CN111154126B - Preparation method of nano-diamond modified boron nitride high-flexibility high-thermal conductivity composite film - Google Patents
Preparation method of nano-diamond modified boron nitride high-flexibility high-thermal conductivity composite film Download PDFInfo
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Abstract
A preparation method of a nano-diamond modified boron nitride high-flexibility high-thermal conductivity composite film relates to a preparation method of a boron nitride composite film. The invention aims to solve the technical problem that the existing polymer-based composite film is low in thermal conductivity. According to the invention, the hexagonal boron nitride is subjected to stripping treatment and surface modification, then the nano diamond particles are combined through electrostatic force, and then the nano diamond particles and polyvinyl alcohol are uniformly mixed to obtain a mixed solution, the mixed solution is uniformly coated on a PET film, the PET film is subjected to standing drying under a heating condition, and finally the nano diamond boron nitride composite film obtained through demoulding has the advantages of large size, high flexibility and high thermal conductivity. And the production is quick, the cost is low, and the method has great industrial popularization value. The invention is applied to preparing the high-thermal-conductivity composite film.
Description
Technical Field
The invention relates to a preparation method of a boron nitride composite film.
Background
In recent years, with the rapid development of chip manufacturing, the development of electronic communication devices toward integration, portability and flexibility has become a necessary trend. However, it remains a challenge to effectively address the issues of heat conduction and dissipation in electronic devices. With the rise of the working temperature of the equipment, the service performance of the equipment is influenced, and the electronic components are irreversibly damaged, so that the stability and the reliability of the electronic components are reduced, and the service life of the electronic components is shortened. In general, polymer-based composite films are widely used in the field of thermal management because of their excellent electrical insulation, processability and low cost. However, their extremely low thermal conductivity in itself has greatly limited their application. In previous studies, the thermal conductivity of polymer matrices has been improved by adding thermally conductive particles, including metal nanoparticles, metal oxides, metal nitrides, graphene, carbon nanotubes, and the like, to the polymer matrix. Among these fillers, hexagonal boron nitride (h-BN) has a layered structure similar to graphite, and its thermal conductivity is anisotropic. The thermal conductivity between h-BN layers is about 600W/m.K, while the out-of-plane thermal conductivity is about 1.5-2.5W/m.K due to phonon scattering between the layers. In addition, compared with the material h-BN such as graphene and the like, the material has good electrical insulation and thermal stability, and has wide application prospect in the aspect of thermal management. Meanwhile, diamond is a material currently known to have the highest thermal conductivity at room temperature and to have good electrical insulation properties, and has excellent thermal conductivity in terms of Nanodiamond (ND) itself, but since ND particles are extremely easy to agglomerate and use cost is high, there has been little research on use of a thermally conductive filler.
Disclosure of Invention
The invention provides a preparation method of a nano-diamond modified boron nitride high-flexibility high-thermal-conductivity composite film, aiming at solving the technical problem of low thermal conductivity of the existing polymer-based composite film.
