A cnt / mxene nanofiltration membrane sensor and a preparation method thereof

Abstract

The application discloses a CNT / Mxene nanofiltration film sensor and a preparation method thereof, belongs to the field of nanometer film sensors, and has the advantages that the CNT / Mxene nanometer film sensor prepared by the method has higher sensitivity, better mechanical properties, less cost and better adhesion, can replace the CNT film sensor prepared by the traditional nanofiltration method, and can be used for real-time health monitoring of a composite structural member. The sensor and the insulating packaging are integrally formed, the packaging problem of the sensor when the sensor is used for monitoring the conductive composite structural member is solved, the influence of the packaging on the performance of the sensor is reduced to the minimum, and the application range of the sensor is not limited by the types of materials. The method has high precision, designability and operability, high production efficiency, and is favorable for application and promotion.

Description

Technical Field

[0001] This invention belongs to the field of nanofilm sensors, specifically relating to a CNT / MXene nanofiltration film sensor for health monitoring of composite material structures and its preparation method. Background Technology

[0002] Composite materials possess numerous advantages, including excellent mechanical properties, high design flexibility, corrosion resistance, and aging resistance, leading to their widespread application as load-bearing structures in engineering fields such as aerospace and mechanical manufacturing. However, structural components subjected to long-term loads are prone to damage and failure, primarily due to differences in strength, stiffness, and wear resistance between the matrix and reinforcing materials. Under external loads exceeding their limits, composite materials can experience problems such as matrix cracking, interfacial debonding, and delamination. Damage to composite materials is difficult to observe macroscopically, and fracture often begins from minute internal defects. Therefore, effective real-time health monitoring is essential to ensure the long-term stable operation of composite structural components.

[0003] Health monitoring methods for composite material structures can be divided into two categories: online monitoring techniques and offline monitoring techniques. Offline monitoring techniques mainly refer to traditional non-destructive testing techniques, such as ultrasonic C-scanning and acoustic emission techniques. These testing methods are complex to operate and have stringent requirements. Online monitoring techniques mainly involve embedding or attaching different sensors inside or to the surface of the composite material. By analyzing changes in the data output by the sensors, the internal information of the composite material is reflected, enabling real-time monitoring and prediction and avoidance of material damage. Currently commonly used sensors include resistance strain gauges and FBG fiber optic grating sensors. Resistance strain gauges offer advantages such as high sensitivity, low mechanical hysteresis and creep, and high frequency response. However, their large temperature coefficient of resistance significantly affects the sensitivity, leading to poor stability and a narrow linear relationship between strain and resistance. FBG (fiber optic grating) sensors are chemically stable, resistant to electromagnetic interference, and capable of long-distance transmission. They are suitable for measuring static or quasi-static physical quantities based on stress-strain and temperature changes and are considered the most frequently used online monitoring technology for composite materials. However, these sensors are typically millimeter-sized, nearly two orders of magnitude smaller than typical composite reinforcements. Embedding them within composite materials introduces new defects, affecting load transmission paths, causing stress concentration, and reducing tensile and bending properties. Carbon nanotubes (CNTs), one-dimensional nanomaterials, are on the same order of magnitude smaller than common composite reinforcements and possess unique electrical properties. When fabricated into sensors and embedded within composite materials, defects can be avoided. However, thin-film sensors made from pure CNTs have inferior mechanical properties and stability compared to composite structures, making them unsuitable for long-term, stable, and accurate monitoring of internal changes in composite structures. Summary of the Invention

[0004] To address the problems existing in current online monitoring sensors, the purpose of this invention is to use a new process to prepare a high-efficiency, convenient, low-cost, self-encapsulated carbon nanotube (CNT) / transition metal carbide (MXene) nanofiltration film sensor with excellent mechanical properties. This sensor can be used for real-time health monitoring of composite material structures, enabling damage prediction and avoidance, reducing losses, and preventing accidents caused by the failure of composite material structures. It has significant practical application value.

[0005] The present invention discloses a CNT / MXene nanofiltration membrane sensor, which is composed of a polysulfone (PSU) porous membrane, conductive silver paste, a CNT / MXene nanofiltration membrane, and an aqueous polyamide (PA) membrane. Its preparation method includes the following steps:

[0006] Step 1: A certain amount of transition metal carbide (MXene) powder is added to the organic solvent 1-methyl-2-pyrrolidone (NMP) and mixed evenly to obtain a low-concentration MXene solution. The low-concentration MXene solution is ultrasonically exfoliated, centrifuged at high speed, and the supernatant is removed. The precipitate is a high-concentration MXene dispersion, which is stored under vacuum for later use. The mass-volume ratio of MXene powder to organic solvent is 1:(2.11-2.85).

[0007] Step 2: After vacuum drying a certain amount of polysulfone (PSU) resin and polyvinylpyrrolidone (PVP) resin, mix them with a certain amount of high-concentration MXene dispersion and organic solvent 1-methyl-2-pyrrolidone (NMP), stir evenly, and obtain MXene / PSU / PVP solution.

[0008] Step 3: Coat the prepared MXene / PSU / PVP solution onto a clean glass plate to form a thin film. Quickly immerse the glass plate in deionized water and wait for the film to detach from the glass plate to obtain an MXene / PSU porous membrane.

