A method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers

Abstract

The present invention proposes a preparation method of a stretchable piezoelectric sensor based on oriented PVDF fibers, which relates to the technical field of intelligent sensors. The piezoelectric sensor includes a packaging layer, a positive TPU film layer, a negative TPU film layer and a PVDF piezoelectric film. The outer surfaces of the positive TPU film layer and the negative TPU film layer are provided with carbon nanotube particles. The packaging layer is located on the outer surfaces of the positive TPU film layer, the negative TPU film layer and the PVDF piezoelectric film. The present invention proposes a preparation method of a stretchable piezoelectric sensor based on oriented PVDF fibers, and uses electrostatic spinning technology to prepare a PVDF nanofiber membrane with oriented fiber characteristics. By regulating the electrostatic spinning process parameters, a high piezoelectric and highly stretchable PVDF piezoelectric film is obtained. The film has high stability and exhibits good mechanical properties after testing. At the same time, after being packaged into a sensor, the open circuit voltage is stable under different elongations after testing, and can effectively detect mechanical strains of different surface features.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent sensors, and in particular to a method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers. Background Art

[0002] Piezoelectric materials have attracted widespread attention in the sensor field due to their piezoelectric properties. Polyvinylidene fluoride (PVDF) has excellent chemical stability and mechanical properties, making it an ideal material for flexible sensors. The main methods for preparing PVDF piezoelectric films are solution casting and electrospinning. The solution casting method has the advantages of simple process and low cost, but the prepared film is relatively thick, making it difficult to achieve high-precision nanostructure control, and it requires polarization under a high-voltage electric field before use. The electrospinning method uses a high-voltage electric field to spray a polymer solution into a nanofiber membrane. The PVDF film prepared by electrospinning technology not only has good flexibility but also exhibits high piezoelectric properties, and has a wide range of applications in the medical and health fields. In the sensor field, piezoelectric materials are mainly used to detect changes in mechanical stress and strain. For example, in the medical field, piezoelectric sensors can be used to detect important physiological parameters such as heart rate, respiratory rate, and blood pressure. In industrial and other fields, piezoelectric sensors can detect vibration and stress of mechanical equipment to prevent equipment failure and damage. In addition, piezoelectric sensors can also be used in environmental monitoring, smart wearable devices, and human-computer interaction.

[0003] Current PVDF piezoelectric sensors are mainly aimed at improving electrical performance. The mainstream method is to incorporate different piezoelectric materials into them to make the composite PVDF piezoelectric film have higher piezoelectric performance than the pure film. However, for some application scenarios with non-developable surface characteristics, this type of sensor cannot be perfectly applied to such application scenarios due to its low stretchability, so the measured data will have certain errors. At the same time, the effective packaging method of flexible stretchable electrodes and stretchable piezoelectric films is also a key problem. The packaging layer needs to maintain a certain stretchability without affecting the normal operation of the sensor, otherwise the sensor will be easily affected by interference from the external environment.

[0004] In order to overcome the above problems, the present invention proposes a preparation method of a stretchable piezoelectric sensor based on PVDF oriented fibers, aiming to solve the problems of insufficient stretchability and packaging of piezoelectric sensors in the prior art. Electrospinning technology is adopted to regulate the spinning process parameters to obtain a PVDF nanofiber membrane with oriented fiber arrangement. Subsequently, an elastomeric thermoplastic polyurethane (TPU) is selected as the substrate, and carbon nanotubes (CNT) are ultrasonically impregnated to obtain a flexible electrode with high stretchability. The piezoelectric film and the stretchable electrode are encapsulated by electrospraying thermoplastic polyurethane (TPU) solution to form a piezoelectric sensor. The sensor obtained by this process has high stretchability and its dielectric properties are also significantly improved, and it can ultimately be applied to the detection needs of complex surfaces. Summary of the Invention

[0005] In order to solve the above problems, the present invention proposes a preparation method of a stretchable piezoelectric sensor based on oriented PVDF fibers, so as to more accurately solve the above-mentioned current PVDF piezoelectric sensors which are mainly aimed at improving electrical performance. The mainstream method is to add different piezoelectric materials therein to make the composite PVDF piezoelectric film have higher piezoelectric performance than the pure film. However, for some application scenarios with non-developable surface characteristics, this type of sensor cannot be perfectly applied to such application scenarios due to its low stretchability, so the measured data will have certain errors. At the same time, the effective packaging method of flexible stretchable electrodes and stretchable piezoelectric films is also a key problem. The packaging layer needs to maintain a certain stretchability without affecting the normal operation of the sensor, otherwise the sensor will be easily affected by interference from the external environment.

