A leak-proof liquid metal / melamine insulating and heat-conducting film and its preparation method

Abstract

The present invention discloses a leak-proof liquid metal / melamine insulating and heat-conducting film and its preparation method, relating to the technical field of polymer materials. (1) Selection of sponge matrix: The selected matrix is a composite modified sponge; (2) Selection of liquid metal; (3) Preparation of liquid metal / ethanol dispersion; (4) Impregnation treatment of melamine sponge; (5) Drying treatment; (6) Multiple impregnations; (7) Pressing of liquid metal components; (8) Preparation of PDMS / ethyl acetate solution; (9) Molding. The composite modified sponge of the present invention has larger pore diameters and a rich three-dimensional network structure, so it has both extremely low density and excellent flexibility. The sponge after composite modification treatment has a higher intrinsic thermal conductivity, and the adsorption effect on liquid metal is also significantly improved. The extremely high porosity of the composite sponge and the interaction force with the liquid metal also enable it to carry a filler filling amount of more than 60 vol% without leakage. The coating layer of PMDS provides insulation performance for the composite material and further enhances its anti-leakage performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a leak-proof liquid metal / melamine insulating and heat-conducting film and a preparation method thereof. Background Art

[0002] Thermal interface materials are currently widely used in various electronic and electrical devices that require efficient thermal management. Their main function is to fill the interface gaps, reduce the contact thermal resistance, thereby improving the heat dissipation capacity of the devices and ensuring the thermal stability and reliability of the devices. In traditional thermally conductive composite materials, metal materials and carbon-based materials are generally used. Although they have high thermal conductivity, since the fillers are rigid particles, at low filling amounts, the fillers cannot construct a dense and effective thermal conduction network in the matrix, which limits the improvement of the thermal conductivity of the composite materials; while when the filling amount is too high, it is often accompanied by a significant decrease in mechanical properties, showing insufficient flexibility or unstable compression performance in the interfaces of complex structures, being unable to fully fill the microvoids, and difficult to exert the thermal conductivity of the composite materials. Moreover, the disordered arrangement of the fillers in the composite materials also greatly reduces their utilization rate. In some special scenarios (such as new energy vehicle battery modules), it is required that the materials have excellent thermal conductivity and meet specific electrical insulation at the same time. It is very difficult for traditional composite materials to achieve a balance in these aspects.

[0003] As a new material, liquid metal, with its unique physical state - being liquid at room temperature and having high thermal conductivity (>16.5 W / m·K), has opened up a new path for the innovative design of flexible composite materials. The fluidity of liquid metal enables it to penetrate into the internal structure of the composite material and form a stable and efficient heat conduction path.

[0004] Melamine sponge is made of melamine. Its bendable flexibility makes it an excellent choice as the matrix of thermal interface materials. Its fine, rich three-dimensional wire mesh structure and large pore size enable it to effectively carry a higher content of liquid metal to form an efficient heat conduction network while avoiding the leakage of liquid metal. Melamine sponge has good processing performance and can be made into various shaped and sized fittings through processes such as molding to adapt to various complex application scenarios.

[0005] Chinese Patent with Publication No. CN114940829B discloses a two-dimensional graphene / liquid metal / PDMS composite film and a preparation method thereof. This invention uses a photosensitive resin as the skeleton, fills PDMS and then demolds to obtain a flexible PDMS matrix, which can endow the fillers with heat conduction paths, thereby improving the thermal conductivity. However, this method fills too much PDMS, which has an inhibitory effect on the improvement of the thermal conductivity. Although it can endow the composite material with a certain degree of flexibility, it is easy to block the heat conduction path under mechanical deformation and there is a risk of liquid metal leakage.

[0006] The Chinese patent with the application number CN202210597791.5 discloses a composite high - thermal - conductivity sandwich gasket based on liquid - metal filling and its preparation method. However, the hardness of this composite material is still relatively high, it does not have flexibility, and the thermal conductivity is less than 5 / W·m -1 ·K -1 , which cannot meet the thermal - conductivity requirements in complex scenarios.

