50ml beaker, placed in a 90 ℃ water bath and heated, and mixed for 30min with magnetic stirring.
Step 2: casting of PEG/BN slurries
Pouring the slurry obtained in the step 1 into an iron mold with the thickness of 1cm and the diameter of 2.54cm, repeatedly applying pressure and relieving pressure at 90 ℃, discharging redundant bubbles in the system, and keeping the pressure at 10Mpa for 5 min. And finally, carrying out cold pressing under the pressure of 10Mpa for 5min, and demoulding to obtain the randomly oriented PEG/BN composite heat conduction material.
TABLE 1 thermal conductivity of the composites obtained in examples 1 to 7 and comparative examples 1 to 2
Table 1 shows the thermal conductivity of the composite materials obtained in examples 1 to 7 and comparative examples 1 to 2. As can be seen from the table, in different polymer matrixes and filling systems, the multi-orientation structure is beneficial to simultaneously improving the heat conductivity coefficients of the composite material in all directions, so that uniform and rapid heat conduction is realized simultaneously.
Fig. 1 shows the water transport structure inside a natural conifer, (a) is an SEM cross-sectional view of the conifer branch along the longitudinal axis, and (b) is an SEM cross-sectional view of the conifer branch along the longitudinal axis, and it can be seen that the channels are aligned along the longitudinal axis in the vertical direction and the water transport channels are oriented along the radial direction in the horizontal direction.
Fig. 2(a) is a schematic view of a preparation flow of the GO-BN skeleton having a multidirectional orientation structure in example 1, GO being a binder between BNs. FIG. 2(b) is Raman spectrum of GO and BN and GO-BN hybrid filler, FIG. 2(c-d) is SEM image of cross section of pure GO and GO-BN obtained by preparation, and FIG. 2(e) is digital image of GO-BN three-dimensional framework. After BN and GO form the hybrid filler, the characteristic peak of BN and the G band peak of GO both have obvious offset, reflecting that the BN and the GO have good interaction.
Fig. 3(a) is a schematic view of a mold for multi-directional freeze casting in example 1, fig. 3(b) is a schematic view of ice crystal growth during freeze casting, and fig. 3(c) is a digital view of different times during freeze casting in example 1. As can be seen from fig. 3, even the naked eye can see that the ice crystals are oriented in the radial direction in the horizontal direction during the freeze-casting process.
FIG. 4(a) is a schematic representation of the BN arrangement in the GO-BN framework obtained in example 1. FIG. 4(b) SEM photograph of a part of the upper surface of the skeleton in example 1. FIG. 4(c) is a schematic view of the longitudinal section of the GO-BN framework obtained in example 1, and FIG. 4(d) is an SEM image of the longitudinal interface of the GO-BN framework in example 1, from a cross-section of the framework structure it can be seen that GO-BN is oriented in the horizontal direction along the radial direction, and in the vertical direction, BN is also oriented in the vertical direction. Fig. 4(e) is a XRD analysis result diagram of the GO-BN framework structures obtained in example 1 and comparative example 1, and the spectra obtained from incident X-ray characterization above the cross section of the framework show that boron nitride is oriented in the vertical direction in both the frameworks obtained in example 1 and comparative example 1 (the intensity ratio of the ((100) peak and the (002) peak is significantly greater than 1). The spectra obtained by incidence of X-rays on the longitudinal section of the skeleton show that the boron nitride in example 1 is oriented horizontally in the direction of the section ((intensity ratio of 100) peak to (002) peak significantly less than 1), whereas the boron nitride in comparative example 1 is randomly dispersed ((intensity ratio of 100 peak to (002) peak ≈ 1). Characterization by XRD confirmed that BN in the BN-GO framework obtained in example 1 possesses both radial and homeotropic orientation. FIG. 4(f) is a schematic representation of the PEG/BN composite of example 1. Fig. 4(g) and (h) are SEM images of longitudinal and transverse cross sections of the PEG/BN composite thermal conductive material obtained in example 1, and after vacuum impregnation, BN also maintains its oriented structure in the GO-BN framework in the composite material.
FIG. 5(a) is a schematic view of a mold used for freeze casting in comparative example 1, FIG. 5(b) is a schematic view of ice crystal growth in comparative example 1, FIG. 5(c) is a digital view of GO-BN skeleton obtained in comparative example 1, and FIG. 5(d-e) is an SEM image of cross section and longitudinal section of GO-BN skeleton obtained in comparative example 1, in which BN is vertically oriented in the longitudinal direction and randomly oriented in the horizontal direction can be seen.
