Preparation method of polyion liquid modified boron nitride heat-conducting filler and application of polyion liquid modified boron nitride heat-conducting filler in heat-conducting composite material

Abstract

The invention discloses a preparation method of a polyion liquid modified boron nitride heat-conducting filler and application of the polyion liquid modified boron nitride heat-conducting filler in a heat-conducting composite material. According to the preparation method, a powerful and continuous macromolecular interface layer, namely an imidazole polyion liquid (PIL) modification layer, is constructed on the surface of a boron nitride nanosheet (BNNS) in situ in an in-situ polymerization manner so as to improve the bonding effect at an interface and enhance the interface heat transfer efficiency of the composite material; the interface bonding force between the filler and a polymer matrix is remarkably enhanced, the interface thermal resistance is reduced, the interface heat transfer efficiency is improved, and finally the high-performance composite material with the high heat conductivity coefficient and the uniform and compact interface structure is obtained so as to meet the urgent requirement of high-frequency and high-power-density electronic devices in the 5G era for efficient heat management.

Description

Technical Field

[0001] The present invention belongs to the field of thermal conductive materials, and in particular relates to a preparation method of a polyionic liquid modified boron nitride thermal conductive filler and an application of the same in thermal conductive composite materials. Background Art

[0002] With the popularization of 5G communications, autonomous driving, the Internet of Things, and high-density storage technologies, electronic devices are developing towards high frequency, high power density, and miniaturization. The large amount of heat energy (heat accumulation) generated during device operation can cause material aging, performance degradation, and even failure. Studies have shown that the reliability of electronic devices decreases by 50% for every 10-15°C increase in temperature. Therefore, the development of high thermal conductivity thermal management materials is a core challenge in ensuring the reliability of modern electronic systems.

[0003] Polymers are ideal matrices due to their light weight, insulation, and easy processing properties, but their intrinsic thermal conductivity is extremely low, making it difficult to meet the heat dissipation needs of high-power electronic devices. Existing technologies mainly improve thermal conductivity by filling inorganic fillers with high thermal conductivity, such as boron nitride nanosheets (BNNS). However, there are serious problems with simple filling and blending: due to the mismatch of the phonon vibration spectrum and the weak physical interface bonding between the filler and the polymer matrix, there is severe phonon scattering at the interface; the poor compatibility between the filler and the polymer matrix causes serious agglomeration of the filler in the matrix, resulting in the inability to evenly disperse the filler, which in turn results in the inability to form a continuous thermal conduction path inside the composite material, making it impossible to effectively transfer heat. Ultimately, this hinders the improvement of the thermal conductivity of the composite material: even if the filler loading is >50wt%, the thermal conductivity of the composite material is still far lower than the theoretical value (usually <5W·m -1 ·K -1 ), it is difficult to meet the heat dissipation requirements of 5G devices.

[0004] In order to reduce interfacial thermal resistance and improve the compatibility between fillers and the matrix, some inventors have proposed an interfacial non-covalent bond modification method: using small molecule modifiers to modify the fillers: through π-π interactions, electrostatic interactions, hydrogen bonds, and other modes of action, the internal interface interactions of the composite material are enhanced, the dispersion of the filler in the matrix is ​​improved, and the thermal conductivity of the composite material is increased to a certain extent. However, the small molecule modifiers used in non-covalent modification have the following problems when applied:

[0005] (1) Insufficient interaction strength: The short chain structure of small molecule modifiers makes it difficult to form a long-range continuous interface;

[0006] (2) Poor thermal stability: small molecules are easily desorbed at high temperatures, and the interface structure degrades;

[0007] (3) Low process compatibility: Solution mixing easily leads to filler agglomeration, and interface uniformity is difficult to control. Summary of the Invention

[0008] The present invention addresses the problem of insufficient thermal conductivity of existing filled polymer-based thermally conductive composite materials due to weak interface interaction between the filler and the matrix and high interface thermal resistance. The present invention provides a method for preparing a polyionic liquid-modified boron nitride thermally conductive filler and its application in thermally conductive composite materials. The present invention uses in-situ polymerization to construct a strong and continuous macromolecular interface layer, an imidazole polyionic liquid (PIL) modified layer, on the surface of boron nitride nanosheets (BNNS) to improve the bonding effect at the interface and enhance the interfacial heat transfer efficiency of the composite material. Combined with an optimized composite process, the interfacial bonding between the filler and the polymer matrix is ​​significantly enhanced, the interfacial thermal resistance is reduced, and the interfacial heat transfer efficiency is improved. Ultimately, a high-performance composite material with high thermal conductivity and a uniform and dense interface structure is obtained to meet the urgent demand for efficient thermal management of high-frequency, high-power density electronic devices in the 5G era.