[0007] Existing preparation methods of liquid - metal - based thermal - conductive composite materials have problems such as leakage caused by high filling and the contradiction between high thermal conductivity and flexibility of thermal - conductive composite materials. At the same time, good insulation performance needs to be ensured in specific scenarios. Based on this, the present invention provides a leak - proof liquid metal / melamine insulating and thermal - conductive film and its preparation method to solve the existing technical problems. Summary of the Invention

[0008] The purpose of the present invention is to provide a leak - proof liquid metal / melamine insulating and thermal - conductive film and its preparation method to solve the deficiencies in the existing technology.

[0009] The technical scheme adopted by the present invention is as follows:

[0010] A preparation method of a leak - proof liquid metal / melamine insulating and thermal - conductive film, the preparation method includes the following steps:

[0011] (1) Selection of sponge matrix: The selected matrix is a composite - modified sponge;

[0012] (2) Selection of liquid metal: Gallium - indium alloy is adopted;

[0013] (3) Preparation of liquid - metal / ethanol dispersion: Mix liquid metal and ethanol, and then put them into an ultrasonic cell disruptor for crushing to obtain a liquid - metal / ethanol dispersion;

[0014] The mass ratio of liquid metal to ethanol is 1:12 - 1:18, the ultrasonic power is 400W, and the treatment time is 2 - 6min;

[0015] (4) Impregnation treatment of melamine sponge: Put the composite - modified sponge obtained in step (1) into the liquid - metal / ethanol dispersion obtained in step (3) for impregnation treatment according to a volume ratio of 1:5, and then take it out to obtain an impregnated sample;

[0016] (5) Drying treatment: Put the vacuum - impregnated sample obtained in step (4) into a forced - air drying oven for drying treatment until the ethanol evaporates completely;

[0017] Among them, the air speed in the forced - air drying oven is 0.5m / s, the temperature is 50°C, and the time is 0.5 hours;

[0018] (6) Multiple impregnations: Repeat steps (4) and (5) multiple times to obtain a multi - impregnated composite material;

[0019] (7) Sintering of liquid metal components: Mechanically sinter the multi-impregnated composite material obtained in step (6) to obtain a film specimen;

[0020] (8) Preparation of PDMS / ethyl acetate solution: Take PDMS and curing agent in a mass ratio of 9:1, mix them evenly to obtain a preliminary mixture, pour the preliminary mixture into a centrifuge tube according to a mass ratio of the preliminary mixture: ethyl acetate of 1:9, centrifuge and stir for 5 minutes to prepare a 10% PDMS / ethyl acetate solution, and dilute the obtained solution by 10 times to obtain a 1% PDMS / ethyl acetate solution;

[0021] (9) Molding: Suspend the film specimen obtained in step (7) on an aluminum mesh support to reduce the contact between the liquid metal and the support; Use a pipette to suck the 1% PDMS / ethyl acetate solution obtained in step (8), drop it on both sides of the film specimen, evenly cover it, and place it in a blast drying oven to evaporate the ethyl acetate, and finally obtain a leak-proof liquid metal / melamine insulating and heat-conducting film;

[0022] Among them, the blast wind speed in the blast drying oven is 0.5 m / s, the temperature is 60 °C, and the time is 2 hours.

[0023] As a further technical solution, the selected composite modified sponge has a density of 0.0080 - 0.0085 g / cm 3 , and the thickness is 0.4 - 0.6 cm.

[0024] As a further technical solution, the curing agent described in step (8) is tetrathioxanthone;

[0025] As a further technical solution, the preparation method of the composite modified sponge includes the following steps:

[0026] (1) Repeatedly rinse the melamine sponge with absolute ethanol and deionized water for 10 min respectively, and then vacuum dry it at 55 °C for 2 h to obtain a cleaned melamine sponge;

[0027] (2) Uniformly disperse silver nanowires into deionized water to obtain a silver nanowire dispersion.

