Graphene-sponge capacitor sensor and method of making same

Abstract

The application relates to the technical field of sensors, in particular to a graphene-sponge capacitor sensor and a preparation method thereof. The preparation method of the graphene-sponge capacitor sensor comprises the following steps: immersing a polymer sponge in a first graphene solution and then performing a hydrothermal reaction to prepare a graphene-modified sponge with dielectricity; immersing two ends of the graphene-modified sponge in a second graphene solution and a third graphene solution respectively and then performing a hydrothermal reaction to form electrode layers with conductivity at the two ends of the graphene-modified sponge; the first graphene solution, the second graphene solution and the third graphene solution all comprise graphene oxide and a reducing agent. The graphene-sponge capacitor sensor prepared by the above preparation method has excellent air permeability and integrity, and has high sensitivity.

Description

Technical Field

[0001] This application relates to the field of sensor technology, and in particular to a graphene-sponge capacitive sensor and its fabrication method. Background Technology

[0002] Flexible electronic sensors are characterized by high sensitivity, rapid response, wearability, and multifunctionality, and are widely used in robotic sensing, electronic skin, wearable devices, and medical diagnostics. Flexible capacitive pressure sensors, which convert applied stress into a change in capacitance, are widely used due to their simple structure, high strain sensitivity, static measurement compatibility, low power consumption, low cost, and suitability for large-area applications.

[0003] Traditional capacitive sensors consist of a three-layer structure: an electrode layer, a dielectric layer, and another electrode layer. Due to their inherent structure and mechanism, traditional capacitive sensors struggle to simultaneously achieve high measurement accuracy, high resolution, and environmental adaptability. To address these issues, current research largely focuses on the following aspects: 1) Microstructuring of the electrode / dielectric layer: This involves designing surface / dielectric layer materials with special microstructures to alter the Young's modulus of the bulk material, thereby controlling the capacitance change of the sensor. However, the microstructuring process for the surface and dielectric layers typically involves template preparation, which is complex, costly, and limits the pressure detection range of high-sensitivity sensors; 2) Coating / doping elastomers with high-dielectric-constant fillers or conductive nanofillers to obtain high-dielectric-constant composite materials, which serve as the dielectric layer to improve the capacitance and signal-to-noise ratio of the capacitive sensor. However, this method is difficult to effectively improve the sensor's sensitivity (the change in capacitance under unit pressure), and the high dielectric constant filler material is relatively hard, which reduces the sensor's flexibility and wearing comfort; 3) Multifunctional integration, such as using flexible conductive rubber as the conductive electrode plate and pure liquid rubber as the dielectric layer, and obtaining a flexible capacitive sensor with good mechanical signal response through layered spraying, stepwise or overall curing; however, both the electrode plate and the dielectric layer are rubber materials with low dielectric constants and poor air permeability, resulting in a low initial capacitance value and poor comfort of the sensor. Some researchers have also fabricated flexible composite response pressure sensors by laminating conductive porous nanocomposite materials with ultrathin dielectric layers, but the overall integrity and durability of sensors assembled / bonded from multiple layers are poor. Summary of the Invention

[0004] Therefore, it is necessary to provide a graphene-sponge capacitive sensor with breathability and integrity, and which can improve sensitivity, as well as a method for its preparation.

[0005] In a first aspect, this application provides a method for preparing a graphene-sponge capacitive sensor, which includes the following steps:

[0006] A graphene-modified sponge with dielectric properties was prepared by impregnating a polymer sponge with a first graphene solution followed by a hydrothermal reaction; and

[0007] The graphene-modified sponge is immersed in a second graphene solution and a third graphene solution at both ends, and then subjected to a hydrothermal reaction to form conductive electrode layers at both ends of the graphene-modified sponge.

[0008] The first graphene solution, the second graphene solution, and the third graphene solution all include graphene oxide and a reducing agent.

[0009] In some embodiments, the concentration of graphene oxide in the first graphene solution is 0.1 mg / mL to 0.6 mg / mL, and the mass ratio of graphene oxide to the reducing agent is 1:(0.5 to 2).

[0010] In some embodiments, the concentration of graphene oxide in the second graphene solution and the third graphene solution is independently 4 mg / mL to 10 mg / mL, and the mass ratio of graphene oxide to the reducing agent is independently 1:(0.5 to 4).

[0011] In some embodiments, the reducing agents in the first graphene solution, the second graphene solution, and the third graphene solution are each independently selected from one or more of ascorbic acid, hydrogen iodide, and tea polyphenols.

