Polyvinylidene fluoride piezoelectric film and preparation and application thereof

Abstract

The application belongs to the technical field of piezoelectric sensing, and particularly relates to a polyvinylidene fluoride piezoelectric film and preparation and application thereof. The material of the polyvinylidene fluoride piezoelectric film is polyvinylidene fluoride homopolymer, and the surface of the polyvinylidene fluoride piezoelectric film has roughness, wherein the profile arithmetic average deviation of the roughness is 0.01-100, and the root mean square is 0.006-60 microns. The PVDF piezoelectric film has good piezoelectric performance and good temperature stability; and the sensor prepared by using the PVDF piezoelectric film has a high use temperature, which is conducive to its wide use.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric sensing technology, specifically relating to a polyvinylidene fluoride piezoelectric film and its preparation and application. Background Technology

[0002] In recent years, with the rapid development of the Internet of Things (IoT) and wearable electronics, the demand for flexible piezoelectric sensors and actuators has become increasingly urgent. Polymer piezoelectric films have attracted much attention due to their combination of good flexibility and excellent piezoelectric properties. Among polymer piezoelectric materials, β-phase polyvinylidene fluoride (PVDF) exhibits good piezoelectricity and ferroelectricity due to its large dipole moment. Therefore, PVDF piezoelectric films have been widely used in medical devices, the Internet of Things, and wearable electronics.

[0003] To date, the preparation process of PVDF-based piezoelectric films mainly involves two steps. The first step primarily involves controlling the formation of the β phase. Since PVDF materials readily form the α phase during crystallization, and the α phase does not possess piezoelectric properties, researchers have developed three main methods to control the formation and content of the β phase. One method is a stretching method, which uses mechanical stretching to transform the α phase in PVDF materials into the β phase. Another method involves blending PVDF with inorganic nanoparticles, promoting the formation of the β phase PVDF through the interaction between the nanoparticles and PVDF. A third method involves copolymerizing vinylidene fluoride with materials such as trifluoroethylene and vinyl chloride to form PVDF copolymers, thereby inducing the transformation of the α phase in PVDF materials into the β phase. The second step primarily involves controlling the orientation of the β phase crystals through electric field polarization.

[0004] For PVDF-based piezoelectric films prepared by stretching and blending methods, piezoelectric properties are lost at higher temperatures due to the release of residual stress. For PVDF copolymers, the Curie transition temperature decreases with increasing comonomer content, and their operating temperature must be below the Curie transition temperature. Currently, the operating temperature of PVDF-based piezoelectric films and sensors is typically below 80°C. Furthermore, β-phase PVDF-based piezoelectric films often exhibit pyroelectric effects. Therefore, when β-phase PVDF-based piezoelectric films are used as sensors, the output electrical signal is affected not only by pressure but also by temperature, leading to a decrease in the linearity of the piezoelectric film sensor. Summary of the Invention

[0005] This invention aims to solve the above-mentioned problems by providing a polyvinylidene fluoride (PVDF) piezoelectric film, its preparation and application, which solves the temperature stability problem of PVDF-based piezoelectric films and sensors, and improves the maximum operating temperature of PVDF-based piezoelectric films and sensors.

[0006] According to the technical solution of the present invention, the polyvinylidene fluoride piezoelectric film is made of polyvinylidene fluoride homopolymer, and the surface of the polyvinylidene fluoride piezoelectric film has roughness, wherein the profile arithmetic mean deviation (Ra) of the roughness is 0.01-100 and the root mean square (RMS) is 0.006-60 μm.

[0007] Preferably, Ra is 0.02-1, more preferably 0.02-0.05, and even more preferably 0.03-0.04.

[0008] Preferably, the RMS is 0.5-5μm, more preferably 0.07-2μm, and even more preferably 1.4-2μm.

[0009] Furthermore, to ensure the continuity of the polyvinylidene fluoride piezoelectric film, the thickness of the polyvinylidene fluoride piezoelectric film should be greater than the root mean square roughness.

[0010] Furthermore, the roughness primarily affects the piezoelectric coefficient of the polyvinylidene fluoride piezoelectric film.