[0028] (3) Immerse the cleaned melamine sponge into the silver nanowire dispersion, apply a pressure of 0.5 MPa to the cleaned melamine sponge, keep the pressure for 10 s, then release the pressure, maintain for 20 s, and then perform 5 cycles and take it out, and vacuum dry it at 55 °C in a vacuum drying oven for 4 hours to obtain a melamine sponge composite;

[0029] (4) Add dopamine hydrochloride to Tris solution, and stir and mix evenly to obtain a treatment solution;

[0030] Add the melamine sponge composite to the treatment liquid, disperse it ultrasonically for 10 min, adjust the temperature to 65 °C, impregnate it in a sealed manner for 15 hours, take it out, and then vacuum dry it at 55 °C for 4 hours to obtain the composite modified sponge.

[0031] As a further technical solution, the mass fraction of silver nanowires in the silver nanowire dispersion is 10-13 wt%.

[0032] The cleaned melamine sponge is immersed in the silver nanowire dispersion at a volume ratio of 1:10.

[0033] The mixing ratio of dopamine hydrochloride and Tris solution is 1-1.2 g: 120 mL.

[0034] The volume ratio of the melamine sponge composite to the treatment liquid is 1:5.

[0035] As a further technical solution, for the gallium-indium alloy, the mass fraction of gallium is 75.5% and the mass fraction of indium is 24.5%.

[0036] As a further technical solution, the time for vacuum impregnation is 4-5 hours, the vacuum degree is 0.1 Pa, and the temperature is 70 °C.

[0037] As a further technical solution, the repeated steps (4) and (5) are specifically repeated 1-4 times.

[0038] As a further technical solution, the mechanical sintering step is as follows: Divide the obtained multi-impregnated composite material into four parts, put them into a tablet press for automatic pressing. Each time, the tablet press acts on one of the four parts, and four times form a cycle, with a total of 10-12 cycles.

[0039] It should be noted that the mechanical sintering in the present invention is not the traditional high-temperature sintering. Instead, it realizes the bonding between liquid metals by applying pressure at room temperature, that is, the process of mechanical sintering. This mechanical sintering is a solid-state connection technology. It does not rely on the traditional high-temperature sintering process, but realizes the connection between materials by applying external pressure.

[0040] As a further technical solution, the pressure for pressing is 1 MPa, and the pressing time is 2 s / time.

[0041] As a further technical solution, the dropping amounts on both sides of the film specimen in step (9) are 20 μL / cm² respectively. Beneficial effects

[0042] 1. The melamine sponge is mainly composed of melamine resin. Its surface chemical properties have weak compatibility with liquid metal, mainly combined by physical embedding and weak van der Waals forces, with a low binding energy. In the present invention, the melamine sponge matrix is subjected to a composite modification treatment, and silver nanowires are introduced for binding. Silver nanowires have a high free electron density and may produce a stronger interaction with the surface electron cloud of liquid metal. In addition, gallium in liquid metal can usually form a stable gallium oxide film, and this oxide layer can be combined with the silver surface through van der Waals forces or chemical bonds on the metal surface, obtaining a higher binding energy, thereby enabling the composite-modified melamine sponge to have a higher adsorption capacity for liquid metal.

[0043] 2. In the present invention, the modified melamine sponge is impregnated in a liquid metal / ethanol dispersion. The liquid metal in the dispersion fully penetrates and fills the pores of the modified melamine sponge through capillary action, forming a good physical bond; at the same time, liquid metal has a high surface tension and will automatically shrink and adhere to the pore wall surface in the pores. When drying with air blowing, the increase in temperature causes the liquid metal to flow further, fully covering the pore walls of the melamine sponge and further enhancing its adhesion; in the subsequent step-by-step sintering process, the liquid metal fills the voids due to void compression, and the excess part flows to the edge. After multiple cycles, a liquid metal film with a micron-level thickness is finally formed. The liquid metal changes from the shape of small droplets attached to the skeleton to the shape of a sheet after sintering and fills the inside of the film.

