Preparation method and application of low-filling graphene-nano silver composite coating

Abstract

The application discloses a preparation method and application of a low-filling graphene-nano silver composite coating, and specifically, GO is modified by using CS and EDTA, a CS-EDTA-RGO@AgNPs composite heat-conducting filler is prepared by a simple chemical reduction method, and is doped into PDMS to prepare a heat-conducting coating. After preparation, the coating is scraped on an aluminum sheet as a sample, wherein the aluminum sheet serves as a radiator aluminum shell in contact with a heat source. The actual heat dissipation capacity of the coating is explored, and the results show that finally, the CS-EDTA-RGO@AgNPs composite filler constructs a heat-conducting connection in the PDMS matrix. The heat conductivity of the prepared coating is significantly improved, and the sample has an excellent heat transfer effect.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, to the field of heat dissipation technology for electronic components, and specifically to a method for preparing a low-filling-content graphene-nano silver composite coating and its application. Background Technology

[0002] With the advent of the 5G era, the high power consumption and heat accumulation of chips pose challenges to the lifespan and performance of electronic devices. Thermal interface materials (TIMs) with high thermal conductivity can ensure the normal operation of components. Polymer-based high thermal conductivity composite coatings applied between heat sources and heat sinks can quickly transfer and dissipate the heat generated by the device. Polydimethylsiloxane (PDMS) is a good matrix for thermally conductive coatings due to its low cost and high processing flexibility. However, it typically has an intrinsic thermal conductivity of less than 0.2 W / (m·K), which cannot meet the thermal conductivity requirements, necessitating the addition of fillers to form thermally conductive coatings. In recent years, graphene has attracted widespread attention as a filler with high intrinsic thermal conductivity; some monolayer graphene even has an in-plane thermal conductivity as high as 5300 W / (m·K), but its tendency to stack limits the improvement of thermal conductivity. In-situ growth of metal nanoparticles on the graphene surface can improve the dispersion of graphene and facilitate the construction of thermally conductive pathways.

[0003] Ethylenediaminetetraacetic acid (EDTA-2Na) exists in solution as its disodium salt and can act as a polydentate ligand for metal ions. It possesses four carboxyl groups and two imine groups as coordination sites, forming stable metal complexes by immobilizing metal ions within chelating cages. Grafting it onto graphene oxide utilizes the EDTA ligand to... Ag+ The coordination between them allows more silver ions to be adsorbed onto the graphene surface and gradually nucleate and grow, which increases the active sites for metal particles to grow on graphene.

[0004] Chitosan (CS) is a substance obtained from chitin through deacetylation and belongs to the category of biomass materials. It possesses advantages such as being green and non-toxic, low-cost, and readily available in nature. Furthermore, it has active functional groups that coordinate with metal ions, making it widely applicable in environmental protection and adsorption fields. CS-EDTA composite chitosan (CS-EDTA) was chosen to modify graphene oxide (GO). On one hand, CS grafting increases the hydrophilicity of GO; on the other hand, the limited surface area of ​​CS can be compensated for by interconnecting GO with large specific surface areas. CS-EDTA-modified GO offers advantages such as a larger thermally conductive sheet area and abundant active sites for silver particle growth, and the modification process is environmentally friendly.

[0005] Sodium borohydride ( NaBH4As a common reducing agent, it is used to reduce silver ions to zero-valent silver, which then aggregates into nuclei to form silver nanoparticles. Compared to other reducing agents such as hydrazine hydrate and glucose, NaBH4 It has higher safety, lower toxicity, moderate reaction rate, and most importantly, the prepared nanoparticles are not prone to agglomeration and have uniform size.

