Silver / liquid metal double-layer flexible conductive coating and preparation method and application thereof

Abstract

The application provides a silver / liquid metal double-layer flexible conductive coating and a preparation method and application thereof, and belongs to the technical field of flexible electrode materials. The coating is arranged on a substrate and sequentially comprises a liquid metal particle layer and a silver particle layer from bottom to top. The silver particle layer and the liquid metal particle layer are bonded by a flexible polymer elastomer, and the particles in the silver particle layer and the liquid metal particle layer are also bonded by the flexible polymer elastomer. The application realizes encapsulation design of the dense silver particle conductive layer, so that the double-layer film retains similar electromechanical properties as the liquid metal single-layer film, greatly enhances the wear resistance, and greatly inhibits the leakage of the liquid metal in a severe mechanical and chemical environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible electrode materials, and more particularly to a silver / liquid metal double-layer flexible conductive coating and a preparation method and application thereof. BACKGROUND

[0002] Liquid metal (LM)-based stretchable interfaces open a new way for seamless system-level integration of soft electronics and pave the way for non-invasive biological monitoring. However, the inherent fluidity of gallium-indium alloys not only weakens the interfacial adhesion between liquid metal and elastomer, but also poses a risk of leakage under harsh mechanical and chemical environments, which seriously hinders the long-term durability of daily wearable applications. The existing potential solutions to the wear resistance and leakage problem of liquid metal electronic devices mainly include polymer ligand modification, multi-component hybridization and acoustic activation, which improve the durability by changing the inherent conductive fluid properties and realize the potential application potential.

[0003] In-situ polymer modification and acoustic activation are proposed as potential solutions to the robustness and leakage problem of liquid metal electronic devices. The former modifies the polymer rich in hydroxyl groups to the surface of the liquid metal particle oxide layer through hydrogen bonding to provide excellent processability and adhesion to the skin. This method can achieve a certain mechanical stability enhancement, but it cannot solve the problem of liquid metal leakage under complex mechanical-chemical stimuli. The latter uses acoustic energy to generate nanoscale liquid metal particles connected to larger particles, thereby improving mechanical stability and anti-leakage. However, this method is high in cost, low in efficiency and slow in speed, and cannot realize large-scale industrial production. At the same time, both methods use homogeneous liquid metal-polymer composites, which lack a physical barrier layer to prevent liquid metal leakage under harsh mechanical or chemical conditions. In addition, in the application of epidermal electronics, it is quite challenging to combine ultra-thin thickness with a strong interface to resist friction and wear, as the device directly contacts the skin-fabric when the body is moving. These problems are more prominent in high-intensity monitoring scenarios, especially during long-term biological monitoring during daily activities, when the device is subjected to large strain deformation and shear wear, which is prone to failure.

[0004] In the prior art, CN118668209A reports a method for preparing a liquid metal film using the impregnation phenomenon, which deposits a metal layer on a polymer substrate with a microstructure, and then coats a liquid metal layer. However, the liquid metal film has poor wear resistance, which can cause liquid metal leakage. SUMMARY

[0005] Based on the problems in the prior art, the present application provides a silver / liquid metal double-layer flexible conductive coating and a preparation method and application thereof, through dense wear-resistant silver particle conductive layer packaging design, the double-layer coating retains similar electromechanical properties with the liquid metal single-layer coating, while greatly enhancing the wear resistance thereof, and greatly inhibiting the leakage of the liquid metal in severe mechanical and chemical environments. The silver / liquid metal double-layer flexible conductive coating has good tensile property, wear resistance, corrosion resistance, and no leakage risk of the liquid metal, and can be used for the preparation of a flexible electrode material.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] A silver / liquid metal double-layer flexible conductive coating is arranged on a substrate, and a liquid metal particle layer and a silver particle layer are sequentially arranged from bottom to top, the silver particle layer and the liquid metal particle layer are bonded by a flexible polymer elastomer, and the particles in the silver particle layer and the liquid metal particle layer are bonded by the flexible polymer elastomer; preferably, the conductivity of the silver / liquid metal double-layer flexible conductive coating is 1.2*10 5 ~5.3*10 5 S·m -1 .

