Composite heat-conducting gel and preparation method thereof

Abstract

The application provides a composite heat-conducting gel and a preparation method thereof. The composite heat-conducting gel comprises the following components in parts by mass: 1-10 parts of a polymer matrix; 50-99 parts of a liquid metal filler; 0.2-2 parts of an interface functional modifier; and 1-20 parts of a ceramic heat-conducting filler. The liquid metal filler comprises liquid metal droplets, and the interface functional modifier is adsorbed on exposed metal surfaces and / or surface oxide layers of the liquid metal droplets. The ceramic heat-conducting filler is distributed between adjacent liquid metal droplets and separates the adjacent liquid metal droplets from each other. The composite heat-conducting gel has high heat conduction capacity and good structural stability due to the synergistic cooperation among the liquid metal droplets, the interface functional modifier and the ceramic heat-conducting filler, which improves the interface stability of the liquid metal droplets and inhibits the coalescence of the liquid metal droplets.

Description

Technical Field

[0001] This application relates to the field of functional materials and electronic device thermal management technology, and in particular to a composite thermally conductive gel with high thermal conductivity, high stability and good processability, as well as a preparation method for preparing the composite thermally conductive gel. Background Technology

[0002] With the rapid development of high-end electronic devices such as 5G communication, high-performance computing chips, and power batteries for new energy vehicles, the power density and heat flux of electronic devices are increasing dramatically. To reduce the contact thermal resistance between heat-generating devices and heat sinks, thermal interface materials such as thermally conductive gels are typically placed between them to fill the microscopic gaps at the contact interface and improve the efficiency of heat transfer from the heat-generating device to the heat sink. At the same time, higher requirements are being placed on the thermal conductivity, interfacial contact performance, and long-term reliability of thermal interface materials (TIMs).

[0003] Existing thermally conductive gels typically use polymer materials such as silicone as the matrix, and incorporate ceramic thermally conductive fillers to improve the material's thermal conductivity. However, the polymer matrix itself has low thermal conductivity, and relying solely on ceramic thermally conductive fillers to improve thermal conductivity usually requires increasing the amount of ceramic filler added. Increasing the amount of ceramic thermally conductive filler can easily lead to increased system viscosity, difficulties in filler dispersion, and increased challenges in mixing and degassing, thus affecting the processability and interfacial filling capacity of the thermally conductive gel. Therefore, traditional polymer-based thermally conductive gels struggle to simultaneously achieve both high thermal conductivity and good processability.

[0004] Liquid metals combine the thermal conductivity of metallic materials with the fluidity of liquid materials. Adding liquid metals as thermally conductive fillers to polymer matrices can improve the thermal conductivity of thermally conductive gels. However, liquid metals typically have high density and surface tension, and oxide layers easily form on their surfaces. When the interfacial compatibility between the liquid metal and the polymer matrix is ​​insufficient, it is difficult for the liquid metal to form droplets with stable size and distribution within the polymer matrix, leading to problems such as uneven droplet size, localized aggregation, and uneven distribution. These problems become more pronounced with increasing amounts of liquid metal filler, thus limiting the application of liquid metals in highly filled composite thermally conductive gels.

[0005] Liquid metal droplets exhibit fluidity. When adjacent liquid metal droplets come into direct contact, they are prone to coalescence (collision merging or secondary fusion), which affects the structural stability of the composite thermally conductive gel during preparation, storage, and use. Although existing technologies allow for the co-incorporation of liquid metal fillers and ceramic thermally conductive fillers into the polymer matrix, conventional mixing methods often result in a random distribution of the ceramic thermally conductive fillers, making it difficult to effectively maintain the spacing between adjacent liquid metal droplets. Furthermore, existing interface control methods are insufficient in addressing the exposed metal surface and its oxide layer, making it difficult to maintain the interfacial stability of liquid metal droplets over long periods with high liquid metal loading levels.

[0006] Therefore, existing composite thermally conductive gels still struggle to simultaneously address the issues of limited thermal conductivity of the polymer matrix, insufficient interfacial stability of liquid metal droplets, and easy contact and aggregation of adjacent liquid metal droplets, making it difficult to achieve a balance between high thermal conductivity, stability, and processability.

[0007] Therefore, how to stabilize the interfacial state of liquid metal droplets while increasing the content of liquid metal filler, and how to maintain the spacing between adjacent liquid metal droplets using ceramic thermally conductive fillers, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The composite thermally conductive gel and its preparation method provided in this application are intended to solve at least some of the defects of existing composite thermally conductive gels.

