Three-dimensional porous carbon nano piezoelectric material and application thereof in preparation of tactile sensor

Abstract

This invention discloses a method for preparing a three-dimensional porous carbon nanopiezoelectric material, comprising the following steps: (1) mixing an aromatic compound containing both nitro and amino groups with concentrated sulfuric acid at high temperature and heating to a molten state; (2) after becoming molten, continuing to heat the mixture a second time to rapidly expand the molten liquid to form carbon foam; (3) using a vacuum filtration method to repeatedly wash the obtained porous carbon material with water and ethanol until the washing liquid is neutral, and drying it after washing to obtain the three-dimensional porous carbon nanopiezoelectric material. This invention also discloses the application of the above-mentioned three-dimensional porous carbon nanopiezoelectric material in the preparation of flexible piezoelectric devices, specifically: the flexible piezoelectric device uses a PDMS-modified three-dimensional porous carbon nanopiezoelectric composite material as the central layer, with metal electrode layers adhered above and below the central layer, and the flexible piezoelectric device is encapsulated with a flexible insulating film; the piezoelectric composite material uses a three-dimensional porous carbon material as the piezoelectric material, with PDMS filling the pores of the porous carbon material, and PDMS serving as the supporting structure of the three-dimensional carbon skeleton.

Description

Technical Field

[0001] This invention relates to a method for preparing a three-dimensional porous carbon nanopiezoelectric material, and also to the application of the above-mentioned piezoelectric material in the preparation of flexible piezoelectric devices. Background Technology

[0002] Piezoelectric materials are functional materials that enable the conversion between mechanical energy and electrical energy. They are a class of electronic materials that are sensitive to electricity, sound, light, and heat, and are widely used in industrial sectors and high-tech fields. Piezoelectric devices composed of piezoelectric materials have many advantages, such as large electromechanical coupling effect, high power density, fast response speed, and compact structure. These characteristics make piezoelectric devices highly favored in nanogenerators and miniaturized sensors.

[0003] The most widely used traditional piezoelectric materials are inorganic piezoelectric materials, including inorganic ceramics and inorganic crystals. These materials possess high mechanical strength and a high piezoelectric coefficient (d-value), and have already found practical applications in fields such as ultrasonic transducers and sensors. However, inorganic piezoelectric ceramics and crystals also suffer from drawbacks such as high dielectric loss, poor toughness, and difficulty in processing. After high-temperature sintering, they are difficult to process using simple methods. Furthermore, the most widely used lead-containing ceramic (PZT) is prone to lead volatilization during use, posing significant harm to the environment and human health. Organic piezoelectric materials, represented by polyvinylidene fluoride (PVDF) films, have seen rapid development in recent years. They are lightweight and flexible, but their weaknesses include deformation at high temperatures, poor chemical stability, and the requirement for high polarization voltage. These existing characteristics limit the development of small, flexible tactile sensors that possess good flexibility, lightweight properties, high chemical stability, and excellent piezoelectric performance. Summary of the Invention

[0004] Purpose of the Invention: The purpose of this invention is to provide a method for preparing three-dimensional porous carbon nanopiezoelectric materials. The piezoelectric materials prepared by this method have a three-dimensional structure and are characterized by good flexibility, lightweight, chemical stability, and a high piezoelectric coefficient d-value. Another purpose of this invention is to provide the application of the above-mentioned piezoelectric materials in the preparation of flexible piezoelectric devices, which can achieve good piezoelectric performance even with extremely low piezoelectric material content.

[0005] Technical solution: The preparation method of the three-dimensional porous carbon nanopiezoelectric material of the present invention includes the following steps:

[0006] (1) Mix an aromatic compound containing both nitro and amino groups with concentrated sulfuric acid at high temperature and heat until it melts;

[0007] (2) After becoming molten, the temperature is raised again to cause the molten liquid to expand rapidly and form carbon foam;

[0008] (3) The porous carbon material obtained by vacuum filtration is repeatedly washed with water and ethanol until the washing liquid is neutral. After washing, it is dried to obtain three-dimensional porous carbon nanopiezoelectric material.