[0012] In some embodiments, the polymer sponge is made of polyurethane, melamine, silicone rubber, natural rubber, polydimethylsiloxane, acrylate, nitrile rubber, vinyl fluorosilicone rubber, ethylene-vinyl acetate rubber, chlorinated polyethylene rubber, or polyamide rubber.

[0013] In some embodiments, the conditions for each of the hydrothermal reactions independently include:

[0014] The temperature is 80℃~120℃, and the time is 6h~15h.

[0015] In some embodiments, the impregnation method includes vacuuming, wherein the vacuum level achieved is 10 kPa to 80 kPa.

[0016] In some embodiments, after forming electrode layers at both ends of the graphene-modified sponge, the method further includes the step of setting wires on the electrode layers.

[0017] In some embodiments, the thickness of the polymer sponge is 10 mm to 30 mm, and the ratio of the thickness of each electrode layer to the thickness of the polymer sponge is (0.1 to 0.3):1.

[0018] Secondly, this application also provides a graphene-sponge capacitive sensor, which is prepared using the preparation method described in the first aspect of this application.

[0019] The method for fabricating the graphene-sponge capacitive sensor provided in this application uses polymer sponge as the substrate of the capacitive sensor, retaining the original porous structure of the polymer sponge, thereby endowing the sensor with excellent air permeability. Simultaneously, utilizing the porous structure of the polymer sponge, both variable area and variable electrode spacing working mechanisms can be simultaneously achieved, forming a composite-response capacitive sensor, which is beneficial for improving sensitivity. Specifically, during the sensor's compression process, due to the porous structure of the polymer sponge, both the dielectric graphene-modified sponge and the electrode layer can deform. On one hand, the conductive network of the graphene-modified sponge, acting as the electrode layer, changes from sparse to dense, increasing the effective coverage area of ​​the two electrode plates, equivalent to a capacitor, resulting in a larger capacitance change. On the other hand, the dielectric graphene-modified sponge, acting as the dielectric layer, is compressed, which can be considered a change in the spacing between the electrode plates, also producing a capacitance change. The simultaneous response of these two sensing mechanisms can induce a larger capacitance change, thereby improving the sensor's sensitivity.

[0020] Furthermore, this application allows for the in-situ loading of different amounts of graphene at different locations (both ends and the middle) of a polymer sponge via impregnation, resulting in varying conductivity at different parts of the polymer sponge. This enables the fabrication of an integrated capacitive sensor, giving the sensor better overall integrity. In addition, loading graphene onto the polymer sponge as the dielectric layer increases its dielectric constant, thereby improving the sensor's signal-to-noise ratio. Moreover, the preparation method employed in this application does not involve toxic or harmful reagents, making the process green and pollution-free. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the process flow for preparing the graphene-sponge capacitive sensor in Example 1;

[0023] Figure 2 This is a scanning electron microscope image of the dielectric layer of the graphene-sponge capacitive sensor prepared in Example 1.

[0024] Figure 3This is a schematic cross-sectional view of the graphene-sponge capacitive sensor prepared in Example 1.

[0025] Figure 4 This is a scanning electron microscope image of the electrode layer in the graphene-sponge capacitive sensor prepared in Example 1;

[0026] Figure 5 and Figure 6 This is a photograph of the graphene-sponge capacitive sensor prepared in Example 1.

[0027] Figure 7 This is a schematic diagram of the capacitive sensing principle of the graphene-sponge capacitive sensor prepared in Example 1.

[0028] Figure 8 The graph shows the relationship between the capacitance value and pressure of the graphene-sponge capacitive sensors prepared in Example 1 and Comparative Example 1.

[0029] Figure 9 The graph shows the relationship between the capacitance change rate and pressure of the graphene-sponge capacitive sensors prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0030] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0031] 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 herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] Traditional capacitive sensors often use separate electrode and dielectric layers, making it impossible to form a unified capacitive sensor with poor overall integrity. Furthermore, the electrode and dielectric layers are relatively rigid, resulting in poor flexibility and wearing comfort. In addition, capacitive sensors suffer from deficiencies in breathability, sensitivity, and signal-to-noise ratio. Therefore, this application provides a graphene-sponge capacitive sensor and its fabrication method to improve upon the aforementioned problems.

[0033] In a first aspect, this application provides a method for preparing a graphene-sponge capacitive sensor, which includes steps S10 to S20.