[0009] The preparation method of the polyionic liquid modified boron nitride thermal conductive filler of the present invention comprises the following steps:

[0010] 0.5 mmol of 1-vinyl-3-methylimidazolium bromide ([VEIM]Br) and 0.5 mmol of sodium p-styrenesulfonate (SSNa) were dissolved in 20 mL of water, followed by the addition of 200 mg of BNNS. The mixture was stirred at 60°C under nitrogen for 40 minutes. The mixture was then heated to 80°C and stirred for 10 hours with the addition of 6 mL of a 1 wt% aqueous ammonium persulfate solution as an initiator. After the reaction, the mixture was centrifuged at 12,000 rpm for 20 minutes, washed three times with water to remove NaBr and free PIL, and freeze-dried to yield the hydrophilic PIL@BNNS.

[0011] The invention discloses an application of a polyionic liquid modified boron nitride thermal conductive filler in preparing a thermal conductive composite material.

[0012] Furthermore, aramid nanofibers are used as a polymer material matrix and mixed with the polyionic liquid modified boron nitride thermal conductive filler to prepare a thermal conductive composite material.

[0013] The specific steps include:

[0014] A suspension of aramid nanofibers was prepared, and PIL@BNNS was added to the suspension. The suspension was sheared at 10,000 rpm for 5 minutes to obtain a homogeneous dispersion of PIL@BNNS / ANF. The dispersion was continuously vacuum-assisted filtered (PTFE membrane, pore size 0.45 μm) and then hot-pressed (100°C, 15 MPa) to obtain PIL@BNNS. x / ANF composite film. Where x represents the mass of PIL@BNNS to the mass of PIL@BNNS x / the ratio of the total mass of the ANF composite membrane, x=10wt%-40wt%, such as 10wt%, 20wt%, 30wt%, 40wt%.

[0015] This invention modifies the BNNS surface with an imidazolium polyionic liquid (PIL) through in-situ polymerization to improve interfacial bonding and enhance the interfacial heat transfer efficiency of the composite material. The monomers used for the polymerization are 1-vinyl-3-methylimidazolium bromide (cation) and sodium p-styrenesulfonate (anion). The PIL is formed after in-situ polymerization, and the overall stacking creates a strong interfacial interaction.

[0016]

[0017] The PIL synthesized by the present invention has strong hydrophilicity, which effectively enhances the hydrophilicity of PIL@BNNS, thereby improving the dispersion of the filler in the matrix. The modified boron nitride is mixed with the selected polymer matrix, aramid nanofiber, to obtain a composite material. PIL bridges the filler and the matrix in the composite material, effectively reducing the interfacial thermal resistance. In addition, due to the charged characteristics of sulfonic acid functionalized imidazole trifluoroacetate, it may have a certain heat transfer ability itself, which provides the possibility for the formation of a thermal conduction path inside the composite material. This invention uses green, stable and pollution-free polymer monomers, and prepares a new modified filler (PIL@BNNS) through a mild and easy-to-operate in-situ polymerization process. The filler is evenly distributed in the matrix and is tightly bonded to the matrix, forming a long-range ordered thermal conduction path, which makes the composite material have excellent thermal conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the preparation flow chart of PIL@BNNS / aramid nanocomposites.

[0019] Figure 2 The scanning electron microscope images of BNNS (left) and PIL@BNNS (right). Figure 2 As can be seen in the right figure, PIL was successfully synthesized in granular form and evenly coated on the surface of BNNS, providing good filler dispersion for subsequent composite material preparation.

[0020] Figure 3 It's BNNS x / aramid nanocomposites (left) and PIL@BNNS x SEM image of the cross section of the aramid nanocomposite (right). Figure 3 As can be seen from the figure, the PIL@BNNS in the right figure is evenly distributed inside the composite material, forming a complete heat conduction path, while the BNNS in the left figure is agglomerated inside the composite material and it is difficult to form a heat conduction path.

