PVDF / ba tio3 microstructure piezoelectric sensor and preparation method thereof

Abstract

The application provides a preparation method of a PVDF / BaTiO3 piezoelectric sensor, and comprises the following steps: S1: PVDF powder is poured into a mixed solution of dimethyl sulfoxide and acetone and stirred to obtain a PVDF solution; BaTiO3 nano powder is poured into the PVDF solution and ultrasonic dispersion is performed to obtain a mixed solution; S2: the mixed solution is subjected to near-field direct writing to obtain a PVDF / BaTiO3 composite piezoelectric film, which is laid on a microstructure mold, and then a mold with recessed microstructure is covered, and after drying, a microstructure film is obtained; PDMS and a curing agent are stirred and mixed, then poured on the microstructure mold, heated and dried, and after curing, a PDMS flexible substrate is obtained; S3: copper foils are covered on both sides of the microstructure film as electrodes, and lead wires are led out from the copper foils, and then recessed and convex microstructure PDMS substrates are respectively covered on the outer sides of the copper foils to complete packaging, and a PVDF / BaTiO3 piezoelectric sensor is obtained. The application provides a preparation method of a piezoelectric sensor which is simple to operate and low in cost, and the prepared sensor has excellent comprehensive performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of piezoelectric sensors, in particular to a PVDF / BaTiO3 microstructure piezoelectric sensor and a preparation method thereof. BACKGROUND

[0002] Flexible sensors are paid much attention due to their advantages such as soft deformability, lightness, high sensitivity and the like. The biggest feature of flexible piezoelectric sensors compared with piezoresistive and capacitive sensors is the ability of converting mechanical energy into electrical energy, which means that the sensor does not need external power supply in practical application and has the ability of self-power supply. The flexible piezoelectric sensor has great application prospect in motion detection, personal health monitoring, robots (electronic skin) and the like. The core of the flexible sensor is a flexible piezoelectric film element with piezoelectric effect, and polyvinylidene fluoride (PVDF) is widely used in the preparation of piezoelectric films as a polymer with excellent piezoelectric properties.

[0003] Traditional methods for preparing the PVDF piezoelectric film include flow casting, spin coating and stretching, etc. The basic principle of the three methods is to coat the solution into a film form, and then the piezoelectric film is obtained after the solvent is evaporated. The flow casting method is relatively simple to operate, but it is difficult to control the thickness of the film and high-pressure polarization needs to be performed in the later stage to improve the piezoelectricity of the film; the spin coating method is to disperse the solution on the surface of the substrate by using a high-speed centrifuge to obtain a circular film. The film prepared by this method has a uniform thickness, but the surface roughness is poor and high-pressure polarization is also needed in the later stage; the stretching method is to stretch the PVDF solution film at a constant temperature by using a stretching machine, because a large number of studies have shown that the piezoelectricity of PVDF comes from the beta phase thereof, and the relative content of the beta phase in PVDF can be increased in the stretching process to improve the piezoelectricity of the film. The disadvantage of this method is that the steps are complex and the sample is prone to breakage and damage during the stretching process. Meanwhile, with the increasingly wide application of flexible sensors, the requirements for the sensitivity, flexibility, durability and other performance of the sensors are also higher and higher.

[0004] Near-field direct writing is a new technology for preparing Weaire-Phelan fibers, which has the advantages of simple operation, low cost, good controllability and low experimental environment requirement, is a spinning process formed by modifying the related experimental parameters on the basis of electrospinning technology, and is very suitable for the preparation of piezoelectric films. However, the technical gap in this field is still relatively large, especially in the research on the PVDF / BaTiO3 microstructure piezoelectric sensor, and there is no mature technical solution at present. SUMMARY

[0005] The technical problem solved by the present application is to provide a preparation method of a PVDF / BaTiO3 piezoelectric sensor, so as to fill the technical gap in the field and provide a piezoelectric sensor preparation method which is simple to operate, low in cost, good in controllability and low in experimental environment requirement.

[0006] To solve the above problems, the present application provides a preparation method of a PVDF / BaTiO3 piezoelectric sensor, comprising the following steps:

[0007] S1: Pouring PVDF powder into a mixed solution of dimethyl sulfoxide and acetone and stirring to obtain a PVDF solution; then pouring BaTiO3 nano powder into the PVDF solution, continuing to stir, and then ultrasonic dispersion to obtain a mixed solution;

[0008] S2: Preparation of a PVDF / BaTiO3 microstructure film: pouring the mixed solution of step S1 into a barrel of a near-field direct writing device, obtaining a PVDF / BaTiO3 composite piezoelectric film by near-field direct writing, laying the film on a 3D-printed convex microstructure mold, covering it with a mold with a concave microstructure, and placing it in a constant temperature drying oven for drying; after the solvent is completely evaporated, a PVDF / BaTiO3 microstructure film is obtained;

[0009] Preparation of a PDMS flexible substrate: after stirring and mixing PDMS with a curing agent, pouring it on a microstructure negative mold and a microstructure positive mold, placing it in a constant temperature drying oven for heating and drying, and curing to obtain a PDMS flexible substrate with concave and convex microstructures;

[0010] S3: Covering the microstructure film obtained in step S2 with copper foil as electrodes on both sides, and leading wires from the copper foil; covering the copper foil outside with the concave and convex microstructure PDMS substrates obtained in step S2 to complete packaging, and obtaining a PVDF / BaTiO3 piezoelectric sensor.