[0009] Step 4: Using the prepared MXene / PSU porous membrane as the filtration substrate, 300-600 ml of CNT monodisperse aqueous solution was uniformly filtered into the MXene / PSU porous membrane. After vacuum drying, CNT / MXene nanofiltration membrane was obtained. The vacuum degree of the vacuum drying oven was -0.06 MPa, the drying temperature was 30-50℃, and the drying time was 1-2 h.

[0010] Step 5: After vacuum drying a certain amount of PSU resin and PVP resin, add them to an organic solvent and stir magnetically to obtain a PSU / PVP film-forming solution. Coat the solution onto a clean glass plate to prepare a thin film, quickly immerse it in deionized water, soak it, and then vacuum dry it to obtain a PSU substrate film. The vacuum degree of the vacuum drying oven is -0.06MPa, the drying temperature is 50-70℃, and the drying time is 1-2h.

[0011] Step 6: Print the circuit on the PSU substrate film using conductive silver paste, cut the CNT / MXene nanofiltration film and connect it to the printed circuit to obtain an uninsulated CNT / MXene nanofilm sensor.

[0012] Step 7: Dissolve a certain amount of waterborne polyamide (PA) in deionized water to prepare a solution with a mass fraction of 0.2-1.0%. Using an uninsulated and encapsulated CNT / MXene nanofiltration membrane sensor as the substrate, filter 100-300 ml of the PA solution and vacuum dry it to obtain the CNT / MXene nanofiltration membrane sensor. The vacuum degree of the vacuum drying oven is -0.06 MPa, the drying temperature is 30-50℃, and the drying time is 1-2 h.

[0013] CNT / MXene nanofilm sensors are arrayed within composite material structures, either pre-embedded or externally attached. The external loads on the composite material connection structure are transmitted through the interface, causing corresponding changes in sensor resistance. By measuring the real-time changes in sensor resistance and plotting a resistance rate-strain curve, the microscopic changes within or on the surface of the composite material connection structure can be reflected, enabling real-time health monitoring.

[0014] The above-mentioned method for fabricating a CNT / MXene nanofiltration film sensor, wherein:

[0015] In step 1, the transition metal carbide (MXene) is Ti3C2. The low-concentration MXene solution is centrifuged at a high speed of 7000-10000 rpm.

[0016] In step 4, the CNT monodisperse aqueous solution is prepared using the preparation method in patent CN2012104391772 (Preparation method of temperature sensor based on carbon nanotube three-dimensional network film), and the resulting CNT / MXene nanofiltration film has a thickness of 80-100 μm.

[0017] In step 5, the resulting PSU substrate film has a thickness of 60-90 μm. The organic solvent is selected from N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and 1-methyl-2-pyrrolidone (NMP). The viscosity of the PSU / PVP resin solution is affected by the type of organic solvent, and viscosity affects the pore structure formed during the phase transformation of the film, which in turn affects many film properties. Experiments show that the resin solution prepared with NMP solvent has the highest viscosity.

[0018] In step 7, the thickness of the obtained CNT / MXene nanofiltration film sensor is 145-195 μm.

[0019] Based on the application requirements of sensors in monitoring composite material structures, the material ratio and preparation process of the MXene / resin porous membrane have been optimized. The preparation process of the MXene / PSU porous membrane of this invention specifically includes:

[0020] (1) After vacuum drying a certain amount of PSU resin granules for 20-24h, add them in portions to the organic solvent 1-methyl-2-pyrrolidone (NMP) and stir magnetically at 60-80℃ for 3-4h to obtain a PSU resin solution; wherein the mass ratio of PSU resin to NMP is 1:(2.5-3.6).

[0021] (2) A certain amount of high-concentration MXene dispersion was added to the PSU resin solution and stirred magnetically at room temperature to obtain an MXene / PSU solution; wherein the mass ratio of MXene dispersion to PSU resin solution was 1:(3-4);

[0022] (3) After vacuum drying a certain amount of PVP resin powder for 20-24h, add it to the MXene / PSU solution in portions and perform constant temperature magnetic stirring at room temperature to obtain the MXene / PSU / PVP solution. Let it stand for 20-24h to defoam; wherein, the mass ratio of PSU resin to PVP resin is 1:(0.3-0.7).

[0023] (4) Using a coating machine, adjust the coating thickness to 0.1-0.15 mm, apply the MXene / PSU / PVP solution to a clean, scratch-free glass plate to prepare a thin film, quickly immerse the glass plate in deionized water at 30-50℃, wait for the film to fall off the glass plate, wash it several times until the deionized water no longer becomes turbid, and obtain the MXene / PSU porous membrane, transfer it to clean room temperature deionized water for storage.

[0024] The PSU substrate thin film preparation process of the present invention specifically includes:

[0025] (1) After vacuum drying a certain amount of PSU resin and PVP resin, add them to an organic solvent and stir magnetically at a constant temperature of 60-80℃ to obtain a PSU / PVP film-forming solution, and let it stand to defoam; wherein, the mass ratio of PSU resin to PVP resin is 1:(0.4-0.7), and the mass ratio of PSU resin to organic solvent is 1:(4.1-4.8).

[0026] (2) Using a coating machine, adjust the coating thickness to 0.1-0.15mm, apply the PSU / PVP coating solution to a clean, scratch-free glass plate to prepare a thin film, quickly immerse the glass plate in deionized water at 20-30℃, wait for the film to fall off the glass plate, soak in deionized water for 6-8 hours, and then vacuum dry to obtain the PSU substrate film.