[0008] Preferably, the substrate comprises a flexible polymer elastomer. It can be understood that the flexible polymer elastomer in the substrate and the flexible polymer elastomer in the coating are of the same material, so that the coating and the substrate are firmly bonded.

[0009] Preferably, the liquid metal in the liquid metal particle layer comprises gallium or a gallium-based alloy, wherein the gallium-based alloy comprises gallium and at least any one metal selected from the group consisting of indium, tin and zinc.

[0010] Preferably, the flexible polymer elastomer is any one of a linear three-embedded copolymer (SEBS), a thermoplastic polyurethane elastomer (TPU) and a polydimethylsiloxane (PDMS).

[0011] Preferably, the thickness of the silver particle layer is 3.0-12.5 μm, the thickness of the liquid metal particle layer is 3.3-13.4 μm, and the thickness of the coating is 6.3-25.9 μm.

[0012] The present application also provides a preparation method of the silver / liquid metal double-layer flexible conductive coating, which comprises the following steps:

[0013] S1, mixing liquid metal particles and silver particles with a flexible polymer elastomer and a solvent respectively, homogenizing, to obtain silver particle slurry with a particle size of 0.8-1 μm and liquid metal particle slurry with a particle size of 1-10 μm respectively;

[0014] S2, coating or screen printing the liquid metal microparticle slurry on the substrate to form a liquid metal microparticle layer after thermal curing; coating or screen printing the silver microparticle slurry on the liquid metal microparticle layer to obtain a silver / liquid metal double-layer flexible conductive coating after thermal curing.

[0015] Preferably, the solvent is terpineol.

[0016] Preferably, the silver microparticle slurry contains silver 60-80 wt%, terpineol 15-30 wt%, and flexible polymer elastomer 5-10 wt%; and the liquid metal microparticle slurry contains liquid metal 60-80 wt%, terpineol 15-30 wt%, and flexible polymer elastomer 5-10 wt%.

[0017] Preferably, the thermal curing temperature is 100-150°C, and the time is 5-30 min.

[0018] The application also provides a flexible electrode comprising a substrate and the silver / liquid metal double-layer flexible conductive coating disposed on the substrate. The substrate can be a silicon substrate coated with a flexible polymer elastomer. More preferably, the silicon substrate can be tiled by multiple silicon wafers and connected by a flexible polymer elastomer to meet the stretching requirement.

[0019] Compared with the prior art, the application has the following beneficial effects:

[0020] The coating of the application uses a flexible polymer elastomer as a bridge to firmly bond the liquid metal microparticle layer and the silver microparticle layer by polymer cross-linking, thereby realizing an ultra-thin (6 µm) and skin-compatible interface. The silver / liquid metal double-layer flexible conductive coating provided by the application has good wear resistance and maintains structural integrity throughout the 1500-second paper tape rubbing test, with negligible change in electrical conductivity. In addition, the coating does not leak liquid metal and the strain sensitivity does not decay under extreme mechanical-chemical conditions (900% tensile strain and 2M hydrochloric acid / sodium hydroxide medium solution). The application provides a new idea for realizing soft, ultra-thin, and stable biological signal acquisition under extreme mechanical-chemical conditions, and can be used for the construction of wearable physiological and pressure sensors.

[0021] The preparation method provided by the application can directly prepare silver and liquid metal slurry on a large scale, and excellent electromechanical properties can be obtained without additional activation means, while realizing wear resistance, leakage prevention, and other functions. The process is simple and conducive to large-scale industrialization. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to make the purpose, technical solutions and beneficial effects of the application clearer, the application is described below with reference to the following drawings:

[0023] Figure 1 SEM images and EDS energy spectrum of the silver / liquid metal bilayer flexible conductive coating prepared in Example 1 of the present application;

[0024] In the figure, a, SEM, b-e respectively represent the EDS energy spectrum of different elements.

