Preparation of difunctional ionic liquid modified boron nitride heat-conducting filler and application of difunctional ionic liquid modified boron nitride heat-conducting filler in heat-conducting composite material

Abstract

The invention discloses preparation of a dual-functionalized ionic liquid modified boron nitride heat-conducting filler and application of the dual-functionalized ionic liquid modified boron nitride heat-conducting filler in a heat-conducting composite material, and belongs to the field of heat-conducting materials. A novel modified filler (f-IL (at) BNNS) is prepared by using a green, stable and pollution-free ionic liquid, namely sulfonyl functionalized imidazole trifluoroacetate (f-IL), through a mild and easy-to-operate reaction process, and the filler is tightly combined with a matrix to form a long-range ordered heat conduction path, so that the composite material has excellent heat conduction performance.

Description

Technical Field

[0001] The present invention belongs to the field of thermal conductive materials, and particularly relates to the preparation of a bifunctional ionic liquid modified boron nitride thermal conductive filler and its application in thermal conductive composite materials. Background Art

[0002] With the advent of the 5G era, modern electronic products are becoming increasingly integrated, miniaturized, and sophisticated, inevitably generating significant heat accumulation within confined or enclosed spaces. This accumulated heat can negatively impact the reliability and stability of electronic devices during operation and, if not dissipated promptly, can even cause fires. It is widely believed in the industry that the bottleneck for the future development of electronic products lies in the development of effective heat dissipation materials that address the thermal failures of modern electronic products. Polymer materials have attracted widespread attention due to their significant advantages over traditional thermally conductive materials. Their excellent flexibility, lightweight, and extensive design freedom meet the needs of emerging technologies such as flexible electronics. However, their potential as ideal heat dissipation materials remains challenging, particularly due to their low thermal conductivity. Embedding high-performance inorganic fillers, particularly two-dimensional nanomaterials with high surface area and aspect ratio, into a matrix to create highly thermally conductive polymer-based composites is considered a viable strategy. Boron nitride nanosheets are considered an ideal filler for the preparation of highly thermally conductive and electrically insulating polymer-based composites. However, boron nitride is easy to agglomerate, making it difficult to distribute evenly in polymers. Its surface inertness causes it to produce a large number of interfaces inside the matrix. The lattice mismatch between the filler and the polymer matrix will produce a large amount of interfacial thermal resistance inside the composite material, hindering the improvement of thermal conductivity and limiting its practical application.

[0003] Currently, a common practice is to surface-modify boron nitride with modifiers, ensuring a uniform distribution of boron nitride within the polymer while reducing the interfacial thermal resistance within the material, thereby improving the thermal conductivity of the composite material. Researchers have primarily used covalent or non-covalent modification of boron nitride to improve interfacial thermal resistance. Covalent modification often uses strong acids and bases to prepare functionalized boron nitride nanosheets with surface hydroxylation and carboxylation. However, this is often accompanied by violent reactions that destroy the crystal structure of boron nitride and affect its intrinsic thermal conductivity. Furthermore, the use of strong acids and bases is hazardous, and improper disposal of wastewater after use can cause serious environmental pollution. Non-covalent modification, on the other hand, often uses surfactants and polydopamine, which bind to the boron nitride surface through weak non-covalent interactions such as π-π conjugation and electrostatic adsorption. However, these agents exhibit weak binding strength and low loading capacity, resulting in limited improvement in the thermal conductivity of composite materials. Furthermore, most chemical modifiers lack heat transfer capabilities, potentially compromising the thermal efficiency of composite materials. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a preparation method of a bifunctional ionic liquid modified boron nitride thermal conductive filler and its application in a thermal conductive composite material.

[0005] The present invention uses sulfonic acid-functionalized imidazole trifluoroacetate, a bifunctional ionic liquid capable of forming strong non-covalent interactions with boron nitride and a polymer matrix, as a modifier. This ionic liquid constructs a strong interface structure through a mild non-covalent interaction, combining the advantages of strong covalent bonding with the mild reaction of non-covalent interactions. This significantly improves the problem of excessive interfacial thermal resistance within boron nitride-polymer composites and effectively enhances the thermal conductivity of the composite. In the present invention, aramid nanofibers are used as the polymer matrix, and polyethylene glycol is used as the reinforcing matrix. These fibers are then combined with ionic liquid-modified boron nitride to prepare a thermally conductive composite material to verify the method's improved thermal conductivity.