[0027] Compared with existing sensor fabrication technologies, the advantages and beneficial effects of this invention are as follows:

[0028] (1) The method of this invention optimizes the material ratio and preparation process, and prepares a CNT / MXene nanofiltration membrane, which improves the mechanical properties of the membrane and makes it more suitable for real-time health monitoring of composite material structures. Through a two-step method, an MXene / PSU porous membrane is first prepared, and the obtained MXene distribution presents a three-dimensional framework structure. Then, CNTs are filled by filtration, which makes the internal conductive network more uniform and compact. The two-dimensional sheet structure of MXene and the one-dimensional linear structure of CNTs work together to effectively improve the sensitivity of the sensor and solve the problem of inaccurate monitoring of small strains and small defects in materials.

[0029] (2) The method of the present invention uses PSU resin, an engineering plastic with excellent mechanical properties, high temperature resistance and wear resistance, to provide good mechanical properties and beneficial heat resistance for CNT / MXene nanofiltration film sensor. At the same time, because it has a porous structure, during the composite material molding process, the resin matrix of the composite material will penetrate into the porous structure of the sensor. After curing, it will generate a strong interface strength with the sensor, which will improve the stability of the sensor and can also more effectively and accurately transmit the internal condition of the composite material structure. It is suitable for high-precision and high-stability monitoring of damage and destruction of composite material structure.

[0030] (3) Compared with the pure CNT thin film sensor prepared by the traditional filtration method, the CNT / MXene nanofilm sensor prepared by the method of the present invention has higher sensitivity, better mechanical properties, lower cost and better fit. It can replace the CNT thin film sensor prepared by the traditional filtration method for real-time health monitoring of composite material structures.

[0031] (4) The method of the present invention realizes the integrated molding of sensor and insulating package, solves the packaging problem of sensor when monitoring conductive composite material structure, minimizes the impact of packaging on sensor performance, and ensures that the application range of sensor is not limited by material type.

[0032] (5) The CNT / MXene nanofilm sensor prepared by the method of this invention is safe and environmentally friendly. It can be used to prepare sensors of any shape and size. According to the shape of the test piece and the monitoring requirements, the sensors can be deployed in different positions to form a sensor array, thereby realizing real-time and accurate monitoring of composite material structures. This method has high precision, designability and operability, high production efficiency, and is conducive to application and promotion. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the CNT / MXene nanofiltration film sensor prepared by the method of the present invention.

[0034] Figure 2 This is a schematic diagram of the composite material structure made of glass fiber laminate in Embodiment 1 of the present invention.

[0035] Figure 3 The CNT / MXene nanofiltration membrane sensor prepared by the method of the present invention is used in Example 1 to monitor the resistance change rate-strain curve of a glass fiber laminate structure during the tensile process. Detailed Implementation

[0036] The present invention will now be described in more detail with reference to the accompanying drawings.

[0037] The schematic diagrams of the finished CNT / MXene nanofiltration film sensors prepared in Examples 1-4 of this invention are shown below. Figure 1 As shown.

[0038] Example 1

[0039] In this embodiment of the invention, the PSU resin is granules produced by BASF AG, Germany; the PVP resin is produced by Yatai United Chemical Co., Ltd.; the MXene powder is Ti3C2 with a particle size of 200 mesh produced by Forsmann Technology (Beijing) Co., Ltd.; the carbon nanotubes are multi-walled carbon nanotubes with a diameter of 8-15 nm and a length of 50 μm produced by Zhongke Nanotech Co., Ltd.; the 1-methyl-2-pyrrolidone (NMP) solvent is produced by Sinopharm Chemical Reagent Co., Ltd.; the N,N-dimethylacetamide (DMAc) solvent is produced by Sinopharm Chemical Reagent Co., Ltd.; the conductive silver paste is produced by Shenzhen Mingbo Electronic Materials Co., Ltd.; and the glass fiber / epoxy resin unidirectional prepreg is produced by Weihai Guangwei Composite Materials Co., Ltd. The monitoring object is a bolted connection structure composed of glass fiber laminates prepared by composite material compression molding process, and the internal material damage under tension is monitored.

[0040] A method for fabricating a CNT / MXene nanofiltration film sensor, comprising the following steps:

[0041] Step 1: Add 94mg of MXene powder to 200ml of NMP solvent and mix well. Perform ultrasonic exfoliation with an ultrasonic power of 80W, and then centrifuge at 7000rpm to obtain a paste-like precipitate, which is a high-concentration MXene dispersion.

[0042] Step 2: After vacuum drying 20g of PSU resin for 20h, add it in portions to 50g of NMP. Stir magnetically at 60℃ for 3h to obtain a PSU resin solution. Then add a certain amount of high-concentration MXene dispersion to the PSU resin solution and stir magnetically at room temperature until homogeneous to obtain an MXene / PSU solution. Finally, after vacuum drying 6g of PVP resin for 20h, add it in portions to the MXene / PSU solution and stir magnetically at room temperature until homogeneous to obtain an MXene / PSU / PVP solution. Let it stand for 20h to defoam. The mass ratio of MXene dispersion to PSU resin solution is 1:3.

[0043] Step 3: Using a coating machine, apply the MXene / PSU / PVP solution to a clean glass plate to prepare a thin film. Quickly immerse the glass plate in deionized water at 30°C and wait for the film to detach from the glass plate. After multiple washes, a porous MXene / PSU membrane with a thickness of 0.1 mm is obtained.