[0044] Since the binding force between liquid metals is mainly determined by surface tension, and the skeleton of the melamine sponge is extremely thin, its resilience is much smaller than the binding force between liquid metals, so that the film will not return to the porous sponge shape after formation. After cleaning the liquid metal inside the film with absolute ethanol, the film can rebound into a porous sponge shape again, which also proves that the present invention does not achieve the non-rebound effect by permanently destroying the skeleton of the melamine sponge, but uses the difference between the binding force between liquid metals and the resilience of the melamine sponge to realize the stability control of the film shape.

[0045] 3. In the present invention, through specific ultrasonic time and ultrasonic power, the average particle size of liquid metal particles in the liquid metal / ethanol dispersion is controlled. At this average particle size, the binding degree between liquid metal and melamine sponge is the highest, which is most advantageous for the shaping of the material.

[0046] 4. The present invention also forms a micron-level protective layer on the surface of the thin film by using PDMS. Without much change to the overall morphology, it further prevents the leakage of liquid metal, provides effective insulation performance, and significantly improves the flexibility and durability of the material, enabling it to maintain stable mechanical properties within a wide temperature range of 20 °C to 150 °C. Especially in multiple cyclic deformation (such as bending, compression) tests, after more than 1000 cycles, its mechanical properties, insulation performance, and thermal conductivity show no obvious attenuation, demonstrating excellent fatigue resistance.

[0047] 5. The production process of the present invention is simple, with low cost and good performance, and can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Attached Figure 1 Scanning electron microscope of liquid metal / ethanol dispersion at 2 minutes of ultrasonic time in Example 6;

[0049] Attached Figure 2 Scanning electron microscope of liquid metal / ethanol dispersion at 4 minutes of ultrasonic time in Example 1;

[0050] Attached Figure 3 Cross-sectional scanning electron microscope of the thermal conductive film prepared in Comparative Example 4;

[0051] Attached Figure 4 Scanning electron microscope image after surface coating with PDMS in Example 5;

[0052] Attached Figure 5 Schematic diagrams of Example 5 under pressures of 100, 300, and 500 kPa.

[0053] Attached Figure 6 Schematic process flow diagram of the preparation method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0054] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0055] The following are specific examples:

[0056] Example 1

[0057] A preparation method of a leak-proof liquid metal / melamine insulating and thermal conductive thin film, the preparation method comprising the following steps:

[0058] (1) Selection of sponge matrix: The selected matrix is a composite modified sponge;

[0059] (2) Selection of liquid metal: Gallium-indium alloy is used;

[0060] (3) Preparation of liquid metal / ethanol dispersion: Liquid metal and ethanol are mixed and then put into an ultrasonic cell crusher for crushing to obtain a liquid metal / ethanol dispersion;

[0061] The mass ratio of liquid metal to ethanol is 1:12, the ultrasonic power is 400 W, and the treatment time is 4 min;

[0062] (4) Impregnation treatment of melamine sponge: The composite modified sponge obtained in step (1) is put into the liquid metal / ethanol dispersion obtained in step (3) for impregnation treatment according to a volume ratio of 1:5, and then taken out to obtain an impregnated sample;

[0063] (5) Drying treatment: The impregnated sample obtained in step (4) is put into a forced air drying oven for drying treatment until the ethanol evaporates completely;

[0064] Among them, the wind speed in the forced air drying oven is 0.5 m / s, the temperature is 50 °C, and the time is 0.5 hours;

[0065] (6) Multiple impregnations: In this embodiment, steps (4) and (5) are not repeated to obtain an impregnated composite material;

[0066] (7) Sintering of liquid metal component: The multiple impregnated composite material obtained in step (6) is mechanically sintered to obtain a film sample;

[0067] (8) Preparation of PDMS / ethyl acetate solution: PDMS and curing agent are mixed evenly according to a mass ratio of 9:1 to obtain a preliminary mixture, and then poured into a centrifuge tube according to a mass ratio of preliminary mixture: ethyl acetate of 1:9, and centrifugally stirred for 5 minutes to prepare a 10% PDMS / ethyl acetate solution. The obtained solution is diluted 10 times to obtain a 1% PDMS / ethyl acetate solution;

[0068] The curing agent is tetrathiotetramethylenedisulfide;

[0069] (9) The film sample obtained in step (7) is suspended on an aluminum mesh support to reduce the contact between the liquid metal and the support; A pipette is used to suck the 1% PDMS / ethyl acetate solution obtained in step (8), drop it on both sides of the film sample, evenly cover it, and put it into a forced air drying oven to evaporate the ethyl acetate, and finally obtain a leak-proof liquid metal / melamine insulating and heat-conducting film;

[0070] The wind speed in the forced air drying oven is 0.5 m / s, the temperature is 60 °C, and the time is 2 hours.

