Freezing transfer method for porous carbon electrodes based on subzero temperature

Abstract

To provide freezing transfer methods for porous carbon electrodes based on subzero temperature, and sensors.SOLUTION: Porous carbon electrodes to be transferred are formed on a base. A hydrogel film is introduced between the porous carbon electrodes and a flexible / elastomeric material that is to receive the electrodes. The hydrogel film is expanded by subzero freezing, thereby forming a structural coupling with the porous carbon. Thereafter, before fully recovering from the frozen state, the base is removed to perform peeling, thereby completing the transfer of the porous carbon electrodes. By using an interfacial control system as the hydrogel, transfer of the porous carbon material to the flexible and elastic base under a low-temperature environment is realized.EFFECT: Not only the porous carbon electrodes can be separated quickly and completely, but also, compared with conventional transfer-peeling technique, the required thickness of the flexible and elastic base is made thinner. The electroconductive stretchability of the resulting composite electrode becomes superior. This contributes to realizing the manufacturing of conformal flexible electronics such as ultrathin flexible sensors.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention belongs to the technical field of the manufacture of sensors and electrodes, and relates to a method for manufacturing a stretchable ultra-thin conductive electrode. Specifically, it relates to a freezing transfer method of a porous carbon electrode based on a sub-zero temperature and a sensor.

Background Art

[0002] Electronic devices such as skin can be seamlessly attached to the human skin or inside the body, and have great potential for applications in health monitoring, medical research related to implants, human-computer interaction, flexible robots, and augmented reality technologies. Reducing the thickness and improving the stretchability of the above devices not only improves the wearing comfort, but also increases the effective contact between the device and the measured surface, and significantly improves the fidelity of signal acquisition from the skin and tissues. The development of stretchable electronic devices that conform to and mechanically adapt to the human skin and living tissues requires characteristics such as high carrier mobility, low elastic modulus, and a wide range of conductive stretchability. However, there are still challenges in the scalable manufacturing and performance of such stretchable electronics, especially when using simple and reproducible methods. Currently reported manufacturing methods for stretchable semiconductors include photolithography and thermal evaporation, but they are complex and costly.

[0003] Laser-induced graphene (LIG) is a porous conductive carbon material obtained by high-temperature carbonization on a polyimide thin film using a direct laser writing technique. It has the advantages of convenient digital patterning and controllable physical and chemical properties, and is widely used in the manufacture of various physical, chemical, and electrophysiological sensors. Since the polyimide thin film has low ductility and a high Young's modulus, LIG is usually transferred to other flexible and elastic bases with a low Young's modulus and excellent stretchability, including but not limited to polymer polymers such as polydimethylsiloxane (PDMS), styrene-ethylene-butylene-styrene block copolymer (SEBS), polyurethane (PU), and ecoflex. However, when transferring LIG electrodes using these polymer flexible and elastic bases, a larger elastomer thickness (usually more than 45 μm thick) is required to provide a large interfacial peeling force. On the other hand, the difference in Young's modulus between LIG and the elastic polymer is large, and the inherent stretchable conductivity of the composite electrode formed by both of them after transfer (usually, the stretch ratio is about 40%) is limited.

Summary of the Invention

Problems to be Solved by the Invention

[0004] To solve the problems described in the background art, the present invention proposes a freezing transfer method and a sensor for a porous carbon electrode based on sub-zero temperature. In this method, by using a hydrogel as an interface control system, the transfer of a porous carbon material to a flexible / elastic base in a low-temperature environment is realized. In addition, the hydrogel interface can further improve the problem of the mismatch in mechanical properties between the brittle carbon electrode and the flexible / elastic base. After the transfer is successful, the carbon electrode has a small resistance change and maintains the physical and chemical properties of the porous carbon material. The required thickness of the flexible / elastic base in the present invention is thin (thickness 1 to 10 microns), which helps to realize the manufacture of ultrathin conformal flexible electronics. Furthermore, in this method, the device manufactured using the viscous hydrogel has a conductive stretchability reaching 220%, and the stretch ratio increases by more than five times compared with the prior art. Based on the proposed freezing ultrathin transfer technology, various ultrathin flexible conformal sensors can be designed to realize the real-time monitoring of physical signals, chemical signals, and electrophysiological signals.

