Preparation method of Nafion-MXene ionomer reinforced PVDF piezoelectric composite film

Abstract

The invention relates to the field of piezoelectric materials, in particular to a preparation method of a Nafion-MXene ionomer reinforced PVDF (polyvinylidene fluoride) piezoelectric composite film. The method comprises the following steps: preparing a PVDF film: adding PVDF powder into a DMF solution, carrying out magnetic stirring under a water bath heating condition to obtain a uniform and transparent PVDF solution, removing bubbles, dispensing the PVDF solution to a substrate, and drying to obtain the PVDF film; preparing a Nafion-MXene film: mixing MXene powder with a Nafion solution, magnetically stirring to obtain a uniform Nafion / MXene solution, dispensing the uniform Nafion / MXene solution to a substrate, and drying to obtain the Nafion-MXene film; and hot pressing: sequentially superposing one PVDF film, the Nafion-MXene film and the other PVDF film, and carrying out hot pressing to obtain the piezoelectric composite film. The piezoelectric composite film with excellent performance can be prepared, high-voltage polarization is not needed, the process is simplified, and the safety is improved.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric materials, and more specifically to a method for preparing a piezoelectric composite film of Nafion-MXene ionomer-reinforced PVDF. Background Technology

[0002] Flexible pressure sensors have broad application prospects in fields such as smart wearables and robotics. Among them, piezoelectric sensors have attracted much attention due to their self-powered characteristics, and PVDF is a commonly used material. However, the stable α phase of PVDF does not possess piezoelectricity and must be transformed into a β phase with piezoelectric effect through polarization treatment. Traditional polarization methods, such as high-voltage polarization or electrospinning, suffer from complex processes, high energy consumption, and the risk of breakdown; while methods that add nanomaterials often have shortcomings such as weak interfacial polarization effect and limited improvement in electromechanical performance.

[0003] In recent years, the piezoelectric ion effect based on Nafion ionomers has provided a new path for PVDF polarization: Nafion can form a built-in electric field through proton migration under external force, which induces the directional alignment of the PVDF β phase. The piezoelectric-ion-electronic composite devices constructed in this way have shown good application prospects.

[0004] However, performance improvement is still limited by proton transport efficiency and β-phase induction capability. Therefore, it is urgent to solve this technical problem. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a method for preparing a piezoelectric composite film of Nafion-MXene ionomer-reinforced PVDF. This method can prepare a piezoelectric composite film with excellent performance without high-voltage polarization, simplifying the process and improving safety.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for preparing a piezoelectric composite film of Nafion-MXene ionomer-reinforced PVDF, the method comprising: Preparation of PVDF film: PVDF powder is added to DMF solution and magnetically stirred under water bath heating to obtain a uniform and transparent PVDF solution. After removing air bubbles, the solution is drop-coated onto a substrate and dried to obtain a PVDF film. Preparation of Nafion-MXene thin film: Mix MXene powder with Nafion solution, stir magnetically to obtain a uniform Nafion / MXene solution, drop-coat it onto a substrate, and dry it to obtain Nafion-MXene thin film; Hot pressing: A PVDF film, a Nafion-MXene film, and another PVDF film are stacked in sequence and hot pressed to obtain a piezoelectric composite film.

[0007] Furthermore, the method also includes: Electrode preparation: Conductive silver paste is drop-coated onto the upper and lower surfaces of the piezoelectric composite film to form electrodes.

[0008] Furthermore, the method also includes: Encapsulation: Conductive adhesive is applied to the edges of the two electrodes to form device leads; then, TPU films are applied to the upper and lower surfaces of the piezoelectric composite film.

[0009] Furthermore, the method also includes: Activation: The piezoelectric composite film is bent multiple times in the same outward bending moment direction to activate its piezoelectric properties.

[0010] Furthermore, in the step of preparing the PVDF film, the concentration of the PVDF solution is 0.02-0.2 g / mL.

[0011] Furthermore, in the step of preparing Nafion-MXene thin films, the mass ratio of MXene powder to Nafion solution is (1~2.5):100.

[0012] The present invention also relates to a piezoelectric composite film of PVDF reinforced by Nafion-MXene ionomer, which is prepared based on a method for preparing a piezoelectric composite film of PVDF reinforced by Nafion-MXene ionomer.