The preparation method of the nano-diamond modified boron nitride high-flexibility high-thermal conductivity composite film is carried out according to the following steps:
firstly, dispersing hexagonal boron nitride powder in a mixed solution of isopropanol and deionized water according to the concentration of 15 mg/mL-20 mg/mL, and carrying out ultrasonic treatment for 10 h-11 h under the power of 300W-400W; then centrifuging for 10-15 min under the condition that the rotating speed is 4000-5000 rpm, collecting supernatant, carrying out suction filtration on the supernatant, and drying a filter cake for 6-10 h at 50-55 ℃ to obtain less-layer boron nitride powder;
the volume ratio of the isopropanol to the deionized water in the mixed solution of the isopropanol and the deionized water is 1 (1-1.1);
secondly, dispersing the few-layer boron nitride powder prepared in the first step into a sodium hydroxide aqueous solution according to the concentration of 30-40 mg/mL, stirring for 18-20 h at 120-130 ℃, performing suction filtration, repeatedly washing with deionized water until the pH value of the filtrate is 7-8, and then drying for 6-10 h at 50-55 ℃ to obtain BN-OH powder;
The concentration of the sodium hydroxide aqueous solution is 5-10 mol/L;
thirdly, the BN-OH powder obtained in the second step is dispersed in deionized water, and the mass ratio of the BN-OH powder obtained in the second step to the volume ratio of the deionized water is 1g (500 mL-600 mL); then slowly dropwise adding a polydiallyl dimethyl ammonium chloride aqueous solution, stirring for 2-4 h at room temperature, centrifuging for 20-25 min at a rotating speed of 9000-9500 rpm, repeatedly washing for 2-3 times by using deionized water in a suction filtration device to remove redundant polydiallyl dimethyl ammonium chloride, collecting a filter cake, and drying for 6-10 h at 50-60 ℃ to obtain P-BN powder;
the mass fraction of the poly diallyl dimethyl ammonium chloride aqueous solution is 20-30%;
the mass ratio of the BN-OH powder obtained in the second step to the polydiallyldimethylammonium chloride aqueous solution is 1 (10-11);
dispersing the nano-diamond in dimethyl sulfoxide according to the concentration of 0.05-0.1 wt.%, and dispersing for 10-12 h through ultrasonic treatment to obtain a mixed solution 1;
ultrasonically dispersing the P-BN powder obtained in the step three in deionized water according to the concentration of 0.15-0.2 wt.% for 30-35 min to obtain a mixed solution 2;
Adding the mixed solution 1 into the mixed solution 2, stirring for 2-4 h at room temperature, repeatedly washing with deionized water for 4-5 times by a filtering device to remove residual dimethyl sulfoxide, drying a filter cake in an oven at 50-60 ℃ for 6-10 h, and collecting ND-BN powder grafted with ND;
the mass ratio of the nano diamond in the mixed solution 1 to the P-BN powder in the mixed solution 2 is 1 (10-100);
fifthly, dispersing the ND-BN powder grafted by the ND obtained in the fourth step into a polyvinyl alcohol aqueous solution, and sequentially stirring for 12-13 h and ultrasonically dispersing for 2-4 h to obtain white viscous slurry; coating a layer of vaseline on a glass plate, then paving a layer of PET film on the vaseline, spreading white viscous slurry on the PET film by a doctor blade method to obtain an ND-BN/PVA film on the PET film, drying for 2-4 h at 40-45 ℃, and finally demoulding from the PET film to obtain the nano-diamond modified boron nitride high-flexibility high-heat-conductivity composite film; the thickness of the ND-BN/PVA film is 100-400 mu m;
the mass fraction of the polyvinyl alcohol aqueous solution is 8%;
the mass ratio of the ND-BN powder grafted by the ND obtained in the fourth step to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 1 (1-9).
According to the invention, the hexagonal boron nitride is subjected to stripping treatment and surface modification, then nano diamond particles are combined through electrostatic force, and then the nano diamond particles and polyvinyl alcohol are uniformly mixed to obtain a mixed solution, the mixed solution is uniformly coated on a PET film, the PET film is subjected to standing drying under a heating condition, and finally the nano diamond boron nitride composite film obtained by demolding has the advantages of large size, high flexibility and high thermal conductivity. And the production is rapid, the cost is low, and the method has great industrial popularization value.
According to the invention, the surface charge is changed due to the stripping and modification treatment of the hexagonal boron nitride, so that the dispersibility of the filler is improved, and the effect of connecting the nano-diamond with electrostatic force is achieved. The boron nitride sheets grafted with the nano-diamond are arranged along the horizontal force direction under the action of the shearing force, the heat is transferred in the film structure under the synergistic effect of the two, the thermal conductivity is further improved, when the content of the nano-diamond is 3 wt% of that of the boron nitride, the in-plane thermal conductivity reaches the maximum (15.49W/m.K), and meanwhile, the out-plane thermal conductivity reaches 1.23W/m.K, so that the use cost of the nano-diamond is remarkably reduced while the thermal conductivity is effectively improved.