[0006] Based on the above research, EDTA groups were modified onto CS and used to synergistically modify GO, through... NaBH4 By assembling silver nanoparticles with graphene through reduction, we have, for the first time, applied this GO modification mechanism to the preparation of thermally conductive fillers. Firstly, CS (carbon dioxide) makes GO more hydrophilic, resulting in better dispersibility in the reduction reaction solution system. Secondly, the chelating effect of grafted EDTA increases the sites for silver ion adsorption on graphene and enhances the binding force between the two, allowing more AgNPs to grow effectively in situ on the surface of reduced graphene oxide. By modifying graphene oxide with a chitosan-ethylenediaminetetraacetic acid composite, and then using a simple chemical reduction method to grow graphene and silver nanoparticles in situ into a "point-to-surface" composite filler, this filler is filled into polydimethylsiloxane to create a thermally conductive coating, constructing a good phonon heat transfer channel.

[0007] A search revealed a patent document related to silver / graphene composite materials: Chinese patent CN106346016B provides a method for preparing a graphene-silver nanoparticle composite film and its application in an ultraviolet detector, belonging to the field of functional materials technology. This invention prepares a graphene-silver nanoparticle composite film by a two-step in-situ reduction of graphene oxide and silver salt using hydrazine hydrate and sodium citrate. Compared to the single-step reduction method, silver ions crystallize around sheet-like graphene, resulting in more uniform modification of the graphene and effectively improving the problem of silver nanoparticle aggregation. This invention first prepares a graphene-silver nanoparticle composite solution by a two-step in-situ reduction of graphene oxide and silver nitrate using hydrazine hydrate and sodium citrate. This solution is then coated onto a silicon substrate and dried to form a film. Finally, a gold electrode is sputtered as the top electrode to complete the fabrication of the ultraviolet detector. The resulting ultraviolet detector based on the graphene-silver nanoparticle composite film exhibits a large photocurrent and short response and response times. Based on the comparison, the technical solution, product characteristics, and uses provided in this application are quite different. Summary of the Invention

[0008] This invention provides a method for preparing a low-filling-content graphene-silver nanocomposite coating. A simple chemical reduction method is used to prepare a CS-EDTA-RGO@AgNPs composite thermally conductive filler, which is then doped into PDMS to prepare a thermally conductive coating. After preparation, the coating is scraped onto an aluminum sheet (acting as the aluminum shell of a heat sink in contact with the heat source) as a sample. The actual heat dissipation capacity of the coating is tested, and the results show that the sample has excellent heat transfer performance.

[0009] This invention provides a method for preparing a low-filling-content graphene-nano silver composite coating, the steps of which are as follows:

[0010] (1) Pour EDTA-2Na into deionized water and stir to dissolve at 40°C. Weigh CS and add it to the solution. Keep the temperature and stir for 12 h until CS is completely dissolved to synthesize CS-EDTA.

[0011] (2) Weigh GO and sonicate it in deionized water, then add CS-EDTA solution and sonicate until a uniform suspension is formed. Stir in an ice-water bath, dissolve 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDAC) condensing agent in deionized water, add it dropwise to the above suspension, stir in an ice-water bath for 8 h, wash and dry to obtain CS-EDTA-GO.

[0012] (3) Combine the obtained CS-EDTA-GO and AgNO3 Add to deionized water, sonicate until homogeneous, and then... NaBH4 Dissolve completely in deionized water in an ice bath with stirring. AgNO3 The mixture of GO and GO was stirred at 80°C. NaBH4 The solution was quickly added to it, and after the reaction was completed, the mixture was washed and dried to obtain CS-EDTA-RGO@AgNPs;

[0013] (4) The prepared CS-EDTA-RGO@AgNPs were added to PDMS (polydimethylsiloxane) and hexane was added as solvent. After stirring evenly, the mixture was placed in a vacuum oven at 60°C for 30 min to obtain a low-filling graphene-nano silver composite coating.

[0014] (5) Finally, the prepared low-filling graphene-nano silver composite coating was scraped onto the aluminum sheet and cured at 120°C for 2 hours to obtain the aluminum sheet sample coated with the thermally conductive coating.

[0015] Moreover, the amount of EDTA-2Na added in step (1) is 0.172 M, the amount of deionized water is 120 ml, and the amount of CS added is 1 g.