[0044] Step 4: Using an MXene / PSU porous membrane as the filtration membrane, 300 ml of the prepared CNT monodisperse aqueous solution was uniformly filtered into the MXene / PSU porous membrane using a vacuum filter. After vacuum drying, a CNT / MXene nanofiltration film with a thickness of 84 μm was obtained. The vacuum degree of the vacuum drying oven was -0.06 MPa, the drying temperature was 50℃, and the drying time was 1.5 h. The preparation method of the CNT monodisperse aqueous solution adopted the preparation method in patent CN2012104391772.

[0045] Step 5: After vacuum drying 20g of PSU resin and 8g of PVP resin, add them to 82g of DMAc and stir magnetically at 60℃ to obtain a PSU / PVP film-forming solution. After standing to remove bubbles, use a coating machine to coat the PSU / PVP film-forming solution onto a clean glass plate to prepare a thin film. Quickly immerse the glass plate in deionized water at 20℃ and wait for the film to detach from the glass plate. After vacuum drying, a PSU substrate film with a thickness of 67μm is obtained. The vacuum degree of the vacuum drying oven is -0.06MPa, the drying temperature is 70℃, and the drying time is 1.5h.

[0046] Step 6: Print the circuit on the PSU substrate film using conductive silver paste, cut the CNT / MXene nanofiltration film into a rectangle with a size of 20mm×30mm, and connect it to the printed circuit to obtain an uninsulated CNT / MXene nanofiltration film sensor.

[0047] Step 7: Dissolve 0.4g of aqueous PA in 200ml of deionized water. Using an uninsulated CNT / MXene nanofiltration membrane sensor as the substrate, filter 100ml of the aqueous PA solution. After vacuum drying, obtain the following... Figure 1 The CNT / MXene nanofiltration membrane sensor shown has a thickness of 145 μm. The vacuum drying oven was used at a vacuum level of -0.06 MPa, a drying temperature of 50 °C, and a drying time of 1.5 h.

[0048] The CNT / MXene nanofiltration film sensor obtained in this embodiment is arrayed in a pre-embedded manner between the glass fiber reinforced epoxy resin prepreg layers of the composite preform. A glass fiber laminate with the embedded sensor is obtained through a compression molding process. The laminate is then prepared as shown in the figure. Figure 2 The structural component shown was subjected to a tensile test. During the stretching process, the glass fiber / epoxy resin component gradually deformed. Through interfacial transfer, the CNT / MXene sensor deformed, causing the distance between the CNTs and MXenes to increase. This altered the electron tunneling effect of the sensor, resulting in a corresponding change in its resistance value, enabling real-time monitoring of the composite material structural component. Figure 3 The sensor resistance change rate-strain curve shown illustrates the internal changes of the glass fiber / epoxy resin structure during tensile testing. When the strain is between 0-14.422%, the resistance change rate gradually increases, indicating that as the external load increases, the strain within the glass fiber / epoxy resin structure continuously increases, resulting in a regular upward trend in sensor resistance. At 14.422% strain, the resistance change rate reaches its maximum, indicating irreversible fracture damage within the glass fiber / epoxy resin structure. Between 14.422% and 14.533% strain, the resistance change rate drops sharply, indicating that after internal fracture, the sensor did not completely fail but rather detached from the structure. At this point, the sensor exhibits its inherent mechanical properties, and the stretched conductive network recovers to some extent, causing a sudden drop in resistance. The results monitored by the sensor are completely consistent with the comparative experimental results obtained through direct observation. Therefore, this CNT / MXene nanofiltration film sensor can achieve real-time health monitoring of composite material structures.

[0049] Example 2

[0050] In this embodiment of the invention, the PSU resin is granules produced by BASF AG, Germany; the PVP resin is produced by Yatai United Chemical Co., Ltd.; the MXene powder is Ti3C2 with a particle size of 200 mesh produced by Forsmann Technology (Beijing) Co., Ltd.; the carbon nanotubes are multi-walled carbon nanotubes with a diameter of 8-15 nm and a length of 50 μm produced by Zhongke Nanotech Co., Ltd.; the 1-methyl-2-pyrrolidone (NMP) solvent is produced by Sinopharm Chemical Reagent Co., Ltd.; the N,N-dimethylacetamide (DMAc) solvent is produced by Sinopharm Chemical Reagent Co., Ltd.; the conductive silver paste is produced by Shenzhen Mingbo Electronic Materials Co., Ltd.; and the carbon fiber / epoxy resin unidirectional prepreg is produced by Weihai Guangwei Composite Materials Co., Ltd. The monitoring object is a bolted connection structure composed of carbon fiber laminates prepared by composite material compression molding process, and the internal material damage under tension is monitored.

[0051] A method for fabricating a CNT / MXene nanofiltration film sensor, comprising the following steps:

[0052] Step 1: Add 63mg of MXene powder to 180ml of NMP solvent and mix well. Perform ultrasonic exfoliation with an ultrasonic power of 80W, and then centrifuge at 9000rpm to obtain a paste-like precipitate, which is a high-concentration MXene dispersion.