[0009] In a first aspect, embodiments of this application provide a composite material. The composite thermally conductive gel, by mass parts, comprises the following components: 1 to 10 parts of polymer matrix; 50 to 99 parts of liquid metal filler; Interface functional modifier 0.2 to 2 parts; 1 to 20 parts of ceramic thermally conductive filler; The liquid metal filler comprises liquid metal droplets, and the interfacial functional modifier is adsorbed onto the exposed metal surface and / or surface oxide layer of the liquid metal droplets; The ceramic thermally conductive filler is distributed between adjacent liquid metal droplets, and the adjacent liquid metal droplets are spaced apart from each other.

[0010] In some embodiments, the polymer matrix is ​​an addition-type organosilicon system, the liquid metal filler is a eutectic gallium-indium alloy or a gallium-indium-tin alloy, and the ceramic thermally conductive filler is a spherical or near-spherical ceramic powder with a hydrophobic modified surface.

[0011] In some embodiments, the addition-type silicone system includes: Vinyl-terminated silicone oil and hydrogen-containing silicone oil crosslinking agent, wherein the vinyl-terminated silicone oil and the hydrogen-containing silicone oil crosslinking agent are configured to be crosslinked and cured via a hydrosilylation reaction; The viscosity of the vinyl-terminated silicone oil is between 100 cP and 100,000 cP.

[0012] In some embodiments, the spherical or near-spherical ceramic powder is zinc oxide powder, alumina powder, or aluminum nitride powder, and the median particle size of the spherical or near-spherical ceramic powder is 1 μm to 10 μm.

[0013] In some embodiments, the interface functional modifier is at least one of a carbon chain backbone silane coupling agent and a siloxane backbone coupling agent; The matrix-loving end of the carbon chain skeletal silane coupling agent contains vinyl or long-chain alkyl groups, and the metal-loving end of the carbon chain skeletal silane coupling agent contains active functional groups that can coordinate and / or adsorb with the exposed metal surface and / or surface oxide layer of the liquid metal. The siloxane backbone coupling agent has a siloxane backbone and a trialkoxy terminal group located at one end of the siloxane backbone.

[0014] In some embodiments, the vinyl group in the carbon chain backbone silane coupling agent can undergo a crosslinking reaction with the addition-type organosilicon system, the trialkoxy end group is a trimethoxy end group or a triethoxy end group, and the active functional group is at least one of epoxy, mercapto, and amino groups.

[0015] Secondly, embodiments of this application provide a method for preparing a composite thermally conductive gel, the method being used to prepare the aforementioned composite thermally conductive gel. The preparation method includes the following steps: Step 1, providing catalyst and inhibitor, and providing by weight parts: 1 to 10 parts polymer matrix, 50 to 99 parts liquid metal filler, 0.2 to 2 parts interface functional modifier and 1 to 20 parts ceramic thermally conductive filler; The polymer matrix is ​​an addition-type silicone system, which includes end-vinyl silicone oil and a hydrogen-containing silicone oil crosslinking agent. The end-vinyl silicone oil includes a first end-vinyl silicone oil having a first viscosity and a second end-vinyl silicone oil having a second viscosity, wherein the first viscosity is less than the second viscosity. Step 2: Mix all the liquid metal fillers, all the interfacial functional modifiers and all the first-terminal vinyl silicone oil provided in Step 1 to obtain a mixture. Step 3: The mixture obtained in Step 2 is subjected to low-frequency acoustic resonance dispersion treatment, which breaks the liquid metal filler in the mixture into liquid metal droplets, and at the same time, the interfacial functional modifier in the mixture is adsorbed on the exposed metal surface and / or surface oxide layer of the liquid metal droplets to obtain a pre-dispersed precursor. Step 4: Add the catalyst, inhibitor, all ceramic thermally conductive filler, all hydrogen-containing silicone oil crosslinking agent and all second-terminal vinyl silicone oil provided in Step 1 to the pre-dispersed precursor obtained in Step 3, and perform rotational shear mixing under vacuum conditions to obtain a premixed composite. Step 5: The premixed composite obtained in Step 4 is subjected to dual planetary stirring and shear dispersion under vacuum and heating conditions to remove air bubbles from the premixed composite, thereby obtaining the composite thermally conductive gel.

[0016] In some embodiments, the low-frequency acoustic resonance dispersion process includes: The mixture was dispersed for 10 min under conditions of a resonant frequency of 60 Hz to 70 Hz and an oscillation acceleration of 50 G (G is the acceleration due to gravity) to 60 G, and then cooled to room temperature. The mixture cooled to room temperature was dispersed for 10 to 15 minutes under conditions of a resonant frequency of 60 Hz to 70 Hz and an oscillation acceleration of 70 G to 80 G.

