A thiophene-based ionic liquid modified graphene heat-conducting filler and a heat-conducting composite material based thereon

Abstract

The application discloses a kind of thiophene-based ionic liquid modified graphene heat-conducting fillers and heat-conducting composite materials based thereon, the heat-conducting filler is with benzothiophene as raw material and is synthesized 2-methylbenzothiophene by substitution, then with methyl iodide reaction generates thiophene-based ionic liquid, again and electric stripping graphene is modified after blending and obtains filler, it is made into skeleton by ice template method, and vacuum infiltration polydimethylsiloxane process is used, and heat-conducting composite material is prepared.The cation-π and π-π synergistic effect between the thiophene-based ionic liquid synthesized in the application and the filler graphene improves the dispersibility between the fillers and enhances the heat transfer performance between the graphene, thereby significantly improving the heat-conducting performance of the PDMS-based polymer composite material under low filler content.

Description

Technical Field

[0001] This invention relates to the field of thermally conductive polymer composite materials technology, specifically to a method for preparing thiophene-based ionic liquid modified graphene thermally conductive filler and a thermally conductive composite material based thereon. Background Technology

[0002] With the development of new packaging technologies, electronic devices are becoming increasingly miniaturized, generating a significant amount of heat. Without effective heat dissipation, this heat will accumulate, causing the device temperature to rise and affecting its lifespan and stability. Polymer-based composite materials, due to their high thermal conductivity, have become the optimal choice for thermal management materials in electronic components.

[0003] Modifying thermally conductive fillers is an effective means of controlling the interfacial thermal resistance between fillers. Covalent modification mainly improves dispersibility by introducing functional groups into the filler through chemical modification, but the structure of the filler will be damaged to a certain extent, reducing its thermal conductivity. Non-covalent modification can improve the dispersibility without damaging the filler structure, mainly by reducing the interfacial thermal resistance between fillers through interactions such as hydrogen bonding, π-π, and cation-π. For example, patent CN113637275B discloses a charged polythiophene-modified graphene thermally conductive filler and a thermally conductive composite material based thereon. The modified filler is obtained by blending charged poly3-hexylthiophene with graphene nanosheets, and then P3HT-N@GNS / PVA composite material is prepared by vacuum filtration with PVA. This method can improve the thermal conductivity of PVA-based composite materials, but the effect of this filler on improving the thermal conductivity of polydimethylsiloxane (PDMS) is limited, and the preparation process of charged poly3-hexylthiophene in the patent is complex and time-consuming. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a thiophene-based ionic liquid modified graphene thermally conductive filler and a thermally conductive composite material based thereon, aiming to improve the dispersibility of the filler, reduce thermal resistance, and obtain a PDMS-based composite material with better thermal conductivity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention first discloses a thiophene-based ionic liquid modified graphene thermally conductive filler, which is obtained by blending and modifying thiophene-based ionic liquid with graphene nanosheets.

[0007] This invention also discloses a method for preparing the thiophene-based ionic liquid-modified graphene thermally conductive filler, characterized in that:

[0008] First, using benzothiophene as a raw material, it reacts with n-butyllithium and iodomethane to obtain the intermediate 2-methylbenzothiophene. Then, through a charge-changing reaction with iodomethane and silver tetrafluoroborate, it yields the thiophene-based ionic liquid 2-methyl-1-methylbenzothiophene tetrafluoroborate, denoted as BT-S. Next, graphene nanosheets, denoted as GNS, are obtained by electrochemical exfoliation of graphite. Finally, BT-S and GNS are blended and modified to obtain a thiophene-based ionic liquid-modified graphene thermally conductive filler, denoted as BT-S@GNS. The specific steps include the following:

[0009] Step 1: Preparation of 2-methylbenzothiophene

[0010] Under argon protection, 15 mL of tetrahydrofuran and 5 mmol of benzothiophene were added to a three-necked flask. The flask was cooled to -50 to -78 °C using a cryogenic reactor, and then 7.5–8 mmol of n-butyllithium was added dropwise. After the addition was complete, the reaction was allowed to proceed for 30 min, and then 10–20 mmol of iodomethane was added dropwise. The reaction solution became white and turbid. The temperature was raised to room temperature, and the reaction was stirred for 12 h. The reaction was terminated by adding 20 mL of water. The solution was extracted three times with ethyl acetate. The solution was then allowed to stand overnight with anhydrous magnesium sulfate to remove water. The solvent and unreacted benzothiophene were removed by vacuum distillation. The solution was separated by silica gel column chromatography with petroleum ether as the eluent to obtain a pale yellow solid, which is 2-methylbenzothiophene.