The key points of the invention have the following advantages:
1. The invention carries out surface modification on two high-heat-conductivity nano-fillers with different sizes, and enables the nano-diamond particles to be successfully grafted on the surface of the few-layer boron nitride through electrostatic force by a simple and effective means;
2. according to the invention, the thermal conductivity of the composite film is maximally improved under the condition of low dosage of the nano-diamond by regulating and controlling the content ratio of the nano-diamond modified few-layer boron nitride, so that the problem of high use cost of nano-diamond particles is solved;
3. the invention utilizes the shearing force (doctor blade method) to prepare the oriented composite film, and selects a simple and effective method to prepare the nano-diamond modified boron nitride-less large-size, high-flexibility and high-thermal-conductivity polyvinyl alcohol composite film.
Drawings
FIG. 1 is an atomic force microscope image of a layer-less boron nitride powder prepared at step one of experiment one;
FIG. 2 is a TEM image of ND-grafted ND-BN powder prepared in step four of experiment one;
FIG. 3 is an SEM image of a cross section of a nano-diamond modified boron nitride high-flexibility high-thermal conductivity composite film prepared in the first test;
fig. 4 is the thermal conductivity of the composite film.
Detailed Description
The first embodiment is as follows: the embodiment is a preparation method of a nano-diamond modified boron nitride high-flexibility high-thermal-conductivity composite film, which is specifically carried out according to the following steps:
Firstly, dispersing hexagonal boron nitride powder in a mixed solution of isopropanol and deionized water according to the concentration of 15 mg/mL-20 mg/mL, and carrying out ultrasonic treatment for 10 h-11 h under the power of 300W-400W; then centrifuging for 10-15 min under the condition that the rotating speed is 4000-5000 rpm, collecting supernatant, carrying out suction filtration on the supernatant, and drying a filter cake for 6-10 h at 50-55 ℃ to obtain less-layer boron nitride powder;
the volume ratio of the isopropanol to the deionized water in the mixed solution of the isopropanol and the deionized water is 1 (1-1.1);
secondly, dispersing the few-layer boron nitride powder prepared in the first step into a sodium hydroxide aqueous solution according to the concentration of 30-40 mg/mL, stirring for 18-20 h at 120-130 ℃, performing suction filtration, repeatedly washing with deionized water until the pH value of the filtrate is 7-8, and then drying for 6-10 h at 50-55 ℃ to obtain BN-OH powder;
the concentration of the sodium hydroxide aqueous solution is 5-10 mol/L;
thirdly, the BN-OH powder obtained in the second step is dispersed in deionized water, and the mass ratio of the BN-OH powder obtained in the second step to the volume ratio of the deionized water is 1g (500 mL-600 mL); then slowly dropwise adding a polydiallyl dimethyl ammonium chloride aqueous solution, stirring for 2-4 h at room temperature, centrifuging for 20-25 min at a rotating speed of 9000-9500 rpm, repeatedly washing for 2-3 times by using deionized water in a suction filtration device to remove redundant polydiallyl dimethyl ammonium chloride, collecting a filter cake, and drying for 6-10 h at 50-60 ℃ to obtain P-BN powder;
The mass fraction of the poly diallyl dimethyl ammonium chloride aqueous solution is 20-30%;
the mass ratio of the BN-OH powder obtained in the second step to the polydiallyldimethylammonium chloride aqueous solution is 1 (10-11);