[0017] In some embodiments, the revolution speed of the rotation-rotation shear mixing is 500 r / min to 1500 r / min, the rotation speed is 100 r / min to 500 r / min, and the mixing time is 3 min to 15 min; The rotational shearing mixing causes the ceramic thermally conductive filler to be uniformly distributed between the interface-modified liquid metal droplets.

[0018] In some embodiments, the dual planetary stirring and shear dispersion treatment is carried out under a vacuum degree not exceeding -0.095 MPa; The revolution speed of the dual planetary stirring and shear dispersion treatment is 30 r / min to 100 r / min, the rotation speed is 800 r / min to 1200 r / min, and the heating treatment time is 2 h to 3 h.

[0019] Unlike existing technologies, at least one beneficial effect of the composite thermally conductive gel and its preparation method provided in this application is that by setting 50 to 99 parts of liquid metal filler and 1 to 20 parts of ceramic thermally conductive filler in a polymer matrix, the high thermal conductivity of the liquid metal filler and the heat transfer effect of the ceramic thermally conductive filler facilitate the formation of a multiphase heat transfer path involving both liquid metal droplets and ceramic thermally conductive filler within the composite thermally conductive gel, thereby improving the thermal conductivity of the composite thermally conductive gel. Simultaneously, the liquid metal filler exists in the form of liquid metal droplets, and the interface functional modifier is adsorbed on the exposed metal surface and / or surface oxide layer of the liquid metal droplets, which can improve the interface state of the liquid metal droplets, reduce the possibility of interface defects caused by insufficient interfacial bonding between the liquid metal droplets and surrounding materials, improve the interfacial stability of the liquid metal droplets in the composite thermally conductive gel, and reduce the interfacial thermal resistance between different thermally conductive components. Furthermore, the ceramic thermally conductive filler is distributed between adjacent liquid metal droplets, spacing them apart. This reduces the chance of direct contact between the droplets, decreasing the likelihood of droplet aggregation and subsequent microstructural changes. This helps maintain the distribution of the liquid metal droplets and improves the structural stability of the composite thermally conductive gel during preparation, storage, and use. Therefore, through the synergistic effect of the liquid metal droplets, the interfacial functional modifier, and the ceramic thermally conductive filler, this composite thermally conductive gel improves its thermal conductivity while simultaneously enhancing the interfacial stability of the liquid metal droplets and inhibiting their aggregation. This results in a composite thermally conductive gel possessing both high thermal conductivity and good structural stability. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic flowchart illustrating the preparation method of composite thermally conductive gel provided in some embodiments of this application. Detailed Implementation

[0022] The principles and spirit of the invention will be described below with reference to several exemplary embodiments illustrated in the accompanying drawings. It should be understood that these specific embodiments are described merely to enable those skilled in the art to better understand and implement the invention, and are not intended to limit the scope of the invention in any way. In the following description, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

[0023] As used herein, the term "comprising" and similar expressions should be understood as open inclusion, i.e., "including but not limited to". The term "based on" should be understood as "at least partially based on". The terms "an embodiment" or "the embodiment" should be understood as "at least one embodiment". The terms "first", "second", etc., may refer to different or the same objects and are used only to distinguish the objects referred to, without implying a specific spatial order, temporal order, or order of importance of the objects referred to.

[0024] The term "median particle size" refers to the particle size corresponding to a cumulative volume fraction of 50%, that is, the particle size corresponding to a cumulative volume particle size distribution of 50%. Therefore, the median particle size is also called D50.

[0025] The composite thermally conductive gel comprises the following components by weight: 1 to 10 parts polymer matrix, 50 to 99 parts liquid metal filler, 0.2 to 2 parts interface functional modifier, and 1 to 20 parts ceramic thermally conductive filler.

[0026] The polymer matrix is ​​used to provide a continuous phase structure and to provide tunable mechanical and processing properties for the composite thermally conductive gel. In the embodiments of this application, the polymer matrix adopts an addition-type silicone system, which includes a vinyl-terminated silicone oil and a hydrogen-containing silicone oil crosslinking agent, and the viscosity of the vinyl-terminated silicone oil is 100 cP to 100,000 cP; wherein, the vinyl-terminated silicone oil and the hydrogen-containing silicone oil crosslinking agent are configured to be crosslinked and cured by a hydrosilylation reaction; that is, the vinyl-terminated silicone oil and the hydrogen-containing silicone oil crosslinking agent can undergo a hydrosilylation reaction under the action of a catalyst (also referred to as a crosslinking reaction between the vinyl-terminated silicone oil and the hydrogen-containing silicone oil), and the reaction rate and processing stability of the above crosslinking reaction are controlled under the action of an inhibitor (which can also be understood as the inhibitor being able to inhibit the above crosslinking reaction from occurring prematurely); in addition, the catalyst includes, but is not limited to, a platinum catalyst, and the inhibitor includes, but is not limited to, alkynyl alcohol curing inhibitors.