[0011] Step 2: Preparation of the thienyl ionic liquid 2-methyl-1-methylbenzothiophene tetrafluoroborate

[0012] Dissolve 0.3 mmol of 2-methylbenzothiophene in 1,2-dichloroethane, then add 0.44 mmol of silver tetrafluoroborate and 2.5–3 mmol of iodomethane, and react at room temperature for 12 h. Filter to remove the silver iodide precipitate, add anhydrous diethyl ether to the filtrate until a milky white suspension appears, let stand overnight in a -18°C low-temperature reactor, remove the supernatant, collect the precipitate and dry to obtain a white solid product, which is the thienyl ionic liquid 2-methyl-1-methylbenzothiophene tetrafluoroborate, denoted as BT-S.

[0013] Step 3: Preparation of graphene nanosheets

[0014] Using graphite foil as the anode, platinum foil as the cathode, and 0.1 mol / L ammonium sulfate aqueous solution as the electrolyte, the graphite foil was electrochemically exfoliated at a constant voltage of 10–15 V. After filtration, washing, and drying, graphene nanosheets, denoted as GNS, were obtained.

[0015] Step 4: Preparation of thiophene-based ionic liquid modified graphene thermally conductive filler

[0016] 100 mg BT-S was added to 100 mL of deionized water and stirred to dissolve, thus obtaining an aqueous solution of BT-S. Then, 50–100 mg of graphene was slowly added to the aqueous solution of BT-S, and the mixture was magnetically stirred and sonicated three times at room temperature, each time for 3–6 hours. The mixture was then filtered and washed three times with deionized water to remove excess thiophene ionic liquid, and then vacuum dried at 30 °C for 24 hours to obtain BT-S@GNS.

[0017] This invention further discloses a thermally conductive composite material, which is prepared by using the thiophene-based ionic liquid-modified graphene thermally conductive filler BT-S@GNS to obtain a three-dimensional framework thermally conductive network (BT-S@GNS) via an ice template method, and then using a vacuum infiltration polydimethylsiloxane process to prepare the BT-S@GNS / PDMS thermally conductive composite material. The specific preparation steps are as follows:

[0018] Step a: Preparation of the BT-S@GNS 3D skeleton

[0019] BT-S@GNS was dispersed in a 1 wt% aqueous solution of hydroxyethyl cellulose to obtain a BT-S@GNS mixture. After the mixture was evenly dispersed, it was poured into a mold with a polytetrafluoroethylene (PTFE) inner wall and a copper bottom. Then, the bottom of the mold was immersed in liquid nitrogen. By controlling the direction of ice crystal growth, BT-S@GNS formed a three-dimensional oriented structure. The structure frozen in liquid nitrogen was placed in a freeze dryer at -40℃ and 25Pa and freeze-dried for 24 hours to remove water from the framework structure, thus obtaining the BT-S@GNS framework.

[0020] Step b: Preparation of BT-S@GNS / PDMS thermally conductive composite material

[0021] The main agent and curing agent in polydimethylsiloxane (PDMS) were mixed at a mass ratio of 10:1 and stirred for 15 minutes. After degassing for 30 minutes, the BT-S@GNS skeleton was immersed in the rubber mixture and cured at 120℃ for 4 to 8 hours to obtain the BT-S@GNS / PDMS thermally conductive composite material.

[0022] The beneficial effects of this invention are reflected in:

[0023] The method of this invention can synthesize a high-yield thiophene-based ionic liquid BT-S through simple steps. Utilizing the cation-π and π-π interactions formed between BT-S and graphene, BT-S@GNS is obtained by solution blending and modifying graphene. This improves the dispersibility of the filler and enhances the heat transfer performance. Furthermore, by constructing a three-dimensional framework thermally conductive network, the heat conduction path is effectively increased, thereby significantly improving the thermal conductivity of PDMS-based polymer composites with low filler content. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the synthesis process of the thiophene-based ionic liquid 2-methyl-1-methylbenzothiophene tetrafluoroborate (BT-S) in Example 1 of the present invention;

[0025] Figure 2 The BT-S obtained in Embodiment 1 of the invention 1 HNMR spectrum;

[0026] Figure 3 The infrared spectrum of BT-S@GNS obtained in Example 1 of this invention;

[0027] Figure 4 The UV-Vis absorption spectra of BT-S and BT-S@GNS obtained in Example 1 of this invention in water;

[0028] Figure 5 This is a scanning electron microscope image of the BT-S@GNS three-dimensional skeleton in Embodiment 1 of the present invention;

[0029] Figure 6 This is a comparison diagram of the thermal diffusivity of the samples obtained in Example 1 and Comparative Examples 1 and 2 of the present invention. Detailed Implementation

[0030] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0031] Example 1

[0032] This embodiment prepares the BT-S@GNS / PDMS composite material according to the following steps.