dispersing the nano-diamond in dimethyl sulfoxide according to the concentration of 0.05-0.1 wt%, and dispersing for 10-12 h through ultrasonic treatment to obtain a mixed solution 1;
ultrasonically dispersing the P-BN powder obtained in the step three in deionized water according to the concentration of 0.15-0.2 wt% for 30-35 min to obtain a mixed solution 2;
adding the mixed solution 1 into the mixed solution 2, stirring for 2-4 h at room temperature, repeatedly washing with deionized water for 4-5 times by a filtering device to remove residual dimethyl sulfoxide, drying a filter cake in an oven at 50-60 ℃ for 6-10 h, and collecting ND-BN powder grafted with ND;
the mass ratio of the nano diamond in the mixed solution 1 to the P-BN powder in the mixed solution 2 is 1 (10-100);
fifthly, dispersing the ND-BN powder grafted by the ND obtained in the fourth step into a polyvinyl alcohol aqueous solution, and sequentially stirring for 12-13 h and ultrasonically dispersing for 2-4 h to obtain white viscous slurry; coating a layer of vaseline on a glass plate, then paving a layer of PET film on the vaseline, spreading white viscous slurry on the PET film by a doctor blade method to obtain an ND-BN/PVA film on the PET film, drying for 2-4 h at 40-45 ℃, and finally demoulding from the PET film to obtain the nano-diamond modified boron nitride high-flexibility high-heat-conductivity composite film; the thickness of the ND-BN/PVA film is 100-400 mu m;
The mass fraction of the polyvinyl alcohol aqueous solution is 8-9%;
the mass ratio of the ND-BN powder grafted by ND obtained in the fourth step to polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 1 (1-9).
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the average grain diameter of the hexagonal boron nitride powder in the first step is 1-25 μm. The rest is the same as the first embodiment.
The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: and in the second step, the few-layer boron nitride powder prepared in the first step is dispersed in a sodium hydroxide aqueous solution according to the concentration of 30 mg/mL. The others are the same as in the first or second embodiment.
The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: the mass ratio of the BN-OH powder obtained in the second step in the third step to the polydiallyldimethylammonium chloride aqueous solution is 1: 10. The rest is the same as one of the first to third embodiments.
The fifth concrete implementation mode: the fourth difference between this embodiment and the specific embodiment is that: the particle size of the nano-diamond in the fourth step is 5 nm-10 nm. The rest is the same as the fourth embodiment.
The sixth specific implementation mode is as follows: the difference between this embodiment and one of the first to third embodiments is: and the thickness of the PET film in the fifth step is 0.025 mm. The rest is the same as one of the first to third embodiments.
The seventh embodiment: the difference between this embodiment mode and one of the first to third embodiment modes is: the thickness of the ND-BN/PVA film in the step five is 400 mu m. The rest is the same as one of the first to third embodiments.
The specific implementation mode is eight: the difference between this embodiment mode and one of the first to third embodiment modes is: the mass ratio of the ND-BN powder grafted by ND obtained in the fourth step to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 3: 7. The rest is the same as one of the first to third embodiments.