[0006] The present invention is achieved through the following technical solutions:

[0007] The present invention provides a method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers. The piezoelectric sensor includes an encapsulation layer, a positive TPU film layer, a negative TPU film layer, and a PVDF piezoelectric film. Carbon nanotube particles are sprayed on the outer surfaces of the positive TPU film layer and the negative TPU film layer. The encapsulation layer serves as an adhesive to encapsulate the positive TPU film layer, the negative TPU film layer, and the PVDF piezoelectric film into a whole. The preparation method includes the following steps:

[0008] Step 1: stirring a mixture of PVDF solution and N,N-dimethylformamide to obtain a PVDF solution, and preparing a PVDF nanofiber membrane with oriented fiber characteristics by electrospinning technology;

[0009] Step 2: Place a certain amount of carbon nanotubes (CNTs) into anhydrous ethanol in an ultrasonic bath, uniformly disperse the carbon nanotube particles in the anhydrous ethanol in an ice bath, ultrasonically immerse the TPU film, remove it, rinse it with anhydrous ethanol, and then dry it in an oven to obtain a flexible electrode with high stretchability.

[0010] Step 3: Adjust the concentration of the TPU solution so that it forms continuous and stable spray-like tiny particles under high pressure, and place the piezoelectric film and electrode to be encapsulated under the spray to encapsulate both sides.

[0011] Furthermore, the encapsulation layer is a continuous and stable spray of tiny particles formed by a TPU solution under high pressure.

[0012] Furthermore, the positive electrode TPU film layer and the negative electrode TPU film layer are respectively located on both sides of the PVDF piezoelectric film as external positive and negative electrodes of the piezoelectric sensor.

[0013] Furthermore, the positive electrode TPU film layer and the negative electrode TPU film layer are both TPU films ultrasonically impregnated with carbon nanotube particles in a TPU solution.

[0014] Furthermore, in step 1, a magnetic stirrer is used for stirring, the temperature is maintained at 50° and stirring is continued for 24 hours to obtain a completely dissolved PVDF solution.

[0015] Furthermore, the process parameters such as voltage, temperature, propeller injection speed, collection distance, and collection end rotation speed in the electrospinning method can be continuously controlled, and the TPU nanofiber membrane is obtained by the electrospinning method.

[0016] Furthermore, the PVDF nanofiber membrane is cut into appropriate sizes to characterize it and test the piezoelectric and mechanical properties of the film.

[0017] Furthermore, when the TPU film is impregnated, the test results show that when the concentration of the nanofiller is 0.15g, the conductive performance of the TPU film electrode is the best.

[0018] Furthermore, the PVDF piezoelectric film and the positive and negative electrodes are placed and fixed in a "sandwich" structure during packaging, and the packaging process is optimized to improve the durability and environmental adaptability of the sensor, thereby obtaining a piezoelectric sensor with high stretchability and high piezoelectricity.

[0019] Beneficial effects of the present invention:

[0020] 1. The present invention proposes a method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers, using electrospinning technology to prepare a PVDF nanofiber membrane with oriented fiber characteristics, and by regulating the electrospinning process parameters, a PVDF piezoelectric film with high piezoelectricity and high stretchability is obtained. The film has high stability and exhibits good mechanical properties after testing. At the same time, after being packaged into a piezoelectric sensor, the open circuit voltage at different elongations has been tested to be stable, and it can effectively detect the mechanical strain of different surface features.

[0021] 2. The present invention proposes a method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers, and adopts ultrasonic impregnation to prepare a flexible electrode with low resistance and high stretchability. Ultrasonic impregnation can obtain a flexible electrode with low resistance and high stretchability. The electrode can smoothly conduct the charge generated by PVDF during operation, and the resistance still meets the working requirements of most scenarios at a higher elongation.

[0022] 3. The present invention proposes a method for preparing a stretchable piezoelectric sensor based on oriented PVDF fiber, and encapsulates the piezoelectric sensor by electrospraying TPU to obtain a highly stretchable piezoelectric sensor. The encapsulation layer is obtained by high-voltage electrospraying TPU solution, which can perfectly fit the sensor to be encapsulated and protect the sensor from interference and erosion from the external environment. Compared with traditional sensors, the piezoelectric sensor of the present invention has higher flexibility and conformability, and exhibits excellent performance under a variety of complex working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A flow chart of the process for preparing a piezoelectric sensor according to the present invention;

[0024] Figure 2 This is a "sandwich" structure diagram of the piezoelectric sensor of the present invention;

[0025] Figure 3 This is a SEM comparison of the oriented fibers and the non-oriented fibers of the PVDF film of the present invention;

[0026] Figure 4 The tensile fracture diagram of oriented and non-oriented fibers of PVDF piezoelectric film;

[0027] Figure 5 This is a comparison chart of the output open-circuit voltage of PVDF piezoelectric film oriented fibers and non-oriented fibers;

[0028] Figure 6 The open circuit voltage and pressure relationship diagram of PVDF piezoelectric film with oriented fiber characteristics;

[0029] Figure 7Comparison of open circuit voltage of PVDF piezoelectric film with oriented fiber characteristics at different elongation rates;

[0030] Figure 8 Graph showing the relationship between strain and self-resistance of the flexible stretchable electrode of the present invention. DETAILED DESCRIPTION

[0031] In order to more clearly and completely illustrate the technical solution of the present invention, the present invention will be further described below with reference to the accompanying drawings.

