A directional boron nitride nanobelt / polydimethylsiloxane composite material, a preparation method and application thereof

Abstract

The application provides a kind of oriented boron nitride nanobelt / polydimethylsiloxane composite material and preparation method and application, belong to thermal interface and electronic packaging material technical field.The preparation method includes the following steps: melamine diborate precursor hydrogel is carried out directional freezing treatment, then vacuum freeze drying is carried out to obtain melamine diborate precursor aerogel;Melamine diborate precursor aerogel is pyrolyzed to obtain oriented boron nitride nanobelt aerogel;With oriented boron nitride nanobelt aerogel as matrix, polydimethylsiloxane resin is uniformly filled in matrix by using vacuum assisted impregnation method, and solidification is carried out to obtain oriented boron nitride nanobelt / polydimethylsiloxane composite material.The polymer-based composite material has excellent tensile property, high thermal conductivity, excellent electrical insulation performance and excellent mechanical flexibility.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermal interface and electronic packaging materials, and particularly relates to a directional boron nitride nanobelt / polydimethylsiloxane composite material, a preparation method and application thereof. BACKGROUND

[0002] With the rise of the fifth generation mobile network and higher power density in electronic products, higher and higher requirements are put forward for heat dissipation, which requires thermal management materials with high thermal conductivity, excellent electrical insulation, light weight and low cost. The thermally conductive polymer material has great application potential to meet the above requirements; however, the low thermal conductivity (<0.5 W / m k) limits their application in the field of electronic packaging materials. Adding electrically insulating and thermally conductive fillers to the polymer matrix is considered to be an effective strategy to improve the thermal conductivity of polymer materials. These thermally conductive fillers mainly focus on ceramic-based nanomaterials, including 0D nanoparticles (such as alumina and magnesium oxide), 1D nanofibers (such as silicon carbide, silicon nitride, boron nitride) and 2D nanosheets (such as boron nitride), and their mixtures. Due to the factors such as large interfacial thermal resistance between the thermally conductive fillers and the polymer matrix, poor orientation of the fillers and the like, the thermal conductivity of the polymer is difficult to be substantially improved.

[0003] At present, by adjusting the content of the thermally conductive filler or constructing a 3D skeleton in the polymer matrix to form an interconnected network to provide a high aspect ratio heat conduction path for phonons, it has become a research method to significantly improve the thermal conductivity of the polymer. A large number of studies have shown that the polymer composite embedded with the network constructed by 2D nanosheets shows higher thermal conductivity than the polymer composite embedded with 0D nanoparticles or 1D nanofibers. Compared with the "point-to-point" connection mode between 0D or 1D thermally conductive fillers, the "face-to-face" stacking interaction between 2D nanosheets can provide a large heat transfer area. However, the current problem is that the inherent low aspect ratio of the nanosheet makes it easy to form a high interfacial thermal resistance at the stacking joint between the sheets, resulting in low thermal enhancement efficiency of the composite material. SUMMARY

[0004] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a directional boron nitride nanobelt / polydimethylsiloxane composite material, a preparation method and application thereof, which uses a high-thermal-conductivity and high-aspect-ratio nanofiller to construct a long-range ordered heat transport network, so as to solve the technical problem that the inherent low aspect ratio of the nanosheet makes it easy to form a high interfacial thermal resistance at the stacking joint between the sheets, resulting in low thermal enhancement efficiency of the composite material.

[0005] In order to achieve the above-mentioned purpose, the technical scheme is adopted as follows:

[0006] The application provides a preparation method of a directional boron nitride nanobelt / polydimethylsiloxane composite material, comprising the following steps:

[0007] S1: directional freezing treatment is performed on melamine diborate precursor hydrogel, and then vacuum freeze drying is performed to obtain melamine diborate precursor aerogel;

[0008] S2: pyrolysis treatment is performed on the melamine diborate precursor aerogel to obtain directional boron nitride nanobelt aerogel;

[0009] S3: using the directional boron nitride nanobelt aerogel as a matrix, polydimethylsiloxane resin is uniformly filled in the matrix by a vacuum-assisted impregnation method, and solidification is performed to obtain the directional boron nitride nanobelt / polydimethylsiloxane composite material.