[0033] Step 1: Preparation of 2-methylbenzothiophene

[0034] Under argon protection, 15 mL of tetrahydrofuran and 5 mmol of benzothiophene were added to a three-necked flask. The flask was cooled to -78 °C using a cryogenic reactor, and then 7.5 mmol of n-butyllithium was added dropwise. After the addition was complete, the reaction was allowed to proceed for 30 min, and then 15 mmol of iodomethane was added dropwise. The reaction solution became white and turbid. The temperature was raised to room temperature, and the reaction was stirred for 12 h. The reaction was terminated by adding 20 mL of water, and the solution was extracted three times with ethyl acetate. The solution was then allowed to stand overnight with anhydrous magnesium sulfate to remove water. The solvent and unreacted benzothiophene were removed by vacuum distillation. The solution was separated by silica gel column chromatography with petroleum ether as the eluent to obtain a pale yellow solid, which was 2-methylbenzothiophene, in a yield of 78%.

[0035] Step 2: Thiophene-based ionic liquid 2-methyl-1-methylbenzothiophene tetrafluoroborate

[0036] 0.3 mmol of 2-methylbenzothiophene was dissolved in 1,2-dichloroethane, followed by the addition of 0.44 mmol of silver tetrafluoroborate and 3 mmol of iodomethane. The reaction was carried out at room temperature for 12 h. The silver iodide precipitate was removed by filtration, and anhydrous diethyl ether was added to the filtrate until a milky white suspension appeared. The suspension was allowed to stand overnight in a reactor at -18 °C. The supernatant was removed, and the precipitate was collected and dried to obtain a white solid product, which is the thienyl ionic liquid 2-methyl-1-methylbenzothiophene tetrafluoroborate, denoted as BT-S, with a yield of 86%.

[0037] Step 3: Preparation of graphene nanosheets

[0038] Using graphite foil as the anode, platinum foil as the cathode, and 0.1 mol / L ammonium sulfate aqueous solution as the electrolyte, the graphite foil was electrochemically exfoliated at a constant voltage of 10–15 V. After filtration, washing, and drying, graphene nanosheets, denoted as GNS, were obtained.

[0039] Step 4: Preparation of thiophene-based ionic liquid-modified graphene

[0040] 100 mg BT-S was added to 100 mL of deionized water and stirred to dissolve, thus obtaining an aqueous solution of BT-S. Then, 100 mg graphene was slowly added to the aqueous solution of BT-S, and the mixture was magnetically stirred and sonicated three times at room temperature, each time for 6 hours. The mixture was then separated by filtration, washed three times with deionized water to remove excess thiophene ionic liquid, and vacuum dried at 30 °C for 24 hours to obtain BT-S@GNS.

[0041] Step 5: Fabrication of the BT-S@GNS 3D skeleton

[0042] A BT-S@GNS mixture was prepared by dispersing 100 mg of BT-S@GNS in a 1 wt% hydroxyethyl cellulose aqueous solution. After the mixture was evenly dispersed, it was poured into a mold with a polytetrafluoroethylene inner wall and a copper bottom. The bottom of the mold was then immersed in liquid nitrogen. By controlling the direction of ice crystal growth, a three-dimensional oriented structure of BT-S@GNS was formed. The structure frozen in liquid nitrogen was placed in a freeze dryer at -40℃ and 25 Pa for 24 h to remove water from the framework structure, yielding the BT-S@GNS framework.

[0043] Step 6: Preparation of BT-S@GNS / PDMS composite material

[0044] The main agent and curing agent in PDMS were mixed at a mass ratio of 10:1 and stirred for 15 min, then degassed for 30 min to obtain a silicone rubber mixture. The silicone rubber mixture was then dropped into a polytetrafluoroethylene mold. Subsequently, the BT-S@GNS skeleton was immersed in the silicone rubber mixture, vacuum infiltrated at 30℃ for 30 min, and then cured at 120℃ for 6 h to obtain the BT-S@GNS / PDMS thermally conductive composite material.