The invention was verified with the following tests:
test one: the test is a preparation method of the nano-diamond modified boron nitride high-flexibility high-thermal conductivity composite film, and the preparation method specifically comprises the following steps:
firstly, dispersing hexagonal boron nitride powder into a mixed solution of isopropanol and deionized water according to the concentration of 15mg/mL, and carrying out ultrasonic treatment for 10 hours under the power of 300W; then, centrifuging for 10min under the condition that the rotating speed is 4000rpm, collecting supernatant, carrying out suction filtration on the supernatant, and drying a filter cake for 8h at 50 ℃ to obtain less-layer boron nitride powder;
The average particle size of the hexagonal boron nitride powder in the first step is 1 μm;
the volume ratio of the isopropanol to the deionized water in the mixed solution of the isopropanol and the deionized water is 1: 1;
secondly, dispersing the few-layer boron nitride powder prepared in the first step into a sodium hydroxide aqueous solution according to the concentration of 30mg/mL, stirring for 18h at 120 ℃, performing suction filtration, repeatedly washing with deionized water until the pH value of the filtrate is 7, and then drying for 8h at 50 ℃ to obtain BN-OH powder;
the concentration of the sodium hydroxide aqueous solution is 5 mol/L;
thirdly, the BN-OH powder obtained in the second step is dispersed in deionized water, and the volume ratio of the mass of the BN-OH powder obtained in the second step to the volume of the deionized water is 1g:500 mL; slowly dropwise adding a polydiallyl dimethyl ammonium chloride aqueous solution, stirring at room temperature for 2h, centrifuging at a rotating speed of 9000rpm for 20min, repeatedly washing with deionized water for 3 times in a suction filtration device to remove redundant polydiallyl dimethyl ammonium chloride, collecting a filter cake, and drying at 50 ℃ for 8h to obtain P-BN powder;
the mass fraction of the polydiallyldimethylammonium chloride aqueous solution is 20%;
the mass ratio of the BN-OH powder obtained in the second step to the polydiallyldimethylammonium chloride aqueous solution is 1: 10;
Dispersing the nano-diamond in dimethyl sulfoxide according to the concentration of 0.05 wt.%, and dispersing for 10 hours through ultrasonic treatment to obtain a mixed solution 1; the grain size of the nano diamond is 5 nm-10 nm;
ultrasonically dispersing the P-BN powder obtained in the step three in deionized water according to the concentration of 0.15 wt.% for 30min to obtain a mixed solution 2;
adding the mixed solution 1 into the mixed solution 2, stirring for 4h at room temperature, repeatedly washing with deionized water for 5 times through a filtering device to remove residual dimethyl sulfoxide, drying a filter cake in an oven at 50 ℃ for 8h, and collecting ND-BN powder grafted by ND;
the mass ratio of the nano diamond in the mixed solution 1 to the P-BN powder in the mixed solution 2 is 1: 10;
fifthly, dispersing the ND-BN powder grafted by the ND obtained in the fourth step into a polyvinyl alcohol aqueous solution, and sequentially stirring for 12 hours and ultrasonically dispersing for 4 hours to obtain white viscous slurry; coating a layer of vaseline on a glass plate, then paving a layer of PET film on the vaseline, spreading white viscous slurry on the PET film by a doctor blade method to obtain an ND-BN/PVA film on the PET film, drying for 3 hours at 40 ℃, and finally demoulding from the PET film to obtain the nano-diamond modified boron nitride high-flexibility high-thermal-conductivity composite film; the thickness of the ND-BN/PVA film is 400 mu m, the thickness is the thickness of a wet film, and the thickness of the dried film is 25 mu m-35 mu m;
The mass fraction of the polyvinyl alcohol aqueous solution is 8%;
the mass ratio of the ND-BN powder grafted by the ND obtained in the step four to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 1: 2.33;
and the thickness of the PET film in the fifth step is 0.025 mm.
And (2) test II: this test differs from the test one in that: the mass ratio of the nano-diamond in the mixed solution 1 to the P-BN powder in the mixed solution 2 in the fourth step is 7: 100. The rest is the same as test one.
And (3) test III: this test differs from the test one in that: the mass ratio of the nano-diamond in the mixed solution 1 to the P-BN powder in the mixed solution 2 in the fourth step is 3: 100. The rest is the same as test one.