[0053] Step 2: After vacuum drying 25g of PSU resin for 24h, add it in portions to 90g of NMP. Stir magnetically at 60℃ for 3h to obtain a PSU resin solution. Then add a certain amount of high-concentration MXene dispersion to the PSU resin solution and stir magnetically at room temperature until homogeneous to obtain an MXene / PSU solution. Finally, after vacuum drying 17.5g of PVP resin for 24h, add it in portions to the MXene / PSU solution and stir magnetically at room temperature until homogeneous to obtain an MXene / PSU / PVP solution. Let it stand for 24h to defoam. The mass ratio of MXene dispersion to PSU resin solution is 1:4.

[0054] Step 3: Using a coating machine, apply the MXene / PSU / PVP solution to a clean glass plate to prepare a thin film. Quickly immerse the glass plate in deionized water at 50°C and wait for the film to detach from the glass plate. After multiple washes, a porous MXene / PSU membrane with a thickness of 0.15 mm is obtained.

[0055] Step 4: Using an MXene / PSU porous membrane as the filtration membrane, 600 ml of the prepared CNT monodisperse aqueous solution was uniformly filtered into the MXene / PSU porous membrane using a vacuum filter. After vacuum drying, a CNT / MXene nanofiltration film with a thickness of 87 μm was obtained. The vacuum degree of the vacuum drying oven was -0.06 MPa, the drying temperature was 40℃, and the drying time was 1 h. The preparation method of the CNT monodisperse aqueous solution adopted the preparation method in patent CN2012104391772.

[0056] Step 5: After vacuum drying 15g of PSU resin and 10.5g of PVP resin, add them to 72g of DMAc and stir magnetically at 80℃ to obtain a PSU / PVP film-forming solution. After standing to remove bubbles, use a coating machine to coat the PSU / PVP film-forming solution onto a clean glass plate to prepare a thin film. Quickly immerse the glass plate in deionized water at 30℃ and wait for the film to detach from the glass plate. After vacuum drying, a PSU substrate film with a thickness of 70μm is obtained. The vacuum degree of the vacuum drying oven is -0.06MPa, the drying temperature is 60℃, and the drying time is 1h.

[0057] Step 6: Print the circuit on the PSU substrate film using conductive silver paste, cut the CNT / MXene nanofiltration film into a rectangle with a size of 25mm×30mm, and connect it to the printed circuit to obtain an uninsulated CNT / MXene nanofiltration film sensor.

[0058] Step 7: Dissolve 3g of aqueous PA in 300ml of deionized water. Using the uninsulated CNT / MXene nanofiltration membrane sensor as the substrate, filter 300ml of the aqueous PA solution. After vacuum drying, obtain the following... Figure 1 The CNT / MXene nanofiltration membrane sensor shown has a thickness of 195 μm. The vacuum drying oven was used at a vacuum level of -0.06 MPa, a drying temperature of 40 °C, and a drying time of 1 hour.

[0059] The CNT / MXene nanofiltration film sensor obtained in this embodiment is arrayed in a pre-embedded manner between the carbon fiber reinforced epoxy resin prepreg layers of the composite preform. A carbon fiber laminate with the embedded sensor is obtained through a compression molding process. The laminate is then prepared as shown in... Figure 2 The structural component shown was subjected to a tensile test. During the stretching process, the carbon fiber / epoxy resin structural component gradually deformed. Through the interfacial transfer effect, the CNT / MXene sensor deformed, causing the distance between the CNTs and MXenes to continuously increase. This altered the electron tunneling effect of the sensor, resulting in a corresponding change in the sensor's resistance value, enabling real-time monitoring of the composite material structural component. The sensor resistance change rate-strain curve reveals the internal changes of the carbon fiber / epoxy resin structural component during the stretching process. The gradually increasing resistance change rate indicates that as the external load increases, the strain within the carbon fiber / epoxy resin structural component continuously increases, resulting in a regular upward trend in the sensor resistance. At a certain point, when the resistance change rate reaches its maximum value, it indicates irreversible fracture damage has occurred within the carbon fiber / epoxy resin structural component. Subsequently, the resistance change rate drops sharply, indicating that after the internal fracture of the composite material structural component, the sensor did not completely fail but rather detached from it. At this point, the sensor exhibits its inherent mechanical properties, the stretched conductive network recovers to some extent, and the resistance drops instantaneously. The results monitored by the sensor are completely consistent with the comparative experimental results obtained by direct observation. Therefore, the CNT / MXene nanofiltration membrane sensor can realize real-time health monitoring of composite material structures.

[0060] Example 3

[0061] In this embodiment of the invention, the PSU resin is granules produced by BASF AG, Germany; the PVP resin is produced by Yatai United Chemical Co., Ltd.; the MXene powder is Ti3C2 with a particle size of 200 mesh produced by Forsmann Technology (Beijing) Co., Ltd.; the carbon nanotubes are multi-walled carbon nanotubes with a diameter of 8-15 nm and a length of 50 μm produced by Zhongke Nanotech Co., Ltd.; the 1-methyl-2-pyrrolidone (NMP) solvent is produced by Sinopharm Chemical Reagent Co., Ltd.; the N,N-dimethylacetamide (DMAc) solvent is produced by Sinopharm Chemical Reagent Co., Ltd.; the conductive silver paste is produced by Shenzhen Mingbo Electronic Materials Co., Ltd.; and the glass fiber / epoxy resin unidirectional prepreg is produced by Weihai Guangwei Composite Materials Co., Ltd. The monitoring object is a glass fiber laminate prepared by composite material compression molding process, and the internal material damage under impact is monitored.

