Stretchable PEDOT: PSS electrode and preparation method thereof

Abstract

The invention discloses a stretchable PEDOT: PSS electrode and a preparation method thereof. The stretchable PEDOT: PSS electrode comprises a composite elastic stretching substrate and a PEDOT: PSS electrode, wherein the elastic stretching substrate and the PEDOT: PSS electrode are compounded; the PEDOT: PSS electrode is internally provided with a cross-linked polymer network formed by polyethylene glycol dimethacrylate and dithioerythritol; under the irradiation of ultraviolet light, the polyethylene glycol dimethacrylate and the dithioerythritol form a cross-linked polymer network. The polymer network formed in the stretchable PEDOT: PSS electrode can effectively disperse stress borne by the electrode during stretching, and the prepared PEDOT: PSS electrode has excellent stretchability. The stretchable PEDOT: PSS electrode is prepared by adopting a simple and convenient method, a complicated synthesis process and a harsh production environment are not needed, and industrial production is facilitated.

Description

Technical Field

[0001] The present invention relates to a stretchable PEDOT:PSS electrode and a preparation method thereof, belonging to the field of organic electronics. Background Art

[0002] A stretchable electrode is an electronic material that still maintains good electrical conductivity in a stretched state. In recent years, with the development of flexible displays, wearable medical devices, and flexible circuits, stretchable electrodes have attracted much attention from researchers (Standalone real-time health monitoring patch based on a stretchable organic optoelectronic system, Sci. Adv. 2021, 7, 9180; Ultra-conformal skin electrodes with synergistically enhanced conductivity for long-time and low motion artifact epidermal electrophysiology, Nat. Commun. 2021, 12, 4880; Design Considerations and fabrication protocols of high-Performance intrinsically stretchable transistors and integrated circuits, ACS Nano. 2024, 18, 33011-33031). Compared with hard and brittle inorganic conductive materials, organic conductive materials have unique advantages in the application of future flexible electronic products due to their good flexibility, molecular processability design, and liquid-phase preparation. As a typical representative of organic conductive materials, PEDOT:PSS is widely used in various stretchable fields (Skin-like soft thermoelectric composites with a “J-shaped” stress–strain behavior for self-powered strain sensing, Adv. Funct. Mater. 2024, 2420644; High-stretchability, ultralow-hysteresis conducting polymer hydrogel strain sensors for soft machines,Adv. Mater. (2022, 34, 2203650). People are committed to finding a simple and effective method to obtain highly stretchable PEDOT:PSS electrodes.

[0003] Currently, the preparation methods of stretchable PEDOT:PSS electrodes mainly include the following two: (1) One way is to obtain highly stretchable PEDOT:PSS electrodes by adding plasticizers (Enhancing the electrical conductivity and long-term stability of PEDOT:PSS electrodes through sequential treatment with nitric acid and cesium chloride, Adv. Mater. 2024, 36, 2405094; Protic ionic liquids for intrinsically stretchable conductive polymers, ACS Appl. Mater. Interfaces. 2023, 15, 3202 - 321). For example, the Wang Hong team incorporated ionic liquid (IL) into PEDOT:PSS, and the prepared PEDOT:PSS hydrogel has a stretchability of 30% (Ultra-High electrical conductivity in filler-free polymeric hydrogels toward thermoelectrics and electromagnetic interference shielding, Adv. Mater. 2022, 34, 2109904). However, these additives often have certain toxicity and are not suitable for application in wearable bioelectronics; (2) Another way is the polymer blending method. By doping stretchable polymers, the stretchability of PEDOT:PSS can be effectively improved (Stretchable surface electromyography electrode array patch for tendon location and muscle injury prevention, Nat. Commun. 2023, 14, 6494; A stretchable polymer conductor through the mutual plasticization effect, Adv. Mater.2023, 35, 2303245), which is the most commonly used stretching method at present. For example, the Guo Chuanfei team prepared a hydrogel electrode by doping PVA into PEDOT:PSS, which can increase the stretchability of PEDOT:PSS to 150% (Highly conducting and stretchable double-network hydrogel for soft bioelectronics, Adv. Mater. 2022, 34, 2200261). However, the synthesis process of these polymers is complex and very time-consuming, and there are also high requirements for the synthesis environment. It is difficult to prepare in general laboratories and is not universal. These strict conditions limit the application and industrial production of stretchable PEDOT:PSS. Therefore, a new strategy needs to be proposed to achieve the efficient preparation of highly stretchable PEDOT:PSS electrodes with simple materials and methods. Summary of the Invention

[0004] The purpose of the present invention is to provide a stretchable PEDOT:PSS electrode and a preparation method thereof; the method provided by the present invention has a simple process. Only two materials, polyethylene glycol dimethacrylate (PEGDMA) and dithioerythritol (DTE), need to be added to the PEDOT:PSS solution. The molecular structural formulas of the materials are as Figure 2 shown. Under an air environment, a highly stretchable PEDOT:PSS electrode can be prepared by ultraviolet light cross-linking, without including a complex synthesis process; in the method provided by the present invention, the materials used are all commercial materials, and there is no need to synthesize new materials additionally. The prepared PEDOT:PSS electrode has excellent stretchability.