[0010] Further, in S1, the melamine diborate precursor hydrogel is prepared by the following method: melamine and boric acid are dissolved in a cosolvent and fully stirred to obtain the melamine diborate precursor hydrogel.

[0011] Further, the molar ratio of the melamine and the boric acid is (1-10):(1-10), and the dissolving temperature is 50-90 DEG C.

[0012] Further, the cosolvent is a mixture of water and an alcohol compound, and the volume ratio of the water to the alcohol compound is (8-9):(5-11).

[0013] The alcohol compound is any one of methanol, ethanol, isopropyl alcohol, n-butyl alcohol and tert-butyl alcohol.

[0014] Further, in S1, the directional freezing treatment is performed in a liquid nitrogen environment.

[0015] The directional freezing treatment is performed in the following manner:

[0016] The melamine diborate precursor hydrogel is placed on a hollow copper column, the bottom of the hollow copper column is fully contacted with the surface of liquid nitrogen, and directional freezing is performed.

[0017] Further, the height of the precursor hydrogel is 0.5-3 cm, and the treatment time of the vacuum freeze drying is 12-72 h.

[0018] Further, in S2, the pyrolysis atmosphere of the pyrolysis treatment is a mixed atmosphere of ammonia, argon and nitrogen in any ratio; the pyrolysis temperature of the pyrolysis treatment is 500-1400 DEG C; and the pyrolysis time of the pyrolysis treatment is 0.5-5 h.

[0019] Further, in the S3, the process that the vacuum-assisted impregnation method uniformly fills the polydimethylsiloxane resin in the base body is: placing the oriented boron nitride nanobelt aerogel in a polydimethylsiloxane solution, and then placing it in a vacuum oven, and after vacuumizing, impregnating for 1-3 hours;

[0020] The polydimethylsiloxane solution comprises polydimethylsiloxane prepolymer and a curing agent, and the mass ratio of the polydimethylsiloxane prepolymer and the curing agent is 10:1.

[0021] In the S3, the temperature of the curing is 80-200 DEG C, and the time of the curing is 1-4 hours.

[0022] The application further provides an oriented boron nitride nanobelt / polydimethylsiloxane composite material prepared by the preparation method of the oriented boron nitride nanobelt / polydimethylsiloxane composite material.

[0023] The application further provides an application of the oriented boron nitride nanobelt / polydimethylsiloxane composite material prepared by the preparation method of the oriented boron nitride nanobelt / polydimethylsiloxane composite material in the field of electronic packaging.

[0024] Compared with the prior art, the application has the following beneficial effects:

[0025] The application provides a preparation method of an oriented boron nitride nanobelt / polydimethylsiloxane composite material, adopts high-aspect-ratio high-thermal-conductivity BNR, and uses liquid nitrogen directional freezing technology and PDMS polymer filling to obtain high-directional BNNR / PDMS composite material. The high-aspect-ratio directional nanobelt provides a low-interface-thermal-resistance high-speed transmission channel for phonons. Further, liquid nitrogen freezing is used to construct a directional three-dimensional BNNR thermal conduction skeleton. Compared with other 1D and 2D thermal conduction fillers, the directional three-dimensional BNNR thermal conduction skeleton has the advantages of high aspect ratio, continuity, large transmission area and low interface thermal resistance, and provides a rapid thermal conduction superchannel for phonons, so that the heat dissipation capacity of the polymer composite material can be significantly improved. The polydimethylsiloxane polymer is used as a base filling material to backfill the directional BNNR three-dimensional skeleton, so that the polymer composite material is densified, and the mechanical, thermal and electrical insulation properties of the aerogel skeleton are enhanced. Compared with the commonly used epoxy resin (EP), the PDMS has the advantages of easy processing and preparation and low cost, and the synthesis process is more mature and stable, which is more conducive to the densification of the composite material.