[0013] This invention also relates to a pressure sensor, comprising a field-effect transistor and a piezoelectric composite film prepared by a method for preparing a Nafion-MXene ionomer-reinforced PVDF piezoelectric composite film; wherein, One surface of the piezoelectric composite film is electrically connected to the gate of the field-effect transistor, and the other surface is electrically connected to the source of the field-effect transistor; One of the drain and source terminals of a field-effect transistor is connected to an external power supply, while the other is grounded.

[0014] By adopting the above technical solution, the present invention has the following beneficial effects: In the preparation of the piezoelectric composite film, this invention introduces MXene. On one hand, its high conductivity enhances the proton transport efficiency of Nafion, amplifying the piezoelectric ion effect; on the other hand, its two-dimensional layered structure facilitates nucleation, inducing the formation of more β-phase in PVDF. Therefore, this invention not only enhances the proton transport efficiency of Nafion to strengthen the piezoelectric ion effect, but also induces the formation of a large amount of β-phase in PVDF, resulting in a composite film with a wide pressure detection range, high sensitivity, fast response, and high power density, while maintaining excellent long-term stability. The PNMP prepared by this invention achieves self-polarization of the PVDF layer through mechanical pressing, significantly improving the electromechanical properties of the piezoelectric-ion-electron composite film. Simultaneously, it simplifies the traditional polarization process and manufacturing flow.

[0015] (2) The piezoelectric signal output from the piezoelectric composite film is directly coupled to the FET gate. The pressure signal is efficiently converted and amplified by modulating the channel current, eliminating the need for a complex signal conditioning module and significantly improving system integration and detection sensitivity. This technology not only broadens the application potential of flexible self-powered sensors in wearable devices, energy harvesting, mechanical vibration monitoring, and micro-mass detection, but also provides an innovative path for the integrated design of piezoelectric-ion-electronic devices and semiconductor devices, possessing both significant scientific value and application prospects. Attached Figure Description

[0016] Figure 1 This is the preparation process of the PVDF solution and Nafion-MXene mixed solution of the present invention; Figure 2 This is a schematic diagram of the structure of the piezoelectric composite film of Nafion-MXene ionomer-reinforced PVDF according to the present invention; Figure 3 This is a schematic diagram of the pressure sensor structure of the present invention; Figure 4 The graph shows the effect of adding different amounts of MXene to Nafion on the output voltage under the same vertical pressure conditions. Figure 5 The output voltage diagram of the piezoelectric composite film of the present invention under different pressures is shown. Figure 6 This is a test diagram of the pressure sensor of the present invention; Figure 7 This is a curve obtained by linear fitting of the output current-pressure relationship in this invention. In the figure, 1 is the current-limiting resistor; 2 is the field-effect transistor; 3 is the gate; 4 is the drain; 5 is the source; 6 is the electrode; 7 is the PVDF film; and 8 is the Nafion-MXene film. Detailed Implementation

[0017] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0018] like Figure 1 As shown, a method for preparing a piezoelectric composite film of Nafion-MXene ionomer-reinforced PVDF includes: Preparation of PVDF film 7: PVDF powder is added to DMF (dimethylformamide) solution and magnetically stirred for 1 to 2.5 hours under water bath heating at 30 to 50°C to obtain a uniform and transparent PVDF solution. After removing air bubbles by vacuum drying oven, the prepared solution is uniformly dropped onto a clean glass plate and dried at 40 to 65°C for 0.5 to 1 hour to finally obtain a single-layer coated PVDF film 7. Preparation of Nafion-MXene film 8: Mix MXene powder with Nafion solution, first sonicate in an ultrasonic cleaner for 10-20 minutes, then magnetically stir for 5-10 minutes to obtain a uniform Nafion / MXene solution, drop-coat it onto a substrate, and dry it to obtain Nafion-MXene film 8; Hot pressing: A PVDF film 7, a Nafion-MXene film 8 and another PVDF film 7 are stacked in sequence and heated and pressed at 150~170℃ for 10~20 minutes. Finally, a piezoelectric composite film is prepared under a pressure of 50~100MPa.

[0019] In some examples, the method also includes: Electrode 6 is prepared by attaching adhesive tape to the middle of the upper and lower surfaces of the piezoelectric composite film, leaving electrode positions on both sides, and then applying conductive silver paste to the electrode positions. The electrode layer is then formed by scraping with a doctor blade to form an electrode layer of 0.5~2µm thickness, thus forming electrode 6.