[0062] A method for fabricating a CNT / MXene nanofiltration film sensor, comprising the following steps:

[0063] Step 1: Add 170mg of MXene powder to 400ml of NMP solvent and mix well. Perform ultrasonic exfoliation with an ultrasonic power of 80W, and then centrifuge at 8500rpm to obtain a paste-like precipitate, which is a high-concentration MXene dispersion.

[0064] Step 2: After vacuum drying 26g of PSU resin for 24h, add it in portions to 85g of NMP and stir magnetically at 65℃ to obtain a PSU resin solution. Then, add a certain amount of high-concentration MXene dispersion to the PSU resin solution and stir magnetically at room temperature until homogeneous to obtain an MXene / PSU solution. Finally, after vacuum drying 14g of PVP resin for 24h, add it in portions to the MXene / PSU solution and stir magnetically at room temperature until homogeneous to obtain an MXene / PSU / PVP solution. Let it stand for 24h to defoam. The mass ratio of MXene dispersion to PSU resin solution is 1:3.7.

[0065] Step 3: Using a coating machine, apply the MXene / PSU / PVP solution to a clean glass plate to prepare a thin film. Quickly immerse the glass plate in deionized water at 40°C and wait for the film to detach from the glass plate. After multiple washes, a porous MXene / PSU membrane with a thickness of 0.13 mm is obtained.

[0066] Step 4: Using an MXene / PSU porous membrane as the filtration membrane, 500 ml of the prepared CNT monodisperse aqueous solution was uniformly filtered into the MXene / PSU porous membrane using a vacuum filter. After vacuum drying, a CNT / MXene nanofiltration film with a thickness of 94 μm was obtained. The vacuum degree of the vacuum drying oven was -0.06 MPa, the drying temperature was 45℃, and the drying time was 2 h. The preparation method of the CNT monodisperse aqueous solution adopted the preparation method in patent CN2012104391772.

[0067] Step 5: After vacuum drying 20g of PSU resin and 9g of PVP resin, add them to 88g of DMAc and stir magnetically at 65℃ to obtain a PSU / PVP film-forming solution. After standing to defoam, use a coating machine to coat the PSU / PVP film-forming solution onto a clean glass plate to prepare a thin film. Quickly immerse the glass plate in deionized water at 30℃ and wait for the film to detach from the glass plate. After vacuum drying, a PSU substrate film with a thickness of 72μm is obtained. The vacuum degree of the vacuum drying oven is -0.06MPa, the drying temperature is 65℃, and the drying time is 2h.

[0068] Step 6: Print the circuit on the PSU substrate film using conductive silver paste, cut the CNT / MXene nanofiltration film into a rectangle with a size of 20mm×35mm, and connect it to the printed circuit to obtain an uninsulated CNT / MXene nanofiltration film sensor.

[0069] Step 7: Dissolve 1g of aqueous PA in 150ml of deionized water. Using an uninsulated CNT / MXene nanofiltration membrane sensor as the substrate, filter 150ml of the aqueous PA solution. After vacuum drying, obtain the following... Figure 1 The CNT / MXene nanofiltration membrane sensor shown has a thickness of 170 μm. The vacuum drying oven was used at a vacuum level of -0.06 MPa, a drying temperature of 45 °C, and a drying time of 2 hours.

[0070] The CNT / MXene nanofiltration film sensor obtained in this embodiment is pre-embedded in the interlayer of glass fiber reinforced epoxy resin prepreg in a composite preform. A glass fiber laminate with the embedded sensor is obtained through compression molding and subjected to impact testing. During the impact, the glass fiber / epoxy resin laminate gradually undergoes minute deformation. Through interfacial transfer, the CNT / MXene sensor also deforms, causing mechanical deformation and damage to the CNT / MXene conductive network. The sensor's resistance increases rapidly, enabling real-time monitoring of the composite material structure. The resistance change rate-strain curve of the sensor reveals the internal changes of the glass fiber / epoxy resin laminate during the impact process. During the first impact, the resistance change rate increased instantaneously, indicating a rapid increase in mechanical deformation and damage within the fiberglass / epoxy resin laminate. Under no external load impact, the sensor's resistance change rate showed a slight decreasing trend, indicating the closure of some micro-cracks and the re-establishment of the conductive network, leading to a decrease in resistance. After multiple impacts, the sensor's resistance change rate no longer exhibited a regular pattern, indicating the breakage of the sensor's conductive network, a permanent change in resistance, and sensor failure. By pre-embedding sensors in an array, combined with algorithms, the internal impact damage and its location within the fiberglass / epoxy resin laminate can be accurately detected. Therefore, this CNT / MXene nanofiltration film sensor enables real-time health monitoring of composite material structures.

[0071] Example 4

[0072] In this embodiment of the invention, the PSU resin is granules produced by BASF AG, Germany; the PVP resin is produced by Yatai United Chemical Co., Ltd.; the MXene powder is 200-mesh Ti3C2 produced by Forsmann Technology (Beijing) Co., Ltd.; the carbon nanotubes are multi-walled carbon nanotubes with a diameter of 8-15 nm and a length of 50 μm produced by Zhongke Nanotech Co., Ltd.; the 1-methyl-2-pyrrolidone (NMP) solvent is produced by Sinopharm Chemical Reagent Co., Ltd.; the N,N-dimethylacetamide (DMAc) solvent is produced by Sinopharm Chemical Reagent Co., Ltd.; the conductive silver paste is produced by Shenzhen Mingbo Electronic Materials Co., Ltd.; and the carbon fiber / epoxy resin unidirectional prepreg is produced by Weihai Guangwei Composite Materials Co., Ltd. The monitoring object is carbon fiber laminate prepared by composite material compression molding process, and the internal material damage under impact is monitored.