[0071] The density of the composite modified sponge is 0.0083 g / cm 3 , and the thickness is 0.5 cm.

[0072] The preparation method of the composite modified sponge comprises the following steps:

[0073] (1) The melamine sponge is repeatedly rinsed with absolute ethanol and deionized water for 10 min respectively, and then vacuum dried at 55 °C for 2 h to obtain the cleaned melamine sponge;

[0074] (2) The silver nanowires are uniformly dispersed in deionized water to obtain a silver nanowire dispersion.

[0075] (3) The cleaned melamine sponge is immersed in the silver nanowire dispersion, a pressure of 0.5 MPa is applied to the cleaned melamine sponge, the pressure is maintained for 10 s, then the pressure is released, maintained for 20 s, and then circulated 5 times and taken out, and vacuum dried in a vacuum drying oven at 55 °C for 4 hours to obtain a melamine sponge composite;

[0076] (4) Dopamine hydrochloride is added to the Tris solution, and after stirring and mixing evenly, a treatment solution is obtained;

[0077] The melamine sponge composite is added to the treatment solution, ultrasonically dispersed for 10 min, the temperature is adjusted to 65 °C, and after heat preservation and airtight impregnation for 15 hours, it is taken out, and then vacuum dried at 55 °C for 4 hours to obtain the composite modified sponge.

[0078] The mass fraction of silver nanowires in the silver nanowire dispersion is 10 wt%;

[0079] The cleaned melamine sponge is immersed in the silver nanowire dispersion according to a volume ratio of 1:10;

[0080] The mixing ratio of the dopamine hydrochloride and the Tris solution is 1 g:120 mL;

[0081] The volume ratio of the melamine sponge composite to the treatment solution is 1:5.

[0082] For the gallium-indium alloy, the mass fraction of gallium is 75.5% and the mass fraction of indium is 24.5%.

[0083] The time for vacuum impregnation is 4.5 hours, the vacuum degree is 0.1 Pa, and the temperature is 70 °C.

[0084] The specific steps of mechanical sintering are as follows: The obtained multi-impregnated composite material is divided into four parts and put into a tablet press for automatic pressing. Each time, the tablet press acts on one of the four parts, and four times is a cycle, with a total of 10 cycles. The pressure is set to 1 MPa, and the pressing time is 2 s / time.

[0085] 20 μL / cm² of 1%wt% PDMS / ethyl acetate solution is respectively dropped on both sides of the film specimen.

[0086] Example 2

[0087] As a preparation method of a leakage-proof liquid metal / melamine insulating and heat-conducting film according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 1 is that: the impregnation in Step 6 is repeated once.

[0088] Example 3

[0089] As a preparation method of a leakage-proof liquid metal / melamine insulating and heat-conducting film according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 1 is that: in the preparation method of the leakage-proof liquid metal / melamine insulating and heat-conducting film, the number of repetitions of Step 6 is 2 times.

[0090] Example 4

[0091] As a preparation method of a leakage-proof liquid metal / melamine insulating and heat-conducting film according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 1 is that: in the preparation method of the leakage-proof liquid metal / melamine insulating and heat-conducting film, the number of repetitions of Step 6 is 3 times.

[0092] Example 5

[0093] As a preparation method of a leakage-proof liquid metal / melamine insulating and heat-conducting film according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 1 is that: in the preparation method of the leakage-proof liquid metal / melamine insulating and heat-conducting film, the number of repetitions of Step 6 is 4 times.