[0026] The application further provides an oriented boron nitride nanobelt / polydimethylsiloxane composite material. The directional BNNR has a large specific surface area, so that the nanobelt and the PDMS base body have a strong interface coupling effect. The polymer base composite material has excellent tensile property, high thermal conductivity, excellent electrical insulation property and excellent mechanical flexibility.

[0027] The present application has multiple functional characteristics such as high thermal conductivity, excellent electrical insulation performance and high mechanical flexibility when applied in the field of electronic packaging technology as a thermal interface and electronic packaging material. Compared with traditional electronic packaging polymer-based materials, it has great advantages in enhancing heat dissipation and mechanical properties. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Optical photo of the oriented BNNR / PDMS composite material prepared for Example 1 of the present application;

[0029] Figure 2 SEM photo of the oriented BNNR prepared for Example 1 of the present application;

[0030] Figure 3 SEM photo of the oriented BNNR / PDMS composite material prepared for Example 1 of the present application;

[0031] Figure 4 Thermal conductivity performance test chart of the oriented BNNR / PDMS composite material prepared for Example 1 of the present application;

[0032] Figure 5 Mechanical property test chart of the oriented BNNR / PDMS composite material prepared for Example 1 of the present application; wherein chart (a) is a thermal conductivity test chart; chart (b) is an infrared thermal imaging chart. DETAILED DESCRIPTION

[0033] In order for those skilled in the art to understand the characteristics and effects of the present application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used in the text are the usual meanings understood by those skilled in the art for the present application, and in the event of a conflict, the definition in the specification shall prevail.

[0034] Theories or mechanisms described and disclosed herein, whether correct or not, should not be considered limiting the scope of the present application, i.e., the present application can be practiced without relying on any particular theory or mechanism.

[0035] In this text, all features defined in the form of numerical ranges or percentage ranges such as numerical values, quantities, contents and concentrations are for the sake of brevity and convenience. Therefore, the description of numerical ranges or percentage ranges should be considered to have encompassed and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0036] In the present specification, unless particularly stated, "comprising", "including", "containing", "having" or like terms means "consisting essentially of and "consisting essentially of", for example, "A comprising a" means "A comprising a and others" and "A comprising only a".

[0037] In the present specification, all possible combinations of the various technical features in the various embodiments or examples are not described in order to make the description concise. Therefore, as long as the combinations of the technical features do not contradict each other, the technical features in the various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered as falling within the scope of the present specification.

[0038] The application provides a directional boron nitride nanoribbon / polydimethylsiloxane composite material and a preparation method and application thereof.

[0039] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the application after reading the content taught by the application, and these equivalent forms also fall within the scope of the appended claims of the application.

[0040] In the following examples, the instruments and equipment used are conventional in the art. In the following examples, the experimental methods not specified in the specific conditions are generally carried out according to the conventional conditions or according to the conditions recommended by the manufacturer. In the following examples, various raw materials are used, unless otherwise specified, conventional commercially available products are used, and the specifications are conventional specifications in the art. In the specification of the application and the following examples, unless otherwise specified, "%" means weight percent, "parts" means weight parts, and the ratio means weight ratio.

[0041] The application provides a preparation method of a directional boron nitride nanoribbon (BNNR) / polydimethylsiloxane (PDMS) composite material. A melamine diborate (M·2B) precursor hydrogel is subjected to directional freezing treatment in a liquid nitrogen environment, and then vacuum drying is performed to obtain a M·2B precursor aerogel. Through pyrolysis treatment, a directional BNNR aerogel is obtained. The directional BNNR aerogel is used as a matrix, and polydimethylsiloxane resin (PDMS) is uniformly filled in the matrix by a vacuum-assisted impregnation method. After high-temperature curing, a directional BNNR / PDMS composite material is obtained.

[0042] The specific steps of the above preparation method are as follows:

[0043] Step 1) Preparation of melamine diborate precursor hydrogel: melamine and boric acid are dissolved in a cosolvent to obtain a melamine diborate precursor hydrogel.

[0044] Step 2) The melamine diborate precursor hydrogel is subjected to liquid nitrogen directional freezing and freeze-drying treatment to obtain a melamine diborate precursor aerogel. The treatment environment of the directional freezing treatment is a liquid nitrogen environment.