[0027] Liquid metals, due to their high intrinsic thermal conductivity (20 W / m·K to 40 W / m·K) and compressibility, have become potential thermally conductive fillers that can overcome the performance limits of traditional silicone-based thermally conductive gels. Therefore, this liquid metal filler is used to provide a high thermal conductivity transport path. Specifically, highly filled liquid metal dispersed in a siloxane polymer matrix can form a composite thermally conductive gel with low modulus, high thermal conductivity, and excellent interfacial adhesion. In the embodiments of this application, the liquid metal filler is selected from eutectic gallium indium alloy (EGaIn) or gallium indium tin alloy (GaInSn).

[0028] Taking a eutectic gallium-indium alloy as an example, the eutectic gallium-indium alloy includes gallium with a mass percentage of 75.5% and indium with a mass percentage of 24.5%.

[0029] Because liquid metal has high density and high surface tension (the surface tension of liquid metal is usually >400 mN / m), directly adding liquid metal to the polymer system can easily lead to the aggregation, uneven dispersion and insufficient interfacial bonding of liquid metal. Therefore, this application regulates the interface of liquid metal by using an interface functional modifier and combines it with a low-frequency acoustic resonance dispersion method to break up the liquid metal filler into liquid metal droplets.

[0030] While traditional mechanical stirring or planetary shearing can initially break liquid metal into micron-sized droplets, the system is thermodynamically unstable. After shearing stops, traditional liquid metal droplets are prone to collision and fusion under their own gravity and residual stress, which can lead to uncontrolled particle size or even macroscopic metal phase separation.

[0031] In the embodiments of this application, the median particle size of the liquid metal droplets can be controlled within the range of 10 μm to 50 μm, which is a fine emulsion droplet.

[0032] To achieve high thermal conductivity, it is necessary to introduce liquid metal fillers and ceramic thermally conductive fillers with high volume fraction. However, unstabilized liquid metal droplets are prone to strong interference with spherical or near-spherical ceramic powders under high shear, causing local agglomeration and shear thickening, resulting in loss of fluidity and making subsequent degassing and homogenization impossible.

[0033] This interfacial functional modifier is used to modulate the interfacial interaction between liquid metal droplets and the polymer matrix. Specifically, the interfacial functional modifier is adsorbed onto the exposed metal surface and / or surface oxide layer of the liquid metal droplet.

[0034] Exposed metal surfaces of liquid metal refer to the metal surface areas of the liquid metal body that are not completely and continuously covered by a surface oxide layer and can directly contact the interfacial functional modifiers. Exposed metal surfaces include newly formed liquid metal surfaces due to cracking, damage, or redistribution of the original surface oxide layer during the dispersion and breakage of liquid metal fillers to form liquid metal droplets, as well as the surface of the liquid metal body exposed by gaps or discontinuous areas in the oxide layer on the surface of the liquid metal droplets.

[0035] The newly formed surface of liquid metal refers to the outer surface of the liquid metal droplets formed during the mechanical vibration, shearing, and fragmentation of liquid metal fillers, which are transformed from the metal bulk originally located inside the liquid metal. After the formation of the newly formed surface of the liquid metal, interfacial functional modifiers can contact the newly formed surface of the liquid metal and adhere to the newly formed surface of the liquid metal through coordination and / or adsorption. Under oxygen-containing conditions, at least a portion of the newly formed surface of the liquid metal not occupied by interfacial functional modifiers can also form a surface oxide layer, and interfacial functional modifiers can also be adsorbed onto the surface oxide layer.

[0036] Because the newly formed surface of liquid metal is quickly re-oxidized in an oxygen-containing environment, "exposed metal surface" is usually a local, dynamic interface state, rather than an exposed metal surface that remains completely free of oxide layer in the final composite thermal conductive gel for a long time.

[0037] Therefore, the newly formed surface of liquid metal is an exposed metal surface generated during the process of liquid metal breaking down into droplets.

[0038] The ceramic thermally conductive filler is a spherical or near-spherical ceramic powder with a hydrophobic modified surface. The spherical or near-spherical ceramic powder is zinc oxide powder, alumina powder, or aluminum nitride powder, and the median particle size of the spherical or near-spherical ceramic powder is 1 μm to 10 μm.

[0039] It should be noted that the liquid metal filler includes liquid metal droplets, and the interfacial functional modifier is adsorbed on the exposed metal surface and / or surface oxide layer of the liquid metal droplets.

