Liquid metal thermal interface material and method of making the same

Abstract

The application relates to a liquid metal thermal interface material and a preparation method thereof, and relates to the field of interface materials. The liquid metal thermal interface material comprises liquid metal and an ionic liquid; an anion part of the ionic liquid contains a multi-dentate electron-donating coordination group. The application forms a dense solvation protective film on the surface of a liquid metal droplet in situ through the strong multi-point coordination and chemical adsorption between the anion part of the ionic liquid containing the multi-dentate electron-donating coordination group and the surface of the liquid metal, which significantly improves the dispersion stability and oxidation resistance of the liquid metal thermal interface material, and makes up for the defects of the prior art.

Description

Technical Field

[0001] This invention relates to the field of interface materials, and more particularly to a liquid metal thermal interface material and its preparation method. Background Technology

[0002] As microelectronics technology continues to evolve in accordance with Moore's Law, chip power density is growing exponentially. Liquid metals, due to their excellent intrinsic thermal conductivity and good fluidity, are considered key materials for overcoming the "thermal barrier." However, liquid metals face two major challenges in practical commercial packaging and applications. First, their extremely high surface tension means they do not wet mainstream heat dissipation substrates such as copper and silicon, easily forming huge interfacial contact thermal resistance, thus limiting heat dissipation efficiency. Second, their chemical reactivity makes them prone to oxidation and corrosion under harsh environments such as 85°C / 85% relative humidity testing, leading to the collapse of the thermal conductivity network and ultimately causing thermal failure of electronic devices.

[0003] Patents CN104031600B and CN109135685A propose an insulating thermally conductive metal adhesive and its manufacturing method. This method disperses liquid metal microdroplets in an insulating matrix material to form a coating structure, laying the initial technological foundation for liquid metal composite thermal interface materials. However, early basic research mainly focused on the molding and insulation of composite materials. Many engineering challenges remain to be solved regarding long-term stability, anti-settling ability, and resistance to damp heat aging under harsh actual working conditions. This, to some extent, limits the practical application of liquid metal in the field of thermal interface materials.

[0004] Patents CN120310265A and CN116218222A disclose modification methods for introducing solid particulate fillers such as fumed silica and zinc oxide into liquid metal systems. These methods utilize physical steric hindrance to increase the system viscosity, thereby suppressing liquid metal sedimentation. However, this physical thickening method significantly increases the material viscosity, leading to poor coating process performance. Furthermore, the introduction of poorly conductive particles such as fumed silica causes severe phonon scattering within the liquid metal, resulting in a decrease in the overall thermal conductivity of the material.

[0005] To avoid the side effects of rigid fillers, patent CN113789159A discloses a silicon-free liquid metal thermal interface material using epoxy resin, polyurethane, or acrylate as a matrix. Furthermore, patents CN118895109A and CN118667278A disclose a technical solution using polyionic liquid as a matrix. These technical solutions share the common characteristic of encapsulating liquid metal droplets in a semi-solid gel network through the cross-linking reaction of organic monomers or polymer networks. While this curing and encapsulation method suppresses the risk of leakage, the solid matrix restricts the deformation and flow of the liquid metal droplets under minute encapsulation pressures, causing the final thermal interface material to lose its excellent interfacial compliance and significantly increase the interfacial contact thermal resistance. Moreover, under thermal cycling stress, this material is prone to problems such as interfacial delamination, phase separation, or liquid metal leakage.