[0094] Example 6

[0095] As a leakage-proof liquid metal / melamine insulating and heat-conducting film and its preparation method according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 1 is that: the crushing time of the ultrasonic cell disruptor is 2 minutes.

[0096] Example 7

[0097] As a leakage-proof liquid metal / melamine insulating and heat-conducting film and its preparation method according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 1 is that: the crushing time of the ultrasonic cell disruptor is 6 minutes.

[0098] Comparative Example 1

[0099] As a preparation method of a heat-conducting film according to an embodiment of the present invention, the only difference between this comparative example and Example 5 is that: the impregnated film is not mechanically sintered.

[0100] Comparative Example 2

[0101] As a preparation method of a heat-conducting film according to an embodiment of the present invention, the difference between this comparative example and Example 5 is that: in the mechanical sintering step of this comparative example, the sample is not divided into four parts, but is pressed as a whole, and still pressed 10 times.

[0102] Comparative Example 3

[0103] As a preparation method of a thermal conductive film according to an embodiment of the present invention, the difference between this comparative example and Example 5 lies in that: in this comparative example, the melamine sponge is not subjected to composite modification treatment.

[0104] Comparative Example 4

[0105] As a preparation method of a thermal conductive film according to an embodiment of the present invention, the difference between this comparative example and Example 5 lies in that: this comparative example does not perform PDMS coating treatment on the film sample, that is, steps (8) and (9) are not carried out.

[0106] Test:

[0107] The films prepared in Examples 1 to 7 and Comparative Examples 1 to 4 were tested to verify the volume fraction before and after sintering, and the thermal conductivity before and after coating with PDMS. The test results are shown in Table 1:

[0108] Among them, the test of the thermal conductivity refers to GB / T 29313-2012

[0109]

[0110] According to the data analysis of Examples 1 to 5 in Table 1, at least the following points can be obtained:

[0111] 1. After each impregnation process, the volume fraction of the liquid metal attached to the composite-modified melamine sponge is stably maintained at about 1%. Further, after the pressing treatment, the volume fraction of the liquid metal shows a regular change trend. This phenomenon can be attributed to the binding force between the liquid metals and the binding force between the liquid metal and the silver nanowires, which significantly exceeds the resilience of the melamine sponge itself, thereby promoting the effective filling of the voids between the melamine sponges by the liquid metal during the pressing process, as shown in the attachment Figure 3 shown.

[0112] 2. In order to further optimize the performance of the material, a very thin PDMS elastomer was coated on the film surface, as shown in Figure 4 shown. It should be noted that the thickness of this PDMS layer is only at the micron level and does not penetrate into the film interior, so it hardly has a significant impact on the overall thermal conductivity of the material, and this PDMS provides external insulation performance for the film and can further prevent the leakage of liquid metal.

[0113] Correspondingly, a pressure test was carried out on Example 5. As shown in the attachment Figure 5 shown, there is no leakage of liquid metal in the film of Example 5 under the pressures of 100 kPa, 300 kPa, and 500 kPa.

[0114] This is not only due to the encapsulation of PDMS, but also because after the melamine sponge is mechanically sintered into a film, the liquid metal exists more in the form of flakes rather than droplets inside the film. The flaky liquid metal has a relatively large lateral area and a small thickness due to its structural characteristics, and thus has a relatively larger contact area with the substrate surface. This larger contact area enhances the adhesion of the liquid metal to the film and silver nanowires through the surface tension effect, making it more stably fixed on the substrate and reducing the fluidity and leakage risk under external forces.

[0115] The technical solution of the present invention balances the thermal conductivity of the material with the required elasticity, sealing performance and other characteristics to meet the comprehensive performance requirements in specific application scenarios.