Comparative experiment 1: compared with the preparation method of the large-size, high-flexibility and high-thermal-conductivity composite film compounded by few layers of boron nitride and polyvinyl alcohol (PVA) which are not modified by nano diamond, the preparation method specifically comprises the following steps:
firstly, dispersing hexagonal boron nitride powder into a mixed solution of isopropanol and deionized water according to the concentration of 15mg/mL, and carrying out ultrasonic treatment for 10 hours under the power of 300W; then, centrifuging for 10min under the condition that the rotating speed is 4000rpm, collecting supernatant, carrying out suction filtration on the supernatant, and drying a filter cake for 8h at 50 ℃ to obtain less-layer boron nitride powder;
The average particle size of the hexagonal boron nitride powder in the first step is 1 μm;
the volume ratio of the isopropanol to the deionized water in the mixed solution of the isopropanol and the deionized water is 1: 1;
secondly, dispersing the few-layer boron nitride powder obtained in the second step into a polyvinyl alcohol aqueous solution, and sequentially stirring for 12 hours and ultrasonically dispersing for 4 hours to obtain white viscous slurry; coating a layer of vaseline on a glass plate, then laying a layer of PET film on the vaseline, spreading white viscous slurry on the PET film by a doctor blade method to obtain a BN/PVA film on the PET film, drying for 3 hours at 40 ℃, and finally demoulding from the PET film to obtain a composite film; the thickness of the BN/PVA film is 400 mu m;
the mass fraction of the polyvinyl alcohol aqueous solution is 8%;
the mass ratio of the few-layer boron nitride powder obtained in the second step to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 1: 2.33;
and the thickness of the PET film in the fifth step is 0.025 mm.
Comparative experiment 2: compared with the preparation method of the large-size, high-flexibility and high-thermal conductivity composite film compounded by the nanometer diamond directly mixed with the few layers of boron nitride and the polyvinyl alcohol (PVA), the preparation method specifically comprises the following steps:
Firstly, dispersing hexagonal boron nitride powder into a mixed solution of isopropanol and deionized water according to the concentration of 15mg/mL, and carrying out ultrasonic treatment for 10 hours under the power of 300W; then, centrifuging for 10min under the condition that the rotating speed is 4000rpm, collecting supernatant, carrying out suction filtration on the supernatant, and drying a filter cake for 8h at 50 ℃ to obtain less-layer boron nitride powder;
the average particle size of the hexagonal boron nitride powder in the first step is 1 μm;
the volume ratio of the isopropanol to the deionized water in the mixed solution of the isopropanol and the deionized water is 1: 1;
secondly, dispersing the nano-diamond in dimethyl sulfoxide according to the concentration of 0.05 wt.%, and dispersing for 10 hours through ultrasonic treatment to obtain a mixed solution 1; the particle size of the nano diamond is 5 nm-10 nm;
ultrasonically dispersing the few-layer boron nitride powder obtained in the step one in deionized water according to the concentration of 0.15 wt.% for 30min to obtain a mixed solution 2;
adding the mixed solution 1 into the mixed solution 2, stirring for 4h at room temperature, repeatedly washing with deionized water for 5 times through a filtering device to remove residual dimethyl sulfoxide, drying a filter cake in an oven at 50 ℃ for 8h, and collecting ND-BN powder;
the mass ratio of the nano diamond in the mixed solution 1 to the P-BN powder in the mixed solution 2 is 1: 10;
Dispersing the ND-BN powder obtained in the step two in a polyvinyl alcohol aqueous solution, and sequentially stirring for 12 hours and ultrasonically dispersing for 4 hours to obtain white viscous slurry; coating a layer of vaseline on a glass plate, then paving a layer of PET film on the vaseline, spreading white viscous slurry on the PET film by a doctor blade method to obtain an ND-BN/PVA film on the PET film, drying for 3 hours at 40 ℃, and finally demoulding from the PET film to obtain the nano-diamond modified boron nitride high-flexibility high-thermal-conductivity composite film; the thickness of the ND-BN/PVA film is 400 mu m;
the mass fraction of the polyvinyl alcohol aqueous solution is 8%;
the mass ratio of the ND-BN powder grafted by the ND obtained in the step four to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 1: 2.33;
and the thickness of the PET film in the fifth step is 0.025 mm.