[0045] Comparative Example 1

[0046] In this comparative example, GNS / PDMS composite materials were prepared according to the following steps:

[0047] Step 1: Preparation of graphene nanosheets

[0048] Using graphite foil as the anode, platinum foil as the cathode, and 0.1 mol / L ammonium sulfate aqueous solution as the electrolyte, the graphite foil was electrochemically exfoliated at a constant voltage of 10–15 V. After filtration, washing, and drying, graphene nanosheets, denoted as GNS, were obtained.

[0049] Step 2: Preparation of the GNS 3D Skeleton

[0050] A GNS dispersion was prepared by dispersing 100 mg of GNS in a 1 wt% hydroxyethyl cellulose aqueous solution. After uniform dispersion by magnetic stirring and ultrasonication, the dispersion was poured into a mold with a polytetrafluoroethylene inner wall and a copper bottom. The bottom of the mold was then immersed in liquid nitrogen. By controlling the direction of ice crystal growth, a three-dimensional oriented structure of GNS was formed. The structure frozen in liquid nitrogen was placed in a freeze dryer at -40℃ and 25 Pa for 24 h to remove water from the framework structure, yielding the GNS framework.

[0051] Step 3: Preparation of GNS / PDMS composite material

[0052] The main agent and curing agent in PDMS were mixed at a mass ratio of 10:1 and stirred for 15 min, then degassed for 30 min to obtain a silicone rubber mixture. The silicone rubber mixture was then dropped into a polytetrafluoroethylene mold. Subsequently, the GNS skeleton was immersed in the silicone rubber mixture, vacuum infiltrated at 30℃ for 30 min, and then cured at 120℃ for 6 h to obtain a GNS / PDMS thermally conductive composite material.

[0053] Comparative Example 2

[0054] This comparative example prepared pure polydimethylsiloxane (PDMS) according to the following steps:

[0055] The main agent and curing agent in PDMS were mixed at a mass ratio of 10:1 and stirred for 15 minutes, then degassed for 30 minutes to obtain a silicone rubber mixture. The silicone rubber mixture was then dropped into a polytetrafluoroethylene mold and cured at 120°C for 6 hours to obtain pure PDMS.

[0056] Figure 1 The reaction mechanism diagram of the thiophene-based ionic liquid 2-methyl-1-methylbenzothiophene tetrafluoroborate in Example 1 is shown.

[0057] Figure 2 The thiophene-based ionic liquid (BT-S) of Example 1 1 ¹H-NMR, using D₂O as the deuterated reagent, showed δ values ​​of 8.00 (d, J = 8.0 Hz, 1H), 7.72 (dd, J = 13.3, 7.5 Hz, 2H), 7.55 (t, J = 7.6 Hz, 1H), 7.41 (s, 1H), 3.19 (s, 3H), and 2.43 (s, 3H), indicating the successful synthesis of the thiophene-based ionic liquid 2-methyl-1-methylbenzothiophene tetrafluoroborate (BT-S).

[0058] Figure 3 The infrared spectrum of BT-S@GNS obtained in Example 1 is shown at 3438 cm⁻¹. -1 The characteristic peak of -OH appeared at 1600 cm⁻¹. -1 Skeletal vibrations of the benzene ring were observed, at 2931 cm⁻¹. -1 The results, attributed to the stretching vibrations of the benzene ring and the CH group in -CH3, indicate that BT-S was successfully loaded onto the graphene sheet.

[0059] Figure 4 The UV-Vis absorption spectra of BT-S and BT-S@GNS in water are shown in the figure. As can be seen from the figure, the aqueous solution of BT-S has an absorption peak at 222.1 nm, while the dispersion of BT-S@GNS has an absorption peak at 230.9 nm. Compared with the aqueous solution of BT-S, there is a red shift, which indicates that strong cation-π and π-π interactions are generated between BT-S and GNS.

[0060] Figure 5 This is a scanning electron microscope image of the BT-S@GNS three-dimensional framework. As can be seen from the image, the graphene is arranged in an orderly layered manner, forming a long-range ordered orientation structure.

[0061] Figure 6 The figures show the thermal diffusivity test results of the thermally conductive composite materials obtained in each embodiment and comparative example. As can be seen from the figures, after BT-S modification of graphene, the thermal conductivity of the BT-S@GNS / PDMS composite material is significantly improved compared with that of the PDMS and GNS / PDMS composite materials.

[0062] In this invention, benzothiophene is first used as a raw material to synthesize a high-yield thiophene-based ionic liquid BT-S in two steps. The synergistic modification of graphene by cation-π and π-π interactions improves the dispersibility of graphene and reduces the thermal resistance between fillers, thereby significantly improving the thermal conductivity of PDMS-based thermal conductive materials. This composite material has broad application prospects in the field of thermal management materials.