[0011] As a preferred scheme, in step S1, the mass ratio of dimethyl sulfoxide to acetone is 3:2.

[0012] As a preferred scheme, in step S1, the mass fraction of PVDF in the PVDF solution is 15%.

[0013] As a preferred scheme, in step S1, the stirring condition is that stirring is carried out at a set temperature of 60℃ for 1 hour.

[0014] As a preferred scheme, in step S1, the stirring condition is that stirring is carried out at a set temperature of 60℃ for 1 hour.

[0015] As a preferred scheme, in the step S2, the near-field direct writing is performed under the conditions that the applied voltage is 2-3 kV, the applied air pressure is 0.03-0.05 MPa, the spinning needle diameter is 21G, the spinning distance is 6 mm, and the spinning layer number is 5.

[0016] As a preferred scheme, in the step S2, the drying in the constant-temperature drying box is performed under the conditions that the drying temperature is 50 DEG C and the drying time is 2 hours.

[0017] As a preferred scheme, in the step S2, the mass ratio of the PDMS to the curing agent is 10:1.

[0018] As a preferred scheme, in the step S2, the drying is performed under the conditions that the drying temperature is 80 DEG C and the drying time is 1 hour.

[0019] Another technical scheme of the present application provides a PVDF / BaTiO3 piezoelectric sensor,

[0020] To solve the above problems, the present application provides a PVDF / BaTiO3 piezoelectric sensor prepared by the preparation method.

[0021] (1) The near-field direct writing used in the present application is very suitable for the preparation of the PVDF piezoelectric film, and the electric field force provides a pulling force for the PVDF fiber during the spinning process, which helps to convert other crystal phases into the beta phase and increase the relative content of the beta phase, so that the post-stretching treatment is not needed; at the same time, the fiber is under a high-voltage electric field during the spinning process, and the prepared film also does not need subsequent high-voltage polarization treatment.

[0022] (2) The preparation method of the PVDF / BaTiO3 microstructure piezoelectric sensor can better control the shape of the piezoelectric film, and the film thickness, fiber diameter, film shape and layer number can be accurately controlled by adjusting the related parameters of the near-field direct writing such as air pressure, motor feeding speed and path code, so that stable batch manufacturing can be stably performed.

[0023] (3) The piezoelectric film prepared by the preparation method of the PVDF / BaTiO3 microstructure piezoelectric sensor has a microstructure protrusion on the surface, which increases the surface area of the film; at the same time, the PDMS flexible substrate wrapped on both sides of the film also has corresponding protrusions and depressions, which increases the contact area of the film and the substrate without changing the overall size, which means that the effective area of the piezoelectric power generation is increased during the working process, and the piezoelectric performance is improved. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The flow chart of the preparation method of the PVDF / BaTiO3 microstructure piezoelectric sensor.

[0025] Figure 2 The PVDF / BaTiO3 microstructure film prepared in the embodiment is shown in the figure;

[0026] Figure 3 The stress-strain curves of the planar film and the PVDF / BaTiO3 microstructure film in the stretching experiment are compared;

[0027] Figure 4 The time-output voltage images of the sensors in three packaging forms of the planar film and the planar substrate (PPS), the microstructure film and the microstructure substrate (HHS), and the planar film and the microstructure substrate (PHS) under the periodical small load with the frequency of 2.5 Hz and the size of 2N are shown in the figure;

[0028] Figure 5 The voltage signal images generated when the HHS microstructure sensor is attached to the finger joint and the elbow joint and the joints are moved are shown in the figure;

[0029] Figure 6 The voltage signal images generated when the HHS microstructure sensor is attached to the sole and jumps, and the local amplification image of a part of the signal is shown in the figure. DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0031] The present application provides a preparation method of a PVDF / BaTiO3 piezoelectric sensor, comprising the following steps:

[0032] S1: pour the PVDF powder into the mixed solution of dimethyl sulfoxide and acetone and stir to obtain a PVDF solution; then pour the BaTiO3 nano-powder into the PVDF solution, continue to stir, and then perform ultrasonic dispersion to obtain a mixed solution;