[0005] In the present invention, PEGDMA and DTE involved can undergo a thiol-ene click reaction under ultraviolet light under the promotion of a photoinitiator to generate a polymer network, thereby improving the stretchability of PEDOT:PSS. The schematic diagram of the principle is as Figure 3 shown.

[0006] The stretchable PEDOT:PSS electrode provided by the present invention includes a composite elastic stretching substrate and a PEDOT:PSS electrode; In the PEDOT:PSS electrode, there is a cross-linked polymer network formed by polyethylene glycol dimethacrylate and dithioerythritol. The existence of the polymer network is proved as Figure 4 shown. Before curing, the electrode contains C=C double bonds. After curing, the C=C double bonds disappear and combine with SH bonds to form C-S bonds.

[0007] Under ultraviolet light irradiation, the polyethylene glycol dimethacrylate and the dithioerythritol form the cross-linked polymer network.

[0008] The thickness of the PEDOT:PSS electrode is 500 nm - 1 μm; The thickness of the elastic stretchable substrate can be 100 - 200 μm.

[0009] The preparation method of the stretchable PEDOT:PSS electrode provided by the present invention includes the following steps: S1. Add polyethylene glycol dimethacrylate, dithiothreitol and a photoinitiator to PEDOT:PSS to obtain an electrode solution; S2. Spin-coat the electrode solution on a hard substrate, and then perform ultraviolet light curing to crosslink the polyethylene glycol dimethacrylate and the dithiothreitol to form a polymer network, thereby obtaining the PEDOT:PSS electrode; S3. Prepare the elastic stretchable substrate on the PEDOT:PSS electrode, and transfer it from the hard substrate to obtain the stretchable PEDOT:PSS electrode.

[0010] In the above preparation method, the solid content of the PEDOT:PSS is 1.0 - 1.3%, and the mass content of PEDOT is 0.28 - 0.37%.

[0011] In the above preparation method, the mass ratio of the polyethylene glycol dimethacrylate to PEDOT in the PEDOT:PSS is 10:1 - 40:1; The mass ratio of the polyethylene glycol dimethacrylate to the dithiothreitol is 1:1; The mass ratio of the photoinitiator to the polyethylene glycol dimethacrylate is 1:50 - 1:20.

[0012] The absorption wavelength of the photoinitiator includes 365 nm, such as Irgacure 2959.

[0013] In the above preparation method, the hard substrate is modified with octadecyltrichlorosilane, and the modification is carried out according to the following steps: Place the cleaned hard substrate in a mixed solution of concentrated sulfuric acid and hydrogen peroxide; then clean the hard substrate, and then place the hard substrate in a mixed solution of n-heptane and octadecyltrichlorosilane for 0.5 - 2 h; The hard substrate can be silicon, silicon dioxide or glass.

[0014] In the above preparation method, in step S2, light curing is carried out under ultraviolet light with a wavelength of 365 nm; The time of the ultraviolet light curing is 150 - 200 s.

[0015] In the above preparation method, in step S3, the elastic stretchable substrate is formed of an elastic insulating material, and the elastic insulating material is polydimethylsiloxane or hydrogenated styrene-butadiene block copolymer; Spin coat the elastic insulating material on the PEDOT:PSS electrode and heat and cure it at 70 - 100 °C for 30 - 40 min to obtain the elastic stretchable substrate.

[0016] The present invention has the following beneficial effects: The preparation method of the stretchable PEDOT:PSS electrode provided by the present invention has a simple process. Only two materials, polyethylene glycol dimethacrylate (PEGDMA) and dithioerythritol (DTE), need to be incorporated into the PEDOT:PSS solution, without including a complex synthesis process; PEDGMA and DTE undergo a thiol-ene click reaction under ultraviolet light irradiation. This reaction is highly efficient, insensitive to water and oxygen, and there is no need to create an anhydrous and anoxic environment; PEGDMA and DTE form a polymer network in PEDOT:PSS, which can effectively disperse the stress suffered by the electrode during stretching. The prepared PEDOT:PSS electrode has excellent stretchability. The present invention prepares a stretchable PEDOT:PSS electrode by a simple and convenient method, without a complex synthesis process and a harsh production environment, which is conducive to industrial production. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of the PEDOT:PSS electrode.