[0040] It is understandable that the ceramic thermally conductive filler is distributed between adjacent liquid metal droplets, and that adjacent liquid metal droplets are spaced apart from each other.

[0041] In some embodiments, the interface functional modifier is at least one of a carbon chain backbone silane coupling agent (the molecular backbone of the carbon chain backbone silane coupling agent is a flexible carbon chain) and a siloxane backbone coupling agent.

[0042] This carbon-chain backbone silane coupling agent includes a matrix-loving end and a metal-loving end.

[0043] The matrix-loving end contains vinyl or long-chain alkyl groups to improve the compatibility between the interfacial functional modifier and the polymer matrix.

[0044] The metalophilic end contains an active functional group capable of coordination and / or adsorption with the exposed metal surface and / or surface oxide layer of liquid metal, and the active functional group includes at least one of epoxy group, mercapto group (-SH) and amino group (-NH_2).

[0045] In some embodiments, vinyl groups can participate in the crosslinking reaction of addition-type silicone systems, thereby improving the bonding stability between the liquid metal droplet interface and the polymer matrix.

[0046] The siloxane main-chain coupling agent has a siloxane backbone (the siloxane backbone serves as the main chain of the siloxane main-chain coupling agent) and a trimektoxy end group disposed at one end of the siloxane backbone, and the trimektoxy end group can be a trimethoxy end group or a triethoxy end group.

[0047] like Figure 1 As shown, the preparation method for the above-mentioned composite thermally conductive gel includes the following steps: Step 1, providing appropriate amounts of catalyst and inhibitor, and by mass parts: 1 to 10 parts of polymer matrix, 50 to 99 parts of liquid metal filler, 0.2 to 2 parts of interface functional modifier and 1 to 20 parts of ceramic thermally conductive filler.

[0048] The polymer matrix is ​​an addition-type silicone system, which includes end-vinyl silicone oil and hydrogen-containing silicone oil crosslinking agent. The end-vinyl silicone oil includes a first end-vinyl silicone oil with a first viscosity and a second end-vinyl silicone oil with a second viscosity, wherein the first viscosity is less than the second viscosity.

[0049] Step 2: Mix all the liquid metal fillers, all the interfacial functional modifiers and all the first-terminal vinyl silicone oil provided in Step 1 to obtain a mixture.

[0050] Step 3: The mixture obtained in Step 2 is subjected to low-frequency acoustic resonance dispersion treatment, which breaks the liquid metal filler in the mixture into liquid metal droplets, and at the same time, the interfacial functional modifier in the mixture is adsorbed on the exposed metal surface and / or surface oxide layer of the liquid metal droplets to obtain a pre-dispersed precursor.

[0051] Step 4: Add the catalyst, inhibitor, all ceramic thermally conductive filler, all hydrogen-containing silicone oil crosslinking agent, and all second-terminal vinyl silicone oil provided in Step 1 to the pre-dispersed precursor obtained in Step 3, and perform rotational shear mixing under vacuum conditions to obtain a premixed composite.

[0052] Step 5: The premixed composite obtained in Step 4 is subjected to dual planetary stirring and shear dispersion under vacuum and heating conditions to remove air bubbles from the premixed composite, thereby obtaining a composite thermally conductive gel.

[0053] In some embodiments, the low-frequency acoustic resonance dispersion process includes: The mixture was dispersed for 10 min under conditions of a resonant frequency of 60 Hz to 70 Hz and an oscillation acceleration of 50 G (G is the acceleration due to gravity) to 60 G, and then cooled to room temperature.

[0054] The mixture cooled to room temperature is dispersed for 10 to 15 minutes (preferably 10 minutes) under conditions of a resonant frequency of 60 Hz to 70 Hz and an oscillation acceleration of 70 G to 80 G.

[0055] In some embodiments, the revolution speed of the rotational shear mixing is 500 r / min to 1500 r / min, the rotation speed is 100 r / min to 500 r / min (since 100 r / min to 500 r / min is a commonly used or general rotation speed, the rotation speed here does not need to be set), and the shear mixing time is 3 min to 15 min.

[0056] Rotation-shear mixing ensures that the ceramic thermally conductive filler is evenly distributed between the interface-modified liquid metal droplets.

[0057] In some embodiments, the dual planetary stirring and shear dispersion treatment is carried out under a vacuum of no more than -0.095 MPa.

[0058] The revolution speed of the dual planetary stirring and shear dispersion treatment is 30 r / min to 100 r / min (generally 50 r / min), the rotation speed is 800 r / min to 1200 r / min (since 800 r / min to 1200 r / min is not a commonly used or universal rotation speed, the rotation speed here needs to be set), and the heating treatment time is 2 h to 3 h.