[0005] The present invention utilizes the high water content characteristic of the hydrogel and combines it with the porous structure of the conductive carbon electrode to achieve rapid and complete peeling of the carbon electrode under low-temperature freezing conditions. From the perspective of the macrostructure, the porous carbon electrode can form an interlocking structure with the crystal water on the hydrogel surface, thereby ensuring a strong interfacial bonding force during the peeling process. From the perspective of the interaction, the van der Waals interaction and the electrostatic interaction between the porous carbon surface rich in hydrophilic groups and the hydrogel surface containing crystal water can be significantly enhanced in a low-temperature environment. Therefore, at low temperature, the shear strength of the interface is improved, providing excellent conditions for completely transferring the porous carbon electrode. In addition, during the transfer process, the flexible / elastomer material plays a role in supporting the ultrathin gel layer, which is also an essential condition for successful transfer.

[0006] This cryogenic transfer method is applicable to any hydrogel system and provides a general-purpose method that is simple, effective, and can be used to manufacture a large area of soft, conductive, and biocompatible stretchable electronic devices.

Means for Solving the Problems

[0007] Specifically, the technical solution of the present invention is as follows.

[0008] The method for freezing and transferring a porous carbon electrode based on a sub-zero temperature according to the present invention includes forming a porous carbon electrode to be transferred on a base, introducing a hydrogel film between the porous carbon electrode to be transferred and a flexible / elastic material for receiving the electrode, expanding the hydrogel film by cryogenic freezing to structurally bond with the porous carbon material, and then peeling the base before completely recovering from the frozen state to complete the transfer of the porous carbon electrode.

[0009] In the above technical solution, further, the porous carbon electrode to be transferred is a laser-induced carbonized graphene material or a porous carbon material manufactured by any other method. The laser-induced carbonized graphene material may be obtained by performing a laser scan on a polymer thin film such as polyimide to generate a porous graphene conductive electrode pattern, and graphene layers of different thicknesses can be generated depending on the intensity of laser incidence. The wavelength of the laser is preferably in the visible or infrared band. This is because the thermal effect of laser treatment in this wavelength range is more significant and contributes to carbonization. Furthermore, the porous carbon electrode material may be graphene or other carbon materials having a single-layer or multi-layer porous structure manufactured by other methods.

[0010] Furthermore, the flexible / elastic material is a flexible material, an elastic material, or a composite of both. Specifically, it may be a composite of one or more of polyethylene, polypropylene, vinyl chloride, polystyrene, polyimide, polytetrafluoroethylene, polydimethylsiloxane, styrene-butene copolymer, polybutadiene, polyisoprene, natural rubber, ethylene-propylene rubber, butyl rubber, silicone rubber, polyisobutylene, polyethylene-polybutene, amorphous polyethylene, polyether, polyester, polyurethane, etc. The flexible / elastic material functions as a support layer for the introduced hydrogel film and can be made as thin as less than 10 μm in thickness.

[0011] Furthermore, before the low-temperature freezing, the water content in the hydrogel film is controlled to be 10 wt% or more. After introducing the hydrogel film (for example, coating with hydrogel), it may be placed in an oven and allowed to stand or heated. Other methods such as spin coating, spray coating, or brush coating may be used for the coating of the hydrogel.

[0012] Furthermore, the Young's modulus of the flexible / elastic material is greater than that of the hydrogel film.

[0013] Furthermore, the temperature range of the low-temperature freezing is -196°C to -1°C. The lower the freezing transfer temperature, the shorter the time required for transfer.

[0014] Furthermore, before introducing the hydrogel film, the surfaces of both the porous carbon electrode and the flexible / elastomer material are modified by plasma treatment. Plasma treatment is advantageous for improving the transfer success rate and the reproducibility between samples.

[0015] Furthermore, the plasma treatment is performed in an oxygen atmosphere.

[0016] The present invention also provides a stretchable conductive electrode, wherein the hydrogel produced and used by the method according to any of the above is a viscous hydrogel. The viscous hydrogel usually has an adhesion strength, that is, a cross-linked shear strength between the gel and a flexible base (for example, polyimide, polyethylene terephthalate), of 10 kPa or more.

[0017] The present invention also provides multifunctional sensors and system integrations (for example, four types of sensors and one multimodal flexible sensing system), all of which contain the above stretchable conductive electrodes. By principles such as structural design and combination of multi-sensing mechanisms, it is possible to realize real-time monitoring of physical signals, chemical signals, and electrophysiological signals such as strain, temperature, humidity, and electrocardiogram.