[0018] Figure 2 It is the molecular structural formula of PEGDMA and DTE.

[0019] Figure 3 It is the reaction mechanism diagram of the thiol-ene click reaction of PEGDMA and DTE.

[0020] Figure 4 It is the Fourier infrared spectrum of PEDOT:PSS before and after adding PEGDMA / DTE for photocrosslinking.

[0021] Figure 5 It is the tensile microscope photograph of the stretchable PEDOT:PSS electrode prepared in Example 1 of the present invention.

[0022] Figure 6 It is the tensile resistance curve of the stretchable PEDOT:PSS electrode prepared in Example 1 of the present invention.

[0023] Figure 7 It is the tensile microscope photograph of the stretchable PEDOT:PSS electrode prepared in Example 2 of the present invention.

[0024] Figure 8This is the tensile resistance curve of the stretchable PEDOT:PSS electrode prepared in Example 2 of the present invention. Detailed implementation manners

[0025] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0026] Unless otherwise specified, the materials, reagents, etc. used in the following examples can all be obtained from commercial channels.

[0027] Example 1: Preparation of a stretchable PEDOT:PSS electrode (1) Add PEGDMA (mass ratio to PEDOT is 20:1), DTE (molar mass ratio to PEGDMA is 1:1), and photoinitiator Irgacure 2959 (mass ratio to PEGDMA is 1:20) to the PH1000 solution (solid content is 1.1%), and stir at room temperature for 5 h to make it evenly mixed.

[0028] (2) Connect octadecyltrichlorosilane on the surface of the silicon substrate by the liquid phase method: Place the cleaned substrate statically in the mixed solution of concentrated sulfuric acid and hydrogen peroxide; then clean the substrate, and then place the substrate in the mixed solution of n-heptane and octadecyltrichlorosilane for 2 h, that is, octadecyltrichlorosilane is modified on the surface of the substrate.

[0029] (3) Spin-coat the PEDOT:PSS mixed solution obtained in step (1) on the substrate obtained in step (2) at a spin speed of 1000 r, 100 s, and a uniform PEDOT:PSS electrode film with a thickness of 500 nm can be obtained.

[0030] (4) Put the electrode film obtained in step (3) into an ultraviolet curing box and expose it to ultraviolet light of 365 nm for 200 s to cause the polymer in PEDOT:PSS to undergo a photopolymerization reaction to generate a polymer network.

[0031] (5) Spin-coat the elastic insulating material polydimethylsiloxane on the surface of the electrode obtained in step (4) and cure it (temperature is 70 °C, time is 30 min) to form an elastic support layer, which is used as the elastic substrate of the stretchable electrode with a thickness of 100 μm, and transfer it from the substrate, and a PEDOT:PSS electrode with excellent stretchability can be obtained.

[0032] The structural schematic diagram of the stretchable PEDOT:PSS electrode prepared in this example is as Figure 1 shown.

[0033] The tensile microscope photograph of the stretchable PEDOT:PSS electrode prepared in this example is as Figure 5As shown, it can be seen that when stretched to 40%, no cracks are generated in the electrode, proving that the formation of the PEGDMA / DTE polymerization network can inhibit the appearance of cracks during the stretching of PEDOT:PSS.

[0034] The stretching resistance curve of the stretchable PEDOT:PSS electrode prepared in this example is as Figure 6 shown. It can be seen that before adding PEGDMA / DTE, the initial stretching rate of PEDOT:PSS is only 5%. After adding a certain amount of PEGDMA / DTE to form a polymerization network, the stretching rate is increased to 200%, and the resistance only changes by 14 times. This electrode has good stretching stability.

[0035] Example 2: Preparation of highly stretchable PEDOT:PSS electrode (1) Add PEGDMA (mass ratio to PEDOT is 40:1), DTE (molar mass ratio to PEGDMA is 1:1), and photoinitiator Irgacure 2959 (mass ratio to PEGDMA is 1:20) to the PH1000 solution (solid content is 1.1%), and stir at room temperature for 5 h to make it uniformly mixed.

[0036] (2) Connect octadecyltrichlorosilane on the surface of the silicon substrate by the liquid phase method: place the cleaned substrate statically in the mixed solution of concentrated sulfuric acid and hydrogen peroxide; then clean the substrate, and then place the substrate in the mixed solution of n-heptane and octadecyltrichlorosilane for 2 h, that is, octadecyltrichlorosilane is modified on the substrate surface.