[0025] Figure 2 Standard paper tape friction time-resistance change result graph of the flexible electrode (AgPs / LMPs bilayer) with silver / liquid metal bilayer flexible conductive coating prepared in Example 1 of the present application and the liquid metal coating film electrode (LMPs / SEBS) prepared in Comparative Example 1, and the silver coating electrode (AgPs / SEBS) prepared in Comparative Example 2.

[0026] In the figure, a is a schematic diagram of the test process, and b is the paper tape friction-resistance change result.

[0027] Figure 3 Abrasion test result of the flexible electrode (AgPs / LMPs bilayer) with silver / liquid metal bilayer flexible conductive coating prepared in Example 1 of the present application and the liquid metal coating film electrode (LMPs / SEBS) prepared in Comparative Example 1.

[0028] In the figure, a is a schematic diagram of the test process, and b is the abrasion test result.

[0029] Figure 4 SEM images and XPS analysis images of the flexible electrode (AgPs / LMPs bilayer) with silver / liquid metal bilayer flexible conductive coating prepared in Example 1 of the present application before and after stretching;

[0030] In the figure, a represents the SEM image before stretching, b represents the SEM image after stretching, and c represents the XPS analysis image before and after stretching.

[0031] Figure 5 Change graph of the flexible electrode (AgPs / LMPs bilayer) with silver / liquid metal bilayer flexible conductive coating prepared in Example 1 of the present application, the liquid metal coating film electrode (LMPs / SEBS) prepared in Comparative Example 1, and the silver / liquid metal film electrode (Ag-LMPS / SEBS) prepared in Comparative Example 3 before and after acid and alkali environment test.

[0032] Wherein, a is the photo of AgPs / LMPs bilayer soaked in 2M HCl for 1h; b is the photo of LMPs / SEBS soaked in 2M HCl for 1h; c is the photo of Ag-LMPs / SEBS soaked in 2M HCl for 1h; d is the SEM of AgPs / LMPs bilayer soaked in 2M HCl for 1h; e is the SEM of LMPs / SEBS soaked in 2M HCl for 1h; f is the SEM of Ag-LMPs / SEBS soaked in 2M HCl for 1h; g is the photo of AgPs / LMPs bilayer soaked in 2M NaOH for 1h; h is the photo of LMPs / SEBS soaked in 2M NaOH for 1h; i is the photo of Ag-LMPs / SEBS soaked in 2M NaOH for 1h; j is the SEM of AgPs / LMPs bilayer soaked in 2M NaOH for 1h; k is the SEM of LMPs / SEBS soaked in 2M NaOH for 1h; l is the SEM of Ag-LMPs / SEBS soaked in 2M NaOH for 1h.

[0033] Figure 6 The resistance change diagram of the flexible electrode with silver / liquid metal bilayer flexible conductive coating prepared in Example 1 of the present application (upper) and the liquid metal coating film electrode prepared in Comparative Example 1 (lower) before and after acid and alkali environment test.

[0034] Figure 7 The resistance change diagram of the flexible electrode with silver / liquid metal bilayer flexible conductive coating prepared in Example 1 of the present application (upper) and the liquid metal coating film electrode prepared in Comparative Example 1 (lower) before and after acid and alkali environment test. DETAILED DESCRIPTION

[0035] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details set forth in this description. In other instances, well-known methods have not been described in detail in order to avoid obscuring the present application.

[0036] 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 to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application.

[0037] It should be noted that the raw materials, instruments and the like involved in the present application are all ordinary commercially available products.