[0033] S2: preparation of the PVDF / BaTiO3 microstructure film: pour the mixed solution of step S1 into the barrel of a near-field direct writing device, obtain a PVDF / BaTiO3 composite piezoelectric film by near-field direct writing, lay the film on the 3D-printed convex microstructure mold, cover it with a mold with concave microstructure, and place it in a constant-temperature drying box for drying. After the solvent is completely evaporated, the PVDF / BaTiO3 microstructure film is obtained;

[0034] Preparation of PDMS flexible substrate: after mixing PDMS and curing agent, pour them on the microstructure negative mold and the microstructure positive mold, and place them in a constant temperature drying oven for heating and drying, and then obtain the PDMS flexible substrate with concave and convex microstructures after curing;

[0035] S3: cover the copper foil as the electrode on both sides of the microstructure film obtained in the step S2, and lead the wires from the copper foil, and then cover the concave and convex microstructure PDMS substrate obtained in the step S2 on the outer side of the copper foil respectively to complete the packaging, and obtain the PVDF / BaTiO3 piezoelectric sensor.

[0036] Preferably, in the step S1, the mass ratio of dimethyl sulfoxide and acetone is 3:2.

[0037] Preferably, in the step S1, the mass fraction of PVDF in the PVDF solution is 15%.

[0038] Preferably, in the step S1, the stirring condition is that stirring is carried out at a set temperature of 60℃ for 1 hour.

[0039] Preferably, in the step S1, the stirring condition is that stirring is carried out at a set temperature of 60℃ for 1 hour.

[0040] Preferably, in the step S2, the near-field direct writing condition is that the applied voltage is 2-3kV, the applied air pressure is 0.03-0.05Mpa, the diameter of the spinning needle is 21G, the spinning distance is 6mm, and the number of spinning layers is 5.

[0041] Preferably, in the step S2, the drying condition in the constant temperature drying oven is that the drying temperature is 50℃ and the drying time is 2 hours.

[0042] Preferably, in the step S2, the mass ratio of PDMS to the curing agent is 10:1.

[0043] Preferably, in the step S2, the drying condition is that the drying temperature is 80℃ and the drying time is 1h.

[0044] The application further provides a PVDF / BaTiO3 piezoelectric sensor, which is prepared by the preparation method.

[0045] The above scheme of the application is described in detail in combination with specific experimental data and raw materials as follows:

[0046] S1: 6 g of DMSO liquid and 4 g of acetone liquid were weighed and put into a grinding bottle, which was placed on a magnetic stirrer for stirring and mixing. Then 1.5 g of PVDF powder was slowly poured into the mixed solution of DMSO and acetone. The grinding bottle was sealed, the temperature of the stirrer was controlled at 60°C, and the stirring was carried out for 1 h to obtain a clear and uniform PVDF solution. Then 0.4 g of BaTiO3 powder was weighed and poured into the PVDF solution, and the solution was continuously stirred at constant temperature for 5 min, and then ultrasonic dispersion treatment was carried out for 30 min to make the BaTiO3 powder more uniformly dispersed in the solution, and a mixed solution was obtained;

[0047] S2: Preparation of PVDF / BaTiO3 microstructure film: After obtaining the uniform milky white liquid, the liquid was poured into a 10 ml near-field direct writing injection cylinder, a spinning needle with a needle diameter of 21G was installed, and the needle was grounded. The collecting plate was connected to the positive electrode of a high-voltage power supply and the voltage was set to 2.7 kV. The liquid supply pressure was adjusted to 0.04 Mpa, the distance between the needle and the receiving plate was 6 mm, the printing path was set to 5 layers, and the printing time was 14 min. A planar PVDF / BaTiO3 composite piezoelectric film was printed. The film was placed on a microstructure male mold with several semispherical protrusions with a diameter of 2 mm, and a corresponding female mold was placed on it, and then it was placed in a constant temperature drying oven and dried at 50°C for 2 h to evaporate the solvent, thereby obtaining a microstructure piezoelectric film. The structure is shown in Figure 2

[0048] Preparation of PDMS flexible substrate: 20 g of PDMS liquid and 2 g of curing agent were weighed and placed in a beaker and stirred for 5 min, and then poured onto the microstructure female mold and male mold, respectively, and then placed in a constant temperature drying oven and dried at 80°C.

[0049] After drying and curing, a PDMS microstructure flexible substrate with corresponding protrusions and depressions was obtained. The substrate was cut into the same shape and size as the film and used to package the microstructure piezoelectric film.

[0050] S3: Copper foil was attached to both sides of the microstructure film as electrodes and lead wires were drawn. The copper foil was then covered with the cut PDMS microstructure substrate to complete the packaging.