[0059] In one specific embodiment, the formulation components and weighing amounts of the composite thermally conductive gel are as follows (based on a total mass of 100.0 g): 4.5 g (g is a unit of weight) of end-vinyl polydimethylsiloxane with a viscosity of 1000 cP (i.e., the first end-vinyl silicone oil mentioned above, with a first viscosity of 1000 cP), 2.5 g of end-vinyl polydimethylsiloxane with a viscosity of 20000 cP (i.e., the second end-vinyl silicone oil mentioned above, with a second viscosity of 20000 cP), 0.5 g of hydrogen-containing polydimethylsiloxane (i.e., a hydrogen-containing silicone oil crosslinking agent, which includes 0.5% hydrogen by mass), 76.0 g of eutectic gallium indium alloy (EGaIn), 15.0 g of spherical or near-spherical alumina powder (surface hydrophobically modified, median particle size of 5.0 μm), 1.1 g of hexadecanetrimethoxysilane (i.e., an interface functional modifier), 0.1 g of platinum catalyst (active platinum content 5000 ppm), and 0.3 g of other components. g 1-ethynyl-1-cyclohexanol (i.e., the curing inhibitor mentioned above).

[0060] Phase 1: Efficiently breaking up low-frequency resonance, the specific process is as follows: First, 1.1 g of hexadecanetrimethoxysilane, 76.0 g of eutectic gallium-indium alloy, and 4.5 g of vinyl-terminated polydimethylsiloxane with a viscosity of 1000 cp were added together into an explosion-proof mixing tank to obtain a mixture. Then, the explosion-proof mixing tank was fixed in an acoustic resonance mixing device, and the acoustic resonance mixing device was turned on and operated. The mixture was subjected to low-frequency, large-amplitude oscillation mixing for 10 min at a resonance frequency of 65 Hz (this resonance frequency is inherent to the acoustic resonance mixing device and is basically fixed at 70 Hz ± 10, so no setting is needed) and an oscillation acceleration of 55 G (G is the acceleration due to gravity). Afterward, the acoustic resonance mixing device was shut down, and the mixture in the explosion-proof mixing tank was forcibly cooled to room temperature. Then, the oscillation acceleration was increased to 80 G, and acoustic resonance high-energy micro-shear dispersion was continued for 10 min. At this point, the material exhibits a uniformly dispersed, grayish-white, viscous state (specifically, under the isotropic mixing and dispersion effect of the acoustic-gravity flow field, the high-density, high-surface-tension liquid metal is uniformly torn and broken in situ into fine emulsion droplets with a median particle size ranging from 10 μm to 50 μm); finally, the liquid metal filler in the mixture breaks down to form liquid metal droplets, while the interfacial functional modifiers in the mixture are adsorbed onto the exposed metal surface and / or surface oxide layer of the liquid metal droplets, thus obtaining a pre-dispersed precursor.

[0061] It should be noted that at the moment when the newly formed surface of the liquid metal (i.e., the exposed metal surface mentioned above) and the extremely thin surface oxide layer are exposed in large quantities, the metal-loving end of the interface functional modifier rapidly undergoes in-situ physical adsorption on its microscopic surface. This establishes a preliminary spatial steric barrier around the liquid metal droplet, significantly reduces the interfacial tension, and effectively blocks the disordered collision, merging, and secondary fusion between liquid metal droplets.

[0062] The second stage: low-speed pre-dispersion, the specific process is as follows: First, to the pre-dispersed precursor obtained above, 2.5 g of vinyl-terminated polydimethylsiloxane with a viscosity of 20000 cP, 0.5 g of hydrogen-containing polydimethylsiloxane, 0.1 g of platinum catalyst, 0.3 g of 1-ethynyl-1-cyclohexanol, and 15.0 g of spherical or near-spherical alumina powder were added sequentially. Then, the explosion-proof mixing tank was transferred into a planetary rotary vacuum mixer, the chamber was sealed, and the internal vacuum was adjusted to -0.06 MPa (this vacuum is a medium vacuum environment). The rotation speed was set to 600 r / min for bladeless non-contact composite shearing stirring for 5 min. Finally, the premixed composite was obtained.

[0063] Understandably, spherical or near-spherical ceramic powders are embedded in the gaps between modified liquid metal droplets under centrifugal force, forming an emulsion-like stable network that physically blocks droplet contact, eliminates particle blockage, and achieves precise control of liquid metal droplet size from 1µm to 30µm, while maintaining the system's excellent shear-thinning properties.