[0063] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a thiophene-based ionic liquid-modified graphene thermally conductive filler, characterized in that, Includes the following steps: Step 1: Preparation of 2-methylbenzothiophene Under argon protection, 15 mL of tetrahydrofuran and 5 mmol of benzothiophene were added to a three-necked flask. The flask was cooled to -50 to -78 °C using a cryogenic reactor, and then 7.5–8 mmol of n-butyllithium was added dropwise. After the addition was complete, the reaction was allowed to proceed for 30 min, and then 10–20 mmol of iodomethane was added dropwise. The reaction solution became white and turbid. The temperature was raised to room temperature, and the reaction was stirred for 12 h. The reaction was terminated by adding 20 mL of water, and the solution was extracted three times with ethyl acetate. The solution was then allowed to stand overnight with anhydrous magnesium sulfate to remove water. The solvent and unreacted benzothiophene were removed by vacuum distillation. The solution was separated by silica gel column chromatography with petroleum ether as the eluent to obtain a pale yellow solid, which is 2-methylbenzothiophene. Step 2: Preparation of the thienyl ionic liquid 2-methyl-1-methylbenzothiophene tetrafluoroborate Dissolve 0.3 mmol of 2-methylbenzothiophene in 1,2-dichloroethane, then add 0.44 mmol of silver tetrafluoroborate and 2.5–3 mmol of iodomethane, and react at room temperature for 12 h. Filter to remove the silver iodide precipitate, add anhydrous diethyl ether to the filtrate until a milky white suspension appears, let stand overnight in a -18°C low-temperature reactor, remove the supernatant, collect the precipitate and dry to obtain a white solid product, which is the thienyl ionic liquid 2-methyl-1-methylbenzothiophene tetrafluoroborate, denoted as BT-S. Step 3: Preparation of graphene nanosheets Using graphite foil as the anode, platinum foil as the cathode, and 0.1 mol / L ammonium sulfate aqueous solution as the electrolyte, the graphite foil was electrochemically exfoliated at a constant voltage of 10~15V. After filtration, washing, and drying, graphene nanosheets, denoted as GNS, were obtained. Step 4: Preparation of thiophene-based ionic liquid modified graphene thermally conductive filler 100 mg of BT-S was added to 100 mL of deionized water and stirred to dissolve, thus obtaining an aqueous solution of BT-S. Then, 50-100 mg of graphene was slowly added to the aqueous solution of BT-S, and the mixture was magnetically stirred and sonicated three times at room temperature, each time for 3-6 hours. The mixture was then filtered and washed three times with deionized water to remove excess thiophene-based ionic liquid, and vacuum dried at 30 °C for 24 hours to obtain thiophene-based ionic liquid modified graphene thermally conductive filler, denoted as BT-S@GNS.

2. A thermally conductive composite material, characterized in that: The thiophene-based ionic liquid modified graphene thermally conductive filler BT-S@GNS prepared by the preparation method described in claim 1 was used to prepare a three-dimensional skeleton of BT-S@GNS by ice template method, and then BT-S@GNS / PDMS thermally conductive composite material was prepared by vacuum infiltration polydimethylsiloxane process.

3. A method for preparing the thermally conductive composite material according to claim 2, characterized in that, Includes the following steps: Step a: Preparation of the BT-S@GNS 3D skeleton BT-S@GNS was dispersed in an aqueous solution of hydroxyethyl cellulose to obtain a BT-S@GNS mixture. After the mixture was evenly dispersed, it was poured into a mold with a polytetrafluoroethylene inner wall and a copper bottom. Then, the bottom of the mold was immersed in liquid nitrogen. By controlling the direction of ice crystal growth, BT-S@GNS formed a three-dimensional oriented structure. The structure frozen in liquid nitrogen was placed in a freeze dryer at -40℃ and 25 Pa and freeze-dried for 24 h to remove water from the framework structure, thus obtaining a three-dimensional framework of BT-S@GNS. Step b: Preparation of BT-S@GNS / PDMS thermally conductive composite material The main agent and curing agent in PDMS were mixed at a mass ratio of 10:1 and stirred for 15 min. After degassing for 30 min, the BT-S@GNS skeleton was immersed in the rubber mixture. After curing, the BT-S@GNS / PDMS thermally conductive composite material was obtained.

4. The preparation method according to claim 3, characterized in that: In step a, the mass fraction of the hydroxyethyl cellulose aqueous solution is 1 wt%.

5. The preparation method according to claim 3, characterized in that: In step b, the curing is performed at 120 °C for 4 to 8 hours.

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