[0034] The method for fabricating the graphene-sponge capacitive sensor provided in this application uses polymer sponge as the substrate of the capacitive sensor, retaining the original porous structure of the polymer sponge, thereby endowing the sensor with excellent air permeability. Simultaneously, utilizing the porous structure of the polymer sponge, both variable area and variable electrode spacing working mechanisms can be simultaneously achieved, forming a composite-response capacitive sensor, which is beneficial for improving sensitivity. Specifically, during the sensor's compression process, due to the porous structure of the polymer sponge, both the dielectric graphene-modified sponge and the electrode layer can deform. On one hand, the conductive network of the graphene-modified sponge, acting as the electrode layer, changes from sparse to dense, increasing the effective coverage area of ​​the two electrode plates, equivalent to a capacitor, resulting in a larger capacitance change. On the other hand, the dielectric graphene-modified sponge, acting as the dielectric layer, is compressed, which can be considered a change in the spacing between the electrode plates, also producing a capacitance change. The simultaneous response of these two sensing mechanisms can induce a larger capacitance change, thereby improving the sensor's sensitivity.

[0035] Furthermore, this application allows for the in-situ loading of different amounts of graphene at different locations (both ends and the middle) of a polymer sponge via impregnation, resulting in varying conductivity at different parts of the polymer sponge. This enables the fabrication of an integrated capacitive sensor, giving the sensor better overall integrity. In addition, loading graphene onto the polymer sponge as the dielectric layer increases its dielectric constant, thereby improving the sensor's signal-to-noise ratio. Moreover, the preparation method employed in this application does not involve toxic or harmful reagents, making the process green and pollution-free.

[0036] Step S10: The polymer sponge is impregnated with the first graphene solution and then subjected to a hydrothermal reaction to prepare a graphene-modified sponge with dielectric properties. The first graphene solution includes graphene oxide and a reducing agent.

[0037] Dielectricity refers to the property of an object to not conduct electricity under the influence of an external electric field; it is a dielectric material. The graphene-modified sponge prepared above serves as the dielectric layer material for the sensor. The dielectric and conductivity of the graphene-modified sponge can be controlled by adjusting the concentration of graphene oxide in the first graphene solution.

[0038] It is understood that, in order to meet the requirements of capacitive sensors, the polymer sponge can be columnar sponge, block sponge, etc.

[0039] In some embodiments, the concentration of graphene oxide in the first graphene solution is 0.1 mg / mL to 0.6 mg / mL, for example, 0.2 mg / mL, 0.25 mg / mL, 0.3 mg / mL, 0.35 mg / mL, 0.4 mg / mL, 0.45 mg / mL, 0.5 mg / mL, or 0.55 mg / mL. By controlling the concentration of graphene oxide in the first graphene solution within this range, it can be ensured that the graphene-modified sponge prepared in step S10 has excellent dielectric properties but is non-conductive.

[0040] It is understandable that the purpose of adding a reducing agent is mainly to reduce graphene oxide to graphene. In this application, the type of reducing agent and the mass ratio of graphene oxide to reducing agent in the first graphene solution are not limited, as long as the reducing agent can completely reduce graphene oxide to graphene and is non-toxic and harmless.

[0041] In some embodiments, the mass ratio of graphene oxide to reducing agent in the first graphene solution is 1:(0.5-2).

[0042] In some embodiments, the reducing agent in the first graphene solution includes one or more of ascorbic acid, hydrogen iodide, and tea polyphenols.

[0043] In this application, the material of the polymer sponge is not limited; any polymer sponge commonly used in the sensor field can be selected. In some embodiments, the polymer sponge material includes polyurethane, melamine, silicone rubber, natural rubber, polydimethylsiloxane, acrylate, nitrile rubber, vinyl fluorosilicone rubber, ethylene-vinyl acetate rubber, chlorinated polyethylene rubber, or polyamide rubber.

[0044] The purpose of the hydrothermal reaction is primarily to ensure that the reducing agent and graphene oxide can undergo a reduction reaction, thereby reducing graphene oxide to graphene. In some embodiments, the conditions for the hydrothermal reaction in step S10 include: a temperature of 80°C to 120°C and a time of 6 to 15 hours.

[0045] In some embodiments, before immersing the polymer sponge in the first graphene solution, a washing step is included to remove impurities from the polymer sponge. The washing method may involve alternating washing with ethanol and water.

[0046] In some embodiments, the method used in step S10 to impregnate the polymer sponge with the first graphene solution includes vacuuming. The specific steps may be as follows:

[0047] The polymer sponge was immersed in the first graphene solution and then a vacuum was applied.

[0048] The vacuum level achieved during vacuuming is 10 kPa to 80 kPa. The vacuuming time is not specifically limited, but should be sufficient to ensure complete impregnation; for example, it can be 10 to 20 minutes.

[0049] In some embodiments, after the hydrothermal reaction, a step of washing the graphene-modified sponge is included. The washing method may involve alternating washing with ethanol and water. Washing removes any incompletely impregnated first graphene solution from the polymer sponge.