[0006] The preparation method of the dual-functionalized ionic liquid modified boron nitride thermal conductive filler of the present invention comprises the following steps:

[0007] Boron nitride nanosheets (BNNS) were added to an aqueous solution of a bifunctionalized ionic liquid, ultrasonically dispersed at room temperature, and then heated for reaction under stirring. After the reaction, the mixture was centrifuged and washed, and freeze-dried to obtain a bifunctionalized ionic liquid-modified boron nitride thermal conductive filler, abbreviated as f-IL@BNNS.

[0008] Furthermore, the mass volume ratio of the boron nitride nanosheets to the aqueous solution of the bifunctionalized ionic liquid is 10 mg:1 mL. The mass concentration of the aqueous solution of the bifunctionalized ionic liquid is 5-20 wt%, preferably 10 wt%.

[0009] The bifunctionalized ionic liquid is selected from sulfonic acid functionalized imidazole trifluoroacetate ([HSO3PMIM][CF3COO]), sulfonic acid functionalized imidazole acetate ([HSO3PMIM][CH3COO]), sulfonic acid functionalized imidazole trifluoromethanesulfonate ([HSO3PMIM][CF3SO3]), sulfonic acid functionalized imidazole methanesulfonate ([HSO3PMIM][CH3SO3]), sulfonic acid functionalized imidazole hydrogen sulfate ([HSO3PMIM][HSO4]), and sulfonic acid functionalized imidazole dihydrogen phosphate ([HSO3PMIM][H2PO4]).

[0010] The bifunctionalized ionic liquid is a sulfonic acid functionalized imidazole trifluoroacetate (f-IL) having the following structure:

[0011]

[0012] The reaction temperature is 60-90°C and the reaction time is 4-12h.

[0013] The invention discloses an application of a bifunctional ionic liquid modified boron nitride thermal conductive filler in preparing a thermal conductive composite material.

[0014] Furthermore, aramid nanofibers are used as a polymer matrix material, polyethylene glycol is used as a reinforcing matrix, and the fibers are compounded with the bifunctional ionic liquid-modified boron nitride thermal conductive filler to prepare a thermal conductive composite material.

[0015] The specific steps include:

[0016] Step 1: Prepare a suspension of aramid nanofibers and mix it with f-IL@BNNS to obtain a homogeneous f-IL@BNNS / ANF dispersion;

[0017] Step 2: The f-IL@BNNS / ANF homogeneous dispersion obtained in step 1 was subjected to continuous vacuum-assisted filtration (PTFE membrane, pore size 0.22 μm) to remove excess water until the filter cake was in the form of a hydrogel.

[0018] Step 3: The f-IL@BNNS / ANF hydrogel obtained in step 2 was placed on a copper plate filled with liquid nitrogen, freeze-oriented, and then placed in a freeze dryer at -30°C to -50°C for 24 hours to obtain f-IL@BNNS / ANF aerogel;

[0019] Step 4: The f-IL@BNNS / ANF aerogel obtained in step 3 was immersed in a polyethylene glycol (PEG6000) molten liquid at 80°C. The composite film soaked with PEG was then taken out and cooled to room temperature and hot pressed (100°C, 5MPa) to obtain f-IL@BNNS. x / aramid-polyethylene glycol nanocomposite. Where x represents the percentage of f-IL@BNNS mass to the total mass of the composite material, x = 5-35wt%, such as 8wt%, 17wt%, 26wt%, 34wt%.

[0020] The f-IL@BNNS x In the aramid-polyethylene glycol nanocomposite material, the mass percentage of polyethylene glycol is 2wt%-6wt%.