[0009] In step (1), the aromatic compound containing both nitro and amino groups is one of o-nitroaniline, m-nitroaniline, p-nitroaniline, or 2,6-difluoro-4-p-nitroaniline, preferably 2,6-difluoro-4-p-nitroaniline. Introducing highly electronegative F atoms into porous carbon materials increases the asymmetry of the molecular center, thereby increasing the piezoelectric effect of polar molecules.

[0010] In step (1), the mass ratio of the aromatic compound containing both nitro and amino groups to concentrated sulfuric acid is 0.8–1.5:1; preferably 1.1:1. At this mass ratio, the resulting porous carbon material has a large volume and good elasticity (toughness).

[0011] In step (1), the temperature at which the material is heated to the molten state is 190℃~210℃.

[0012] In step (2), the heating temperature for the second heating is 210℃~500℃, and the heating rate is 5℃ / s.

[0013] The application of the above-mentioned three-dimensional porous carbon nanopiezoelectric material in the preparation of flexible piezoelectric devices is as follows: the flexible piezoelectric device uses a three-dimensional porous carbon nanopiezoelectric composite material modified with PDMS (polydimethylsiloxane) as the central layer, and metal electrode layers are adhered above and below the central layer. The flexible piezoelectric device is encapsulated with a flexible insulating film.

[0014] The piezoelectric composite material uses three-dimensional porous carbon material as the piezoelectric material, and PDMS is filled in the pores of the porous carbon material, with PDMS serving as the supporting structure of the three-dimensional carbon skeleton.

[0015] The flexible piezoelectric device is fabricated using the following method, including the following steps:

[0016] (1) Add anhydrous ethanol to the porous carbon material, ultrasonically crush it, vacuum dry it to remove the anhydrous ethanol, then add PDMS liquid component A to it, stir it thoroughly to disperse the porous carbon material evenly; add PDMS curing agent (PDMS component B) to it, stir it thoroughly, and spin coat the uncured composite material onto the polytetrafluoroethylene mold using a spin coater. After curing at high temperature, a composite piezoelectric film is obtained.

[0017] (2) Positive and negative electrodes are respectively set on the upper and lower surfaces of the composite piezoelectric film, and then a flexible insulating film is used for insulating encapsulation; wherein the copper wires connected to the positive and negative electrodes extend out of the flexible insulating film and are electrically connected to the external device.

[0018] In step (1), the amount of porous carbon material added is 1% to 5% of the mass of PDMS; preferably 3%. At this time, the piezoelectric device prepared by the composite material has the best toughness and piezoelectric signal, and the output voltage can reach 2V and the output current is 10nA. When the content of porous carbon material is 1wt.% to 3wt.%, the output voltage signal converted under pressure increases significantly with the increase of the content of porous carbon material. After reaching 3wt.%, the influence of the content on the output voltage weakens and the growth trend tends to be flat.

[0019] In step (1), the thickness of the composite piezoelectric film is 0.1 mm to 0.5 mm.

[0020] The composite piezoelectric thin film underwent polarization treatment; an oil bath polarization method was used, with an oil bath temperature of 60–65℃; an applied voltage of 2kV–10kV was applied, and the polarization time was 3600s; the polarization direction was the normal to the thin film plane, and sufficient polarization was achieved when the polarization time was 1h; d 33 A quasi-static piezoelectric measuring instrument is used to measure the piezoelectric coefficient of a polarized thin film. Polarizing a composite piezoelectric thin film can induce an orientation in its discharge, thereby improving its piezoelectric properties.

[0021] In step (3), the positive and negative electrode materials are copper film, aluminum film or curable flexible silver paste, and the flexible insulating film is PI film or PET film.