[0050] It is understandable that after washing, the process includes drying the graphene-modified sponge. The drying temperature and method are not limited; for example, it can be natural air drying and / or heat drying. The drying temperature can be between 30°C and 60°C.

[0051] Step S20: The two ends of the graphene-modified sponge are respectively immersed in the second graphene solution and the third graphene solution and then subjected to a hydrothermal reaction to form conductive electrode layers at both ends of the graphene-modified sponge. The second graphene solution and the third graphene solution both include graphene oxide and a reducing agent.

[0052] It can be understood that forming conductive electrode layers at both ends of the graphene-modified sponge specifically refers to using the graphene-modified sponge as the dielectric layer, and forming electrode layers on both sides of the dielectric layer, thus forming a "sandwich" structure of electrode layer-dielectric layer-electrode layer. As an example, when the graphene-modified sponge is cylindrical, the two bottom surfaces of the cylinder are impregnated with a second graphene solution and a third graphene solution, respectively.

[0053] In this application, the conductivity of the electrode layer can be controlled by adjusting the concentration of graphene oxide in the second and third graphene solutions, ensuring that the electrode layer formed in step S20 is conductive. In some embodiments, the concentration of graphene oxide in the second and third graphene solutions is independently 4 mg / mL to 10 mg / mL, for example, 4.5 mg / mL, 5 mg / mL, 5.5 mg / mL, 6 mg / mL, 6.5 mg / mL, 7 mg / mL, 7.5 mg / mL, 8 mg / mL, 8.5 mg / mL, 9 mg / mL, and 9.5 mg / mL.

[0054] In this application, the type of reducing agent and the mass ratio of graphene oxide to reducing agent in the second and third graphene solutions are not limited, as long as they can completely reduce graphene oxide to graphene and are non-toxic and harmless.

[0055] In some embodiments, the mass ratio of graphene oxide to reducing agent in the second graphene solution and the third graphene solution is independently 1:(0.5-4). Preferably, the mass ratio of graphene oxide to reducing agent in the second graphene solution and the third graphene solution is the same.

[0056] In some embodiments, the reducing agents in the second and third graphene solutions are independently selected from one or more of ascorbic acid, hydrogen iodide, and tea polyphenols. Preferably, the reducing agents in the second and third graphene solutions are of the same type.

[0057] In some embodiments, the conditions for the hydrothermal reaction in step S20 include: a temperature of 80°C to 120°C and a time of 6 to 15 hours.

[0058] In some embodiments, the method used in step S20 to impregnate both ends of the graphene-modified sponge with the second and third graphene solutions respectively includes vacuuming. The specific steps can be as follows:

[0059] Step S21: Place the second graphene solution in a container, immerse one end of the graphene-modified sponge in the second graphene solution, and draw a vacuum.

[0060] Step S22: Place the third graphene solution in a container, immerse the other end of the graphene-modified sponge in the second graphene solution, and then draw a vacuum.

[0061] The vacuum level achieved during vacuuming is 10 kPa to 80 kPa. The vacuuming time is not specifically limited, but should be sufficient to ensure complete impregnation; for example, it can be 10 to 20 minutes.

[0062] In some embodiments, the process after the hydrothermal reaction includes a drying step of the graphene-modified sponge. The drying temperature and method are not limited; for example, it can be natural air drying and / or heat drying. The drying temperature can be between 30°C and 60°C.

[0063] In some embodiments, after forming electrode layers at both ends of the graphene-modified sponge, the step of setting wires on the electrode layers is further included.

[0064] In this application, there are no restrictions on the method of placing the wires on the electrode layer. Commonly used methods in the sensor field can be selected. For example, conductive silver paste can be used to bond the wires to the electrode layer. It is understood that the material of the wires can be any material known in the art, such as copper wire or copper tape.

[0065] In some embodiments, the thickness of the polymer sponge is 10 mm to 30 mm, and the ratio of the thickness of each electrode layer to the thickness of the polymer sponge is (0.1 to 0.3):1.

[0066] According to a specific embodiment, the fabrication method of the graphene-sponge capacitive sensor includes the following steps:

[0067] 1) Mix graphene oxide and a reducing agent in water to form a first graphene solution. The concentration of graphene oxide in the first graphene solution is 0.1 mg / mL to 0.6 mg / mL, and the mass ratio of graphene oxide to reducing agent is 1:(0.5 to 2).

[0068] 2) The polymer sponge was immersed in the first graphene solution and then vacuumed before a hydrothermal reaction was carried out to prepare a graphene-modified sponge with dielectric properties.