[0006] Therefore, it is evident that the aforementioned existing technologies all suffer from the problem of balancing stability and rheological properties: curing and encapsulation increase contact thermal resistance, while physically adding solid fillers sacrifices flowability and thermal conductivity, resulting in an increase in thermal resistance of the final thermal interface material in practical applications. Furthermore, the oxidation failure problem of liquid metal under 85% aging conditions remains unresolved in these technologies. Therefore, achieving efficient dispersion and long-term stability of liquid metal through the molecular structure design of the carrier medium, without using polymer curing agents and insulating solid fillers, and thus preparing low-viscosity, low-thermal-resistance, and resistant-to-85% aging liquid metal thermal interface materials, remains a significant challenge. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a liquid metal thermal interface material and its preparation method. Specifically, it is a liquid metal thermal interface material based on anion-functionalized ionic liquid. This thermal interface material is a paste-like or viscous liquid colloid formed by dispersing liquid metal microdroplets in an ionic liquid dispersion medium. The ionic liquid is a non-curable carrier, and the anionic portion of the ionic liquid contains multidentate electron-donating coordination groups (such as functional groups containing N, P, S, or O elements) that can specifically adsorb, coordinate, or anchor the surface of gallium-based liquid metal. Based on the principle of matching soft and hard acids and bases, oxygen-containing coordination anionic functional groups are preferred. The coordination between the multidentate electron-donating ligand and the liquid metal surface forms a dense solvation protective film in situ on the surface of the liquid metal microdroplets. The solvation protective film has the following decisive functions: by forming a charged and sterically hindered solvation shell through strong chemical bonding between the anion and the liquid metal surface, it inhibits the aggregation and merging between adjacent liquid metal microdroplets, thereby achieving long-term stable dispersion of liquid metal microdroplets in low-viscosity ionic liquids; at the same time, it physically blocks the penetration of water vapor and oxygen into the interior of the liquid metal, and at the chemical level, it passivates the highly active sites on the surface of the liquid metal, inhibiting the continuous oxidation and electrochemical corrosion of the liquid metal.

[0008] Specifically, the present invention provides the following technical solution:

[0009] In a first aspect, the present invention provides a liquid metal thermal interface material, the liquid metal thermal interface material comprising liquid metal and ionic liquid; the anionic portion of the ionic liquid contains a multidentate electron-donating coordinating group (such as a functional group containing N, P, S or O elements).

[0010] Furthermore, the electron-donating coordinating group includes an oxygen-containing coordination anionic functional group; wherein the anion includes at least one of phosphate, carboxylate, nitrate, and sulfonate groups.

[0011] Furthermore, the anionic portion of the ionic liquid includes at least one of dimethyl phosphate, dibutyl phosphate, methyl phosphate monoester, dimethyl phosphonate, diethyl phosphonate, ethyl sulfate, methanesulfonate, carboxylate, nitrate, and thiocyanate.

[0012] Furthermore, the coordination between the anionic portion of the ionic liquid and the liquid metal surface forms a solvation protective film in situ on the liquid metal surface.

[0013] Furthermore, the cation of the ionic liquid includes at least one of imidazole cations, pyridine cations, pyrrolidine cations, piperidine cations, and quaternary ammonium cations.

[0014] Further, the ionic liquid comprises at least one of the following: 1-ethyl-3-methylimidazolium ethyl phosphate, 1-butyl-3-methylimidazolium dibutyl phosphate, 1,3-dimethylimidazolium dimethyl phosphonate, methyltributylphosphonic acid dimethyl phosphate, tributyl(ethyl)phosphonic acid diethyl phosphonate, 1-butyl-3-methylimidazolium dibutyl phosphate, 1-ethyl-3-methylimidazolium methanesulfonate, 3-methyl-1-octylimidazolium nitrate, 1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazolium sulfate ethyl ester, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium acetate, N-butyl-N-methylpyrrolidine acetate, and N-butyl-N-methylpiperidinedinitrileamine.

[0015] And / or, the liquid metal comprises an alloy consisting of at least one of gallium, indium, tin, zinc, and bismuth.

[0016] Furthermore, the liquid metal includes at least one of gallium-indium alloy with a melting point below 30°C and gallium-indium-tin alloy with a melting point below 30°C.