[0038] The application will be further described below with reference to the drawings. The following examples are only used to more clearly illustrate the technical solutions of the application, and cannot be used to limit the protection scope of the application. Example 1

[0039] The embodiment provides a preparation method of a silver / liquid metal bilayer flexible conductive coating and a flexible electrode, comprising the following steps:

[0040] S1, gallium-indium alloy particles and silver particles are respectively mixed with SEBS and terpineol, and homogenized to obtain a silver particle slurry and a liquid metal particle slurry respectively;

[0041] In the silver particle slurry, the silver accounts for 80 wt%, the terpineol accounts for 12.5 wt%, and the SEBS accounts for 7.5 wt%; in the liquid metal particle slurry, the gallium-indium alloy particles account for 80 wt%, the terpineol accounts for 12.5 wt%, and the SEBS accounts for 7.5 wt%

[0042] S2, the liquid metal particle slurry is spin-coated on a silicon wafer substrate on which SEBS has been spin-coated, and after 120 DEG C heat curing for 5 min, a liquid metal particle layer is formed; the silver particle slurry is spin-coated on the liquid metal particle layer, and after 120 DEG C heat curing for 5 min, a silver / liquid metal bilayer flexible conductive coating is formed on the substrate, thereby obtaining a flexible electrode with the silver / liquid metal bilayer flexible conductive coating (named as AgPs / LMPs bilayer).

[0043] The silver / liquid metal bilayer flexible conductive coating prepared has a thickness of 13.3 μm, wherein the thickness of the silver particle layer is 6.0 μm, and the thickness of the liquid metal particle layer is 7.3 μm; the conductivity of the silver / liquid metal bilayer flexible conductive coating is 5.3 x 10 5 S·m -1 .

[0044] The AgPs / LMPs bilayer is subjected to SEM analysis, and the results are shown in Figs. Figure 1 a, and through eds energy spectrum analysis, as shown in Figs. Figure 1 b-e, it is found that the polymers in the film are basically fused, the silver particle layer contains part of Ga and In, and the liquid metal particle layer contains part of Ag, which is caused by the wetting phenomenon. Example 2

[0045] The embodiment provides another preparation method of a silver / liquid metal bilayer flexible conductive coating and a flexible electrode, comprising the following steps:

[0046] S1, gallium-indium alloy particles and silver particles are respectively mixed with TPU and terpineol, and homogenized to obtain a silver particle slurry and a liquid metal particle slurry respectively;

[0047] The silver particle slurry contains silver 60wt%, terpineol 30wt%, and TPU 10wt%; the liquid metal particle slurry contains gallium-indium alloy particles 60wt%, terpineol 30wt%, and TPU 10wt%;

[0048] S2, spin-coat the liquid metal particle slurry on the silicon wafer substrate on which the TPU has been spin-coated, and form a liquid metal particle layer after heat curing at 120℃ for 5 minutes; spin-coat the silver particle slurry on the liquid metal particle layer, and form a silver / liquid metal double-layer flexible conductive coating on the substrate after heat curing at 120℃ for 5 minutes.

[0049] The silver / liquid metal double-layer flexible conductive coating prepared has a thickness of 25.9μm, wherein the thickness of the silver particle layer is 12.4μm, and the thickness of the liquid metal particle layer is 13.5μm; the conductivity of the silver / liquid metal double-layer flexible conductive coating is 1.2×10 5 S m -1 . Example 3

[0050] The present embodiment provides another method for preparing a silver / liquid metal double-layer flexible conductive coating and a flexible electrode, comprising:

[0051] S1, mix gallium-indium alloy particles and silver particles with PDMS and terpineol respectively, and homogenize to obtain a silver particle slurry and a liquid metal particle slurry respectively;

[0052] The silver particle slurry contains silver 70wt%, terpineol 25wt%, and PDMS 5wt%; the liquid metal particle slurry contains gallium-indium alloy particles 70wt%, terpineol 25wt%, and SEBS 5wt%;

[0053] S2, spin-coat the liquid metal particle slurry on the silicon wafer substrate on which the PDMS has been spin-coated, and form a liquid metal particle layer after heat curing at 120℃ for 5 minutes; spin-coat the silver particle slurry on the liquid metal particle layer, and form a silver / liquid metal double-layer flexible conductive coating on the substrate after heat curing at 120℃ for 5 minutes.