[0069] 3) Mix graphene oxide and reducing agent in water to form a second graphene solution. The concentration of graphene oxide in the second graphene solution is 4 mg / mL to 10 mg / mL, and the mass ratio of graphene oxide to reducing agent is 1:(0.5 to 4).

[0070] 4) Place the second graphene solution obtained in step 3) into a container, immerse one end of the graphene-modified sponge obtained in step 2) in the second graphene solution and then vacuum it to carry out a hydrothermal reaction, so that one end of the graphene-modified sponge forms an electrode layer 1 with conductivity.

[0071] 5) Repeat step 3) to form the third graphene solution;

[0072] 6) Place the third graphene solution obtained in step 5) into a container, immerse one end of the graphene-modified sponge that has not formed electrode layer 1 in step 4) into the third graphene solution and then evacuate it to carry out a hydrothermal reaction so that one end of the graphene-modified sponge that has not formed electrode layer 1 forms a conductive electrode layer 2.

[0073] 7) Set wires on electrode layer 1 and electrode layer 2 respectively.

[0074] Secondly, this application also provides a graphene-sponge capacitive sensor, which is prepared using the preparation method described in the first aspect of this application.

[0075] The graphene-sponge capacitive sensor described above features a monolithic structure with excellent overall integrity. Furthermore, the porous structure of the polymer sponge itself provides the sensor with excellent flexibility and comfortable wearability. Both the electrode layer and the dielectric layer can deform, enabling both variable area and variable electrode spacing operating mechanisms, thus improving the sensor's sensitivity. The polymer sponge, used as the dielectric layer, exhibits excellent dielectric constant after being loaded with graphene, resulting in a superior signal-to-noise ratio for the sensor.

[0076] The present application will be further described in detail below with reference to specific embodiments.

[0077] Example 1

[0078] The process flow for preparing the graphene-sponge capacitive sensor in this embodiment is as follows: Figure 1 As shown.

[0079] (1) A columnar melamine sponge with a thickness of 10 mm and a diameter of 30 mm was washed 5 times with ethanol and deionized water alternately and then dried in an oven at 60℃.

[0080] (2) Graphene oxide was dispersed in water and treated with ultrasound to prepare 100 mL of graphene oxide dispersion with a concentration of 0.2 mg / mL. Then, 20 mg of ascorbic acid was added to the graphene oxide dispersion and mixed evenly to obtain solution A;

[0081] (3) Immerse the melamine sponge treated in step (1) completely in solution A obtained in step (2), and then place it in a vacuum oven with a vacuum degree of 30 kPa for 10 min to ensure that solution A completely impregnates the melamine sponge. Place the impregnated melamine sponge in a hydrothermal reactor, then seal it and place the hydrothermal reactor in a forced-air oven at 90°C for 12 h. After that, wash the melamine sponge several times alternately with ethanol and deionized water, and dry it in an oven at 50°C to obtain graphene-modified sponge GS-D, i.e., graphene-modified sponge dielectric layer material. Its scanning electron microscope (SEM) image is shown below. Figure 2 As shown, where Figure 2 The magnification of image a is 500x, and the magnification of image b is 2000x.

[0082] (4) Graphene oxide was dispersed in water and treated with ultrasound to prepare 50 mL of graphene oxide dispersion with a concentration of 4 mg / mL. Then, 400 mg of ascorbic acid was added to the graphene oxide dispersion and mixed evenly to obtain solution B. Solution B was poured into a square flat-bottomed container to form a liquid surface with a depth of 3 mm;

[0083] (5) Immerse one end of GS-D into the square flat-bottomed container in step (4), and transfer it to a vacuum device with a vacuum degree of 50 kPa. Keep it for 10 min to complete the immersion treatment of the bottom of GS-D. Place the immersed GS-D in a hydrothermal reactor, then seal it and transfer the hydrothermal reactor to a forced-air oven at 120°C for 12 h. After the hydrothermal reaction is completed, dry it in an oven at 50°C to obtain graphene modified sponge GS-ED, namely graphene modified sponge electrode layer - graphene modified sponge dielectric layer material;

[0084] (6) Repeat step (4);

[0085] (7) Immerse the other side of the GS-ED obtained in step (5) (i.e., the side without the electrode layer) into the square flat-bottomed container in step (6), and transfer it to a vacuum device with a vacuum degree of 50 kPa. Keep it for 10 min to complete the impregnation treatment of the top of the GS-ED. Place the impregnated GS-ED in a hydrothermal reactor, then seal it and transfer the hydrothermal reactor to a forced-air drying oven at 120°C for 12 h. After the hydrothermal reaction is completed, dry it in a 50°C oven to obtain the integral graphene-sponge capacitive sensing material GS-EDE, namely graphene modified sponge electrode layer-graphene modified sponge dielectric layer-graphene modified sponge electrode layer material. Its cross-sectional schematic diagram is shown below. Figure 3 As shown; the scanning electron microscope image of the electrode layer is as follows. Figure 4 As shown, where, Figure 4 The magnification of image a is 200x, and the magnification of image b is 500x.