[0116] 3. As can be seen from Examples 1, 6, and 7 in Table 1, too short or too long ultrasonic time will affect the distribution of liquid metal on the skeleton. As shown in Figure 1 , 2 , when the liquid metal dispersion is ultrasonically treated, as the ultrasonic time extends, the particle size of the liquid metal particles generally shows a downward trend. This is because the cavitation effect, shear effect, and microjet effect of ultrasonic waves act on the liquid metal particles, causing them to be strongly impacted and sheared, resulting in the fragmentation and refinement of the particles. However, when the ultrasonic time reaches a certain level, the too small liquid metal droplets will reunite again, causing certain fluctuations in the particle size distribution and an increase in the average particle size. Therefore, in multiple ultrasonic experiments, the inventor found that when the ultrasonic time is about

[0117] 4. As can be seen from Example 1 and Comparative Examples 1 and 2, for the melamine sponge without sintering treatment, its thermal conductivity has not been significantly improved. The root cause of this phenomenon lies in the distribution state of the liquid metal particles on the melamine sponge skeleton - they show an uneven dispersion and fail to effectively build a continuous heat conduction network; and without the mechanical sintering step of dividing the melamine sponge into blocks, the sponge will bear an overall pressure, resulting in a reduced flow range of the liquid metal, unlike the divided mechanical sintering where the liquid metal can flow in the other directions of the sponge that are not under pressure, making the penetration of the liquid metal in the formed film insufficient and affecting the final thermal conductivity.

[0118] 5. As can be seen from Example 1 and Comparative Example 3, for the melamine sponge without composite modification, its adsorption effect on liquid metal is only 80% of that after modification, and its thermal conductivity also decreases significantly. This is because silver nanowires, due to their high free electron density, can form strong interactions with the electron cloud on the surface of liquid metal. In addition, gallium in liquid metal usually forms a stable gallium oxide film, and this oxide film can be firmly bonded to the silver surface through van der Waals forces or chemical bonds, thereby significantly increasing the interfacial binding energy and thus enhancing the adsorption of the sponge to liquid metal. At the same time, silver nanowires also act as a bridging role in the thin film structure, further optimizing the path connection, thereby significantly improving the thermal conductivity of the thin film.

[0119] Therefore, it can be concluded that the uniform dispersion of liquid metal particles on the melamine sponge skeleton and the construction of a continuous thermal conduction network through sintering treatment are the key to significantly improving the thermal conductivity of the melamine sponge; the presence of sheet-like liquid metal inside the thin film increases its adhesion to the matrix, which has a higher contact area and a lower curvature and is not easily moved under the action of gravity or external forces. At the same time, the force between the liquid metal and the silver nanowires is also the key to ensuring that the liquid metal does not leak; the presence of the PDMS protective layer not only provides insulation performance but also further improves the leak-proof ability of the thin film and enhances its flexibility. This discovery has important guiding significance for guiding subsequent material design and preparation processes.