[0017] Further, the thermal interface material comprises, by weight, 5-98 parts of liquid metal (e.g., 5, 10, 20, 30, 40, 50, 80, 85, 98 parts or any range between the aforementioned values) and 2-95 parts of ionic liquid (e.g., 2, 10, 20, 30, 40, 50, 80, 85, 95 parts or any range between the aforementioned values); preferably, the thermal interface material comprises, by weight, 80-98 parts of liquid metal and 2-20 parts of ionic liquid.

[0018] Secondly, the present invention provides a method for preparing the liquid metal thermal interface material described in the first aspect, wherein liquid metal and ionic liquid are mixed and homogenized to obtain the liquid metal thermal interface material.

[0019] Furthermore, the liquid metal and ionic liquid are mixed via a mechanical shearing process. During this mixing process, the liquid metal undergoes in-situ coordination modification with the anions of the ionic liquid, resulting in the dispersion of liquid metal microdroplets within the ionic liquid to obtain the thermal interface material. Specifically:

[0020] The mechanical shearing process is selected from any one of mechanical stirring, grinding, ultrasonication or kneading, preferably stirring and shearing dispersion under negative pressure or vacuum conditions, such as vacuum degree below 1000Pa, rotation speed of 800-2500 rpm, and processing time of 1-10 minutes.

[0021] In the above preparation method, no heating is required during the mixing process. The liquid metal is directly dispersed into micron-sized droplets by high-speed shear force, and the anionic groups of the ionic liquid are used to modify the droplet surface in situ.

[0022] The technical solutions provided in the embodiments of the present invention have at least the following advantages compared with the prior art:

[0023] This invention provides a liquid metal thermal interface material and its preparation method. The invention utilizes the strong multi-point coordination and chemisorption between the anionic portion of the ionic liquid, containing multidentate electron-donating coordinating groups, and the liquid metal surface. This results in the in-situ formation of a dense solvation protective film on the surface of liquid metal microdroplets. This protective film significantly improves the dispersion stability and oxidation resistance of the liquid metal thermal interface material, overcoming the shortcomings of existing technologies. Specifically:

[0024] (1) In the liquid metal thermal interface material provided by this invention, the ionic liquid serves as a non-curable carrier for the liquid metal. Based on the hard-soft acid-base (HSAB) theory and interfacial coordination chemistry, anionic functionalized ionic liquids with highly electronegative coordinating atoms (especially oxygen donors) are preferred as the carrier for the liquid metal. Specifically, gallium atoms on the surface of gallium-based liquid metals (especially the readily formed micro-oxide state gallium) exhibit typical hard acid or interface acid characteristics. According to the principle of 'hard attracts hard' in the HSAB theory, it is attracted to oxygen-containing groups (such as P=O / PO of phosphate ester groups) that exhibit hard base characteristics. - C=O / CO of carboxylate group - It has a strong affinity. Compared with monodentate ligands, these oxygen-rich anions can undergo strong multi-point coordination and chemical adsorption with the surface of liquid metal. The solvation protective film formed in situ plays a decisive role in the application of thermal interface materials: (1) it allows microdroplets to be dispersed stably in low-viscosity ionic liquids without the need for solid additives, solving the problem of stratification and sedimentation of traditional liquid metal emulsions; (2) it physically blocks water and oxygen penetration and chemically passivates highly active sites on the surface, fundamentally inhibiting the continuous oxidation and electrochemical corrosion of liquid metals, ensuring that the material will not experience thermal network collapse and thermal failure due to oxidation crusting under harsh working conditions.

[0025] (2) This invention employs a preparation process based on anionic surface modification. By utilizing the specific coordination interaction between specific anions (such as phosphate and carboxylate groups) in the ionic liquid and the surface of the liquid metal, long-term stable dispersion of liquid metal microdroplets in the ionic liquid medium is achieved. This in-situ formed molecular-level protective layer effectively inhibits the aggregation (demulsification) and oxidation of liquid metal microdroplets, ensuring that the material can still form a uniform and delicate paste structure in the absence of solid surfactants or polymer curing agents, thus solving the technical problem of easy layering and oxidation of traditional liquid metal emulsions.