[0016] Moreover, the amount of GO added in step (2) is 0.15 g, and the amount of EDAC added is 0.75 M.

[0017] Moreover, the steps described in step (3) AgNO3 The addition amount was 2.9 mM. NaBH4 The addition amount is 1.05 M.

[0018] Moreover, in step (4), the mass ratio of PDMS to n-hexane is 10:1.

[0019] Moreover, in step (4), while adding the n-hexane, a curing agent is also added, with the mass ratio of n-hexane to curing agent being 1:1.

[0020] Moreover, in step (4), the CS-EDTA-RGO@AgNPs are used as fillers, and the addition amount is 0.015~0.075:1 with the mass ratio of PDMS.

[0021] An application of a low-filler graphene-nano silver composite coating obtained by the above preparation method is discussed. This coating is a thermally conductive coating with graphene / silver composite filler doped with polydimethylsiloxane. The filler structure has a "point-to-surface" structure and is tightly connected through in-situ growth, ultimately leading to the formation of thermally conductive pathways. Furthermore, the coating application method is relatively simple; the low-filler graphene-nano silver composite coating can be applied to any heat dissipation substrate for use in thermal conductivity applications. It offers advantages such as high thermal conductivity, high yield, and a green and simple preparation method.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The "point-to-surface" structured thermally conductive filler prepared by this invention can effectively transfer heat to the aluminum fins of a simulated heat sink casing. It can be uniformly dispersed in the polydimethylsiloxane matrix, forming a complete thermal conductive path. The resulting thermally conductive coating has advantages such as simple molding method, good mechanical properties, and ease of processing, which helps to solve the thermal management problem of heat transfer in electronic devices. Specifically, it is reflected in:

[0024] (1) The condensing agent EDAC can activate the -COOH group of GO and EDTA. The carboxyl group of EDAC reacts with the carboxyl group of EDTA to form the ester intermediate EDTA-EDAC. The carboxyl group on EDAC is more active than the carboxyl group on EDTA alone. These carboxyl groups react with the amino group on CS. NH2 A condensation reaction occurs to form an amide bond -CO-NH-; and the carboxyl functional group on GO can also react with CS. NH2 An amidation reaction occurs, thus the EDAC acts as a linker, crosslinking GO / EDTA / CS together to form a network-like modified GO. This modification mechanism is used for the first time in the preparation of graphene / silver as a thermally conductive filler. CS increases the specific surface area of ​​graphene and reduces its stacking, while the bound EDTA groups increase the active sites for nanoparticle growth on the graphene surface.

[0025] (2) The modifiers used, chitosan and disodium EDTA, are green and environmentally friendly, inexpensive, and have low cost.

[0026] (3) Thermally conductive coatings prepared by filling silicone rubber with a low amount of thermally conductive filler have high thermal conductivity and high heat transfer efficiency to aluminum sheets.

[0027] (4) The prepared “point-to-surface” structure thermally conductive fillers CS-EDTA-RGO@AgNPs are effectively connected to each other in the matrix to form a complete thermally conductive path.

[0028] (5) The preparation process is simple, the equipment requirements are not high, and it is easy to achieve industrial mass production. Attached Figure Description

[0029] Figure 1 The XRD patterns are of the three composite filler samples prepared in Examples 1-3 of this invention.

[0030] Figure 2 SEM images of the three composite filler samples prepared in Examples 1-3 of this invention.

[0031] Figure 3 The thermal conductivity curves of the three composite filler samples prepared in Examples 1-3 of this invention at different contents are shown. Detailed Implementation

[0032] The present invention will be described in detail below through specific embodiments, but these embodiments are not intended to limit the actual scope of protection of the present invention in any way.

[0033] Example 1

[0034] (1) Weigh 0.05 g of graphene oxide and add it to 160 ml of deionized water. Sonicate for 2-3 h to form a uniform GO suspension.