[0045] The directional freezing treatment has the following steps:

[0046] The melamine diborate precursor hydrogel is placed on a hollow copper column, the bottom of the hollow copper column is in full contact with the surface of the liquid nitrogen, and directional freezing is performed for 10-80 min.

[0047] Step 3) The melamine diborate precursor aerogel is subjected to pyrolysis treatment under a high-temperature atmosphere to obtain a directional boron nitride nanoribbon (BNNR) aerogel.

[0048] The liquid nitrogen freezing is used to construct a directional three-dimensional BNNR heat-conducting skeleton. Compared with other 1D and 2D heat-conducting fillers, the directional three-dimensional BNNR heat-conducting skeleton has the advantages of high aspect ratio, continuity, large transmission area and low interfacial thermal resistance, which provides a fast heat-conducting superchannel for phonons and can significantly improve the heat dissipation capacity of the polymer composite material.

[0049] Step 4) The directional BNNR aerogel is used as a matrix, and polydimethylsiloxane resin (PDMS) is uniformly filled into the matrix by a vacuum-assisted in-situ impregnation method. After high-temperature curing, a directional BNNR / PDMS composite material is obtained.

[0050] The polydimethylsiloxane polymer is used as a matrix filling material to backfill the directional BNNR three-dimensional skeleton to obtain a densified polymer composite material, which enhances the mechanical, thermal and electrical insulation properties of the aerogel skeleton. Compared with the commonly used epoxy resin (EP), the PDMS has the advantages of easy processing and preparation and low cost, and its synthesis process is more mature and stable, which is more conducive to the densification of the composite material. The directional BNNR has a large specific surface area, which enables the nanoribbons and the PDMS matrix to have a strong interfacial coupling effect, and the obtained composite material has excellent tensile properties.

[0051] The specific amount and process conditions are as follows:

[0052] In step 1), the molar ratio of melamine to boric acid is 1:10-10:1, and the dissolution temperature is 50-90°C. The co-solvent is a mixture of water and an alcohol compound, and the mixed volume ratio of water to the alcohol compound (methanol, ethanol, isopropanol, n-butanol or t-butanol) in the co-solvent is 9:11-8:5.

[0053] In step 2), the height of the precursor hydrogel is 0.5-3 cm, and the directional freezing time is 10-80 min. The vacuum freeze-drying process is selected, and the vacuum freeze-drying treatment time is 12-72 h.

[0054] In step 3), the pyrolysis temperature is 500-1400℃, and the high-temperature pyrolysis time is 0.5-5h. The pyrolysis atmosphere of the pyrolysis treatment is ammonia, argon, nitrogen, or a mixture of any two thereof in any ratio; the pyrolysis temperature of the pyrolysis treatment is 500-1400℃; and the pyrolysis time of the pyrolysis treatment is 0.5-5h.

[0055] In step 4), a vacuum-assisted in-situ impregnation process is used: the oriented boron nitride nanoribbon aerogel is placed in a polydimethylsiloxane solution, and then placed in a vacuum oven, impregnated for 1-3h after vacuumizing.

[0056] The PDMS solution is prepared by mixing PDMS prepolymer and curing agent at a mass ratio of 10:1. High-temperature curing is performed at 80-200℃ for 1-4h. The content of BNNR in the oriented BNNR / PDMS composite is 1-15% of the total mass of the composite.

[0057] Preferably, the length of the oriented BNNR is 1-950μm, and the width is 45nm-17μm.

[0058] The main elements of the oriented BNNR / PDMS composite are carbon, boron, nitrogen, and oxygen, and the internal microstructure is a nanoribbon structure. The length of the boron nitride nanoribbon in the oriented BNNR / PDMS composite is 1-950μm, and the width is 45nm-17μm. The thermal conductivity of the oriented BNNR / PDMS composite is 14.11-45.8W / m k.

[0059] The application also provides that the above-mentioned oriented BNNR / PDMS composite can be applied to the field of electronic packaging, and has high thermal conductivity, electrical insulation, and mechanical flexibility.