[0018] The method of the present invention further improves the problem of the mismatch in mechanical properties between the brittle electrode and the elastic base by using a hydrogel as an interface control system. Since the hydrogel is rich in water molecules in its structure, it has excellent flexibility, elasticity, and biocompatibility. General hydrogel films have a Young's modulus that is generally smaller than that of water-free elastomers such as silicone rubber and rubber, so they have attracted more attention in the field of bioelectronic devices. By utilizing the characteristic of the high water content rate of the hydrogel, a structural bond and a high electrostatic interaction with the porous carbon electrode can be generated under sub-zero temperature conditions, and finally, the rapid and complete peeling of the carbon electrode can be achieved. As shown in FIG. 1, this low-temperature freezing transfer technology can be mainly used for the manufacture of ultrathin graphene elastomer composite electrodes and ultrathin sensors, and can also improve the problem of the mismatch in mechanical properties between the brittle graphene material and the elastomer. By introducing a hydrogel film between the brittle material and the elastomer, the volume of the hydrogel is expanded by low-temperature freezing to structurally bond with the porous graphene material, and the interfacial bonding strength between the graphene and the hydrogel is improved. Also, as shown in FIGS. 2 to 4, when a viscous hydrogel is used, the blunt cracks in the graphene elastomer system (without hydrogel) can be changed into bending cracks under the interface control of the hydrogel due to the viscosity of the hydrogel, thereby greatly improving the electrical conductivity and stretchability of the graphene elastic composite electrode.

[0019] The main mechanism of this method for transferring porous carbon electrodes based on sub-zero temperature can be divided into several aspects.

[0020] (1) From the perspective of the macrostructure, as shown in FIG. 6, the porous carbon material forms an interlocked structure with the crystal water on the gel surface to ensure the stability of the interface during the peeling process.

[0021] (2) From the perspective of interaction, as shown in the results of molecular dynamics calculations in Fig. 7 and the results of evaluation of exfoliation characteristics, in an environment with a sub-zero temperature, the interfacial binding force (including van der Waals interaction and electrostatic interaction) between the porous carbon surface rich in hydrophilic groups and the gel surface containing crystal water is significantly improved, and a strong interfacial shear strength is ensured during the exfoliation process.

[0022] (3) During the transfer process, the flexible / elastomeric material plays an auxiliary role in the mechanical properties of the thin gel layer, which is also an indispensable condition for successful transfer.

Advantages of the Invention

[0023] The advantageous effects of the present invention are as follows.

[0024] The method for transferring a porous carbon electrode pattern based on a sub-zero temperature of the present invention is applicable to quickly and effectively transfer a porous carbon material onto any system of hydrogel. The conductive pattern after transfer is clear and complete, the resistance change before and after transfer is small, and the transfer efficiency is high. The carbon material after transfer can maintain the porous structure and the physical and chemical properties of the material. Different from the conventional method of vacuum transferring conductive graphene, this transfer method is not limited by the thickness and type of gel or elastomer, and can be used in the manufacture of extremely thin conductive devices (the base thickness can be less than 10 μm). Furthermore, the electrode manufactured with viscous hydrogel based on this freezing transfer method has a conductive stretchability reaching 220%, and the stretch ratio increases by more than 5 times compared with the prior art. Based on this transfer technology of extremely thin porous carbon electrodes, various conformal flexible sensors for improving the wearing feeling can be designed and manufactured.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0026] Hereinafter, the present invention will be described in more detail with reference to the drawings and specific examples. The viscous hydrogel used in the examples of the present invention may be a hydrogel obtained by mixing a polyvinyl alcohol solution, phytic acid, and saccharides. Other viscous hydrogels used in the method of the present invention can also be used.

[0027] Example 1 (Transfer to Flexible Polyethylene Terephthalate) 1) Prepare a PPH hydrogel with a water content exceeding 10%. That is, first, produce a 10% by mass polyvinyl alcohol solution, and then mix the polyvinyl alcohol solution, phytic acid, and glucose in a mass ratio of 5:5:1, and heat at 80 °C for use. 2) In the grating mode, use a carbon dioxide infrared laser to carbonize the polyimide thin film to produce a conductive graphene pattern. The laser fluence is 7.24 J / cm -2 is. 3) In an oxygen atmosphere, the polyethylene terephthalate thin film and the conductive graphene electrode were surface-hydrophilized by plasma. 4) The hydrogel solution obtained in 1) was spin-coated on the treated hydrophilic polyethylene terephthalate at a rotational speed of 2000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 2.5 μm. 5) The conductive graphene electrode treated in 3) and the hydrogel thin film were bonded face to face. 6) The bonded sample was gripped with tweezers and placed in an environment below freezing point (-196 °C to -1 °C) to be frozen. 7) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was completely transferred to the surface of the gel.