[0035] (2) Weigh 0.385 M sodium borohydride into 40 ml of deionized water and sonicate under ice bath until completely dissolved. Place the GO suspension in a water bath at 80°C and stir magnetically. Quickly add NaBH4 The solution was reacted for 1 h. After the reaction, the sample was centrifuged at 9500 r / min for 8 min, and then centrifuged three times with anhydrous ethanol, water, and anhydrous ethanol until clean. The RGO powder was obtained by freeze-drying. The above experiment was repeated and the sample was stored under vacuum.

[0036] (3) To prepare the RGO coating, take 1 g of PDMS and weigh out RGO with mass fractions of 1.5 wt%, 3 wt%, 4.5 wt%, 6 wt%, and 7.5 wt% respectively. Add the RGO to the PDMS, along with the solvent n-hexane and the curing agent (PDMS: curing agent: n-hexane = 10:1:1). Stir under vacuum until a homogeneous mixture is formed. Finally, place the coating in a vacuum oven at 60°C for 30 min.

[0037] (4) The aluminum sheet was cleaned in advance with sandpaper of different grits, and then ultrasonically dried in anhydrous ethanol to remove aluminum oxide and scratches on the surface of the aluminum sheet, so as to obtain a smooth and clean aluminum sheet coating substrate and reduce unnecessary interfacial resistance. The coating was applied to the polished aluminum sheet and cured at 120℃ for 2 h to obtain aluminum sheet samples coated with thermally conductive coating, which were recorded as pure PDMS and RGO / PDMS samples.

[0038] Example 2

[0039] (1) Weigh 0.05 g of graphene oxide and add it to 160 ml of deionized water. Sonicate for 2-3 h to form an aqueous suspension of GO. Then add 4.35 mM / 2.9 mM (GO: AgNO3 = 2 Add silver nitrate in a ratio of 1 / 3:1 and sonicate for 10 minutes until it is completely dissolved.

[0040] (2) Weigh 0.385 M sodium borohydride into 40 ml of deionized water and sonicate under ice bath until completely dissolved. AgNO3 The mixture of GO and sodium borohydride was placed in a water bath at 80°C and magnetically stirred. Sodium borohydride solution was then rapidly added and the reaction proceeded for 1 hour. After the reaction, the solution was centrifuged at 9500 r / min for 8 minutes. The sample was then centrifuged three times with anhydrous ethanol, water, and anhydrous ethanol until clean. RGO@AgNPs powder was obtained by freeze-drying. The above experiment was repeated and the sample was stored under vacuum.

[0041] (3) To prepare the RGO@AgNPs coating, take 1 g of PDMS and weigh out RGO@AgNPs with mass fractions of 1.5 wt%, 3 wt%, 4.5 wt%, 6 wt%, and 7.5 wt% respectively. Add them to the PDMS along with the solvent n-hexane and the curing agent (PDMS:curing agent:n-hexane = 10:1:1). Stir under vacuum until a homogeneous mixture is formed. Finally, place the coating in a vacuum oven at 60°C for 30 min.

[0042] (4) The aluminum sheet was cleaned with sandpaper of different grits in advance, and then ultrasonicated in anhydrous ethanol and dried to remove aluminum oxide and scratches on the surface of the aluminum sheet, so as to obtain a smooth and clean aluminum sheet coating substrate. The coating was applied to the polished aluminum sheet and cured at 120℃ for 2 h to obtain the aluminum sheet sample coated with thermally conductive coating, which was denoted as RGO@AgNPs / PDMS sample.

[0043] Example 3

[0044] (1) Synthesize CS-EDTA: Weigh 0.172 M EDTA-2Na and pour it into a blue-mouthed bottle containing 120 ml of deionized water. Stir magnetically in a 40°C water bath until dissolved. Then weigh 1 g of CS and add it to the blue-mouthed bottle. Maintain the temperature and stir for 12 h until CS is completely dissolved. Store it in a refrigerator.