[0011] Furthermore, the maximum operating temperature of the polyvinylidene fluoride piezoelectric film sensor can reach 170°C, which is the melting point of polyvinylidene fluoride material.

[0012] Furthermore, the polyvinylidene fluoride piezoelectric film sensor exhibits good temperature stability within a temperature range from room temperature to 170°C.

[0013] A second aspect of the present invention provides a method for preparing the above-mentioned polyvinylidene fluoride piezoelectric film, comprising the following steps:

[0014] S1: A densely distributed micro / nano structure is prepared on the surface of a substrate to form a roughness, wherein the profile arithmetic mean deviation of the roughness is 0.01-100 and the root mean square is 0.006-60 μm;

[0015] S2: Coat the surface of the substrate obtained in step S1 with a polyvinylidene fluoride homopolymer solution or solution;

[0016] S3: After the polyvinylidene fluoride homopolymer crystallizes, the substrate is peeled off to obtain the polyvinylidene fluoride piezoelectric film.

[0017] Furthermore, the substrate requires a solvent that is insoluble in the polyvinylidene fluoride homopolymer solution.

[0018] Furthermore, the substrate is a metallic material, an inorganic material, or an organic polymer material.

[0019] Furthermore, the metallic material is selected from any one of gold, silver, copper, platinum, aluminum, and stainless steel; the inorganic material is selected from any one of glass and silicon wafers; and the organic polymer material is selected from any one of polydimethylsiloxane (PDMS), polytetrafluoroethylene, polysulfone, and polyurethane.

[0020] Furthermore, in step S1, a dense array of micro- and nano-structures is prepared on the surface of the substrate by means of template transfer.

[0021] Furthermore, the concentration of the polyvinylidene fluoride homopolymer solution can be adjusted according to the required film thickness, preferably 5-20 wt%.

[0022] Furthermore, the solvent in the polyvinylidene fluoride homopolymer solution is an organic solvent selected from one or more of dimethyl sulfoxide, trimethyl phosphate, methyl ethyl ketone, N-methylpyrrolidone, acetone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, and triethyl phosphate.

[0023] Furthermore, in step S2, the polyvinylidene fluoride homopolymer solution can be coated onto the surface of the substrate obtained in step S1 by means of spin coating, blade coating, inkjet printing, printing, etc.

[0024] Furthermore, in step S3, the solvent in the polyvinylidene fluoride homopolymer solution is removed by heating and evaporation. The heating temperature is 50-200℃, and the temperature should preferably not exceed the boiling point of the solvent used.

[0025] A third aspect of the present invention provides a sensor comprising the aforementioned polyvinylidene fluoride piezoelectric film and an electrode formed on the surface of the polyvinylidene fluoride piezoelectric film.

[0026] Furthermore, the sensor exhibits high thermal stability and operating temperature.

[0027] Furthermore, the electrode is a metal electrode, and its material is one of copper, silver, aluminum, zinc, iron, nickel, chromium, tungsten, titanium, etc.

[0028] The technical solution of the present invention has the following advantages compared with the prior art:

[0029] 1. The PVDF piezoelectric film of the present invention has excellent piezoelectric properties;

[0030] 2. The PVDF piezoelectric film of the present invention has good temperature stability;

[0031] 3. The sensor prepared using the PVDF piezoelectric film of the present invention has a high operating temperature, which is beneficial for its widespread use. Attached Figure Description

[0032] Figure 1 To determine the piezoelectric coefficient d of the PVDF piezoelectric films prepared using Examples 1-5 of this invention, the PVDF piezoelectric film prepared using Comparative Example 1, and commercially available PVDF piezoelectric films. 33 Comparison chart.

[0033] Figure 2 The output voltage of the sensor prepared using the PVDF piezoelectric film obtained in Example 3 when a periodic pressure of 85 kPa is applied.

[0034] Figure 3 The output voltage of a commercially available PVDF-based piezoelectric thin-film sensor when a periodic pressure of 85 kPa is applied.