[0028] Example 2 (Transfer to elastic-based polydimethylsiloxane) 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was produced. Next, the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a mass ratio of the main solution to the curing agent of 20:1 was prepared. The precursor solution was spin-coated on the polyethylene terephthalate thin film at a rotational speed of 1500 rpm / min for one layer, and then heated and cured at 90 °C. The Young's modulus after curing was 0.12 MPa. 3) In the grating mode, a carbon dioxide infrared laser was used to carbonize the polyimide thin film to produce a conductive graphene pattern. The laser processing energy was 7.24 J / cm -2 was. 4) In an oxygen atmosphere, the polydimethylsiloxane thin film obtained in 2) and the conductive graphene electrode obtained in 3) were surface-hydrophilized by plasma. 5) The hydrogel solution obtained in 1) was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotation speed of 2000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 2.5 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was gripped with tweezers and placed in an environment below freezing point (-196 °C to -1 °C) to be frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was completely transferred to the surface of the gel. 9) Finally, when the polyethylene terephthalate substrate under the polydimethylsiloxane was peeled off, the obtained composite of conductive graphene, gel, and polydimethylsiloxane was stretchable as a whole. In Examples 1 and 2, freeze transfer was performed onto two different hydrogel support materials, flexible polyethylene terephthalate and elastic polydimethylsiloxane substrates. Fig. 8 shows the transfer effect diagram of the hydrogel onto the flexible polyethylene terephthalate. From the figure, it was confirmed that the conductive graphene pattern after transfer was completely peeled off. Fig. 9 shows the actual operation process of the freeze transfer of the graphene conductive pattern based on the PPH hydrogel. From the figure, the successful peeling and transfer of the conductive pattern could be visually confirmed. Fig. 10 is a diagram showing the effect of seamlessly attaching the ultrathin graphene conductive stretchable electrode composite that was successfully freeze-transferred onto the surfaces of elastic objects and skin.

[0029] Example 3 (Effect of the Young's modulus of the elastic base on the transfer efficiency) 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was produced. Next, the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a ratio of the main solution to the curing agent of 5:1 was prepared. The precursor solution was spin-coated onto a polyethylene terephthalate thin film at a rotational speed of 1500 rpm / min in one layer, and then heated and cured at 90°C. The Young's modulus after curing was 0.89 MPa. 3) In the grating mode, a carbon dioxide infrared laser was used to carbonize the polyimide thin film to produce a conductive graphene pattern. The laser processing energy was 7.24 J / cm -2 It was. 4) In an oxygen atmosphere, the surface of the polydimethylsiloxane thin film and the conductive graphene electrode was hydrophilized by plasma. 5) A hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotational speed of 2000 rpm / min, and then heated at 60°C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 2.5 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was gripped with tweezers and placed in an environment below freezing point (-196°C to -1°C) and frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was transferred to the surface of the gel.

[0030] Example 4 (Effect on the transfer efficiency of the Young's modulus based on elasticity) 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was produced, and then the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80°C for use. 2) A polydimethylsiloxane precursor solution with a ratio of the main solution to the curing agent of 10:1 was prepared. The precursor solution was spin-coated onto a polyethylene terephthalate thin film at a rotational speed of 1500 rpm / min in one layer, and then heated and cured at 90°C. The Young's modulus after curing was 0.78 MPa. 3) In the grating mode, a carbon dioxide infrared laser was used to carbonize the polyimide thin film to fabricate a conductive graphene pattern. The laser processing energy was 7.24 J / cm -2 was used. 4) In an oxygen atmosphere, the polydimethylsiloxane thin film and the conductive graphene electrode were surface-hydrophilized by plasma. 5) A hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotational speed of 2000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 2.5 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was gripped with tweezers and placed in an environment below freezing point (-196 °C to -1 °C) to be frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was transferred onto the surface of the gel.

[0031] Example 5 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was manufactured. Next, the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a ratio of main solution to curing agent of 20:1 was prepared. The precursor solution was spin-coated onto a polyethylene terephthalate thin film at a rotational speed of 1500 rpm / min in one layer, and then heated and cured at 90 °C. The Young's modulus after curing was 0.12 MPa. 3) In the grating mode, a carbon dioxide infrared laser was used to carbonize the polyimide thin film to fabricate a conductive graphene pattern. The laser processing energy was 7.24 J / cm -2 was used. 4) In an oxygen atmosphere, the polydimethylsiloxane thin film and the conductive graphene electrode were surface-hydrophilized by plasma. 5) The hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at 2000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 2.5 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was gripped with tweezers and placed in a sub-zero (-196 °C to -1 °C) environment and frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was completely transferred to the surface of the gel.