[0021] The present invention utilizes sulfonic acid functionalized imidazole trifluoroacetate ([HSO3PMIM][CF3COO]) as a modifier to non-covalently modify boron nitride nanosheets through a mild reaction process involving stirring and heating. Multiple non-covalent interfacial interactions, dominated by cation-π and O-H···π, are formed between the positive charge on the imidazole ring and the sulfonic acid functional groups on the side chains of the sulfonic acid functionalized imidazole trifluoroacetate and the boron nitride nanosheets. Strong p-π orbital interactions also arise from the trifluoroacetic acid anions, resulting in a strong interfacial bonding force between the two. The modified boron nitride is then mixed with a selected polymer matrix, aramid nanofibers, to produce a composite material. The sulfonic acid functionalized imidazole trifluoroacetate forms strong hydrogen bonds with the matrix and strong interfacial interactions with the boron nitride nanosheets (BNNS), forming a bridging structure in the composite material that connects the filler to the matrix, effectively reducing interfacial thermal resistance. Furthermore, due to the charged nature of sulfonic acid-functionalized imidazolium trifluoroacetate, it may possess a certain inherent heat transfer capability, potentially enabling the formation of thermal conductivity pathways within the composite material. This study utilizes sulfonic acid-functionalized imidazolium trifluoroacetate (f-IL), a green, stable, and non-polluting ionic liquid, to prepare a novel modified filler (f-IL@BNNS) through a mild and easy-to-use reaction process. This filler tightly bonds with the matrix, forming long-range, ordered thermal conductivity pathways, resulting in a composite material with excellent thermal conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the preparation flow chart of f-IL@BNNS / aramid-polyethylene glycol nanocomposites.

[0023] Figure 2 This is the EDS mapping analysis diagram of the f-IL@BNNS morphology and its B, N, C, and O elements. Figure 2 It can be seen from the figure that f-IL is evenly attached to the surface of BNNS and BNNS is not damaged, indicating that the modification is successful.

[0024] Figure 3 The thermal conductivity diagram of f-IL@BNNSx / aramid-polyethylene glycol nanocomposites and BNNSx / aramid-polyethylene glycol nanocomposites with different filler ratios. Figure 3 It can be seen that the modified composite material f-IL@BNNSx / aramid-polyethylene glycol has better overall thermal conductivity. When the filler content is 34%, the thermal conductivity can reach 17.1W / (m K). In comparison, BNNS with the same filler content x / ANF-PEG κ ∥ Only 9.8W / (m K).

[0025] Figure 4 It is f-IL@BNNS34 / aramid-polyethylene glycol nanocomposite DSC thermal cycling test phase transition stability. Figure 4 As can be seen from the results, the composite material has good phase transition stability and can absorb more heat through phase transition at high temperatures. Furthermore, due to the uniform internal structure and even distribution of polyethylene glycol, the composite material has good thermal stability, with similar heat absorption and release values ​​after ten thermal cycles.

[0026] Figure 5 The mechanical properties comparison data of composite materials. Figure 5 It can be seen that the tensile strength of the composite material prepared by modified BNNS is stronger than that of the unmodified composite material with the same filler content (at 34wt%, 110MPa after modification and 58MPa before modification), indicating that the modification enhances the interfacial strength. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further analyzed below through specific examples.

[0028] Example 1: Preparation of BNNS

[0029] 0.5 g of h-BN was added to 500 mL of a 1:1 volumetric 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.

[0030] Example 2: Preparation of f-IL@BNNS

[0031] 500 mg of BNNS was added to 50 mL of a 10 wt% f-IL aqueous solution and sonicated at room temperature for 20 minutes. The mixture was magnetically stirred at 90°C under reflux for 6 hours. The reaction mixture was then centrifuged at 10,000 rpm for 20 minutes, washed three times with water to remove unattached f-IL, and freeze-dried to obtain f-IL@BNNS.

[0032] Example 3: Preparation of f-IL@BNNS / aramid-polyethylene glycol 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). Magnetic stirring was carried out at 600 rpm for 7 days to form a dark red ANF / DMSO solution (2 mg / mL). 25 mL of the above solution was added to 25 mL DMSO to obtain an ANF / DMSO solution diluted to 1 mg / mL. 500 mL of water was slowly added to the diluted solution during stirring to form ANF flocculation. Residual KOH and DMSO were removed by washing with water until the filtrate was neutral and the ANF suspension was collected.