Fig. 6(a) is a thermal conductivity of the composite materials obtained in example 1 and comparative examples 1 and 2 measured by a hot plate method (hot disk). The thermal conductivity coefficient obtained by a hot plate method (hot disk) reflects that the PEG/BN composite material with the multi-orientation structure is more favorable for improving the overall thermal conductivity coefficient of the composite material compared with a vertically-oriented structure and a randomly-dispersed structure, and when the BN filling amount reaches 11.65 vol%, the thermal conductivity coefficient can be improved to 2.94W/m.K, and is improved by 8.8 times compared with pure PEG.
Fig. 6(b) shows the thermal conductivity in the horizontal (in-plane) and vertical (through-plane) directions of the composite materials obtained in example 1, comparative example 1 and comparative example 2, respectively, at a filler loading of 11.65 vol% (20.00 wt%). When the filler content of BN was 11.65 vol%, the thermal conductivity of PEG/BN with a multi-orientation structure was even higher (2.55W/m.K) than that of vertically oriented PEG/BN in the vertical direction (2.32W/m.K), which was much higher than that of the randomly dispersed PEG/BN composite (comparative example 2, 1.41W/m.K), because the BN skeleton oriented along the longitudinal axis was more favorable for the transfer of phonons in the vertical direction to the horizontal direction. The thermal conductivity of the vertically oriented PEG/BN composite is even lower than that of the randomly dispersed sample, since in possessing a vertically oriented framework, the thermal conductivity in the horizontal direction will be more dependent on the thermal conductivity within the BN plane. The thermal conductivity coefficient of the PEG/BN composite material with the multi-orientation structure obtained in the example 1 can reach 4.41W/m.K, and compared with pure PEG, the thermal conductivity of the PEG/BN composite material is respectively improved by 13.7 times and 7.5 times in the horizontal direction and the vertical direction, namely, rapid thermal conduction can be realized in all directions.
Fig. 7 is a graph of infrared thermal imaging results of the composite heat conductive materials prepared in example 1, comparative example 1 and comparative example 2 when placed under a point heat source, and the heat dissipation performance under a local heating scene is observed. It can be seen that the PEG/BN composite material with a multi-oriented structure obtained in example 1 has the most uniform temperature distribution at the surface, demonstrating that this structure is most beneficial for uniform heat transfer in the composite material.
Claims (10)
1. The polymer-based heat conduction material with high-efficiency and uniform heat conduction is characterized by consisting of a polymer matrix material and a heat conduction filler, wherein the heat conduction filler is in a multi-orientation network structure; the multi-orientation network structure is characterized in that the heat-conducting fillers are vertically oriented along the longitudinal axis in the vertical direction, and the heat-conducting fillers are radially oriented in the horizontal direction, namely, oriented from the periphery to the center.
2. The polymer-based thermally conductive material of claim 1, wherein the polymer is an epoxy, polydimethylsiloxane, or polyethylene glycol; the heat conducting filler is boron nitride, graphene, graphite or carbon nano tubes.
3. The polymer-based thermal conductive material of claim 1 or 2, prepared by an ice-templated method or a 3D printing method.
4. The method for preparing a polymer-based heat conductive material according to claim 1 or 2, comprising the steps of:
step 1, uniformly mixing a heat-conducting filler and an adhesive under strong shearing force to prepare precursor slurry;
step 2, placing the precursor slurry into a multi-orientation mold for freeze casting, wherein the top of the mold is provided with a groove, and the bottom of the groove is padded with a copper bar of silicon rubber;
step 3, immersing the bottom of the mold into liquid nitrogen, and after the mold is completely frozen, obtaining a filler framework with a multi-orientation structure through freeze drying;
and 4, placing the filler framework in a polymer melt or a precursor, and performing vacuum impregnation to obtain the polymer-based heat conduction material with the multi-orientation filler network structure.
5. The method according to claim 4, wherein in step 1, the thermally conductive filler is boron nitride, graphene, graphite or carbon nanotubes.
6. The method according to claim 4, wherein in step 1, the binder is graphene oxide, polyvinyl alcohol, cellulose nanocrystals or regenerated cellulose.
7. The method according to claim 4, wherein in step 2, the mold is a 25 cm long copper bar with a diameter of 3 cm, the top of the mold is provided with a groove with a diameter of 2.54cm and a depth of 1.5 cm, and the bottom of the groove is padded with 1cm thick silicone rubber.
8. The preparation method according to claim 4, wherein in the step 3, the temperature of the freeze-drying is-80 ℃ to-50 ℃, the pressure is 2Pa to 10Pa, and the freeze-drying time is 24h to 56 h.
9. The method according to claim 4, wherein in step 4, the polymer is epoxy resin, polydimethylsiloxane or polyethylene glycol.
10. The preparation method according to claim 4, wherein in the step 4, the negative pressure of the vacuum impregnation is not less than 5MPa, and the impregnation time is 4-15 h.
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