[0032] Example 6 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was produced, and then the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a ratio of main solution to curing agent of 40:1 was prepared. The precursor solution was spin-coated onto a polyethylene terephthalate thin film at 1500 rpm / min in one layer and then cured by heating at 90 °C. The Young's modulus after curing was 0.097 MPa. 3) The polyimide thin film was carbonized using a carbon dioxide infrared laser in a grating mode to produce a conductive graphene pattern. The laser processing energy was 7.24 J / cm -2 It was. 4) In an oxygen atmosphere, the polydimethylsiloxane thin film and the conductive graphene electrode were surface hydrophilized by plasma. 5) The hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at 2000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 2.5 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded face to face. 7) Hold the bonded sample with tweezers and place it in a sub-zero (-196 °C to -1 °C) environment to freeze it. 8) Take out the sample and carefully peel off the polyimide before the sample recovers from the frozen state to the elastic state, and the graphene conductive electrode pattern was transferred onto the surface of the gel. In any of Examples 2 to 6, since polydimethylsiloxane is used as the support material, the manufactured composite is stretchable as a whole. Figure 10 shows the seamless and conformal attachment of the conductive stretchable composite using an elastic material as the support layer to a balloon and the human skin. Figure 11 shows the morphology of the porous surface of the conductive graphene material before and after transfer. Figure 12 shows the comparison of the Raman characteristic peaks of the conductive graphene material before and after transfer. Clearly from the results of the two groups, the freeze transfer method can well maintain the physical and chemical properties of the conductive material itself. In Examples 2 to 6, the Young's modulus of the hydrogel support material is different, which affects the electrical resistance and transfer efficiency of freeze transfer. From the results of Figure 13, it is shown that the Young's modulus (0.12 MPa) of the support material in Example 5 is optimal, and it can ensure that the difference in electrical resistance before and after transfer is reduced and the transfer efficiency is increased.

[0033] Example 7 (Effect of laser processing energy on transfer effect) 1) Prepare a hydrogel with a water content exceeding 10%. That is, first, produce a 10 mass% polyvinyl alcohol solution, then mix the polyvinyl alcohol solution, phytic acid, and glucose in a mass ratio of 5:5:1, and heat at 80 °C for use. 2) Prepare a polydimethylsiloxane precursor solution with a ratio of main solution to curing agent of 20:1, spin-coat the precursor solution onto a polyethylene terephthalate thin film at a rotation speed of 1500 rpm / min for one layer, and then heat and cure at 90 °C. The Young's modulus after curing was 0.12 MPa. 3) In the grating mode, use a carbon dioxide infrared laser to carbonize the polyimide thin film to produce a conductive graphene pattern. The laser processing energy was 6.43 J / cm -2 was. 4) In an oxygen atmosphere, the polydimethylsiloxane thin film and the conductive graphene electrode were surface-hydrophilized by plasma. 5) A hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotational speed of 2000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 2.5 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded together face to face. 7) The bonded sample was gripped with tweezers and placed in an environment below freezing point (-196 °C to -1 °C) to be frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was transferred onto the surface of the gel.

[0034] Example 8 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was produced. Next, the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a ratio of main solution to curing agent of 20:1 was prepared. The precursor solution was spin-coated onto a polyethylene terephthalate thin film at a rotational speed of 1500 rpm / min for one layer, and then heated and cured at 90 °C. The Young's modulus after curing was 0.12 MPa. 3) Using a carbon dioxide infrared laser in a grating mode, the polyimide thin film was carbonized to produce a conductive graphene pattern. The laser processing energy was 7.24 J / cm -2 It was. 4) In an oxygen atmosphere, the polydimethylsiloxane thin film and the conductive graphene electrode were surface-hydrophilized by plasma. 5) A hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotational speed of 2000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 2.5 μm. The conductive graphene electrode processed in 6)4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was grasped with tweezers and placed in a sub-zero (-196 °C to -1 °C) environment and frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was completely transferred to the surface of the gel.

[0035] Example 9 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was produced. Next, the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a ratio of main solution to curing agent of 20:1 was prepared. The precursor solution was spin-coated onto a polyethylene terephthalate thin film at a rotation speed of 1500 rpm / min for one layer, and then heated and cured at 90 °C. The Young's modulus after curing was 0.12 MPa. 3) Using a carbon dioxide infrared laser in the grating mode, the polyimide thin film was carbonized to produce a conductive graphene pattern. The laser processing energy was 8.04 J / cm -2 It was. 4) In an oxygen atmosphere, the polydimethylsiloxane thin film and the conductive graphene electrode were surface hydrophilized by plasma. 5) The hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotation speed of 2000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 2.5 μm. 6) The conductive graphene electrode processed in 6)4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was grasped with tweezers and placed in a sub-zero (-196 °C to -1 °C) environment and frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was transferred to the surface of the gel.