Comparative experiment 3: compared with the preparation method of the large-size, high-flexibility and high-thermal-conductivity composite film compounded by the polyvinyl alcohol (PVA) and the nano-diamond directly mixed with the few layers of boron nitride, the preparation method is different from the comparative experiment 2 in that: and the mass ratio of the nano-diamond in the mixed solution 1 to the P-BN powder in the mixed solution 2 in the step two is 3: 100. The rest was the same as in comparative experiment 2.
FIG. 1 is an atomic force microscope image of the boron nitride powder with few layers prepared in the first step of the first test, and it can be seen from FIG. 1 that the boron nitride sheet with few layers after liquid phase ultrasonic stripping has a smooth and clean surface, reduced lateral dimension under the action of shearing force, about 100nm to 200nm, and a thickness of about 4nm, which shows the feasibility of stripping boron nitride by the method.
Fig. 2 is a TEM image of ND-BN powder grafted ND prepared in step four of experiment one, which reveals that the nanodiamonds still appear in the form of nanoclusters due to their high specific surface area and high surface activity, and are mainly distributed at the edges of the boron nitride flakes, to some extent facilitating the bonding between the boron nitride flakes.
Fig. 3 is an SEM image of a cross-section of a nano-diamond modified boron nitride high-flexibility high-thermal-conductivity composite film prepared in the first test, and it can be seen in fig. 3 that the composite film prepared by the doctor blade method has good directionality in the plane direction, which is why it has thermal conductivity anisotropy, and exhibits excellent thermal conductivity in the plane.
Fig. 4 is a thermal conductivity of the composite film, where point a is an in-plane thermal conductivity of the composite film prepared in comparative test 1, point B is an in-plane thermal conductivity of the composite film prepared in test three, point C is an in-plane thermal conductivity of the composite film prepared in test two, point D is an in-plane thermal conductivity of the composite film prepared in test one, point a is an out-of-plane thermal conductivity of the composite film prepared in comparative test 1, point B is an out-of-plane thermal conductivity of the composite film prepared in test three, point C is an out-of-plane thermal conductivity of the composite film prepared in test two, point D is an out-of-plane thermal conductivity of the composite film prepared in test one, point E is an out-of-plane thermal conductivity of the composite film prepared in comparative test 2, and point F is an out-of-plane thermal conductivity of the composite film prepared in comparative test 3. From fig. 4, it can be seen that when the content of the nanodiamond is 3 wt% of boron nitride, the in-plane thermal conductivity of the nanodiamond reaches the maximum (15.49W/m · K), and the out-of-plane thermal conductivity of the nanodiamond reaches 1.23W/m.k, so that the use cost of the nanodiamond is remarkably reduced while the thermal conductivity is effectively improved.
Claims (6)
1. A preparation method of a nano-diamond modified boron nitride high-flexibility high-thermal conductivity composite film is characterized by comprising the following steps:
firstly, dispersing hexagonal boron nitride powder in a mixed solution of isopropanol and deionized water according to the concentration of 15 mg/mL-20 mg/mL, and carrying out ultrasonic treatment for 10 h-11 h under the power of 300W-400W; then centrifuging for 10-15 min under the condition that the rotating speed is 4000-5000 rpm, collecting supernatant, carrying out suction filtration on the supernatant, and drying a filter cake for 6-10 h at 50-55 ℃ to obtain less-layer boron nitride powder;
the volume ratio of the isopropanol to the deionized water in the mixed solution of the isopropanol and the deionized water is 1 (1-1.1);
the average grain diameter of the hexagonal boron nitride powder is 1-25 mu m;
secondly, dispersing the few-layer boron nitride powder prepared in the first step into a sodium hydroxide aqueous solution according to the concentration of 30-40 mg/mL, stirring for 18-20 h at 120-130 ℃, performing suction filtration, repeatedly washing with deionized water until the pH value of the filtrate is 7-8, and then drying for 6-10 h at 50-55 ℃ to obtain BN-OH powder;