[0054] The silver / liquid metal double-layer flexible film prepared has a thickness of 6.3μm, wherein the thickness of the silver particle layer is 3.3μm, and the thickness of the liquid metal particle layer is 3μm; the conductivity of the silver / liquid metal double-layer flexible film is 3.5×10 5 S m -1 .

[0055] Comparative Example 1

[0056] A method for preparing a liquid metal coating film electrode, comprising:

[0057] S1, mix gallium-indium alloy particles with SEBS and terpineol, and homogenize to obtain a liquid metal particle slurry;

[0058] The liquid metal particle slurry contains gallium-indium alloy particles 80wt%, terpineol 12.5wt%, and SEBS 7.5wt%;

[0059] S2, spin coating the liquid metal particle slurry on the silicon wafer substrate on which SEBS has been spin-coated, and forming a liquid metal particle layer on the substrate after heat curing at 120°C for 5 min, to obtain a liquid metal thin film flexible electrode (named LMPs / SEBS).

[0060] Comparative Example 2

[0061] A preparation method of a silver-coated thin film electrode, comprising:

[0062] S1, mixing silver particles with SEBS and terpineol, and homogenizing to obtain a silver particle slurry;

[0063] The silver particle slurry contains silver particles 80wt%, terpineol 12.5wt%, and SEBS 7.5wt%;

[0064] S2, spin coating the silver particle slurry on the silicon wafer substrate on which SEBS has been spin-coated, and forming a silver particle layer on the substrate after heat curing at 120°C for 5 min, to obtain a silver-coated thin film electrode (named AgPs / SEBS).

[0065] Comparative Example 3

[0066] A preparation method of a silver / liquid metal single-layer flexible coating and flexible electrode, comprising:

[0067] S1, mixing gallium-indium alloy particles and silver particles with SEBS and terpineol, and homogenizing to obtain a silver particle-liquid metal particle slurry;

[0068] The silver particle-liquid metal particle slurry contains silver 40wt%, gallium-indium alloy particles 40wt%, terpineol 12.5wt%, and SEBS 7.5wt%

[0069] S2, spin coating the silver particle-liquid metal particle slurry on the silicon wafer substrate on which SEBS has been spin-coated, and forming a silver / liquid metal single layer on the substrate after heat curing at 120°C for 5 min, to obtain a silver / liquid metal thin film electrode (Ag-LMPs / SEBS).

[0070] Performance test

[0071] 1. Continuous paper tape rubbing test

[0072] A paper tape rub test was performed on the silver / liquid metal bilayer flexible conductive coating (AgPs / LMPs bilayer) prepared in Example 1 and the liquid metal conductive coating (LMPs / SEBS) prepared in Comparative Example 1 and the silver conductive coating (AgPs / SEBS) prepared in Comparative Example 2. The procedure is shown in Figure 2 a. The normal force was 175 grams and the paper tape rub speed was 44 mm / s. The change in electrical conductivity during the rub was measured by a multimeter. The results are shown in Figure 2 b. The AgPs / LMPs bilayer could withstand 1500 seconds of continuous paper tape rub before losing all electrical conductivity.

[0073] 2. Fabric reciprocating rub test

[0074] A fabric rub test was performed on the silver / liquid metal bilayer flexible film (AgPs / LMPs bilayer) prepared in Example 1 and the liquid metal film (LMPs / SEBS) prepared in Comparative Example 1. The procedure is shown in Figure 3 a. The normal force was 200 grams and the fabric rub speed was 20 mm / s. The change in electrical conductivity during the rub was measured by a multimeter. The results are shown in Figure 3 b. The AgPs / LMPs bilayer could withstand 12000 reciprocating fabric rubs before losing all electrical conductivity.

[0075] 3. Mechanical stretch environment test

[0076] The AgPs / LMPs bilayer sample prepared in Example 1 was stretched at a speed of 1 mm / s with a strain of 600% for 10 cycles. The scanning electron micrographs before and after stretching are shown in Figure 4 a and Figure 4 b. The x-ray photoelectron spectroscopy before and after stretching is shown in Figure 4 c. There was no liquid metal leakage.