[0051] As shown in Figure 3 , this data was obtained by uniaxial tensile test measurement by Shimadzu AGS-X tensile testing machine. The tensile displacement speed of the clamp was set to 1 mm / min, the initial length was 15 mm, the film width was 20 mm, and the thickness was 0.30 mm. The stress-strain curve shows that the elastic deformation of the microstructure film is larger than that of the planar film, and the strain at the time of failure is much larger than that of the planar film, which proves that the microstructure film has strong deformation ability.

[0052] As shown in Figure 4 ​As shown, the output voltage images of the three kinds of packaged sensors: planar film and planar substrate (PPS), microstructure film and microstructure substrate (HHS) and planar film and microstructure substrate (PHS) under the periodic load of 2N at a frequency of 2.5Hz are compared. It can be seen that the microstructure sensor in the form of HHS has the highest peak output voltage, reaching 2.32V, and the output is stable. It is proved that the HHS film of the present application has excellent piezoelectric performance and excellent detection ability to weak load.

[0053] As shown in Figure 5 As shown, the microstructure piezoelectric sensor is attached to the finger joints and elbow joints of the human body, and under different periodic movements, the sensor can generate corresponding different periodic signals, and the signal is stable after multiple cycles.

[0054] As shown in Figure 6 As shown, the microstructure piezoelectric sensor is attached to the foot, and can generate a high amplitude and stable signal during jumping. As can be seen from the local enlarged view, the response time of the sensor is only 42ms, which proves that the sensor can respond extremely fast to movement and has great application potential in the field of motion detection.

[0055] Through the above examples, it is further proved that the PVDF / BaTiO3 piezoelectric sensor prepared by the present application has strong deformation ability, excellent piezoelectric performance and stable signal, and has great application potential in the field of motion detection. This further reflects the excellent comprehensive performance of the piezoelectric sensor of the present application. Furthermore, the present application provides a preparation method of the above piezoelectric sensor which is simple to operate, low in cost, good in controllability and low in experimental environment requirement, and has high commercial value and popularization value.

[0056] Although the present disclosure is as above, the protection scope of the present disclosure is not limited to this. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present application.

Claims

1. A method for fabricating a PVDF / BaTiO3 piezoelectric sensor, characterized in that: Includes the following steps: S1: Pour PVDF powder into a mixture of dimethyl sulfoxide and acetone and stir to obtain a PVDF solution; Next, pour BaTiO3 nanopowder into the PVDF solution, continue stirring, and then perform ultrasonic dispersion to obtain a mixed solution; S2: Preparation of PVDF / BaTiO3 microstructure film: Pour the mixed solution from step S1 into the barrel of a near-field direct writing device, obtain a PVDF / BaTiO3 composite piezoelectric film through near-field direct writing, lay it on a 3D-printed raised microstructure mold, cover it with a mold with recessed microstructure, and place it in a constant temperature drying oven for drying. After the solvent has completely evaporated, a PVDF / BaTiO3 microstructure film is obtained; Preparation of PDMS flexible substrate: After stirring and mixing PDMS with curing agent, pour it onto a microstructure negative mold and a microstructure positive mold, place it in a constant temperature drying oven for heating and drying, and obtain a PDMS flexible substrate with recessed and raised microstructures after curing; S3: Copper foil is covered on both sides of the microstructure film obtained in step S2 as electrodes, and wires are led out from the copper foil. The concave and convex microstructure PDMS substrates obtained in step S2 are then covered on the outside of the copper foil to complete the encapsulation, thus obtaining the PVDF / BaTiO3 piezoelectric sensor. In step S1, the mass ratio of dimethyl sulfoxide to acetone is 3:

2. In step S1, the PVDF solution contains 15% PVDF by mass. In step S1, the stirring conditions are: stirring for 1 hour at a set temperature of 60°C. In step S1, the conditions for continuing stirring are: stirring for 5 minutes at a set temperature of 60°C, and ultrasonic dispersion for 30 minutes.

2. The method for fabricating the PVDF / BaTiO3 piezoelectric sensor according to claim 1, characterized in that: In step S2, the conditions for near-field direct writing are: applied voltage of 2-3kV, applied air pressure of 0.03-0.05Mpa, spinning needle diameter of 21G, spinning distance of 6mm, and spinning layer of 5 layers.

3. The method for fabricating the PVDF / BaTiO3 piezoelectric sensor according to claim 1, characterized in that: In step S2, the conditions for drying in a constant temperature drying oven are: drying temperature 50°C and drying time 2 hours.

4. The method for fabricating the PVDF / BaTiO3 piezoelectric sensor according to claim 1, characterized in that: In step S2, the mass ratio of PDMS to curing agent is 10:

1.

5. The method for fabricating the PVDF / BaTiO3 piezoelectric sensor according to claim 1, characterized in that: In step S2, the drying conditions are: drying temperature of 80℃ and drying time of 1 hour.

6. A PVDF / BaTiO3 piezoelectric sensor, characterized in that: The sensor is prepared by the preparation method according to any one of claims 1-5.

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