[0060] The technical solutions of the application are further described in detail below by means of several embodiments and in conjunction with the drawings.

[0061] Embodiment 1:

[0062] 0.2419g of melamine and 0.2381g of boric acid are weighed and added to 50mL of a t-butanol / distilled water co-solvent in which the ratio of t-butanol to distilled water is 9:11, and the concentration of the mixed solution is 10mg / mL, to obtain an M·2B precursor hydrogel. The M·2B precursor hydrogel is transferred to a liquid nitrogen freezing device and directionally frozen for 20min until the M·2B precursor hydrogel is completely converted from a liquid state to a solid state. Then the M·2B precursor hydrogel is transferred to a vacuum freeze dryer and treated for 24h to obtain an M·2B precursor aerogel.

[0063] The M·2B precursor aerogel is transferred to a tube furnace and heated to 1100℃ in an ammonia / nitrogen environment for high-temperature heat treatment for 3h to obtain an oriented BNNR aerogel.

[0064] The PDMS prepolymer and curing agent were mixed in a mass ratio of 10:1 to prepare a PDMS solution. The oriented BNNR aerogel was placed in the PDMS solution, which was transferred to a vacuum oven and immersed in a vacuum environment for 1 h, with the mass fraction of the BNNR aerogel being 10% of the composite material. The BNNR aerogel immersed in PDMS was then placed in an oven for curing. The oven temperature was 80°C, and the curing time was 2 h. An oriented BNNR / PDMS composite material was obtained.

[0065] The oriented BNNR / PDMS composite material has excellent mechanical flexibility. The test results show that the thermal conductivity value is 14.11 W / m·k, and the mechanical performance is 9 MPa. The oriented BNNR / PDMS composite material has excellent bending flexibility. Figure 1 Figure 2 The microstructure of the prepared oriented BNNR aerogel and composite material can be seen. A large number of boron nitride nanobands are distributed along one direction. The oriented BNNR / PDMS composite material has excellent bending flexibility. Figure 3 Figure 4 The microstructure of the prepared oriented BNNR aerogel and composite material can be seen. A large number of boron nitride nanobands are distributed along one direction. The oriented BNNR / PDMS composite material has excellent bending flexibility. Figure 5 In FIG. (a) of the thermal conductivity test, it can be seen that the thermal conductivity of the composite material increases significantly with the increase of the content of the BNNR aerogel. Figure 5 In FIG. (b) of the infrared thermal imaging, it can be seen that the composite material has excellent thermal conductivity.

[0066] Example 2:

[0067] 0.4838 g of melamine and 0.4762 g of boric acid were weighed and added to 50 mL of a t-butanol / distilled water co-solvent, with the ratio of t-butanol to distilled water being 9:11. The concentration of the mixed solution was 20 mg / mL. An M·2B precursor hydrogel was obtained, which was transferred to a liquid nitrogen freezing device and directionally frozen for 20 min until the M·2B precursor hydrogel completely changed from a liquid state to a solid state. Then it was transferred to a vacuum freeze dryer for 24 h to obtain an M·2B precursor aerogel.

[0068] The M·2B precursor aerogel was transferred to a tube furnace and heated to 1100°C in an ammonia / nitrogen environment for high-temperature heat treatment for 3 h to obtain an oriented BNNR aerogel.

[0069] The PDMS prepolymer and curing agent were mixed in a mass ratio of 10:1 to prepare a PDMS solution. The oriented BNNR aerogel was placed in the PDMS solution, which was transferred to a vacuum oven and immersed in a vacuum environment for 1 h, with the mass fraction of the BNNR aerogel being 10% of the composite material. The BNNR aerogel immersed in PDMS was then placed in an oven for curing. The oven temperature was 80°C, and the curing time was 2 h. An oriented BNNR / PDMS composite material was obtained. ​​

[0070] The test results show that the thermal conductivity can reach 33.70 W / m·k, and the mechanical tensile property is 20 MPa.