[0022] The present invention uses a composite material obtained by modifying the carbon material with a flexible polymer polydimethylsiloxane to prepare a small flexible tactile sensor. The composite material can output a sensitive and stable electrical signal when the carbon material content is 3 wt.%, and can measure slight mechanical changes such as light touch of human fingers and pulse.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention can prepare three-dimensional piezoelectric materials through a simple and efficient method. The three-dimensional material has a more complex three-dimensional microstructure. The non-centrosymmetric basic structure arranged in a certain order along the three-dimensional space can obtain more vibration modes, so that the prepared three-dimensional carbon piezoelectric material has good lightweight, chemical stability and a piezoelectric coefficient d value of 46.8pC / N; (2) The flexible piezoelectric device prepared by combining the three-dimensional porous carbon material prepared by the present invention with PDMS can have excellent piezoelectric effect with only 3wt.% three-dimensional porous carbon material and without polarization. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope (SEM) image of the porous carbon piezoelectric material prepared in Example 1;

[0025] Figure 2The Raman spectrum of the porous carbon piezoelectric material prepared in Example 1;

[0026] Figure 3 XRD pattern of the porous carbon piezoelectric material prepared in Example 1;

[0027] Figure 4 A schematic diagram illustrating the use of the porous carbon piezoelectric material prepared in Example 1 for fabricating a tactile sensor;

[0028] Figure 5 Comparison of bending signals in different directions when the porous carbon piezoelectric material prepared in Example 1 is used to prepare a tactile sensor;

[0029] Figure 6 A comparison of the output voltages of the porous carbon piezoelectric material prepared in Example 1 when it is used to prepare a tactile sensor with different content values. Detailed Implementation

[0030] Example 1

[0031] The method for preparing three-dimensional porous carbon nanopiezoelectric materials of the present invention includes the following steps:

[0032] (1) Using a crucible as a reaction vessel, first add 0.5g of 2,6-difluoro-4-p-nitroaniline that has been spread out, and then add 0.45g of concentrated sulfuric acid (98% by mass). The mass ratio of 2,6-difluoro-4-p-nitroaniline to concentrated sulfuric acid is approximately 1.1:1. Place the crucible in the center of an electric heating table, heat it to 200°C, and observe that the mixture in the crucible has completely melted before stirring.

[0033] (2) The reactants are heated a second time. The temperature of the hot plate is adjusted to 500℃ within 1 minute. The molten material expands rapidly when the temperature reaches 500℃, and its volume expands to 80 times that of the raw material within 5 seconds, thus obtaining a porous carbon piezoelectric material, such as... Figure 1 The microstructure shown was analyzed. After washing and drying, 0.18 g of powdered piezoelectric material was obtained, named F-pGN. The piezoelectric coefficient d was measured using a static piezoelectric coefficient tester. 33 It is 46.8 pC / N.

[0034] Example 2

[0035] The method for preparing three-dimensional porous carbon nanopiezoelectric materials of the present invention includes the following steps:

[0036] (1) Using a crucible as a reaction vessel, first add 0.5g of 2,6-difluoro-4-p-nitroaniline, then add 0.625g of concentrated sulfuric acid (98% by mass). The mass ratio of 2,6-difluoro-4-p-nitroaniline to concentrated sulfuric acid is approximately 0.8:1. Place the crucible in the center of an electric heating table, heat it to 200℃, and observe that the mixture in the crucible has completely melted before stirring.

[0037] (2) The reactants are heated a second time, and the temperature of the hot plate is adjusted to 430°C within 46 seconds. The molten material expands rapidly when the temperature reaches 430°C, and its volume expands to 50 times that of the raw material within 5 seconds, thus obtaining porous carbon piezoelectric material. After washing and drying, 0.16g of powdered piezoelectric material is obtained.

[0038] Example 3

[0039] The method for preparing three-dimensional porous carbon nanopiezoelectric materials of the present invention includes the following steps:

[0040] (1) Using a crucible as a reaction vessel, first add 0.5g of 2,6-difluoro-4-p-nitroaniline, then add 0.333g of concentrated sulfuric acid (98% mass concentration). The mass ratio of 2,6-difluoro-4-p-nitroaniline to concentrated sulfuric acid is approximately 1.5:1. Place the crucible in the center of an electric heating table, heat it to 200℃, and observe that the mixture in the crucible has completely melted before stirring.

[0041] (2) The reactants are heated a second time, and the temperature of the hot plate is adjusted to 500°C within 60 seconds. The molten material expands rapidly when the temperature reaches 500°C, and its volume expands to 60 times that of the raw material within 30 seconds, thus obtaining porous carbon piezoelectric material. After washing and drying, 0.15g of powdered piezoelectric material is obtained.