[0032] Please refer to Figures 1-8 The present invention proposes a preparation method of a stretchable piezoelectric sensor based on oriented PVDF fibers. First, a PVDF solution of a certain concentration is prepared. The solution is finally selected as N,N-dimethylformamide through continuous experiments. The mixture of the two is stirred at 50 degrees on a magnetic stirrer for 24 hours to obtain a completely dissolved PVDF solution. Subsequently, by continuously adjusting the process parameters such as voltage, temperature, propeller injection speed, collection distance, and collection end speed in the electrospinning technology, a PVDF nanofiber membrane with oriented fiber characteristics is finally prepared. The fiber membrane is then cut into appropriate sizes for characterization and the piezoelectric and mechanical properties of the film are tested.

[0033] A TPU solution of a certain concentration was prepared, tetrahydrofuran was used to dissolve the TPU solute, and a TPU nanofiber membrane was obtained by electrospinning. Then a certain amount of carbon nanotubes was put into an ultrasonic liquid, and the ultrasonic liquid was selected as anhydrous ethanol. It was pre-ultrasonicated for a period of time in an ice bath state so that the carbon nanotube particles were evenly dispersed in the ultrasonic liquid. Then the TPU film prepared by electrospinning was cut into appropriate sizes and placed in an ultrasonic liquid. Ultrasonic immersion was performed at a certain ultrasonic power under ice bath conditions. After ultrasonication for a period of time, the TPU film was taken out, rinsed with anhydrous ethanol, and placed in an oven for drying. Finally, a flexible electrode with high stretchability was obtained and the conductive properties of the electrode were tested. The test results showed that when the concentration of the nanofiller was 0.15g, the conductive properties of the electrode were the best.

[0034] After the PVDF piezoelectric film and electrodes are placed and fixed in a "sandwich" structure, the concentration of the TPU solution is adjusted to form continuous and stable spray-like tiny particles under high pressure. The piezoelectric film and electrodes to be encapsulated are then placed under the spray and encapsulated on both sides. By optimizing the encapsulation process to improve the durability and environmental adaptability of the sensor, a piezoelectric sensor with high stretchability and high piezoelectricity is obtained after the encapsulation is completed.

[0035] In this embodiment: PVDF of Solvay-6010 of the United States is used as the solute, and N,N-dimethylformamide DMF with a purity of 99.9% is finally selected as the solvent through multiple experiments. After continuous testing and experiments, a PVDF solution with a mass concentration of 15wt% is finally prepared, and the mixture is placed on a magnetic stirrer and stirred at 50° and 100r / min for 24h to completely dissolve the solute. The prepared solution is then extracted into a syringe and placed in an electrospinning device for spinning to prepare a nanofiber membrane with a certain thickness and continuously debug the process parameters to optimize the final effect of the fiber membrane. The electrospinning process parameters are finally determined as follows: electrospinning voltage 10kv, syringe propulsion speed 1.0ml / h, temperature 24°, collection distance 20cm, collection end drum speed 5000r / min, syringe needle size 25G, spinning time 8h , The prepared piezoelectric film was then removed from the aluminum foil and cut into 15mm×40mm strips by a laser cutting machine for mechanical property testing and characterization. After testing with a tensile testing machine, the elongation of the PVDF piezoelectric film with oriented fiber characteristics was increased from about 60% to about 260%. By testing the open circuit voltage of the PVDF piezoelectric film with oriented fiber characteristics at elongations of 0%, 30%, 60%, and 100%, it was found that with the continuous change of elongation, the open circuit voltage output by the PVDF piezoelectric film did not fluctuate significantly, and was stable at about 1.6V. At the same time, after being packaged into a sensor, the film was tapped with an exciter. As the exciter pressure increased, the open circuit voltage also increased, and the linearity was also good. The test results showed that the piezoelectric performance of the film was improved to a certain extent compared with the film with non-oriented fiber characteristics.