[0036] Example 10 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was produced. Next, the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a ratio of main solution to curing agent of 20:1 was prepared. The precursor solution was spin-coated onto a polyethylene terephthalate thin film at a rotational speed of 1500 rpm / min in one layer, and then heated and cured at 90 °C. The Young's modulus after curing was 0.12 MPa. 3) Using a carbon dioxide infrared laser in the grating mode, the polyimide thin film was carbonized to produce a conductive graphene pattern. The laser processing energy was 8.85 J / cm -2 It was. 4) In an oxygen atmosphere, the polydimethylsiloxane thin film and the conductive graphene electrode were surface hydrophilized by plasma. 5) The hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotational speed of 2000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 2.5 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was gripped with tweezers and placed in an environment below freezing point (-196 °C to -1 °C) and frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was transferred to the surface of the gel. In Examples 7 to 10, the laser processing energy for carbonizing the polyimide thin film is different, which affects the change in electrical resistance before and after transfer and the transfer efficiency. The laser processing energy affects the shape and porosity of the graphene voids, and further affects the interfacial adhesion force between the gel and graphene at low temperatures. From the results in Fig. 14, when the laser energy is 7.24 J / cm -2 it is shown that the change rate of the electrical resistance before and after transfer is less than 50%, and the batch transfer efficiency is optimal, reaching 150%.

[0037] Example 11 (Effect of the thickness of the hydrogel on the transfer efficiency) 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was produced. Next, the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a ratio of the main solution to the curing agent of 20:1 was prepared. The precursor solution was spin-coated onto a polyethylene terephthalate thin film at a rotation speed of 1500 rpm / min in one layer, and then heated and cured at 90 °C. The Young's modulus after curing was 0.12 MPa. 3) Using a carbon dioxide infrared laser in the grating mode, the polyimide thin film was carbonized to produce a conductive graphene pattern. The laser processing energy was 8.04 J / cm -2 was. 4) In an oxygen atmosphere, the polydimethylsiloxane thin film and the conductive graphene electrode were surface-hydrophilized by plasma. 5) The hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotation speed of 1000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 3 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was gripped with tweezers and placed in an environment below freezing point (-196 °C to -1 °C) and frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was transferred onto the surface of the gel.

[0038] Example 12 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was produced. Next, the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a ratio of the main solution to the curing agent of 20:1 was prepared. The precursor solution was spin-coated onto a polyethylene terephthalate thin film at a rotational speed of 1500 rpm / min in one layer, and then heated and cured at 90 °C. The Young's modulus after curing was 0.12 MPa. 3) In the grating mode, a polyimide thin film was carbonized using a carbon dioxide infrared laser to produce a conductive graphene pattern. The laser processing energy was 8.04 J / cm -2 It was. 4) In an oxygen atmosphere, the polydimethylsiloxane thin film and the conductive graphene electrode were surface-hydrophilized by plasma. 5) The hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotational speed of 3000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about 1.5 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was gripped with tweezers and placed in an environment below the freezing point (-196 °C to -1 °C) and frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was transferred onto the surface of the gel.

[0039] Example 13 1) Prepare a hydrogel with a water content exceeding 10%. That is, first, produce a 10% by mass polyvinyl alcohol solution. Next, mix the polyvinyl alcohol solution, phytic acid, and glucose in a mass ratio of 5:5:1, and heat at 80 °C for use. 2) Prepare a polydimethylsiloxane precursor solution with a ratio of the main solution to the curing agent of 20:1. Spin-coat the precursor solution onto a polyethylene terephthalate thin film at a rotation speed of 1500 rpm / min for one layer, and then heat and cure at 90 °C. The Young's modulus after curing was 0.12 MPa. 3) In the grating mode, use a carbon dioxide infrared laser to carbonize the polyimide thin film to produce a conductive graphene pattern. The laser processing energy was 8.04 J / cm -2 It was. 4) In an oxygen atmosphere, surface hydrophilic treatment of the polydimethylsiloxane thin film and the conductive graphene electrode was performed by plasma. 5) Spin-coat the hydrogel solution onto the treated hydrophilic polydimethylsiloxane at a rotation speed of 4000 rpm / min, and then heat at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel is about 1.2 μm. 6) Bond the conductive graphene electrode treated in 4) and the hydrogel thin film of 5) face to face. 7) Grasp the bonded sample with tweezers and place it in an environment below freezing point (-196 °C to -1 °C) to freeze it. 8) Take out the sample, and carefully peel off the polyimide before the sample recovers from the frozen state to the elastic state, and the graphene conductive electrode pattern is transferred to the surface of the gel.