[0045] (2) Synthesis of CS-EDTA-GO: 0.15 g of graphene oxide was added to a blue-mouthed flask, followed by 75 ml of deionized water and sonicated for 1 h. 28.8 g of CS-EDTA solution was added and sonicated until a uniform suspension was formed. The mixture was then placed in an ice-water bath and magnetically stirred. 0.75 M EDAC was dissolved in 20 ml of deionized water and added dropwise to the above mixed solution. The mixture was stirred in an ice-water bath for 8 h to obtain the product solution. After the reaction was completed, the product solution was washed and freeze-dried to obtain CS-EDTA-GO. The above experiment was repeated and the product was stored under vacuum.

[0046] (3) Synthesize CS-EDTA-RGO@AgNPs. Add the product CS-EDTA-GO to 160 ml of deionized water and sonicate. Then add... 2.9 mM AgNO3 Sonicate until thoroughly mixed. Weigh 1.05 M sodium borohydride into 40 ml of deionized water and stir in an ice bath until dissolved. [The text then abruptly shifts to a seemingly unrelated topic:] ...the container containing... AgNO3 The blue-mouthed bottle containing the mixed solution of CS-EDTA-GO was placed in a water bath at 80°C and magnetically stirred. Sodium borohydride solution was quickly added to the mixture and reacted for 1 h. After the reaction was completed, the mixture was centrifuged, washed, and freeze-dried to obtain CS-EDTA-RGO@AgNPs. The above experiment was repeated and the mixture was stored under vacuum.

[0047] (4) Preparation of CS-EDTA-RGO@AgNPs coating: Take 1 g of polydimethylsiloxane, and weigh out CS-EDTA-RGO@AgNPs with mass fractions of 1.5 wt%, 3 wt%, 4.5 wt%, 6 wt%, and 7.5 wt% respectively, and add them to PDMS. At the same time, add the solvent n-hexane and the curing agent (PDMS:curing agent:n-hexane = 10:1:1). Stir under vacuum until a homogeneous mixture is formed. Finally, place the coating in a vacuum oven at 60°C for 30 min.

[0048] (5) The aluminum sheet was first polished with sandpaper of different grits, then ultrasonicated in anhydrous ethanol and dried to remove aluminum oxide and scratches from the surface of the aluminum sheet, resulting in a smooth and clean aluminum sheet coating substrate. The coating was applied to the polished aluminum sheet and cured at 120℃ for 2 h to obtain the aluminum sheet sample coated with thermally conductive coating, which was designated as CS-EDTA-RGO@AgNPs / PDMS sample.

[0049] Figure 1The XRD characteristic diffraction patterns of graphene oxide (GO), reduced graphene oxide (RGO), chitosan-EDTA-RGO (CERG), reduced graphene oxide composite silver nanoparticles (RGO@AgNPs), and modified reduced graphene oxide composite silver nanoparticles (CERG@AgNPs) are shown from bottom to top. It can be seen that the diffraction peak of RGO after reduction shifted from 2θ=10.7° to 23.8°, indicating that GO was reduced. RGO@AgNPs and CS-EDTA-RGO@AgNPs both showed diffraction peaks of 2θ=25.3° and 2θ=38°, 44.2°, 64.3°, and 77.4°. The former corresponds to the (002) crystal plane of RGO, and the latter corresponds to the (111), (200), (220), and (311) crystal planes of Ag, proving that AgNPs were successfully grown in situ on the surface of RGO and modified RGO.

[0050] Figure 2 The results are displayed as (a) GO, (b) RGO, (c) CE-GO, and (d) respectively. RGO2@AgNPs ( WGO : WAg = 2 :1), (e) RGO3@AgNPs ( WGO : WAg = 3 :1), (f) CS-EDTA-RGO3@AgNPs ( WGO : WAg = 3 :1). In Figure 2 In (a), graphene oxide is effectively reduced, and RGO is in Figure 2 (b) shows a sheet-like morphology with curled edges, and AgNPs were successfully assembled onto the RGO surface. The CS-EDTA-GO surface exhibits a relatively smooth and dense film-like structure with coral-like protrusions and a large specific surface area. By comparing the SEM images of RGO and AgNPs with different mass ratios, it was found that when RGO:AgNPs = 2:1, AgNPs agglomerated and accumulated on the RGO surface, and could not grow uniformly on the RGO surface; when RGO:AgNPs = 3:1, the agglomeration of AgNPs was relatively improved, but some small areas of particle accumulation still remained. Finally, after using a mass ratio of 3:1 and modifying the graphene, it was found that the agglomeration phenomenon basically disappeared, the particles were uniformly distributed, and the thermal conductivity pathways could be better constructed.