[0064] The third stage: in-situ chemical modification and rheological structure optimization, the specific process of which is as follows: The premixed composite obtained above was transferred to the material vessel of a vacuum dual planetary mixer. Then, the vessel was locked and the high vacuum pump was started to achieve a vacuum level of -0.096 MPa (not exceeding -0.095 MPa). After that, the outer jacket circulating heating was turned on, and the equilibrium temperature of the premixed composite was controlled at 130℃. Then, the revolution speed was set to 30 r / min and the high shear dispersion disk speed was set to 500 r / min. The mixture was continuously run under high temperature, high vacuum and deep anisotropic shear field for degassing and rheological structure optimization for 5 hours (this 5 hours includes 2 to 3 hours of heating treatment time). Finally, after the microscopic internal stress of the premixed composite was fully relaxed and the microscopic air pores were completely discharged, the heating was stopped, the mixture was cooled to room temperature using circulating water and the pressure was released to obtain the composite thermally conductive gel.

[0065] Specifically, the third stage completely eliminates microbubbles and performs rheological reshaping of the high-viscosity gel system in all dimensions. The dual stimulation of temperature and stirring flow field promotes the thermal motion, full wetting and entanglement of polymer long chains at the macromolecular interface, and causes the local residual internal stress accumulated in the stirring stage to spontaneously relax, ultimately obtaining a stable composite thermally conductive gel with highly uniform microstructure, fine macroscopic texture and excellent thixotropic properties.

[0066] In summary, the composite thermally conductive gel prepared by the above method has an extremely fine macroscopic texture. When its microstructure is observed under a high-power microscope, micron-sized liquid metal droplets are found to be uniformly suspended with a narrow distribution. The droplets are tightly wrapped and interspersed with spherical or near-spherical alumina particles. No microscopic defects such as local agglomeration or secondary merging of droplets are observed. No metal phase precipitation, oil separation or bottom sedimentation phase separation occurs. It exhibits excellent kinetic and thermodynamic stability.

[0067] In the embodiments of this application, the composite thermally conductive gel maintains excellent rheological stability during its preparation process through the synergistic effect of "interfacial chemical steric hindrance + ceramic physical network isolation" even in a high solid content system with a mass percentage of up to 84% of liquid metal filler and ceramic thermally conductive filler.

[0068] In this embodiment, the liquid metal droplets are stably controlled within the range of 10~30 μm to avoid the increase in surface energy caused by phase separation and excessive refinement. The resulting composite thermally conductive gel does not settle or fuse after being left to stand for a long time, and its kinetic stability is significantly improved, thereby achieving precise control of the liquid metal droplet particle size and long-term storage stability.

[0069] In traditional preparation methods, a non-dense Ga2O3 oxide film rapidly forms on the newly exposed surface of liquid metal during high shear processes. This oxide film is highly polar and has a large energy difference with the non-polar siloxane body interface, resulting in poor wettability, weak interfacial bonding, difficulty in controlling the rheological properties of the system, and low reproducibility of the preparation.

[0070] In the embodiments of this application, the composite thermally conductive gel can effectively avoid the oxidation and instability of the newly formed surface of liquid metal, thereby enhancing the wetting and anchoring of liquid metal and polymer matrix, improving interfacial compatibility and performance reproducibility, and reducing micro-defects. This significantly reduces the fluctuation of key performance such as thermal conductivity in batch samples, providing a reliable guarantee for material research and development, pilot-scale amplification and industrial application.

[0071] In this embodiment, the preparation of the composite thermal conductive gel relies entirely on conventional dual planetary centrifugal stirring equipment, requiring no complex pretreatment, and is highly controllable, making it suitable for industrial production. This makes the preparation process of the composite thermal conductive gel simple and easy to scale up.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; under the concept of the present invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the present invention as described above, which are not provided in detail for the sake of brevity; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite thermally conductive gel, characterized in that, By mass, it includes the following components: 1 to 10 parts of polymer matrix; 50 to 99 parts of liquid metal filler; Interface functional modifier 0.2 to 2 parts; 1 to 20 parts of ceramic thermally conductive filler; The liquid metal filler comprises liquid metal droplets, and the interfacial functional modifier is adsorbed onto the exposed metal surface and / or surface oxide layer of the liquid metal droplets; The ceramic thermally conductive filler is distributed between adjacent liquid metal droplets, and the adjacent liquid metal droplets are spaced apart from each other.

2. The composite thermally conductive gel according to claim 1, characterized in that, The polymer matrix is ​​an addition-type organosilicon system, the liquid metal filler is a eutectic gallium-indium alloy or a gallium-indium-tin alloy, and the ceramic thermally conductive filler is a spherical or near-spherical ceramic powder with a hydrophobic modified surface.