[0040] Example 14 1) Prepare a hydrogel with a water content exceeding 10%. That is, first, produce a 10% by mass polyvinyl alcohol solution. Next, mix the polyvinyl alcohol solution, phytic acid, and glucose in a mass ratio of 5:5:1, and heat at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a ratio of the main solution to the curing agent of 20:1 was prepared, and the precursor solution was spin-coated onto a polyethylene terephthalate thin film at a rotation speed of 1500 rpm / min for one layer, and then heated and cured at 90 °C. The Young's modulus after curing was 0.12 MPa. 3) In the grating mode, a carbon dioxide infrared laser was used to carbonize the polyimide thin film to produce a conductive graphene pattern. The laser processing energy was 8.04 J / cm -2 It was. 4) In an oxygen atmosphere, the surface of the polydimethylsiloxane thin film and the conductive graphene electrode was hydrophilized by plasma. 5) The hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotation speed of 5000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about <1 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was gripped with tweezers and placed in an environment below freezing point (-196 °C to -1 °C) and frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was at least partially transferred to the surface of the gel. In Examples 11 to 14, the spin-coating speeds of the gel solution were different, and the thicknesses of the obtained hydrogels were different, which affected the change in electrical resistance before and after transfer and the transfer efficiency. From the results in Fig. 15, in Examples 12 and 13, when the thickness range of the hydrogel was 1 to 1.5 μm, that is, when the spin-coating speeds were 3000 and 4000 rpm / min, the change in electrical resistance before and after transfer was the smallest, and the effect after transfer was the most optimal. From this result, it was shown that, while ensuring the uniformity of the gel and eliminating defects, the thinner the gel thickness, the higher the interfacial peeling adhesion strength between the gel and graphene at low temperature.

[0041] Example 15 (Manufacture of Multifunctional Flexible Sensor) 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was produced. Next, the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a ratio of main solution to curing agent of 20:1 was prepared. The precursor solution was spin-coated onto a polyethylene terephthalate thin film at a rotational speed of 1500 rpm / min in one layer, and then heated and cured at 90 °C. The Young's modulus after curing was 0.12 MPa. 3) In a grating mode, a polyimide thin film was carbonized using a carbon dioxide infrared laser to produce a conductive graphene pattern. The laser processing energy was 7.24 J / cm -2 It was. 4) In an oxygen atmosphere, the surface of the polydimethylsiloxane thin film and the conductive graphene electrode were surface-hydrophilized by plasma. 5) The hydrogel solution obtained in 1) was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotational speed of 4000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about <1 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was gripped with tweezers and placed in a sub-zero (-196 °C to -1 °C) environment and frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was at least partially transferred to the surface of the gel. 9) Based on the above method, in combination with the prior art, strain sensors, temperature sensors, humidity sensors, and electrocardiogram sensors were manufactured. Examples 1 to 14 provided the optimal transfer parameters for the graphene material, which form the basis for the technology of manufacturing multiple types of sensors in Example 15. Figure 16 shows the performance of the strain sensor. Due to the design of the serpentine structure, a balance between sensitivity and stretchability is achieved, and the gauge factor (GF) is approximately 30. Figure 17 shows the performance of the temperature sensor. This temperature sensor has a wide temperature measurement range (10 to 75 °C), a linear response with low hysteresis, and a good negative temperature coefficient (0.35% °C -1 ). Figure 18 shows the performance of the humidity sensor. Here, the gel is a moisture-sensitive material, and graphene is the sensing electrode. The sensitivity of the obtained humidity sensor is 0.81% %RH -1 . Figure 19 shows the performance of the electrocardiogram sensor. The compatibility between the ultrathin elastomer composite (LIG / PPH / PDMS) and the skin is high, which facilitates the detection of highly faithful electrophysiological signals.