[0086] (8) Two copper tapes were fixed to both sides of the GS-EDE (i.e., the two electrode layers) with conductive silver paste, and then encapsulated with non-woven fabric tape to obtain a graphene-sponge capacitive sensor. Its physical image is shown below. Figure 5 and Figure 6 As shown.

[0087] The sensing principle of the graphene-sponge capacitive sensor prepared in this embodiment is as follows: Figure 7 As shown. By Figure 7 It is known that during the compression process, the polymer sponge has a porous structure, causing deformation in both the dielectric graphene-modified sponge and the electrode layer. On one hand, the conductive network of the graphene-modified sponge, acting as the electrode layer, changes from sparse to dense, increasing the effective coverage area of ​​the two electrode plates (equivalent to a capacitor) and altering the capacitance. This process is a variable-area working mechanism. On the other hand, the dielectric graphene-modified sponge, acting as the dielectric layer, is compressed, reducing the distance between the two electrode plates of the capacitive sensor, also resulting in a capacitance change. This process is a variable-gap working mechanism. The simultaneous response of these two sensing mechanisms can induce a larger capacitance change, thereby improving the sensor's sensitivity.

[0088] Example 2

[0089] The preparation method of this embodiment is basically the same as that of Example 1, except for the material and size of the block sponge, the concentration and volume of the graphene oxide dispersion in steps (2), (4) and (6), and the type and content of the reducing agent. The specific steps are as follows:

[0090] (1) A columnar polyurethane sponge with a thickness of 15 mm and a diameter of 20 mm was washed 5 times with ethanol and deionized water alternately and then dried in an oven at 60℃.

[0091] (2) Graphene oxide was dispersed in water and treated with ultrasound to prepare 200 mL of graphene oxide dispersion with a concentration of 0.35 mg / mL. Then, 35 mg of tea polyphenols was added to the graphene oxide dispersion and mixed evenly to obtain solution A;

[0092] (3) Immerse the polyurethane sponge treated in step (1) completely in solution A obtained in step (2), and then place it in a vacuum oven with a vacuum degree of 30 kPa for 10 min to completely impregnate the polyurethane sponge with solution A. Place the impregnated polyurethane sponge in a hydrothermal reactor, then seal it and place the hydrothermal reactor in a forced-air oven at 90°C for 12 h. After that, wash the polyurethane sponge several times with ethanol and deionized water alternately, and dry it in an oven at 50°C to obtain graphene-modified sponge GS-D, that is, graphene-modified sponge dielectric layer material;

[0093] (4) Graphene oxide was dispersed in water and treated with ultrasound to prepare 200 mL of graphene oxide dispersion with a concentration of 7 mg / mL. Then, 1400 mg of tea polyphenols was added to the graphene oxide dispersion and mixed evenly to obtain solution B. Solution B was poured into a square flat-bottomed container to form a liquid surface with a depth of 3 mm;

[0094] (5) Immerse one end of GS-D into the square flat-bottomed container in step (4), and transfer it to a vacuum device with a vacuum degree of 50 kPa. Keep it for 10 min to complete the immersion treatment of the bottom of GS-D. Place the immersed GS-D in a hydrothermal reactor, then seal it and transfer the hydrothermal reactor to a forced-air oven at 120°C for 12 h. After the hydrothermal reaction is completed, dry it in an oven at 50°C to obtain graphene modified sponge GS-ED, namely graphene modified sponge electrode layer - graphene modified sponge dielectric layer material;

[0095] (6) Repeat step (4);

[0096] (7) Immerse the other side of the GS-ED obtained in step (5) (i.e., the side without the electrode layer) into the square flat-bottomed container in step (6), and transfer it to a vacuum device with a vacuum degree of 50 kPa. Keep it for 10 min to complete the impregnation treatment of the top of the GS-ED. Place the impregnated GS-ED in a hydrothermal reactor, then seal it and transfer the hydrothermal reactor to a forced-air oven at 120°C for 12 h. After the hydrothermal reaction is completed, place it in a 50°C oven to dry, and obtain the integral graphene-sponge capacitive sensing material GS-EDE, namely graphene modified sponge electrode layer-graphene modified sponge dielectric layer-graphene modified sponge electrode layer material;

[0097] (8) Two copper tapes are fixed to the two sides of GS-EDE (i.e., the two electrode layers) with conductive silver paste and then encapsulated with non-woven tape to obtain a graphene-sponge capacitive sensor.