[0036] First, the TPU film was prepared by electrospinning technology. After many tests, tetrahydrofuran (THF) was finally used as a solvent to dissolve TPU. Because of its low boiling point and high volatility, tetrahydrofuran can appropriately increase the propulsion speed of the syringe during electrospinning, and the TPU base membrane can be spun out in a short time. After continuous attempts, the mass fraction of the TPU solution was finally determined to be 18wt%. At the same time, the specific parameters of the electrospinning TPU base membrane were tested as follows: electrospinning voltage 14kv, syringe injection speed 8.0ml / h, needle distance from the drum collector 20cm, drum speed 100r / min, syringe needle size 22G, and then 0.15g of carbon nanotubes CN were taken. T was placed in 40ml of anhydrous ethanol and pre-ultrasonic dispersed at 200W power for 40 minutes in an ice bath to evenly disperse the CNT particles in the anhydrous ethanol. The TPU base membrane was then cut into appropriate sizes and ultrasonically impregnated. It was ultrasonically impregnated at 800W ultrasonic power for 20 minutes in an ice bath. The membrane was taken out and rinsed with anhydrous ethanol. After rinsing, it was placed in an oven for drying to finally obtain a low-resistance, highly stretchable electrode. 0.15gd carbon nanotubes (CNTs) were used for ultrasonic impregnation. As the strain continued to increase, its resistance also continued to increase. Performance testing of the electrode found that its resistance still met application requirements at a higher elongation.

[0037] After the piezoelectric film and electrodes are prepared, they are arranged into a "sandwich" structure for packaging. The two sides are encapsulated by electrospraying TPU solution. Under high pressure, TPU particles are sprayed out from the needle instead of nanofiber filaments. After 10 minutes of electrospraying, an encapsulation layer is formed on the surface of the material to be encapsulated and a stretchable piezoelectric sensor is obtained. Its encapsulation layer can prevent erosion by factors such as skin sweat to a certain extent.

[0038] Of course, the present invention may have many other implementations. Based on this implementation, other implementations obtained by ordinary technicians in this field without any creative work are all within the scope of protection of the present invention.

Claims

1. A method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers. The piezoelectric sensor comprises an encapsulation layer, a positive TPU film layer, a negative TPU film layer, and a PVDF piezoelectric film. Carbon nanotube particles are sprayed onto the outer surfaces of the positive and negative TPU film layers. The encapsulation layer acts as an adhesive to encapsulate the positive, negative TPU film layers, and PVDF piezoelectric film into a single unit. It is characterized by: The preparation method comprises the following steps: Step 1: A mixture of a PVDF solution and N,N-dimethylformamide (DMF) is stirred to obtain a PVDF solution, and a PVDF nanofiber membrane having oriented fiber characteristics is prepared by electrospinning; Step 2: Prepare a TPU solution of a certain concentration, use tetrahydrofuran to dissolve the TPU solute, and obtain a TPU film by electrospinning. Place a certain amount of carbon nanotubes (CNTs) in an ultrasonic liquid of anhydrous ethanol, and evenly disperse the carbon nanotube particles in the anhydrous ethanol under an ice bath. Cut the TPU film into appropriate sizes and place it in an ultrasonic liquid for ultrasonic immersion, then remove it, rinse it with anhydrous ethanol, and dry it in an oven to obtain a flexible electrode with high stretchability. Step 3. Adjust the concentration of the TPU solution so that it forms continuous and stable spray-like tiny particles under high pressure, and place the piezoelectric film and electrode to be encapsulated under the spray to encapsulate both sides.

2. The method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers according to claim 1, characterized in that: The encapsulation layer is a TPU solution formed under high pressure to form continuous and stable spray-like tiny particles.

3. The method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers according to claim 1, characterized in that: The positive electrode TPU film layer and the negative electrode TPU film layer are respectively used as external positive and negative electrodes of the piezoelectric sensor and are located on both sides of the PVDF piezoelectric film.

4. The method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers according to claim 1, wherein: In step 1, a magnetic stirrer is used for stirring, the temperature is maintained at 50° and stirring is continued for 24 hours to obtain a completely dissolved PVDF solution.

5. The method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers according to claim 1, characterized in that: The process parameters of the electrospinning method, such as voltage, temperature, propeller injection speed, collection distance, and collection end rotation speed, are adjustable.

6. The method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers according to claim 1, characterized in that: The PVDF nanofiber membrane is cut into appropriate sizes to characterize it and test the piezoelectric and mechanical properties of the film.

7. The method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers according to claim 1, characterized in that: When the TPU film is impregnated, when the test concentration of the nanofiller is 0.15 g, the conductive performance of the TPU film electrode is optimal.

8. The method for preparing a stretchable piezoelectric sensor based on oriented PVDF fibers according to claim 1, characterized in that: The PVDF piezoelectric film and the positive and negative electrodes are placed and fixed in a "sandwich" structure during packaging, and the packaging process is optimized to improve the durability and environmental adaptability of the sensor, thereby obtaining a piezoelectric sensor with high stretchability and high piezoelectricity.

Images