[0073] A method for fabricating a CNT / MXene nanofiltration film sensor, comprising the following steps:

[0074] Step 1: Add 150mg of MXene powder to 350ml of NMP solvent and mix well. Perform ultrasonic exfoliation with an ultrasonic power of 80W, and then centrifuge at 9500rpm to obtain a paste-like precipitate, which is a high-concentration MXene dispersion.

[0075] Step 2: After vacuum drying 18g of PSU resin for 24h, add it in portions to 60g of NMP and stir magnetically at 70℃ to obtain a PSU resin solution. Then, add a certain amount of high-concentration MXene dispersion to the PSU resin solution and stir magnetically at room temperature until homogeneous to obtain an MXene / PSU solution. Finally, after vacuum drying 10g of PVP resin for 24h, add it in portions to the MXene / PSU solution and stir magnetically at room temperature until homogeneous to obtain an MXene / PSU / PVP solution. Let it stand for 24h to defoam. The mass ratio of MXene dispersion to PSU resin solution is 1:3.3.

[0076] Step 3: Using a coating machine, apply the MXene / PSU / PVP solution to a clean glass plate to prepare a thin film. Quickly immerse the glass plate in deionized water at 35°C and wait for the film to detach from the glass plate. After multiple washes, a porous MXene / PSU membrane with a thickness of 0.12 mm is obtained.

[0077] Step 4: Using an MXene / PSU porous membrane as the filtration membrane, 400 ml of the prepared CNT monodisperse aqueous solution was uniformly filtered into the MXene / PSU porous membrane using a vacuum filter. After vacuum drying, a CNT / MXene nanofiltration film with a thickness of 90 μm was obtained. The vacuum degree of the vacuum drying oven was -0.06 MPa, the drying temperature was 30℃, and the drying time was 2 h. The preparation method of the CNT monodisperse aqueous solution adopted the preparation method in patent CN2012104391772.

[0078] Step 5: After vacuum drying 10g of PSU resin and 6g of PVP resin, add them to 47g of NMP and stir magnetically at 70℃ to obtain a PSU / PVP film-forming solution. After standing to defoam, use a coating machine to coat the PSU / PVP film-forming solution onto a clean glass plate to prepare a thin film. Quickly immerse the glass plate in deionized water at 25℃ and wait for the film to detach from the glass plate. After vacuum drying, a PSU substrate film with a thickness of 69μm is obtained. The vacuum degree of the vacuum drying oven is -0.06MPa, the drying temperature is 50℃, and the drying time is 2h.

[0079] Step 6: Print the circuit on the PSU substrate film using conductive silver paste, cut the CNT / MXene nanofiltration film into a rectangle with a size of 25mm×35mm, and connect it to the printed circuit to obtain an uninsulated CNT / MXene nanofiltration film sensor.

[0080] Step 7: Dissolve 3g of aqueous PA in 500ml of deionized water. Using an uninsulated CNT / MXene nanofiltration membrane sensor as the substrate, filter 180ml of the aqueous PA solution. After vacuum drying, obtain the following... Figure 1 The CNT / MXene nanofiltration membrane sensor shown has a thickness of 164 μm. The vacuum drying oven was used at a vacuum level of -0.06 MPa, a drying temperature of 30 °C, and a drying time of 2 hours.

[0081] The CNT / MXene nanofiltration film sensor obtained in this embodiment is pre-embedded in the interlayer of carbon fiber reinforced epoxy resin prepreg in a composite preform. A carbon fiber laminate with the embedded sensor is obtained through compression molding and subjected to impact testing. During the impact, the carbon fiber / epoxy resin laminate gradually undergoes minute deformation. Through interfacial transfer, the CNT / MXene sensor also deforms, causing mechanical deformation and damage to the CNT / MXene conductive network. The sensor's resistance increases rapidly, enabling real-time monitoring of the composite material structure. The resistance change rate-strain curve of the sensor reveals the internal changes of the carbon fiber / epoxy resin laminate during impact. During the first impact, the resistance change rate increased instantaneously, indicating a rapid increase in mechanical deformation and damage within the carbon fiber / epoxy resin laminate. Under no external load impact, the sensor's resistance change rate showed a slight decreasing trend, indicating the closure of some micro-cracks and the re-establishment of the conductive network, leading to a decrease in resistance. After multiple impacts, the sensor's resistance change rate no longer exhibited a regular pattern, indicating the breakage of the sensor's conductive network, a permanent change in resistance, and sensor failure. By pre-embedding sensors in an array, combined with algorithms, the internal impact damage and its location within the carbon fiber / epoxy resin laminate can be accurately detected. Therefore, this CNT / MXene nanofiltration film sensor enables real-time health monitoring of composite material structures.