[0098] Example 3

[0099] The preparation method of this embodiment is basically the same as that of Example 1, except for the material and size of the block sponge, the concentration and volume of the graphene oxide dispersion in steps (2), (4) and (6), and the type and content of the reducing agent. The specific steps are as follows:

[0100] (1) A columnar acrylic sponge with a thickness of 12 mm and a diameter of 15 mm was washed 5 times with ethanol and deionized water alternately and then dried in an oven at 60°C.

[0101] (2) Graphene oxide was dispersed in water and treated with ultrasound to prepare 80 mL of graphene oxide dispersion with a concentration of 0.6 mg / mL. Then, 24 mg of tea polyphenols was added to the graphene oxide dispersion and mixed evenly to obtain solution A;

[0102] (3) Immerse the acrylic sponge treated in step (1) completely in solution A obtained in step (2), and then place it in a vacuum oven with a vacuum degree of 30 kPa for 10 min to completely impregnate the acrylic sponge with solution A. Place the impregnated acrylic sponge in a hydrothermal reactor, then seal it and place the hydrothermal reactor in a forced-air oven at 90°C for 12 h. After that, wash the acrylic sponge several times with ethanol and deionized water alternately, and dry it in an oven at 50°C to obtain graphene-modified sponge GS-D, that is, graphene-modified sponge dielectric layer material;

[0103] (4) Graphene oxide was dispersed in water and treated with ultrasound to prepare 80 mL of graphene oxide dispersion with a concentration of 10 mg / mL. Then, 1600 mg of ascorbic acid was added to the graphene oxide dispersion and mixed evenly to obtain solution B. Solution B was poured into a square flat-bottomed container to form a liquid surface with a depth of 3 mm;

[0104] (5) Immerse one end of GS-D into the square flat-bottomed container in step (4), and transfer it to a vacuum device with a vacuum degree of 50 kPa. Keep it for 10 min to complete the immersion treatment of the bottom of GS-D. Place the immersed GS-D in a hydrothermal reactor, then seal it and transfer the hydrothermal reactor to a forced-air oven at 120°C for 12 h. After the hydrothermal reaction is completed, dry it in an oven at 50°C to obtain graphene modified sponge GS-ED, namely graphene modified sponge electrode layer - graphene modified sponge dielectric layer material;

[0105] (6) Repeat step (4);

[0106] (7) Immerse the other side of the GS-ED obtained in step (5) (i.e., the side without the electrode layer) into the square flat-bottomed container in step (6), and transfer it to a vacuum device with a vacuum degree of 50 kPa. Keep it for 10 min to complete the impregnation treatment of the top of the GS-ED. Place the impregnated GS-ED in a hydrothermal reactor, then seal it and transfer the hydrothermal reactor to a forced-air oven at 120°C for 12 h. After the hydrothermal reaction is completed, place it in a 50°C oven to dry, and obtain the integral graphene-sponge capacitive sensing material GS-EDE, namely graphene modified sponge electrode layer-graphene modified sponge dielectric layer-graphene modified sponge electrode layer material;

[0107] (8) Two copper tapes are fixed to the two sides of GS-EDE (i.e., the two electrode layers) with conductive silver paste and then encapsulated with non-woven tape to obtain a graphene-sponge capacitive sensor.

[0108] Comparative Example 1

[0109] The preparation method of this comparative example is basically the same as that of Example 1, except that the dielectric layer is not loaded with graphene, but is pure melamine sponge. The specific steps are as follows:

[0110] (1) A columnar melamine sponge with a thickness of 10 mm and a diameter of 30 mm was washed 5 times with ethanol and deionized water alternately and then dried in an oven at 60℃.

[0111] (2) Graphene oxide was dispersed in water and treated with ultrasound to prepare a 50 mL graphene oxide dispersion with a concentration of 4 mg / mL. Then, 400 mg of ascorbic acid was added to the graphene oxide dispersion and mixed evenly to obtain solution B. Solution B was poured into a square flat-bottomed container to form a liquid surface with a depth of 3 mm;

[0112] (3) Immerse one end of the melamine sponge into the square flat-bottomed container in step (2), and transfer it to a vacuum device with a vacuum degree of 50 kPa. Keep it for 10 min to complete the impregnation treatment of the bottom of the melamine sponge. Place the impregnated melamine sponge in a hydrothermal reactor, then seal it and transfer the hydrothermal reactor to a forced-air oven at 120°C for 12 h. After the hydrothermal reaction is completed, dry it in an oven at 50°C to obtain graphene-modified sponge GS-E, namely graphene-modified sponge electrode layer-melamine sponge dielectric layer material;