[0021] Figure 4PIL@BNNS with different filler ratios x / Aramid nanocomposites and BNNS x / Aramid nanocomposite thermal conductivity diagram. Figure 4 It can be seen that when the filler content is only 30wt%, PIL@BNNS x The thermal conductivity of the BNNS / aramid nanocomposite can reach 20.8W / (m K), while the thermal conductivity of the BNNS / aramid nanocomposite can reach 20.8W / (m K). x The thermal conductivity of the PIL / aramid nanocomposite is only 8.4 W / (m K), which confirms the improvement of the thermal conductivity of the composite material by in situ growth of PIL.

[0022] Figure 5 PIL@BNNS with 30wt% filler content x / Aramid nanocomposites and BNNS x / Mechanical properties of aramid nanocomposites, from Figure 5 It can be seen that the tensile strength of the former is 163.3MPa, while that of the latter is only 79.6MPa, indicating that PIL coating also improves the mechanical properties of the composite material.

[0023] Figure 6 Comparison of the dispersibility of different polyionic liquid-modified boron nitride thermal conductive fillers in water. The left image shows the dispersion effect of PIL-MI@BNNS in water, and the right image shows the dispersion effect of PIL@BNNS in water.

[0024] Figure 7 This is a scanning electron micrograph of BNNS modified with a high-concentration precursor. The image shows excessive PIL growth on the BNNS surface, blocking the heat transfer path of the BNNS itself and significantly reducing its intrinsic thermal conductivity. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further analyzed and explained below through specific embodiments.

[0026] Example 1: Preparation of BNNS

[0027] 0.5 g of h-BN was added to 500 mL of a 1:1 volume ratio of isopropanol and water. The mixture was magnetically stirred and then ultrasonicated for 24 hours. The sonicated mixture was centrifuged at 1000 rpm for 10 minutes to remove the unstripped h-BN from the lower layer. The supernatant was centrifuged at 10,000 rpm for 10 minutes, and the sediment was vacuum-dried at 70°C for 24 hours to obtain BNNS.

[0028] Example 2: Preparation of PIL@BNNS

[0029] 0.5 mmol of 1-vinyl-3-methylimidazolium bromide ([VEIM]Br) and 0.5 mmol of sodium p-styrenesulfonate (SSNa) were dissolved in 20 mL of water, followed by the addition of 200 mg of BNNS. The mixture was stirred at 60°C under nitrogen for 40 minutes. Subsequently, the mixture was heated to 80°C and 6 mL of a 1 wt% aqueous solution of ammonium persulfate was added, followed by stirring for 10 hours. After the reaction, the mixture was centrifuged at 12,000 rpm for 20 minutes, washed three times with water to remove NaBr and free PIL, and freeze-dried to yield the hydrophilic PIL@BNNS.

[0030] This research group used other polyimidazole ionic liquids such as PIL-MI for comparative research. Due to the poor hydrophilicity of polyimidazole ionic liquid (PIL-MI), the modified PIL-MI@BNNS has a much lower dispersibility in water than PIL@BNNS. And since the polymer matrix aramid is a hydrophilic substance, if the filler has poor hydrophilicity, the filler dispersion in the subsequent composite material will be poor, thus affecting the thermal conductivity of the composite material. Figure 6 As shown in the figure, the left side shows the dispersion effect of PIL-MI@BNNS in water, and the right side shows the dispersion effect of PIL@BNNS in water. Due to the excellent hydrophilicity of PIL, it can be seen from the figure that PIL@BNNS can be evenly dispersed in water, while PIL-MI@BNNS cannot maintain a stable dispersion in water. This phenomenon also occurs in polyionic liquids with poor hydrophilicity synthesized from other ionic liquid monomers (anions include: bis(trifluoromethanesulfonyl)imide salts, hexafluorophosphate, etc., and cations include: quaternary ammonium salts or quaternary phosphonium salt vinyl monomers with long-chain alkyl groups, etc.).