[0026] (3) This invention uses a non-curable ionic liquid as a dispersion medium, enabling the thermal interface material to possess excellent rheological properties and surface wetting ability. The extremely low volatility and good chemical stability of the ionic liquid ensure that the material does not dry out or harden under long-term high-temperature working conditions, and maintains its conformal liquid / paste state during thermal cycling. It can fill the extremely small gaps and textures on the surface of the heat sink and the chip, greatly reducing the contact thermal resistance. Furthermore, the interface formed by the coordination adsorption of anions in the ionic liquid tightly blocks the penetration of water vapor and oxygen and passivates the surface active sites, allowing the material to work for a long time under the 85℃ / 85%RH dual 85% reliability test conditions without oxidation failure.

[0027] (4) The thermal interface material prepared by this invention has the characteristics of simple preparation process (one-step physical shearing), no heating required, low cost and easy industrial production, and has broad application prospects in the field of high-performance electronic heat dissipation. It can be widely used in the heat dissipation packaging of high-performance CPUs / GPUs, high-power IGBT modules, optical communication equipment and aerospace electronic equipment. By adjusting the type of anions and the loading ratio of liquid metal, the viscosity and thermal conductivity of the material can be customized to meet the heat dissipation requirements of devices with different power densities. Attached Figure Description

[0028] Figure 1 Physical images of the samples prepared in Examples 1, 9 and Comparative Example 1.

[0029] Figure 2 Infrared spectrum of the thermal interface material prepared in Example 1.

[0030] Figure 3 Comparison of physical changes of the samples before and after Double 85 in Example 1 and Comparative Example 3. Detailed Implementation

[0031] The present invention will be specifically described below through embodiments. It should be noted that these embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above description of the present invention.

[0032] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. Furthermore, unless otherwise specified or detailed, the steps and parameters involved can be performed according to existing processing techniques or using existing equipment; these will not be elaborated upon in detail in this invention document.

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Example 1

[0035] This example provides a liquid metal thermal interface material, comprising a liquid metal and an ionic liquid; wherein the ionic liquid used is 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP), and the liquid metal is metallic gallium (Ga). The raw materials are weighed at a mass ratio of Ga:EMIMDEP = 93:7. The metallic gallium and EMIMDEP are added to the mixing container of a vacuum mixer and mixed and dispersed under negative pressure at a rotation speed of 1500 rpm for 5 minutes. After mixing, a homogeneous and fine paste-like liquid metal thermal interface material is obtained.

[0036] Example 2

[0037] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the ratio of liquid metal to EMIMDEP is adjusted from 93:7 to 5:95, while the remaining steps are the same as in Example 1.

[0038] Example 3

[0039] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP) with 1-butyl-3-methylimidazolium dibutyl phosphate (BMIMDBP), while the remaining steps are the same as in Example 1.

[0040] Example 4

[0041] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by 1,3-dimethylimidazolium diethyl phosphate (EMIMDEP) with 1,3-dimethylimidazolium dimethylphosphonate (MMIMDMP), while the remaining steps are the same as in Example 1.

[0042] Example 5

[0043] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by methyl tributylphosphonium phosphate dimethyl phosphate (EMIMDEP) instead of 1-ethyl-3-methylimidazolium diethyl phosphate (P1444DMP), while the remaining steps are the same as in Example 1.

[0044] Example 6

[0045] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by ethyl tributylphosphonium diethylphosphonate (P2444DEP) instead of 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP). The remaining steps are the same as in Example 1.

[0046] Example 7

[0047] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP) with 1-butyl-3-methylimidazolium dibutyl phosphate (BMIMDBP), while the remaining steps are the same as in Example 1.