[0071] Example 3

[0072] 0.7962g of melamine and 0.7962g of boric acid were weighed and sequentially added to 50mL of a t-butanol / distilled water co-solvent, wherein the ratio of t-butanol to distilled water was 9:11, and the concentration of the mixed solution was 30mg / mL. An M·2B precursor hydrogel was obtained, which was transferred to a liquid nitrogen freezing device and directionally frozen for 20min until the M·2B precursor hydrogel completely changed from a liquid state to a solid state. Then it was transferred to a vacuum freeze dryer for processing for 24h, and an M·2B precursor aerogel was obtained.

[0073] The M·2B precursor aerogel was transferred to a tube furnace and heated to 1100°C in an ammonia / nitrogen environment for high-temperature heat treatment for 3h, and a directional BNNR aerogel was obtained.

[0074] PDMS prepolymer and curing agent were mixed in a mass ratio of 10:1 to prepare a PDMS solution. The directional BNNR aerogel was placed in the PDMS solution, which was transferred to a vacuum oven and immersed in a vacuum environment for 1h, and the BNNR aerogel content was 10% of the composite material. The BNNR aerogel immersed in PDMS was placed in an oven for curing. The oven temperature was 80°C, and the curing time was 2h. A directional BNNR / PDMS composite material was obtained.

[0075] The test results show that the thermal conductivity value is 45.8 W / m·k, and the mechanical property is 35 MPa.

[0076] Example 4

[0077] 0.7962g of melamine and 0.7962g of boric acid were weighed and sequentially added to 50mL of a t-butanol / distilled water co-solvent, wherein the ratio of t-butanol to distilled water was 9:11, and the concentration of the mixed solution was 30mg / mL. An M·2B precursor hydrogel was obtained, which was transferred to a liquid nitrogen freezing device and directionally frozen for 20min until the M·2B precursor hydrogel completely changed from a liquid state to a solid state. Then it was transferred to a vacuum freeze dryer for processing for 24h, and an M·2B precursor aerogel was obtained.

[0078] The M·2B precursor aerogel was transferred to a tube furnace and heated to 1100°C in an ammonia / nitrogen environment for high-temperature heat treatment for 3h, and a directional BNNR aerogel was obtained.

[0079] The PDMS prepolymer and curing agent were mixed in a mass ratio of 10:1 to prepare a PDMS solution. The oriented BNNR aerogel was placed in the PDMS solution, which was transferred to a vacuum oven and immersed in a vacuum environment for 1.5 h, and the mass of the BNNR aerogel accounted for 10% of the composite material. The PDMS-impregnated BNNR aerogel was then placed in an oven for curing. The oven temperature was 80°C, and the curing time was 1 h. An oriented BNNR / PDMS composite material was obtained.

[0080] Example 5:

[0081] 0.7962 g of melamine and 0.7962 g of boric acid were weighed and sequentially added to 50 mL of a co-solvent of ethanol / distilled water, with a ratio of 5:8, and the concentration of the mixed solution was 30 mg / mL. An M·2B precursor hydrogel was obtained, which was transferred to a liquid nitrogen freezing device and directionally frozen for 50 min until the M·2B precursor hydrogel completely changed from a liquid state to a solid state. Then it was transferred to a vacuum freeze dryer for 36 h to obtain an M·2B precursor aerogel.

[0082] The M·2B precursor aerogel was transferred to a tube furnace and heated to 1200°C in an ammonia / nitrogen environment for high-temperature heat treatment for 2 h to obtain an oriented BNNR aerogel.

[0083] The PDMS prepolymer and curing agent were mixed in a mass ratio of 10:1 to prepare a PDMS solution. The oriented BNNR aerogel was placed in the PDMS solution, which was transferred to a vacuum oven and immersed in a vacuum environment for 1.5 h, and the mass of the BNNR aerogel accounted for 10% of the composite material. The PDMS-impregnated BNNR aerogel was then placed in an oven for curing. The oven temperature was 80°C, and the curing time was 1 h. An oriented BNNR / PDMS composite material was obtained.