[0031] In addition, in the in situ polymerization process, changing factors such as the amount, concentration and time of the precursor will cause uneven growth of PIL on the BNNS surface or cause PIL to account for too much in PIL@BNNS, affecting the intrinsic thermal conductivity of the filler. Figure 7 The scanning electron microscope image of BNNS after modification was obtained by dissolving 2 mmol of high-concentration precursors 1-vinyl-3-methylimidazolium bromide ([VEIM]Br) and 2 mmol of sodium p-styrenesulfonate (SSNa) in 20 mL of water and then adding BNNS (200 mg). It can be seen from the image that PIL grows excessively on the surface of BNNS, blocking the heat transfer path of BNNS itself, resulting in a significant decrease in its intrinsic thermal conductivity.

[0032] Example 3: Preparation of PIL@BNNS / aramid nanocomposite

[0033] First, through the The fibers were deprotonated to obtain aramid nanofiber (ANF) solution. and 1.5 g KOH were added to 500 mL dimethyl sulfoxide (DMSO). The mixture was stirred magnetically at 600 rpm for 7 days to form a dark red ANF / DMSO solution (2 mg mL -1 ). Take 25 mL of the above solution and add 25 mL of DMSO to obtain a solution diluted to 1 mg mL -1 Prepare an ANF / DMSO solution. Slowly add 500 mL of water to the diluted solution while stirring to form ANF flocculation. Wash with water to remove residual KOH and DMSO until the filtrate is neutral, and collect the ANF gel.

[0034] The prepared ANF suspension was mixed with a certain amount of PIL@BNNS and high-speed sheared at 10,000 rpm for 5 minutes to obtain a homogeneous PIL@BNNS / ANF dispersion. The dispersion was continuously vacuum-assisted filtered (PTFE membrane, pore size 0.45 μm) and hot-pressed (100°C, 15 MPa) to obtain PIL@BNNS. x / ANF composite membranes (x = 10, 20, 30, 40 (wt%)). For comparison, the same method was used to prepare BNNS-loaded composite membranes (BNNS x / ANF).

Claims

1. A method for preparing a polyionic liquid modified boron nitride thermal conductive filler, characterized in that The steps include: 1-Vinyl-3-methylimidazolium bromide and sodium p-styrenesulfonate were dissolved in water, and then BNNS was added. The mixture was stirred at 60°C for 40 minutes under nitrogen protection. The temperature was then raised and an initiator, ammonium persulfate aqueous solution, was added and stirred for reaction. After the reaction, the mixture was centrifuged and washed, and then freeze-dried to obtain hydrophilic PIL@BNNS.

2. The preparation method according to claim 1, wherein: The molar ratio of 1-vinyl-3-methylimidazolium bromide and sodium p-styrenesulfonate is 1:

1.

3. The preparation method according to claim 2, wherein: Based on the addition amount of BNNS being 200 mg, the addition amounts of 1-vinyl-3-methylimidazolium bromide and sodium p-styrenesulfonate were each 0.5 mmol.

4. The preparation method according to claim 1, wherein: The temperature was raised to 75-85°C and an aqueous solution of ammonium persulfate as an initiator was added.

5. The preparation method according to claim 4, characterized in that: After adding the initiator, the reaction temperature is controlled at 75-85°C, and the reaction time is 8-10 hours.

6. Use of the polyionic liquid modified boron nitride thermal conductive filler prepared by the preparation method according to any one of claims 1 to 5 in the preparation of a thermal conductive composite material.

7. The use according to claim 6, characterized in that: Aramid nanofibers are used as a polymer material matrix and mixed with the polyionic liquid modified boron nitride thermal conductive filler to prepare a thermal conductive composite material.

8. The use according to claim 7, characterized in that The steps include: A suspension of aramid nanofibers was prepared, and PIL@BNNS was added to the suspension. The suspension was sheared at 10,000 rpm for 5 minutes to obtain a homogeneous dispersion of PIL@BNNS / ANF. The homogeneous dispersion was subjected to continuous vacuum-assisted filtration and then hot-pressed to obtain PIL@BNNS. x / ANF composite membrane.

9. The use according to claim 8, characterized in that: The vacuum-assisted filtration uses a PTFE membrane with a pore size of 0.45 μm.

10. The use according to claim 8, characterized in that: The hot pressing temperature is 100°C and the pressure is 15 MPa.

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