[0048] Example 8

[0049] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP) with 1-ethyl-3-methylimidazolium methanesulfonate (EMIMMSA), while the remaining steps are the same as in Example 1.

[0050] Example 9

[0051] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP) with 1-octyl-3-methylimidazolium nitrate (OMIMNO3), while the remaining steps are the same as in Example 1.

[0052] Example 10

[0053] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP) with 1-ethyl-3-methylimidazolium thiocyanate (EMIMSCN), while the remaining steps are the same as in Example 1.

[0054] Example 11

[0055] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP) with 1-ethyl-3-methylimidazolium ethyl sulfate (EMIMESO4), while the remaining steps are the same as in Example 1.

[0056] Example 12

[0057] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP) with 1-ethyl-3-methylimidazolium acetate (EMIMAc), while the remaining steps are the same as in Example 1.

[0058] Example 13

[0059] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP) with 1-butyl-3-methylimidazolium acetate (BMIMAc), while the remaining steps are the same as in Example 1.

[0060] Example 14

[0061] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by N-methyl-N-butylpyrrolidone acetate (Pyr14Ac) instead of 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP). The remaining steps are the same as in Example 1.

[0062] Example 15

[0063] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the anionic functionalized ionic liquid is replaced by N-methyl-N-butylpiperidine dinitrile amine salt (PP14DCA) instead of 1-ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP). The remaining steps are the same as in Example 1.

[0064] Example 16

[0065] This example provides a liquid metal thermal interface material, which differs from Example 1 in that a stirring head is used instead of a vacuum mixer for mixing and dispersion, and degassing is performed after stirring to obtain the thermal interface material.

[0066] Example 17

[0067] This example provides a liquid metal thermal interface material, which differs from Example 1 in that the liquid metal is replaced by a gallium indium alloy with a gallium indium tin alloy, while the remaining steps are the same as in Example 1.

[0068] Comparative Example 1

[0069] A liquid metal thermal interface material differs from Example 1 in that 1,3-dimethylimidazolium diethyl phosphate is replaced with 1,3-dimethylimidazolium tetrafluoroborate, while the remaining steps are the same as in Example 1.

[0070] Comparative Example 2

[0071] A liquid metal thermal interface material differs from Example 1 in that 1,3-dimethylimidazolium diethyl phosphate is replaced with 1,3-dimethylimidazolium hexafluorophosphate, while the remaining steps are the same as in Example 1.

[0072] Comparative Example 3

[0073] A liquid metal thermal interface material differs from Example 1 in that 1,3-dimethylimidazolium diethyl phosphate is replaced with 1000cs dimethyl silicone oil, while the remaining steps are the same as in Example 1.

[0074] Test case

[0075] In this example, the thermal resistance of the above-mentioned examples and comparative samples was tested under low pressure (10 psi) using the ASTM D5470 standard. The thermal resistance change of the samples after aging at 85°C / 85%RH for 30 days was further tested. The test results are shown in Table 1.

[0076] Table 1 Thermal resistance of each embodiment and comparative example

[0077] sample Mixing uniformity <![CDATA[Thermal resistance (mm 2 K / W)]]> <![CDATA[Double 85 post-heat resistance (mm 2 K / W)]]> Example 1 Mix evenly 2.52 2.63 Example 2 Mix evenly 2.87 3.02 Example 3 Mix evenly 2.03 3.06 Example 4 Mix evenly 2.91 2.17 Example 5 Mix evenly 2.27 2.63 Example 6 Mix evenly 2.37 2.55 Example 7 Mix evenly 2.39 2.89 Example 8 Mix evenly 2.80 2.88 Example 9 Mix evenly 2.15 2.12 Example 10 Mix evenly 2.38 2.71 Example 11 Mix evenly 2.97 3.54 Example 12 Mix evenly 2.70 3.12 Example 13 Mix evenly 2.87 2.86 Example 14 Mix evenly 2.80 2.78 Example 15 Mix evenly 2.91 3.42 Example 16 Mix evenly 2.33 2.28 Example 17 Mix evenly 2.41 2.44 Comparative Example 1 Cannot be mixed Cannot be mixed / Comparative Example 2 Cannot be mixed Cannot be mixed / Comparative Example 3 Mix evenly 5.56 ＞100

[0078] As shown in Table 1, the anionic functionalized ionic liquid used in this invention can form a uniform and stable colloidal system with liquid metal, and significantly improve the interfacial heat transfer performance and damp heat aging stability of the material.