[0035] Figure 4 This is a comparison chart of the temperature stability of the PVDF piezoelectric thin film sensor prepared using the method of Example 5 of the present invention and a commercially available PVDF piezoelectric thin film sensor. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0037] Example 1:

[0038] This embodiment relates to a method for preparing a polyvinylidene fluoride piezoelectric thin film, specifically including the following steps:

[0039] 1) Provide a template with a densely distributed micro / nano structure on its surface, with Ra of 0.05 and RMS of 1.957 μm;

[0040] 2) The surface structure of the template is replicated using polydimethylsiloxane (PDMS) to form a substrate with micro- and nano-structures;

[0041] 3) Prepare a PVDF solution using dimethyl sulfoxide as the organic solvent; the solution concentration is 20 mg / mL. Apply the PVDF solution to the surface of a PDMS substrate, evaporate and crystallize at 130 °C, then peel off the substrate. The prepared PVDF piezoelectric film has a thickness of 10 μm.

[0042] Example 2

[0043] This embodiment relates to a method for preparing a polyvinylidene fluoride piezoelectric thin film, specifically including the following steps:

[0044] 1) Provide a template with a densely distributed micro / nano structure on its surface, with an Ra of 0.042 and an RMS of 1.646 μm;

[0045] 2) The surface structure of the template is replicated using polydimethylsiloxane (PDMS) to form a substrate with micro- and nano-structures;

[0046] 3) Prepare a PVDF solution using dimethyl sulfoxide as the organic solvent; the solution concentration is 20 mg / mL. Apply the PVDF solution to the surface of a PDMS substrate, evaporate and crystallize at 130 °C, then peel off the substrate. The prepared PVDF piezoelectric film has a thickness of 10 μm.

[0047] Example 3:

[0048] This embodiment relates to a method for preparing a polyvinylidene fluoride piezoelectric thin film, specifically including the following steps:

[0049] 1) Provide a template with a densely distributed micro / nano structure on its surface, with an Ra of 0.037 and an RMS of 1.46 μm;

[0050] 2) The surface structure of the template is replicated using polydimethylsiloxane (PDMS) to form a substrate with micro- and nano-structures;

[0051] 3) Prepare a PVDF solution using dimethyl sulfoxide as the organic solvent; the solution concentration is 20 mg / mL. Apply the PVDF solution to the surface of a PDMS substrate, evaporate and crystallize at 130 °C, then peel off the substrate. The prepared PVDF piezoelectric film has a thickness of 10 μm.

[0052] Example 4:

[0053] This embodiment relates to a method for preparing a polyvinylidene fluoride piezoelectric thin film, specifically including the following steps:

[0054] 1) Provide a template with a densely distributed micro / nano structure on its surface, with an Ra of 0.026 and an RMS of 1.041 μm;

[0055] 2) The surface structure of the template is replicated using polydimethylsiloxane (PDMS) to form a substrate with micro- and nano-structures;

[0056] 3) Prepare a PVDF solution using dimethyl sulfoxide as the organic solvent; the solution concentration is 20 mg / mL. Apply the PVDF solution to the surface of a PDMS substrate, evaporate and crystallize at 130 °C, then peel off the substrate. The prepared PVDF piezoelectric film has a thickness of 10 μm.

[0057] Example 5:

[0058] This embodiment relates to a method for preparing a polyvinylidene fluoride piezoelectric thin film, specifically including the following steps:

[0059] 1) Provide a template with a densely distributed micro-nano structure on the surface, with Ra of 0.02 and RMS of 0.792 μm.

[0060] 2) The surface structure of the template is replicated using polydimethylsiloxane (PDMS) to form a substrate with micro- and nano-structures.

[0061] 3) Prepare a PVDF solution using dimethyl sulfoxide as the organic solvent; the solution concentration is 20 mg / mL. Apply the PVDF solution to the surface of a PDMS substrate, evaporate and crystallize at 130 °C, then peel off the substrate. The prepared PVDF piezoelectric film has a thickness of 10 μm.

[0062] Example 6:

[0063] This embodiment relates to a method for preparing a polyvinylidene fluoride piezoelectric thin film, specifically including the following steps:

[0064] 1) Provide a template with a densely packed micro-nano structure on the surface, with Ra of 0.037 and RMS of 1.46 μm.

[0065] 2) The surface structure of the template is replicated using polydimethylsiloxane (PDMS) to form a substrate with micro- and nano-structures.