3. The composite thermally conductive gel according to claim 2, characterized in that, The addition-type organosilicon system includes: Vinyl-terminated silicone oil and hydrogen-containing silicone oil crosslinking agent, wherein the vinyl-terminated silicone oil and the hydrogen-containing silicone oil crosslinking agent are configured to be crosslinked and cured via a hydrosilylation reaction; The viscosity of the vinyl-terminated silicone oil is between 100 cP and 100,000 cP.

4. The composite thermally conductive gel according to claim 2, characterized in that, The spherical or near-spherical ceramic powder is alumina powder or aluminum nitride powder, and the median particle size of the spherical or near-spherical ceramic powder is 1 μm to 10 μm.

5. The composite thermally conductive gel according to claim 2, characterized in that, The interface functional modifier is at least one of carbon chain backbone silane coupling agents and siloxane backbone coupling agents; The matrix-loving end of the carbon chain skeletal silane coupling agent contains vinyl or long-chain alkyl groups, and the metal-loving end of the carbon chain skeletal silane coupling agent contains active functional groups that can coordinate and / or adsorb with the exposed metal surface and / or surface oxide layer of the liquid metal. The siloxane backbone coupling agent has a siloxane backbone and a trialkoxy terminal group located at one end of the siloxane backbone.

6. The composite thermally conductive gel according to claim 5, characterized in that, The vinyl group in the carbon chain skeletal silane coupling agent can undergo a crosslinking reaction with the addition-type organosilicon system, the trialkoxy end group is a trimethoxy end group or a triethoxy end group, and the active functional group is at least one of epoxy, mercapto and amino groups.

7. A method for preparing a composite thermally conductive gel, used to prepare the composite thermally conductive gel as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: Step 1, providing a catalyst and an inhibitor, and providing the following by weight parts: 1 to 10 parts of polymer matrix, 50 to 99 parts of liquid metal filler, 0.2 to 2 parts of interfacial functional modifier and 1 to 20 parts of ceramic thermally conductive filler; The polymer matrix is ​​an addition-type silicone system, which includes end-vinyl silicone oil and a hydrogen-containing silicone oil crosslinking agent. The end-vinyl silicone oil includes a first end-vinyl silicone oil having a first viscosity and a second end-vinyl silicone oil having a second viscosity, wherein the first viscosity is less than the second viscosity. Step 2: Mix all the liquid metal fillers, all the interfacial functional modifiers and all the first-terminal vinyl silicone oil provided in Step 1 to obtain a mixture. Step 3: The mixture obtained in Step 2 is subjected to low-frequency acoustic resonance dispersion treatment, which breaks the liquid metal filler in the mixture into liquid metal droplets, and at the same time, the interfacial functional modifier in the mixture is adsorbed on the exposed metal surface and / or surface oxide layer of the liquid metal droplets to obtain a pre-dispersed precursor. Step 4: Add the catalyst, inhibitor, all ceramic thermally conductive filler, all hydrogen-containing silicone oil crosslinking agent and all second-terminal vinyl silicone oil provided in Step 1 to the pre-dispersed precursor obtained in Step 3, and perform rotational shear mixing under vacuum conditions to obtain a premixed composite. Step 5: The premixed composite obtained in Step 4 is subjected to dual planetary stirring and shear dispersion under vacuum and heating conditions to remove air bubbles from the premixed composite, thereby obtaining the composite thermally conductive gel.

8. The preparation method according to claim 7, characterized in that, The low-frequency acoustic resonance dispersion treatment includes: The mixture was dispersed for 10 min under conditions of a resonant frequency of 60 Hz to 70 Hz and an oscillation acceleration of 50 G to 60 G, and then cooled to room temperature. The mixture cooled to room temperature was dispersed for 10 to 15 minutes under conditions of a resonant frequency of 60 Hz to 70 Hz and an oscillation acceleration of 70 G to 80 G.

9. The preparation method according to claim 7, characterized in that, The revolution speed of the rotation-rotation shear mixing is 500 r / min to 1500 r / min, the rotation speed is 100 r / min to 500 r / min, and the mixing time is 3 min to 15 min. The rotational shearing mixing causes the ceramic thermally conductive filler to be uniformly distributed between the interface-modified liquid metal droplets.

10. The preparation method according to claim 7, characterized in that, The dual planetary stirring and shear dispersion treatment is carried out under a vacuum degree not exceeding -0.095 MPa; The revolution speed of the dual planetary stirring and shear dispersion treatment is 30 r / min to 100 r / min, the rotation speed is 800 r / min to 1200 r / min, and the heating treatment time is 2 h to 3 h.

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