[0079] Specifically, in Example 1, EMIMDEP was combined with metallic gallium. The resulting material could be uniformly mixed, with an initial thermal resistance of 2.52 mm²K / W. After aging at 85°C / 85%RH for 30 days, the thermal resistance only increased to 2.63 mm²K / W, indicating that the system has low interfacial thermal resistance and good long-term stability.

[0080] In Example 2, even after reducing the proportion of liquid metal, the resulting material could still be mixed uniformly, although the thermal resistance increased to 2.87 mm. 2 K / W, the thermal resistance after 30 days of aging with dual 85 is 3.02mm. 2 Despite its low K / W, it still boasts low interfacial thermal resistance while maintaining good stability.

[0081] After replacing the functionalized ionic liquids with different anion types in Examples 3-15, the resulting materials were all able to achieve uniform mixing without significant phase separation; the initial thermal resistance of the materials was 2.03-2.97 mm. 2 The thermal resistance of K / W after 30 days of aging with dual 85 is 2.12~3.54mm. 2K / W, thermal resistance showed no significant deterioration, and the overall performance remained stable. The results indicate that, in addition to phosphate ester anions, various coordination anions, such as phosphonates, carboxylates, sulfonic acids, sulfates, nitrates, thiocyanates, and dinitrileamines, can effectively adsorb, coordinate, or anchor at the liquid metal surface, exhibiting excellent interface regulation and aging stabilization effects.

[0082] Example 16 uses a stirring head combined with subsequent degassing treatment, and the resulting material can still be uniformly mixed with a thermal resistance of 2.33 mm. 2 K / W, the thermal resistance after 30 days of aging with dual 85 is 2.28mm. 2 K / W indicates that the present invention is not limited to a specific device such as a vacuum mixer; high-performance thermal interface materials can also be obtained through conventional mechanical stirring combined with degassing treatment.

[0083] In Example 17, after replacing the liquid metal with a gallium-indium alloy, the resulting material could still be uniformly mixed, and the initial thermal resistance was 2.41 mm. 2 K / W, the thermal resistance after 30 days of aging with dual 85 is 2.44mm. 2 K / W indicates that the solution of the present invention is applicable not only to a single liquid metal system, but also to a variety of gallium-based liquid metal systems, and has good versatility.

[0084] In contrast, when using ionic liquids with tetrafluoroborate and hexafluorophosphate anions in Comparative Examples 1 and 2, respectively, the samples could not be effectively mixed. This indicates that not all ionic liquids can form a stable system with liquid metals. Anions must have the ability to specifically adsorb, coordinate, or anchor at the interface with the surface of liquid metals in order to achieve stable dispersion.

[0085] In Comparative Example 3, when dimethyl silicone oil was used to replace the anionic functionalized ionic liquid, although uniform mixing could be achieved in the initial state, its thermal resistance was as high as 5.56 mm²K / W. After 30 days of aging with double 85, the thermal resistance increased significantly to over 100 mm²K / W. This indicates that ordinary non-reactive organic media can only achieve apparent mixing and cannot form a stable and effective interface layer on the liquid metal surface. Therefore, it is difficult to achieve both low thermal resistance and long-term reliability.