[0120] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A preparation method of a leakage-proof liquid metal / melamine insulating and heat-conducting film, characterized in that The preparation method comprises the following steps: (1) Selection of sponge matrix: The selected matrix is a composite modified sponge; (2) Selection of liquid metal: Gallium-indium alloy is adopted; (3) Preparation of liquid metal / ethanol dispersion: The liquid metal and ethanol are mixed and then put into an ultrasonic cell disruptor for crushing to obtain the liquid metal / ethanol dispersion; The mass ratio of the liquid metal to ethanol is 1:12 - 1:18, the ultrasonic power is 400W, and the treatment time is 2 - 6min; (4) Impregnation treatment of melamine sponge: The composite modified sponge obtained in step (1) is put into the liquid metal / ethanol dispersion obtained in step (3) for impregnation treatment according to a volume ratio of 1:5, and then taken out to obtain an impregnated sample; (5) Drying treatment: The impregnated sample obtained in step (4) is put into a forced air drying oven for drying treatment until the ethanol is completely evaporated; Among them, the wind speed in the forced air drying oven is 0.5m / s, the temperature is 50°C, and the time is 0.5 hour; (6) Multiple impregnations: Steps (4) and (5) are repeated multiple times to obtain a multi-impregnated composite material; (7) Sintering of liquid metal component: The multi-impregnated composite material obtained in step (6) is mechanically sintered to obtain a film sample; The mechanical sintering steps are: The obtained multi-impregnated composite material is divided into four parts and put into a tablet press for automatic pressing. Each time, the tablet press acts on one part of the four parts, and four times form a cycle, with a total of 10 - 12 cycles; (8) Preparation of PDMS / ethyl acetate solution: PDMS and curing agent are mixed evenly according to a mass ratio of 9:1 to obtain a preliminary mixture. According to a mass ratio of the preliminary mixture: ethyl acetate of 1:9, it is poured into a centrifuge tube and centrifugally stirred for 5 minutes to prepare a 10% PDMS / ethyl acetate solution. The obtained solution is diluted 10 times to obtain a 1% PDMS / ethyl acetate solution; (9) Molding: The film sample obtained in step (7) is suspended on an aluminum mesh support, and a pipette is used to suck the 1% PDMS / ethyl acetate solution obtained in step (8) and drop it onto both sides of the film sample to evenly cover it, and then put it into a forced air drying oven to evaporate the ethyl acetate, and finally obtain a leak-proof liquid metal / melamine insulating and heat-conducting film; The air blowing speed in the forced air drying oven is 0.5m / s, the temperature is 60°C, and the time is 2 hours; The preparation method of the composite modified sponge comprises the following steps: (1) The melamine sponge is repeatedly rinsed with absolute ethanol and deionized water for 10min respectively, and then vacuum dried at 55°C for 2h to obtain a cleaned melamine sponge; (2) The silver nanowires are uniformly dispersed in deionized water to obtain a silver nanowire dispersion; The mass fraction of silver nanowires in the silver nanowire dispersion is 10 - 13wt%; (3) The cleaned melamine sponge is immersed in the silver nanowire dispersion, a pressure of 0.5MPa is applied to the cleaned melamine sponge, the pressure is maintained for 10s, then the pressure is released and maintained for 20s, and then the cycle is repeated 5 times and then taken out and vacuum dried in a vacuum drying oven at 55°C for 4 hours to obtain a melamine sponge composite; (4) Add dopamine hydrochloride to the Tris solution, stir and mix evenly to obtain a treatment solution; add the melamine sponge composite to the treatment solution, disperse it ultrasonically for 10 min, adjust the temperature to 65 °C, impregnate it tightly for 15 hours while maintaining the temperature, take it out, and then dry it in vacuum at 55 °C for 4 hours to obtain a composite modified sponge.

2. The preparation method of a leakage-proof liquid metal / melamine insulating and heat-conducting thin film according to claim 1, wherein The selected composite modified sponge has a density of 0.0080 - 0.0085 g / cm 3 , and a thickness of 0.4 - 0.6 cm.

3. The preparation method of a leak-proof liquid metal / melamine insulating and heat-conducting thin film according to claim 1, characterized in that, In step (8), the curing agent is tetrathioxane disulfide.

4. The preparation method of a leak-proof liquid metal / melamine insulating and heat-conducting film according to claim 1, wherein The cleaned melamine sponge is immersed in the silver nanowire dispersion liquid at a volume ratio of 1:

10. The mixing ratio of the dopamine hydrochloride and the Tris solution is 1-1.2 g: 120 mL. The volume ratio of the melamine sponge composite to the treatment solution is 1:

5.

5. The preparation method of a leak-proof liquid metal / melamine insulating and heat-conducting thin film according to claim 1, wherein, For the gallium-indium alloy, the mass fraction of gallium is 75.5%, and the mass fraction of indium is 24.5%.

6. The preparation method of a leak-proof liquid metal / melamine insulating and heat-conducting thin film according to claim 1, wherein The repeated implementation of steps (4) and (5) specifically means repeating 1-4 times.

7. The preparation method of a leak-proof liquid metal / melamine insulating and heat-conducting film according to claim 1, characterized in that, The pressure for pressing is 1 MPa, and the pressing time is 2 s / time.

8. The preparation method of a leak-proof liquid metal / melamine insulating and heat-conducting thin film according to claim 1, characterized in that, The dropping amounts on both sides of the thin film specimen described in step (9) are 20 μL / cm respectively 2 .

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