[0037] (3) Spin-coat the PEDOT:PSS mixed solution obtained in step (1) on the substrate obtained in step (2) at a spin-coating speed of 1000 r for 100 s, and a uniform PEDOT:PSS electrode film with a thickness of 500 nm can be obtained.

[0038] (4) Put the electrode film obtained in step (3) into an ultraviolet curing box and expose it to ultraviolet light of 365 nm for 200 s to cause a photopolymerization reaction of the polymer in PEDOT:PSS to generate a polymer network.

[0039] (5) Spin-coat the elastic insulating material polydimethylsiloxane on the surface of the electrode obtained in step (4) and cure it (temperature is 70 °C, time is 30 min) to form an elastic support layer, which is used as the elastic substrate of the stretchable electrode with a thickness of 100 μm, and transfer it from the substrate, that is, a PEDOT:PSS electrode with excellent stretchability is obtained.

[0040] The structural schematic diagram of the stretchable PEDOT:PSS electrode prepared in this example is as Figure 1 shown.

[0041] The tensile microscope photograph of the stretchable PEDOT:PSS electrode prepared in this example is as Figure 7 shown. It can be seen that when stretched to 100%, there are still no cracks in the electrode, proving that increasing the content of the PEGDMA / DTE polymerization network can effectively inhibit the appearance of cracks during the stretching of PEDOT:PSS.

[0042] The tensile resistance curve of the stretchable PEDOT:PSS electrode prepared in this example is as Figure 8 shown. It can be seen that when the electrode is stretched to 200%, the resistance only changes about 6 times, proving that increasing the content of the PEGDMA / DTE polymerization network can enhance the stretching stability of the electrode.

Claims

1. A stretchable PEDOT:PSS electrode, characterized in that: It includes a composite elastic stretchable substrate and a PEDOT:PSS electrode; The PEDOT:PSS electrode has a cross-linked polymer network formed by polyethylene glycol dimethacrylate and dithioerythritol; Under ultraviolet light, the polyethylene glycol dimethacrylate and the dithioerythritol form the cross-linked polymer network.

2. The stretchable PEDOT:PSS electrode according to claim 1, characterized in that: The thickness of the PEDOT:PSS electrode is 500 nm-1 μm; The elastic stretch substrate may have a thickness of 100-200 μm.

3. The method for preparing the stretchable PEDOT:PSS electrode according to claim 1 or 2, characterized in that: The steps include: S1, adding polyethylene glycol dimethacrylate, dithioerythritol and a photoinitiator to PEDOT:PSS to obtain an electrode solution; S2, spin coating the electrode solution on a hard substrate, and then curing it under ultraviolet light to cross-link the polyethylene glycol dimethacrylate and the dithioerythritol to form a polymer network, thereby obtaining the PEDOT:PSS electrode; S3. Preparing the elastic stretchable substrate on the PEDOT:PSS electrode to obtain the stretchable PEDOT:PSS electrode.

4. The preparation method according to claim 3, characterized in that: The solid content of the PEDOT:PSS is 1.0-1.3%.

5. The preparation method according to claim 3 or 4, characterized in that: The mass ratio of the polyethylene glycol dimethacrylate to the PEDOT in the PEDOT:PSS is 10:1-40:1; The mass ratio of the polyethylene glycol dimethacrylate to the dithioerythritol is 1:1; The mass ratio of the photoinitiator to the polyethylene glycol dimethacrylate is 1:50-1:20; The absorption wavelength of the photoinitiator includes 365 nm.

6. The preparation method according to claim 3 or 4, characterized in that: The hard substrate is modified with octadecyltrichlorosilane according to the following steps: The cleaned hard substrate is placed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide; then the hard substrate is cleaned, and then the hard substrate is placed in a mixed solution of n-heptane and octadecyltrichlorosilane for 0.5-2 h.

7. The preparation method according to claim 3 or 4, characterized in that: In step S2, light curing is performed under ultraviolet light with a wavelength of 365 nm; The UV curing time is 150-200 s.

8. The preparation method according to claim 3 or 4, characterized in that: In step S3, the elastic stretch substrate is formed of an elastic insulating material, and the elastic insulating material is polydimethylsiloxane or hydrogenated styrene-butadiene block copolymer.

9. The preparation method according to claim 8, characterized in that: The elastic insulating material is spin-coated on the PEDOT:PSS electrode, and heated and cured at 70-100° C. for 30-40 min to obtain the elastic stretchable substrate.

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