[0086] In addition, physical images of the samples prepared in Example 1, Example 9 and Comparative Example 1 are shown below. Figure 1 As shown, the infrared spectrum of the thermal interface material prepared in Example 1 is as follows. Figure 2 As shown in the figure, the physical changes of the samples before and after the double 85 test in Example 1 and Comparative Example 3 are compared. Figure 3 As shown.

[0087] In summary, this invention introduces functional groups into the ionic liquid anion that can adsorb, coordinate, or interfacially anchor with the surface of gallium-based liquid metals, enabling the liquid metal to be stably dispersed and form a uniform and fine colloidal material. This results in lower initial thermal resistance and excellent 85% aging stability. The technical effect of this invention cannot be achieved by simply changing the dispersion medium, but rather stems from the specific interaction between the anion-functionalized ionic liquid and the liquid metal interface.

[0088] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A liquid metal thermal interface material, characterized in that, It includes liquid metals and ionic liquids; the anionic portion of the ionic liquid contains polydentate electron-donating coordinating groups.

2. The liquid metal thermal interface material according to claim 1, characterized in that, The electron-donating coordinating group includes an oxygen-containing coordination anionic functional group; wherein the anion includes at least one of phosphate, carboxylate, nitrate, and sulfonate groups.

3. The liquid metal thermal interface material according to claim 1, characterized in that, The anionic portion of the ionic liquid includes at least one of dimethyl phosphate, dibutyl phosphate, methyl phosphate monoester, dimethyl phosphonate, diethyl phosphonate, ethyl sulfate, methanesulfonate, carboxylate, nitrate, and thiocyanate.

4. The liquid metal thermal interface material according to any one of claims 1 to 3, characterized in that, The anionic portion of the ionic liquid coordinates with the surface of the liquid metal to form a solvation protective film in situ on the surface of the liquid metal.

5. The liquid metal thermal interface material according to any one of claims 1 to 3, characterized in that, The cations of the ionic liquid include at least one of imidazole cations, pyridine cations, pyrrolidine cations, piperidine cations, and quaternary ammonium cations.

6. The liquid metal thermal interface material according to any one of claims 1 to 3, characterized in that, The ionic liquid comprises at least one of the following: 1-ethyl-3-methylimidazolium ethyl phosphate, 1-butyl-3-methylimidazolium dibutyl phosphate, 1,3-dimethylimidazolium dimethyl phosphonate, methyltributylphosphonic acid dimethyl ester salt, tributyl(ethyl)phosphonic acid diethyl phosphonate, 1-butyl-3-methylimidazolium dibutyl phosphate salt, 1-ethyl-3-methylimidazolium methanesulfonate, 3-methyl-1-octylimidazolium nitrate, 1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazolium ethyl sulfate salt, 1-ethyl-3-methylimidazolium acetate salt, 1-butyl-3-methylimidazolium acetate salt, N-butyl-N-methylpyrrolidine acetate salt, and N-butyl-N-methylpiperidinedinitrileamine salt; And / or, the liquid metal comprises an alloy consisting of at least one of gallium, indium, tin, zinc, and bismuth.

7. The liquid metal thermal interface material according to claim 6, characterized in that, The liquid metal includes at least one of gallium-indium alloy with a melting point below 30°C and gallium-indium-tin alloy with a melting point below 30°C.

8. The liquid metal thermal interface material according to any one of claims 1 to 3, characterized in that, The thermal interface material comprises, by mass, 5-98 parts of liquid metal and 2-95 parts of ionic liquid.

9. A method for preparing a liquid metal thermal interface material according to any one of claims 1 to 8, characterized in that, The liquid metal thermal interface material is prepared by uniformly mixing the liquid metal and the ionic liquid.

10. The method for preparing a liquid metal thermal interface material according to claim 9, characterized in that, The liquid metal and ionic liquid are mixed by a mechanical shearing process. During the mixing process, the liquid metal and the anions of the ionic liquid undergo in-situ coordination modification, so that the liquid metal microdroplets are dispersed in the ionic liquid to obtain the thermal interface material.

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