Claims

1. A method for fabricating a CNT / Mxene nanofiltration thin film sensor, characterized in that, Includes the following steps: Step 1: A certain amount of transition metal carbide powder is added to 1-methyl-2-pyrrolidone and mixed evenly to obtain a low-concentration MXene solution. The low-concentration MXene solution is ultrasonically exfoliated, centrifuged at high speed, and the supernatant is removed. The precipitate is a high-concentration MXene dispersion, which is stored under vacuum for later use. The mass-to-volume ratio of transition metal carbide powder to 1-methyl-2-pyrrolidone is 1:(2.11-2.85). Step 2: After vacuum drying a certain amount of PSU resin and PVP resin, mix them with a certain amount of high-concentration MXene dispersion and 1-methyl-2-pyrrolidone, stir evenly, and obtain MXene / PSU / PVP solution. Step 3: Coat the prepared MXene / PSU / PVP solution onto a clean glass plate to form a thin film. Quickly immerse the glass plate in deionized water and wait for the film to detach from the glass plate to obtain an MXene / PSU porous membrane. Step 4: Using the prepared MXene / PSU porous membrane as the filtration substrate, 300-600 ml of CNT monodisperse aqueous solution was uniformly filtered into the MXene / PSU porous membrane. After vacuum drying, CNT / MXene nanofiltration membrane was obtained. The vacuum degree of the vacuum drying oven was -0.06 MPa, the drying temperature was 30-50℃, and the drying time was 1-2 h. Step 5: After vacuum drying a certain amount of PSU resin and PVP resin, add them to an organic solvent and stir to obtain a PSU / PVP film-forming solution. Coat the solution onto a clean glass plate to prepare a thin film, quickly immerse it in deionized water, soak it, and then vacuum dry it to obtain a PSU substrate film. The vacuum degree of the vacuum drying oven is -0.06MPa, the drying temperature is 50-70℃, and the drying time is 1-2h. Step 6: Print the circuit on the PSU substrate film using conductive silver paste, cut the CNT / MXene nanofiltration film and connect it to the printed circuit to obtain an uninsulated CNT / MXene nanofilm sensor. Step 7: Dissolve a certain amount of aqueous polyamide in deionized water to prepare a solution with a mass fraction of 0.2-1.0%. Using an uninsulated and encapsulated CNT / MXene nanofiltration membrane sensor as the substrate, filter 100-300 ml of the PA solution. After vacuum drying, the CNT / MXene nanofiltration membrane sensor is obtained. The vacuum degree of the vacuum drying oven is -0.06 MPa, the drying temperature is 30-50℃, and the drying time is 1-2 h.

2. The method for preparing a CNT / Mxene nanofiltration film sensor according to claim 1, characterized in that, In step 1, the transition metal carbide is Ti3C2; the low-concentration MXene solution is centrifuged at a speed of 7000-10000 rpm.

3. The method for preparing a CNT / Mxene nanofiltration film sensor according to claim 1, characterized in that, In step 4, the thickness of the obtained CNT / MXene nanofiltration film is 80-100 μm.

4. The method for preparing a CNT / Mxene nanofiltration film sensor according to claim 1, characterized in that, In step 5, the thickness of the obtained PSU substrate film is 60-90 μm.

5. The method for preparing a CNT / Mxene nanofiltration film sensor according to claim 1, characterized in that, In step 5, the organic solvent is selected from DMAc, DMF and NMP.

6. The method for fabricating a CNT / Mxene nanofiltration film sensor according to claim 1, characterized in that, In step 7, the thickness of the obtained CNT / MXene nanofiltration film sensor is 145-195 μm.

7. The method for preparing a CNT / Mxene nanofiltration film sensor according to claim 1, characterized in that, The MXene / PSU porous membrane preparation process specifically includes: (1) After vacuum drying a certain amount of PSU resin granules for 20-24 hours, add them to NMP in portions and stir at 60-80℃ for 3-4 hours to obtain a PSU resin solution; wherein the mass ratio of PSU resin to NMP is 1:(2.5-3.6). (2) A certain amount of high-concentration MXene dispersion was added to the PSU resin solution and stirred evenly to obtain an MXene / PSU solution; wherein the mass ratio of MXene dispersion to PSU resin solution was 1:(3-4); (3) After vacuum drying a certain amount of PVP resin powder for 20-24h, add it to the MXene / PSU solution in portions, stir magnetically at constant temperature to obtain the MXene / PSU / PVP solution, and let it stand to defoam for 20-24h; wherein, the mass ratio of PSU resin to PVP resin is 1:(0.3-0.7). (4) The MXene / PSU / PVP solution is coated on a clean, scratch-free glass plate to prepare a thin film. The glass plate is then quickly immersed in deionized water at 30-50℃. The film is allowed to detach from the glass plate and is then washed until the deionized water no longer becomes cloudy. The resulting MXene / PSU porous membrane is then transferred to clean room temperature deionized water for storage.

8. The method for preparing a CNT / Mxene nanofiltration film sensor according to claim 1, characterized in that, The PSU substrate thin film preparation process specifically includes: (1) After vacuum drying a certain amount of PSU resin and PVP resin, add them to an organic solvent and stir at 60-80℃ to obtain PSU / PVP film-forming solution, and let it stand to defoam; wherein, the mass ratio of PSU resin to PVP resin is 1:(0.4-0.7), and the mass ratio of PSU resin to organic solvent is 1:(4.1-4.8). (2) The PSU / PVP film-forming solution is coated on a clean, scratch-free glass plate to prepare a thin film. The glass plate is then quickly immersed in deionized water at 20-30℃. The film is allowed to detach from the glass plate and soaked in deionized water for 6-8 hours before being vacuum dried to obtain the PSU matrix film.

9. A CNT / Mxene nanofiltration membrane sensor, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

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