the concentration of the sodium hydroxide aqueous solution is 5-10 mol/L;
Thirdly, the BN-OH powder obtained in the second step is dispersed in deionized water, and the volume ratio of the mass of the BN-OH powder obtained in the second step to the volume of the deionized water is 1g (500 mL-600 mL); then slowly dropwise adding a polydiallyl dimethyl ammonium chloride aqueous solution, stirring for 2-4 h at room temperature, centrifuging for 20-25 min at a rotating speed of 9000-9500 rpm, repeatedly washing for 2-3 times by using deionized water in a suction filtration device to remove redundant polydiallyl dimethyl ammonium chloride, collecting a filter cake, and drying for 6-10 h at 50-60 ℃ to obtain P-BN powder;
the mass fraction of the poly diallyl dimethyl ammonium chloride aqueous solution is 20-30%;
the mass ratio of the BN-OH powder obtained in the second step to the polydiallyldimethylammonium chloride aqueous solution is 1 (10-11);
dispersing the nano-diamond in dimethyl sulfoxide according to the concentration of 0.05-0.1 wt.%, and dispersing for 10-12 h through ultrasonic treatment to obtain a mixed solution 1;
ultrasonically dispersing the P-BN powder obtained in the step three in deionized water according to the concentration of 0.15-0.2 wt% for 30-35 min to obtain a mixed solution 2;
adding the mixed solution 1 into the mixed solution 2, stirring for 2-4 h at room temperature, repeatedly washing with deionized water for 4-5 times by a filtering device to remove residual dimethyl sulfoxide, drying a filter cake in an oven at 50-60 ℃ for 6-10 h, and collecting ND-BN powder grafted with ND;
The mass ratio of the nano diamond in the mixed solution 1 to the P-BN powder in the mixed solution 2 is 1 (10-100);
the grain size of the nano diamond is 5 nm-10 nm;
fifthly, dispersing the ND-BN powder grafted by the ND obtained in the fourth step into a polyvinyl alcohol aqueous solution, and sequentially stirring for 12-13 h and ultrasonically dispersing for 2-4 h to obtain white viscous slurry; coating a layer of vaseline on a glass plate, then paving a layer of PET film on the vaseline, spreading white viscous slurry on the PET film by a doctor blade method to obtain an ND-BN/PVA film on the PET film, drying for 2-4 h at 40-45 ℃, and finally demoulding from the PET film to obtain the nano-diamond modified boron nitride high-flexibility high-heat-conductivity composite film; the thickness of the ND-BN/PVA film is 100-400 mu m;
the mass fraction of the polyvinyl alcohol aqueous solution is 8-9%;
the mass ratio of the ND-BN powder grafted by the ND obtained in the fourth step to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 1 (1-9).
2. The method for preparing a nano-diamond modified boron nitride high-flexibility high-thermal conductivity composite film according to claim 1, wherein in the second step, the few-layer boron nitride powder prepared in the first step is dispersed in a sodium hydroxide aqueous solution according to a concentration of 30 mg/mL.
3. The method for preparing the nano-diamond modified boron nitride high-flexibility high-thermal-conductivity composite film according to claim 1, wherein the mass ratio of the BN-OH powder obtained in the second step to the poly (diallyldimethylammonium chloride) aqueous solution in the third step is 1: 10.
4. The method for preparing the nano-diamond modified boron nitride high-flexibility high-thermal conductivity composite film according to claim 1, wherein the thickness of the PET film in the fifth step is 0.025 mm.
5. The method for preparing the nano-diamond modified boron nitride high-flexibility high-thermal-conductivity composite film according to claim 1, wherein the thickness of the ND-BN/PVA film in the fifth step is 400 μm.
6. The method for preparing a nano-diamond modified boron nitride high-flexibility high-thermal conductivity composite film according to claim 1, wherein the mass ratio of the ND-BN powder grafted with ND obtained in the step four in the step five to polyvinyl alcohol in a polyvinyl alcohol aqueous solution is 3: 7.
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