[0066] 3) The PVDF melt was coated onto the surface of the PDMS substrate, and after natural cooling and crystallization, the substrate was peeled off. The thickness of the prepared PVDF piezoelectric film was 10 μm.

[0067] Example 7:

[0068] This embodiment relates to a method for preparing a polyvinylidene fluoride piezoelectric thin film, specifically including the following steps:

[0069] 1) Provide a template with a densely packed micro-nano structure on the surface, with Ra of 0.037 and RMS of 1.46 μm.

[0070] 2) The surface structure of the template is replicated using polydimethylsiloxane (PDMS) to form a substrate with micro- and nano-structures.

[0071] 3) Prepare a PVDF solution using N,N-dimethylacetamide as the organic solvent; the solution concentration is 20 mg / mL. Apply the PVDF solution to the surface of a PDMS substrate, evaporate and crystallize at 130°C, then peel off the substrate. The resulting PVDF piezoelectric film has a thickness of 10 μm.

[0072] Comparative Example 1:

[0073] This comparative example provides a method for preparing a polyvinylidene fluoride film with a smooth surface, specifically including the following steps:

[0074] 1) Take a flat silicon wafer as the substrate. The Ra and RMS of the silicon wafer are 0.00009 and 0.0037μm, respectively.

[0075] 2) Prepare a PVDF solution using dimethyl sulfoxide as the organic solvent; the solution concentration is 20 mg / mL. Apply the PVDF solution to the surface of a silicon wafer substrate, evaporate and crystallize at 130°C, then peel off the substrate. The resulting PVDF piezoelectric film has a thickness of 10 μm.

[0076] Results analysis:

[0077] To verify the piezoelectric properties of the PVDF films prepared by the method of the present invention, a comparative study was conducted on the piezoelectric properties of the PVDF films prepared in Examples 1-5, the PVDF film prepared in Comparative Example 1, and commercially available PVDF-based piezoelectric films.

[0078] I purchased a piece of commercial PVDF-based piezoelectric film from PolyK, Inc. in the United States. Its thickness is 28 μm, and the piezoelectric coefficient d is specified in the instruction manual. 33 The value is -20 to -35 pC / N. Utilizing the SA1303A model from Shiao Technology Co., Ltd. 33 Its piezoelectric coefficient d was measured by a quasi-static instrument 33 The value is -21.9 pC / N, which is within the range specified in the instruction manual.

[0079] The PVDF films prepared using Examples 1-5 had an average thickness of 10 μm. The films were then analyzed using a d-type membrane (model SA1303A) from Shiao Technology Co., Ltd. 33 Its piezoelectric coefficient d was measured by a quasi-static instrument 33 The value ranges from -14.6 to 22.1 pC / N (specific details are as follows). Figure 1 As shown in the figure, the specific values ​​are related to Ra and RMS.

[0080] The PVDF film prepared using Comparative Example 1 had an average thickness of 10 μm. The film was then processed using a d-type membrane (model SA1303A) from Shiao Technology Co., Ltd. 33 Its piezoelectric coefficient d was measured by a quasi-static instrument 33 It is -0.9pC / N.

[0081] Figure 1 The piezoelectric coefficient d of the PVDF films prepared in Examples 1-5 and Comparative Example 1 and the commercial PVDF-based piezoelectric film. 33 Comparison chart. It can be seen that a piezoelectric film can be prepared by forming a certain roughness on the surface of the PVDF film. When Ra and RMS are 0.037 and 1.46 μm respectively (Example 3), the piezoelectric coefficient d of the PVDF film is... 33 The piezoelectric coefficient d of commercially available PVDF-based piezoelectric films 33 quite.

[0082] To further verify the temperature stability and piezoelectric performance of the PVDF piezoelectric thin film sensor prepared by the method of the present invention, a comparative study was conducted on the PVDF piezoelectric thin film sensor prepared by the method of the present invention and a commercially available PVDF-based piezoelectric thin film sensor.