[0084] Example 6:

[0085] 0.7962 g of melamine and 0.7962 g of boric acid were weighed and sequentially added to 50 mL of a co-solvent of ethanol / distilled water, with a ratio of 5:8, and the concentration of the mixed solution was 30 mg / mL. An M·2B precursor hydrogel was obtained, which was transferred to a liquid nitrogen freezing device and directionally frozen for 50 min until the M·2B precursor hydrogel completely changed from a liquid state to a solid state. Then it was transferred to a vacuum freeze dryer for 36 h to obtain an M·2B precursor aerogel.

[0086] The M·2B precursor aerogel was transferred to a tube furnace and heated to 1200°C in an ammonia / nitrogen environment for high-temperature heat treatment for 2 h to obtain an oriented BNNR aerogel.

[0087] The PDMS prepolymer and curing agent were mixed in a mass ratio of 10:1 to prepare a PDMS solution. The oriented BNNR aerogel was placed in the PDMS solution, and was transferred to a vacuum oven for impregnation in a vacuum environment for 3 h, with the mass fraction of the BNNR aerogel in the composite being 10%. The BNNR aerogel impregnated with PDMS was then placed in an oven for curing. The oven temperature was 200°C, and the curing time was 4 h. An oriented BNNR / PDMS composite material was obtained.

[0088] Example 7:

[0089] 0.7962 g of melamine and 0.7962 g of boric acid were weighed out and added to 50 mL of a co-solvent of n-butanol / distilled water in a ratio of 7:9, and the concentration of the mixed solution was 30 mg / mL. An M·2B precursor hydrogel was obtained, which was transferred to a liquid nitrogen freezing device and directionally frozen for 60 min until the M·2B precursor hydrogel was completely converted from a liquid state to a solid state. It was then transferred to a vacuum freeze dryer for processing for 72 h, and an M·2B precursor aerogel was obtained.

[0090] The M·2B precursor aerogel was transferred to a tube furnace and heated to 1400°C in an ammonia / argon environment for high-temperature heat treatment for 3 h, and an oriented BNNR aerogel was obtained.

[0091] The PDMS prepolymer and curing agent were mixed in a mass ratio of 10:1 to prepare a PDMS solution. The oriented BNNR aerogel was placed in the PDMS solution, and was transferred to a vacuum oven for impregnation in a vacuum environment for 3 h, with the mass fraction of the BNNR aerogel in the composite being 10%. The BNNR aerogel impregnated with PDMS was then placed in an oven for curing. The oven temperature was 150°C, and the curing time was 3 h. An oriented BNNR / PDMS composite material was obtained.

[0092] Among many 2D thermal conductive fillers, boron nitride nanoribbons (BNNRs) have excellent thermal conductivity, high aspect ratio, and wide band gap (about 5.9 eV), and can become the most ideal nanofiller for constructing a long-range ordered heat transfer network with high thermal conductivity enhancement and excellent electrical insulation performance. Through reasonable directional freezing structure design, an oriented BNNR aerogel structure is prepared, and the pores are filled with polymers by vacuum-assisted impregnation to provide a directional high-speed transmission channel for phonon transmission, achieving a substantial improvement in the thermal conductivity of polymer-based composites. Specifically, using oriented BNNRs as the matrix, PDMS is uniformly filled in the matrix by vacuum-assisted in-situ impregnation, and an oriented BNNRs / PDMS composite material is prepared by infiltrating polydimethylsiloxane (PDMS) into the oriented boron nitride nanoribbons (BNNRs) framework, realizing a phonon superchannel with low interfacial thermal resistance.

[0093] The BNNR / PDMS composite material has high thermal conductivity, excellent electrical insulation performance and high mechanical flexibility, etc. The oriented BNNR / PDMS composite material has a three-dimensional continuous high aspect ratio thermal conductive network, which is composed of oriented BNNR, and PDMS is filled in the skeleton of the oriented BNNR to form a dense high aspect ratio three-dimensional thermal conductive composite material.

[0094] In summary, the prepared oriented BNNR / PDMS composite material not only has excellent thermal conductivity and electrical insulation performance, but also has high mechanical flexibility. Compared with the traditional electronic packaging polymer base material, it has great advantages in enhancing the heat dissipation and mechanical properties. It can be applied to thermal interface and electronic packaging materials.