[0113] (4) Repeat step (2);

[0114] (5) Immerse the other side of the GS-E obtained in step (3) (i.e., the side without the electrode layer) into the square flat-bottomed container in step (4), and transfer it to a vacuum device with a vacuum degree of 50 kPa. Keep it for 10 min to complete the impregnation treatment of the top of the GS-E. Place the impregnated GS-E in a hydrothermal reactor, then seal it and transfer the hydrothermal reactor to a forced-air oven at 120°C for 12 h. After the hydrothermal reaction is completed, place it in a 50°C oven to dry, and obtain the integral graphene-sponge capacitive sensing material GS-EE, namely graphene modified sponge electrode layer-melamine sponge dielectric layer-graphene modified sponge electrode layer material;

[0115] (6) Two copper tapes are fixed to the two sides of GS-EE (i.e., the two electrode layers) with conductive silver paste and then encapsulated with non-woven tape to obtain a graphene-sponge capacitive sensor.

[0116] The sensing performance of the graphene-sponge capacitive sensors prepared in Example 1 and Comparative Example 1 was tested, as shown below. Figure 8 and 9 As shown. Among them, Figure 8 The graphs shown are plots illustrating the relationship between the capacitance and pressure of the graphene-sponge capacitive sensors prepared in Example 1 and Comparative Example 1. Figure 8 It can be seen that, due to the dielectric layer with a high dielectric constant, the initial capacitance value of Example 1 is higher than that of Comparative Example 1. A higher initial capacitance value indicates a higher signal-to-noise ratio. Within the pressure range of 0 to 20 kPa, the capacitance value of Example 1 is higher than that of Comparative Example 1. Figure 9 The graphs show the relationship between the capacitance change rate and pressure of the graphene-sponge capacitive sensors prepared in Example 1 and Comparative Example 1. Figure 9 It can be seen that within the pressure range of 0 to 20 kPa, the capacitance change rate under unit pressure of Example 1 is higher than that of Comparative Example 1, indicating that the sensor of Example 1 has higher sensitivity.

[0117] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0118] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the scope of the claims.

Claims

1. A method for fabricating a graphene-sponge capacitive sensor, characterized in that, Includes the following steps: A graphene-modified sponge with dielectric properties was prepared by impregnating a polymer sponge with a first graphene solution and then carrying out a hydrothermal reaction. as well as The graphene-modified sponge is immersed in a second graphene solution and a third graphene solution at both ends, and then subjected to a hydrothermal reaction to form conductive electrode layers at both ends of the graphene-modified sponge. The first graphene solution, the second graphene solution, and the third graphene solution all include graphene oxide and a reducing agent; in the first graphene solution, the concentration of graphene oxide is 0.1 mg / mL to 0.6 mg / mL, and in the second graphene solution and the third graphene solution, the concentration of graphene oxide is independently 4 mg / mL to 10 mg / mL, respectively. Each of the impregnation methods independently includes vacuuming, and the vacuum level achieved by the vacuuming is 10 kPa to 80 kPa.

2. The preparation method according to claim 1, characterized in that, In the first graphene solution, the mass ratio of graphene oxide to the reducing agent is 1:(0.5~2).

3. The preparation method according to claim 1, characterized in that, In the second graphene solution and the third graphene solution, the mass ratio of graphene oxide to the reducing agent is independently 1:(0.5~4).

4. The preparation method according to claim 1, characterized in that, The reducing agents in the first graphene solution, the second graphene solution, and the third graphene solution are each independently selected from one or more of ascorbic acid, hydrogen iodide, and tea polyphenols.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The polymer sponge is made of materials including polyurethane, melamine, silicone rubber, natural rubber, polydimethylsiloxane, acrylate, nitrile rubber, vinyl fluorosilicone rubber, ethylene-vinyl acetate rubber, chlorinated polyethylene rubber, or polyamide rubber.

6. The preparation method according to any one of claims 1 to 4, characterized in that, The conditions for each of the aforementioned hydrothermal reactions independently include: The temperature is 80 ℃~120 ℃, and the time is 6 h~15 h.

7. The preparation method according to any one of claims 1 to 4, characterized in that, After forming electrode layers at both ends of the graphene-modified sponge, the method further includes the step of setting wires on the electrode layers.

8. The preparation method according to any one of claims 1 to 4, characterized in that, The thickness of the polymer sponge is 10 mm to 30 mm, and the ratio of the thickness of each electrode layer to the thickness of the polymer sponge is (0.1 to 0.3):

1.

9. A graphene-sponge capacitive sensor, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

Images