[0020] In some examples, the method also includes: Encapsulation: Conductive adhesive is applied to the edges of the two electrodes 6 to form device leads; then, TPU (thermoplastic polyurethane) films are applied to the upper and lower surfaces of the piezoelectric composite film. The TPU films are slightly larger than the piezoelectric composite film, and care is taken to ensure no obvious air bubbles exist between the films during the application process.

[0021] In some examples, the method also includes: Activation: The piezoelectric composite film is bent multiple times in the same out-of-plane bending direction, with no less than 50 bends, to induce the ion polarization electric field generated by the piezoelectric ion effect of the Nafion interlayer. This allows the upper and lower PVDF layers to achieve overall dipole alignment under the action of the built-in ion electric field, thereby activating the overall piezoelectric properties of the piezoelectric composite film.

[0022] In some examples, the concentration of the PVDF solution in step 7 of preparing the PVDF film is 0.02-0.2 g / mL.

[0023] In some examples, during the 8-step preparation of Nafion-MXene films, the mass ratio of MXene powder to Nafion solution was (1~2.5):100 (using a 5wt% Nafion solution).

[0024] Among them, keeping other conditions constant, the output voltage change of the composite material under a vertical pressure of 502.9 kPa after adding different mass fractions of MXene to the Nafion solution is as follows: Figure 4 As shown; from Figure 4 The data clearly demonstrates the performance differences: In the 0wt% group, the output voltage fluctuates slightly around 3V, and the piezoelectric signal output is small, reflecting its extremely weak piezoelectric response and low charge collection efficiency; in the 1wt% MXene group, the peak output voltage increases to about 6V, and the piezoelectric response is improved by 2 times; in the 2wt% MXene group, the peak output voltage further increases to about 15V, and the response amplitude is improved by 5 times compared to the 0wt% solution; in the 2.5wt% MXene group, the peak output voltage reaches about 24V, which is the best performance shown in the figure. Not only is the signal strength far superior to the 0wt% solution, but the response stability is also significantly enhanced; while in the 3wt% MXene solution, the output voltage drops slightly (peak value about 12V), but it is still much higher than the signal level of the 0wt% solution.

[0025] This embodiment verifies the technical value of introducing MXene into the proposed solution. Compared to the 0wt% solution, which lacks the ability of a conductive network to efficiently transmit and collect piezoelectric charges, resulting in a weak output signal and no effective response, the solution fails to address the performance limitations of traditional piezoelectric materials. In contrast, this solution, by introducing MXene to construct a conductive network, enhances both the piezoelectric response intensity and the charge collection efficiency, leading to a breakthrough improvement in the system's signal-to-noise ratio and response characteristics. In particular, the addition of 2.5wt% MXene maximizes the output performance, fully demonstrating the targeted improvement of this solution to the shortcomings of the compared patented technology.

[0026] Because the piezoelectric composite film in this embodiment outputs a strong and stable signal, which can meet the precise control requirements of the FET on the input signal, it can be directly coupled to the FET. Based on this, as... Figure 3 As shown, a pressure sensor includes a field-effect transistor 2 and a piezoelectric composite film prepared by the above-described method for preparing a Nafion-MXene ionomer-reinforced PVDF piezoelectric composite film; wherein, One surface of the piezoelectric composite film (electrode 6 on this surface) is electrically connected to the gate 3 of the field-effect transistor 2, and the other surface (electrode 6 on this surface) is electrically connected to the source 5 of the field-effect transistor 2. One of the drain 4 and source 5 of the field-effect transistor 2 is connected to an external power supply through a current-limiting resistor 1, and the other is grounded.

[0027] The pressure sensor in this embodiment solves the problem that the connection between the traditional piezoelectric diaphragm and the detection circuit often relies on complex signal conditioning modules. The detection method of this pressure sensor includes: (1) Apply mechanical pressure to the piezoelectric composite film to generate a piezoelectric signal under the action of the piezoelectric effect and input it into the gate 3 of the field effect transistor 2.

[0028] (2) Fix the voltage between the source and drain of the test, and test the relationship between the source and drain current and time. The voltage of the input FET gate modulates the channel current of the FET, and the mechanical pressure is detected by the current signal output through the drain electrode.

[0029] The solutions involved in the above embodiments will be described in detail below with reference to specific examples.