[0077] 4. Chemical environment test

[0078] The AgPs / LMPs bilayer sample prepared in Example 1, the LMPs / SEBS sample prepared in Comparative Example 1 and the Ag-LMPs / SEBS sample prepared in Comparative Example 3 were immersed in 2M HCl and 2M NaOH for one hour. The phase changes were observed by scanning electron microscopy. As shown in Figure 5 , there was no liquid metal leakage for the AgPs / LMPs bilayer sample prepared in Example 1, but there was liquid metal leakage for the samples prepared in Comparative Examples 1 and 3. The change in resistance was measured by a multimeter. As shown in Figure 6As shown, the conductivity of the AgPs / LMPs bilayer sample prepared in Example 1 changed less than 5%.

[0079] 5. Mechanical environment test

[0080] The AgPs / LMPs bilayer sample prepared in Example 1 and the LMPs / SEBS sample prepared in Comparative Example 1 were respectively placed in a drum washing machine for 0, 1, 2, 3, 4, 5, and 6 hours of machine washing, and the resistance change was measured by an electronic multimeter. The results are shown in Table 2. Figure 7 The conductivity of the AgPs / LMPs bilayer sample changed less than 20%.

[0081] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, can make equivalent replacements or changes within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A silver / liquid metal bilayer flexible conductive coating disposed on a substrate, characterized in that, A liquid metal particle layer and a silver particle layer are sequentially arranged from bottom to top, the silver particle layer and the liquid metal particle layer are adhered by a flexible polymer elastomer, and the silver particle layer and the liquid metal particle layer are adhered by the flexible polymer elastomer.

2. The silver / liquid metal bilayer flexible conductive coating of claim 1, wherein, The silver / liquid metal double-layer flexible conductive coating has a conductivity of 1.2 x 10 5 ~ 5.3 x 10 5 S·m -1 .

3. The silver / liquid metal bilayer flexible conductive coating of claim 1, wherein, The substrate comprises a flexible polymer elastomer; the liquid metal in the liquid metal particle layer comprises gallium or a gallium-based alloy, wherein the gallium-based alloy comprises gallium and at least any one metal selected from the group consisting of indium, tin and zinc.

4. The silver / liquid metal bilayer flexible conductive coating of claim 3, wherein, The flexible polymer elastomer is any one of a linear tri-block copolymer, a thermoplastic polyurethane elastomer or a polydimethylsiloxane.

5. The silver / liquid metal bilayer flexible conductive coating of claim 1, wherein, The thickness of the silver particle layer is 3.0-12.5 μm, the thickness of the liquid metal particle layer is 3.3-13.4 μm, and the thickness of the coating layer is 6.3-25.9 μm.

6. The method of producing a silver / liquid metal bilayer flexible conductive coating according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: S1, mixing liquid metal particles and silver particles respectively with a flexible polymer elastomer and a solvent, homogenizing to obtain a silver particle slurry and a liquid metal particle slurry respectively; S2, coating or screen printing the liquid metal particle slurry on the substrate to form a liquid metal particle layer after heat curing; coating or screen printing the silver particle slurry on the liquid metal particle layer to obtain a silver / liquid metal double-layer flexible conductive coating layer after heat curing.

7. The preparation method according to claim 6, characterized in that, The solvent is terpineol.

8. The preparation method according to claim 7, characterized in that, The silver particle slurry contains silver 60-80 wt%, terpineol 15-30 wt% and flexible polymer elastomer 5-10 wt%; the liquid metal particle slurry contains liquid metal 60-80 wt%, terpineol 15-30 wt% and flexible polymer elastomer 5-10 wt%.

9. The preparation method according to claim 6, characterized in that, The heat curing temperature is 100-150 °C, and the time is 5-30 min.

10. A flexible electrode comprising a substrate and a silver / liquid metal double-layer flexible conductive coating layer as claimed in any one of claims 1-5 arranged on the substrate.

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