[0083] The PVDF piezoelectric film prepared in Example 3, with a thickness of approximately 10 μm and an area of ​​2 cm × 2 cm, was placed on a hot plate after a silver metal electrode was deposited on its surface. The temperature of the hot plate was set to room temperature, 30°C, 60°C, 90°C, 120°C, 150°C, and 170°C. Figure 2 The output voltage of the PVDF piezoelectric film sensor is shown when a periodic pressure of 85 kPa is applied. It can be seen that the output voltage of the PVDF piezoelectric film sensor remains essentially constant within a temperature range from room temperature to 170°C, and does not drift with temperature changes. The operating temperature can reach 170°C.

[0084] A commercially available PVDF-based piezoelectric film, 28 μm thick and 2 cm × 2 cm in area, was purchased from PolyK Corporation in the United States. After depositing silver metal electrodes on its surface, it was placed on a hot plate with the temperature of the hot plate set to room temperature, 30°C, 60°C, 90°C, 120°C, 150°C, and 170°C. Figure 3 The output voltage of a commercially available PVDF-based piezoelectric thin-film sensor is shown when a periodic pressure of 85 kPa is applied. It can be seen that the output voltage of the PVDF-based piezoelectric thin-film sensor increases as the temperature changes from room temperature to approximately 60°C. However, when the temperature further increases to approximately 150°C, the output voltage decreases. When the temperature rises to approximately 170°C, the PVDF-based piezoelectric thin-film sensor completely loses its piezoelectric properties.

[0085] Figure 4 This is a comparison of the temperature stability of the PVDF piezoelectric thin film sensor prepared using Example 3 of the present invention and a commercially available PVDF-based piezoelectric thin film sensor. It can be seen that the PVDF piezoelectric thin film sensor prepared using Example 3 of the present invention exhibits extremely high temperature stability.

[0086] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A polyvinylidene fluoride piezoelectric film, characterized in that, The polyvinylidene fluoride piezoelectric film is made of polyvinylidene fluoride homopolymer. The surface of the polyvinylidene fluoride piezoelectric film has roughness, and the profile arithmetic mean deviation of the roughness is 0.03-0.04, and the root mean square is 1.4-2 μm. The method for preparing the polyvinylidene fluoride piezoelectric film includes the following steps: S1: A roughness is formed by preparing densely distributed micro-nano structures on the surface of a substrate through template transfer. S2: Coat the surface of the substrate obtained in step S1 with a polyvinylidene fluoride homopolymer melt or solution; S3: After the polyvinylidene fluoride homopolymer crystallizes, the substrate is peeled off to obtain the polyvinylidene fluoride piezoelectric film.

2. The polyvinylidene fluoride piezoelectric film as described in claim 1, characterized in that, The thickness of the polyvinylidene fluoride piezoelectric film is greater than the root mean square roughness.

3. The polyvinylidene fluoride piezoelectric film as described in claim 1, characterized in that, The substrate is insoluble in the solvent of the polyvinylidene fluoride homopolymer solution.

4. The polyvinylidene fluoride piezoelectric film as described in claim 1 or 3, characterized in that, The substrate is a metallic material or an organic polymer material.

5. The polyvinylidene fluoride piezoelectric film as described in claim 4, characterized in that, The metallic material is selected from gold, silver, copper, platinum, aluminum, or stainless steel; the organic polymer material is selected from polydimethylsiloxane, polytetrafluoroethylene, polysulfone, or polyurethane.

6. The polyvinylidene fluoride piezoelectric film as described in claim 1, characterized in that, The substrate is selected from glass or silicon wafer.

7. The polyvinylidene fluoride piezoelectric film as described in claim 1, characterized in that, The concentration of the polyvinylidene fluoride homopolymer solution is 5-20 wt%.

8. The polyvinylidene fluoride piezoelectric film as described in claim 1 or 7, characterized in that, The solvent in the polyvinylidene fluoride homopolymer solution is selected from one or more of dimethyl sulfoxide, trimethyl phosphate, methyl ethyl ketone, N-methylpyrrolidone, acetone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, and triethyl phosphate.

9. A sensor, characterized in that, It includes the polyvinylidene fluoride piezoelectric film according to any one of claims 1-8, and the electrode formed on the surface of the polyvinylidene fluoride piezoelectric film.

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