[0030] Example 1:

[0031] like Figure 1 As shown, a method for preparing a piezoelectric composite film of Nafion-MXene ionomer-reinforced PVDF includes: (1) Preparation of PVDF / DMF coating precursor solution: Weigh 1g of PVDF powder on weighing paper using an electronic balance and pour it into a glass sample bottle with a magnetic stir bar already placed inside. Use a pipette to measure 20mL of N,N-dimethylformamide (DMF) and add it to the glass sample bottle. Place the glass sample bottle in a magnetically stirred constant temperature water bath and maintain the temperature at 50℃ and magnetic stirring speed at 20rpm for 2.5h until the solution becomes completely transparent, resulting in a PVDF solution with a concentration of approximately 0.15g / mL. Place the glass sample bottle open in a vacuum drying oven and evacuate the air inside the oven to a negative pressure of -0.8MPa. It can be observed that bubbles continuously move from the bottom to the mouth of the viscous solution in the glass bottle and escape. After there are no more bubbles escaping, open the vent valve, restore the normal pressure, and remove the sample bottle to obtain a dense, bubble-free PVDF / DMF coating precursor solution. (2) Preparation of single-layer PVDF film 7: The prepared PVDF / DMF pre-coating liquid was dropped onto a 5×5cm² clean substrate and stretched into a flat hydrogel film. The substrate was removed and placed in a 50℃ oven for 12 hours. During this process, the solvent DMF gradually evaporated, and the hydrogel film gradually dried and formed a film from the periphery to the center until the DMF completely evaporated, thus obtaining single-layer PVDF film 7; (3) Preparation of Nafion-MXene mixed solution: Weigh 2.55 mg of MXene powder (corresponding to 2.5% of the mass of Nafion solution) using an electronic balance and pour it into 2 mL of Nafion solution. Place the mixed solution in an ultrasonic cleaner and treat it at a frequency of 40 kHz for 20 min to uniformly disperse the MXene. Then transfer the solution to a magnetic stirrer and stir at a speed of 800 rpm for 10 min to obtain a uniform Nafion-MXene mixed solution; (4) Preparation of Nafion-MXene film 8: Using the same drop coating process as in step (2), 2 mL of Nafion-MXene mixed solution was drop coated onto the substrate, and then the substrate was placed in a 35°C oven to dry for 1 h to allow the solvent to evaporate, thus obtaining Nafion-MXene film 8. (5) Preparation of three-layer composite film by hot pressing: Cut two 30mm×20mm rectangular pieces from the single-layer PVDF film 7 obtained in step (2), and cut one rectangular piece of the same size from the Nafion-MXene film 8 obtained in step (4). Stack the two films in the order of PVDF film 7, Nafion-MXene film 8, and PVDF film 7 with tweezers, and perform hot pressing. Set the hot pressing pressure to 50MPa and adjust the temperature to 170℃. Under this temperature and pressure conditions, press for 10min to obtain the target product - PVDF / Nafion-MXene / PVDF multilayer film (abbreviated as PNMP). (6) Fabrication of patterned electrodes: On the upper and lower surfaces of the PNMP film, cover the central area with tape, leaving an electrode area of ​​25-15 mm. Drop conductive silver paste into the reserved area and spread it evenly with a scraper, controlling the electrode layer thickness to 1 μm to form the upper and lower electrodes. Apply conductive tape to the edge of the electrodes as lead-out device wires; (7) Encapsulating piezoelectric devices: Cut two pieces of thermoplastic polyurethane (TPU) film that are slightly larger than the piezoelectric film, and tightly attach the PNMP film in the middle, ensuring that there are no obvious air bubbles between the films. This completes the encapsulation of the piezoelectric composite film and yields the piezoelectric composite film sensor. (8) Activation of piezoelectric device: Drive the piezoelectric device obtained in step (7) to bend multiple times (no less than 50 times) in the same outward bending moment direction with the help of external force to activate the overall piezoelectric properties of the piezoelectric device and obtain a PVDF flexible piezoelectric sensor (piezoelectric composite film) with Nafion-MXene interlayer.

[0032] The output voltage of this piezoelectric composite film under different pressures is as follows: Figure 5 As shown.

[0033] Example 2:

[0034] like Figure 3 As shown, a piezoelectric sensor is fabricated through a process including: PNMP composite films (piezoelectric composite films) were prepared according to the process in Example 1.