[0095] The above is only to illustrate the technical idea of the present application, and cannot limit the protection scope of the present application. Any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the claims of the present application.

Claims

1. A method for preparing an aligned boron nitride nanoribbon / polydimethylsiloxane composite material, characterized in that, The method comprises the following steps: S1: subjecting a melamine diborate precursor hydrogel to directional freezing treatment, and then vacuum freeze-drying to obtain a melamine diborate precursor aerogel; S2: subjecting the melamine diborate precursor aerogel to pyrolysis treatment to obtain a directional boron nitride nanobelt aerogel; S3: using the directional boron nitride nanobelt aerogel as a substrate, uniformly filling polydimethylsiloxane resin in the substrate by vacuum-assisted impregnation, and then solidifying to obtain a directional boron nitride nanobelt / polydimethylsiloxane composite material; In the S1, the directional freezing treatment is performed in a liquid nitrogen environment; The directional freezing treatment is performed as follows: The melamine diborate precursor hydrogel is placed on a hollow copper column, the bottom of the hollow copper column is in full contact with the surface of liquid nitrogen, and directional freezing is performed.

2. The method for preparing the oriented boron nitride nanoribbon / polydimethylsiloxane composite material according to claim 1, characterized in that, In the S1, the melamine diborate precursor hydrogel is prepared as follows: melamine and boric acid are dissolved in a cosolvent, and then subjected to sufficient stirring to obtain a melamine diborate precursor hydrogel.

3. The method of claim 2, wherein the oriented boron nitride nanoribbons / polydimethylsiloxane composite is prepared by the steps of: (a) providing a mixture of boron nitride nanoribbons and polydimethylsiloxane; (b) applying a magnetic field to the mixture; and (c) removing the oriented boron nitride nanoribbons / polydimethylsiloxane composite. The molar ratio of the melamine to the boric acid is (1-10):(1-10); and the dissolving temperature is 50-90℃.

4. The method for preparing the oriented boron nitride nanoribbon / polydimethylsiloxane composite material according to claim 2, characterized in that, The cosolvent is a mixture of water and an alcohol compound, and the volume ratio of the water to the alcohol compound is (8-9):(5-11). The alcohol compound is any one of methanol, ethanol, isopropyl alcohol, n-butanol and tert-butyl alcohol.

5. The method of claim 1, wherein the oriented boron nitride nanoribbons / polydimethylsiloxane composite is prepared by the steps of: The height of the precursor hydrogel is 0.5-3 cm, and the treatment time of the vacuum freeze-drying is 12-72 h.

6. The method of claim 1, wherein the oriented boron nitride nanoribbons / polydimethylsiloxane composite is prepared by the steps of: In the S2, the pyrolysis atmosphere of the pyrolysis treatment is one or a mixture of any ratio of ammonia, argon and nitrogen; the pyrolysis temperature of the pyrolysis treatment is 500-1400℃; and the pyrolysis time of the pyrolysis treatment is 0.5-5 h.

7. The method for preparing the oriented boron nitride nanoribbon / polydimethylsiloxane composite material according to claim 1, characterized in that, In the S3, the process of uniformly filling polydimethylsiloxane resin in the substrate by vacuum-assisted impregnation is as follows: the directional boron nitride nanobelt aerogel is placed in a polydimethylsiloxane solution, and then placed in a vacuum oven, and then immersed for 1-3 h after vacuumizing. The polydimethylsiloxane solution comprises a polydimethylsiloxane prepolymer and a curing agent, and the mass ratio of the polydimethylsiloxane prepolymer to the curing agent is 10:

1. In the S3, the solidification temperature is 80-200℃, and the solidification time is 1-4 h.

8. A directional boron nitride nanobelt / polydimethylsiloxane composite material prepared by the preparation method of the directional boron nitride nanobelt / polydimethylsiloxane composite material according to any one of claims 1-7.

9. Application of the directional boron nitride nanobelt / polydimethylsiloxane composite material prepared by the preparation method of the directional boron nitride nanobelt / polydimethylsiloxane composite material according to any one of claims 1-7 in the field of electronic packaging.

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