[0051] By adjusting the relative ratio of GO and silver nitrate, different fillers were prepared and filled into PDMS using a solvothermal method and a simple chemical reduction method, resulting in RGO / PDMS, RGO@AgNPs / PDMS, and CS-EDTA-RGO@AgNPs / PDMS (abbreviated as CERG@@AgNPs / PDMS). The thermal conductivity of the three groups of samples was then investigated. Figure 3 It can be seen that, under different filler contents, the thermal conductivity of the thermally conductive coating using modified reduced graphene oxide composite silver nanoparticles as filler is much higher than that of coatings with added RGO or RGO@AgNPs. Specifically, when the CS-EDTA-RGO@AgNPs filler content is 7.5 wt% and the mass ratio of RGO to Ag content is 3:1, the prepared coating achieves a thermal conductivity of 0.7209 W / (m·K), which is 103.24% higher than that of the pure PDMS coating, indicating that the prepared thermally conductive coating has excellent heat transfer capabilities.

[0052] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for preparing a low-filling-content graphene-nano silver composite coating, characterized in that: The steps are as follows: (1) Pour EDTA-2Na into deionized water and stir to dissolve at 40°C. Weigh out chitosan and add it to the solution. Maintain the temperature and stir for 12 h until chitosan is completely dissolved to synthesize CS-EDTA; (2) Weigh graphene oxide and sonicate it in deionized water, then add CS-EDTA solution and sonicate until a uniform suspension is formed. Stir in an ice-water bath, dissolve 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride condensing agent in deionized water, add it dropwise to the above suspension, stir in an ice-water bath for 8 h, wash and dry to obtain CS-EDTA-GO. (3) Add the obtained CS-EDTA-GO and AgNO3 to deionized water and sonicate until homogeneous. Separately, dissolve NaBH4 in deionized water and stir in an ice bath until completely dissolved. Stir the mixed solution of CS-EDTA-GO and AgNO3 at 80°C and quickly add the NaBH4 solution. After the reaction is complete, wash and dry to obtain CS-EDTA-RGO@AgNPs. (4) The prepared CS-EDTA-RGO@AgNPs were added to polydimethylsiloxane and hexane was added as solvent. After stirring evenly, the mixture was placed in a vacuum oven at 60°C for 30 min to obtain a low-filling graphene-nano silver composite coating.

2. The preparation method of the low-filling-content graphene-nano silver composite coating according to claim 1, characterized in that: The amount of EDTA-2Na added in step (1) is 0.172 mol, the amount of deionized water added is 120 ml, and the amount of chitosan added is 1 g.

3. The preparation method of the low-filling-content graphene-nano silver composite coating according to claim 1, characterized in that: The amount of graphene oxide added in step (2) is 0.15 g, and the amount of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride condensing agent added is 0.75 mol.

4. The preparation method of the low-filling-content graphene-nano silver composite coating according to claim 1, characterized in that: The amount of AgNO3 added in step (3) is 2.9 mmol, and the amount of NaBH4 added is 1.05 mol.

5. The preparation method of the low-filling-content graphene-nano silver composite coating according to claim 1, characterized in that: In step (4), the CS-EDTA-RGO@AgNPs are used as fillers, and the addition amount is in a mass ratio of 0.015 to 0.075:1 with polydimethylsiloxane.

6. The application of a coating obtained by the preparation method of low-filling-content graphene-nano silver composite coating according to any one of claims 1-5, characterized in that: The low-filling-content graphene-nano silver composite coating can be applied to any heat dissipation substrate for use in the field of thermal conductivity.

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