[0035] FET system setup: An N-channel enhancement-mode field-effect transistor (model: DMG2305ux) is selected and soldered onto the PCB board; one end of the current-limiting resistor (1kW) is connected to the drain 4 of the FET, and the other end is connected to the DC power supply; the source 5 is grounded; the drain 4 of the FET is connected to the data acquisition card through a wire. Circuit connection: One electrode 6 of the PNMP is connected to the gate 3 of the FET, and the other electrode 6 is grounded with the source 5 of the FET, forming a closed-loop system of "piezoelectric signal → gate modulation → current output". Sensor Testing: Under different pressures, the PNMP membrane outputs a voltage signal of corresponding strength due to the piezoelectric effect. This voltage acts on the gate of a field-effect transistor (FET), changing the channel conductivity by adjusting the gate 3 potential, ultimately manifesting as a regular change in the channel current. This current change characteristic directly reflects the intensity of the piezoelectric signal generated by the PNMP membrane, achieving precise conversion between pressure and electrical signal. See [link to related documentation] Figure 6 .

[0036] The piezoelectric output performance was systematically evaluated by adjusting the applied pressure. Within the range of 4.3 kPa to 260 kPa, the real-time output current increased with increasing applied pressure. Figure 7 In our study, we plotted the current-pressure relationship, showing good linearity in two segments: 4.3 to 173.4 kPa and 173.4 to 260 kPa. Linear fitting of the output current-pressure relationship yielded sensitivities of 0.0015 mA / kPa and 2.53866E-4 mA / kPa for the two pressure ranges, further demonstrating the beneficial effects of adding MXene.

[0037] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a Nafion-MXene ionomer reinforced PVDF piezoelectric composite film, characterized in that, The method comprises: Preparation of a PVDF film (7): PVDF powder is added to a DMF solution, and magnetic stirring is performed under water bath heating conditions to obtain a uniform transparent PVDF solution. After removing the bubbles, the solution is dropped onto a substrate and dried to obtain a PVDF film (7); Preparation of a Nafion-MXene film (8): MXene powder is mixed with a Nafion solution, and magnetic stirring is performed to obtain a uniform Nafion / MXene solution. The solution is dropped onto a substrate and dried to obtain a Nafion-MXene film (8); Hot pressing: a PVDF film (7), a Nafion-MXene film (8), and another PVDF film (7) are stacked in order and hot pressed to obtain a piezoelectric composite film.

2. The method for preparing a Nafion-MXene ionomer reinforced PVDF piezoelectric composite film according to claim 1, characterized in that, The method further comprises: Preparation of an electrode (6): conductive silver paste is dropped on the upper and lower surfaces of the piezoelectric composite film to form electrodes (6) respectively.

3. The method for preparing a Nafion-MXene ionomer reinforced PVDF piezoelectric composite film according to claim 1, characterized in that, The method further comprises: Packaging: conductive glue is attached to the edges of the two electrodes (6) to form device leads; then, TPU adhesive film is attached to the upper and lower surfaces of the piezoelectric composite film.

4. The method for preparing a Nafion-MXene ionomer reinforced PVDF piezoelectric composite film according to claim 1, characterized in that, The method further comprises: Activation: the piezoelectric composite film is bent multiple times in the same bending moment direction to activate the piezoelectric properties.

5. The method for preparing a Nafion-MXene ionomer reinforced PVDF piezoelectric composite film according to claim 1, characterized in that, In the step of preparing the PVDF film (7), the concentration of the PVDF solution is 0.02-0.2 g / mL.

6. The method for preparing a Nafion-MXene ionomer reinforced PVDF piezoelectric composite film according to claim 1, characterized in that, In the step of preparing the Nafion-MXene film (8), the mass ratio of MXene powder to Nafion solution is (1-2.5):

100.

7. A Nafion-MXene ionomer reinforced PVDF piezoelectric composite film, characterized in that, It is prepared based on the method for preparing a Nafion-MXene ionomer reinforced PVDF piezoelectric composite film according to any one of claims 1-7.

8. A pressure sensor, characterized in that, It comprises a field effect tube (2) and a piezoelectric composite film prepared based on the method for preparing a Nafion-MXene ionomer reinforced PVDF piezoelectric composite film according to any one of claims 1 to 6; wherein, One surface of the piezoelectric composite thin film is electrically connected to the gate (3) of the field effect transistor (2), and the other surface is electrically connected to the source (5) of the field effect transistor (2); One of the drain (4) and the source (5) of the field effect transistor (2) is connected to an external power supply, and the other is grounded.

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