[0034] The prepared ANF suspension was mixed with a certain amount of f-IL@BNNS and sheared at 10,000 rpm for 5 minutes to obtain a homogeneous dispersion of f-IL@BNNS / ANF. The dispersion was subjected to continuous vacuum-assisted filtration (PTFE membrane, pore size 0.22 μm) to remove excess water until the filter cake was in a hydrogel state. The f-IL@BNNS / ANF hydrogel was placed on a copper plate filled with liquid nitrogen below, frozen and oriented, and then placed in a freeze dryer for 24 hours to obtain f-IL@BNNS / ANF aerogel. The above-mentioned aerogel was immersed in a molten liquid of polyethylene glycol (PEG) at 80°C, and then the composite membrane impregnated with PEG was taken out, cooled to room temperature, and then hot pressed (100°C, 5MPa) to obtain f-IL@BNNS. x / aramid-polyethylene glycol nanocomposites (x=8, 17, 26, 34 (wt%)).

[0035] For comparison, BNNS was not modified and was prepared using the same method. x / aramid-polyethylene glycol nanocomposite.

Claims

1. A method for preparing a bifunctional ionic liquid modified boron nitride thermal conductive filler, characterized in that The steps include: Boron nitride nanosheets were added to an aqueous solution of a bifunctionalized ionic liquid, ultrasonically dispersed at room temperature, and then heated for reaction under stirring. After the reaction, the sheets were centrifuged and washed, and freeze-dried to obtain a bifunctionalized ionic liquid-modified boron nitride thermal conductive filler, abbreviated as f-IL@BNNS.

2. The preparation method according to claim 1, wherein: The mass volume ratio of the boron nitride nanosheets to the aqueous solution of the bifunctionalized ionic liquid is 10 mg:1 mL, and the mass concentration of the aqueous solution of the bifunctionalized ionic liquid is 5-20 wt %.

3. The preparation method according to claim 1, wherein: The bifunctionalized ionic liquid is selected from sulfonic acid functionalized imidazole trifluoroacetate, sulfonic acid functionalized imidazole acetate, sulfonic acid functionalized imidazole trifluoromethanesulfonate, sulfonic acid functionalized imidazole methanesulfonate, sulfonic acid functionalized imidazole hydrogen sulfate or sulfonic acid functionalized imidazole dihydrogen phosphate.

4. The preparation method according to claim 1, wherein: The reaction temperature is 60-90°C and the reaction time is 4-12h.

5. Use of the bifunctional ionic liquid modified boron nitride thermal conductive filler prepared by the preparation method according to any one of claims 1 to 4 in the preparation of a thermal conductive composite material.

6. The use according to claim 5, characterized in that: A thermally conductive composite material is prepared by compounding aramid nanofiber as a polymer matrix material and polyethylene glycol as a reinforcing matrix with the bifunctional ionic liquid modified boron nitride thermally conductive filler.

7. The use according to claim 6, characterized in that The steps include: Step 1: Prepare a suspension of aramid nanofibers and mix it with f-IL@BNNS to obtain a homogeneous f-IL@BNNS / ANF dispersion; Step 2: The f-IL@BNNS / ANF homogeneous dispersion obtained in step 1 was subjected to continuous vacuum-assisted filtration to remove excess water until the filter cake was in the form of a hydrogel. Step 3: The f-IL@BNNS / ANF hydrogel obtained in step 2 was placed on a copper plate filled with liquid nitrogen, freeze-oriented, and then dried in a freeze dryer to obtain f-IL@BNNS / ANF aerogel. Step 4: The f-IL@BNNS / ANF aerogel obtained in step 3 was immersed in polyethylene glycol molten liquid at 80 ° C, and then the composite film soaked with PEG was taken out and cooled to room temperature and hot pressed to obtain f-IL@BNNS x / aramid-polyethylene glycol nanocomposite.

8. The use according to claim 7, characterized in that: In step 2, a PTFE membrane with a pore size of 0.22 μm was used for vacuum-assisted filtration.

9. The use according to claim 7, characterized in that: In step 4, the hot pressing temperature is 100° C. and 5 MPa.

10. The use according to claim 7, characterized in that: The mass of f-IL@BNNS accounts for 5-35wt% of the total mass of the composite.

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