[0042] Example 16 (Multimodal Flexible Sensor Integration System) 1) A hydrogel with a water content exceeding 10% was prepared. That is, first, a 10% by mass polyvinyl alcohol solution was produced. Next, the polyvinyl alcohol solution, phytic acid, and glucose were mixed at a mass ratio of 5:5:1 and heated at 80 °C for use. 2) A polydimethylsiloxane precursor solution with a ratio of main solution to curing agent of 20:1 was prepared. The precursor solution was spin-coated onto a polyethylene terephthalate thin film at a rotational speed of 1500 rpm / min for one layer, and then heated and cured at 90 °C. The Young's modulus after curing was 0.12 MPa. Two pieces were prepared. 3) In the grating mode, a carbon dioxide infrared laser was used to carbonize the polyimide thin film to produce a conductive graphene pattern. The four types of sensors in Example 15 were included, and the laser processing energy was 7.24 J / cm -2 . 4) In an oxygen atmosphere, the surface of the polydimethylsiloxane thin film and the conductive graphene electrode was hydrophilized by plasma. 5) The hydrogel solution was spin-coated onto the treated hydrophilic polydimethylsiloxane at a rotational speed of 4000 rpm / min, and then heated at 60 °C to rapidly semi-cure the hydrogel so that the thickness of the semi-cured gel was about <1 μm. 6) The conductive graphene electrode treated in 4) and the hydrogel thin film in 5) were bonded face to face. 7) The bonded sample was grasped with tweezers and placed in a sub-zero (-196 °C to -1 °C) environment and frozen. 8) When the sample was taken out and the polyimide was carefully peeled off before the sample recovered from the frozen state to the elastic state, the graphene conductive electrode pattern was at least partially transferred to the surface of the gel. 9) Liquid metal was printed on the surface of the polydimethylsiloxane in 2) by a screen printing method. 10) Since the humidity sensor and the electrocardiogram sensor directly contact the skin, holes were selectively opened on the thin film in 9) using a laser cutter to expose the humidity sensor and the electrocardiogram sensor. 11) The graphene pattern on the gel in 8) was aligned with the liquid metal electrode in 10), bonded, and low-temperature peeling was performed in a liquid nitrogen environment to remove the excess polyethylene terephthalate (PET) thin film. According to Example 16, a multimodal flexible sensing system having flexibility, extreme thinness, and stretchability can be obtained. The specific manufacturing steps are shown in FIG. 20. This sensing system can be conformally attached to the chest of the human body, connected to a flexible printed circuit board, and can monitor the respiratory rate, electrocardiogram, heart rate, body surface temperature, and body surface humidity in real time. Among them, the respiratory rate is obtained by monitoring the expansion and contraction of the chest with a strain sensor, and the heart rate is obtained by analyzing the ECG signal. FIG. 21 shows the results of real-time monitoring of multiple signals by a multimodal flexible sensing system that can monitor the physiological states of the human body in various states. The above embodiments are merely some preferred aspects of the present invention and are not used to limit the present invention. Those skilled in the relevant technical fields can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by means of equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A freeze transfer method for a porous carbon electrode based on subzero temperatures, comprising:

1. A method for freeze-transferring a porous carbon electrode, comprising the steps of forming a porous carbon electrode to be transferred on a base, introducing a hydrogel film between the porous carbon electrode to be transferred and a flexible / elastic material to receive the electrode, expanding the hydrogel film by low-temperature freezing to structurally bond it to the porous carbon, and then peeling off the base before the porous carbon electrode has fully recovered from its frozen state, thereby completing the transfer of the porous carbon electrode, and controlling the water content in the hydrogel film to 10 wt % or more before the low-temperature freezing.

2. The method for freeze-transferring a porous carbon electrode based on subzero temperatures according to claim 1, characterized in that the porous carbon electrode to be transferred is a laser-induced carbonized graphene material or a porous carbon material manufactured by any other method.

3. 2. The method of freeze transfer of a porous carbon electrode based on subzero temperatures according to claim 1, wherein the flexible / elastic material is a flexible material, an elastic material, or a combination of both.

4. 2. The subzero temperature based freeze transfer method of porous carbon electrode of claim 1, wherein the Young's modulus of the flexible / elastic material is greater than the Young's modulus of the hydrogel film.

5. The method for freeze-transfer of a porous carbon electrode based on a subzero temperature according to claim 1, characterized in that the temperature range of the low-temperature freezing is -196°C to -1°C.

6. The freeze transfer method of a porous carbon electrode based on subzero temperatures, as described in claim 1, characterized in that before the hydrogel film is introduced, both the surfaces of the porous carbon electrode and the flexible / elastic material are modified by plasma treatment.

7. 7. The method for freeze-transfer of a porous carbon electrode based on a subzero temperature according to claim 6, wherein the plasma treatment is performed in an oxygen atmosphere.

8. A stretchable conductive electrode produced by the method according to any one of claims 1 to 7, wherein the hydrogel used is a viscous hydrogel.

9. A multi-function sensor comprising the stretchable conductive electrode of claim 8 and used to monitor one or more of a physical signal, a chemical signal, and an electrophysiological signal.

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