[0042] Example 4

[0043] The present invention provides a method for preparing three-dimensional porous carbon nanopiezoelectric materials without introducing F atoms, comprising the following steps:

[0044] (1) Using a crucible as a reaction vessel, first add 0.5g of p-nitroaniline that has been spread out, and then add 0.57g of concentrated sulfuric acid (98% mass concentration). The mass ratio of p-nitroaniline to concentrated sulfuric acid is about 1:1.15. Place the crucible in the center of an electric heating table, heat it to 200℃, and stir it after observing that the mixture in the crucible has completely melted.

[0045] (2) The reactants were heated a second time. The temperature of the hot plate was adjusted to 500℃ within 1 minute. The molten material expanded rapidly when the temperature reached 500℃, and its volume expanded to 120 times that of the raw material within 5 seconds, thus obtaining a porous carbon piezoelectric material, such as... Figure 1The microstructure shown was analyzed. After washing and drying, 0.26 g of powdered piezoelectric material was obtained, named pGN. The piezoelectric coefficient d of pure pGN was measured using a static piezoelectric coefficient tester. 33 With a ratio of 32.5 pC / N, carbon materials with piezoelectric properties can be obtained without introducing highly electronegative F atoms.

[0046] Example 5

[0047] The three-dimensional porous carbon nanopiezoelectric material prepared in Example 1 was used to fabricate a flexible tactile sensor for the detection of minute touches.

[0048] (1) Add 1 mL of anhydrous ethanol to a glass bottle containing 0.03 g of F-pGN and sonicate for 30 s; add 1 g of PDMS liquid component A and stir magnetically for 30 minutes to disperse F-pGN evenly; dry in a vacuum oven at 50 °C for 3 h to remove solvent, add PDMS curing agent (PDMS component B) and stir on a magnetic stirrer for 30 minutes; spin coat the uncured composite material onto a polytetrafluoroethylene mold at 600 rpm using a spin coater, and cure in an oven at 80 °C for 1 h to obtain a piezoelectric film (F-pGN / PDMS film) with an F-pGN content of 3 wt.% and a size of 20*30*0.5 mm;

[0049] (2) The F-pGN / PDMS thin film was polarized using a high-voltage polarization device. The oil bath temperature was set to 60℃, a voltage of 5kV was applied in the direction perpendicular to the plane of the thin film, and the polarization time was set to 3600s.

[0050] (3) Positive and negative electrodes were respectively placed on the upper and lower surfaces of the thin film. The positive electrode was a silver nanowire, and the negative electrode was an aluminum foil. The positive and negative electrode materials were adhered to the surface of the thin film using silver paste. Copper wires were connected to each electrode using metal epoxy resin adhesive. The outermost layer was encapsulated with a flexible insulating film. The prepared device was tested on a KIETHLEY multimeter, and the open-circuit voltage signal of the thin film output was measured. See [link to relevant documentation]. Figure 6 .

[0051] Piezoelectric films with F-pGN contents of 0 wt.%, 1 wt.%, and 5 wt.%, and dimensions of 20*30*0.5 mm, were prepared using the same method as in Example 5. Piezoelectric devices were then fabricated based on these films with F-pGN contents of 0 wt.%, 1 wt.%, and 5 wt.%, using the same method as in Example 5. The fabricated devices were tested using a Kiethley multimeter, and the open-circuit voltage signal output by the film was measured. Figure 6The specific peak output signal values ​​are shown in Table 1. Films with an F-pGN content of 3 wt.% exhibit better flexibility, and their output voltage shows only a slight difference compared to films with higher F-pGN content. Overall, films with 3 wt.% F-pGN content are preferred. Testing revealed that the piezoelectric coefficient d of the piezoelectric film with 3 wt.% F-pGN content is... 33 It is 13.9 pC / N.

[0052] Example 6

[0053] F-pGN / PDMS films were prepared from the three-dimensional porous carbon nanoparticle piezoelectric material obtained in Example 1: 1 mL of anhydrous ethanol was added to a glass bottle containing 0.03 g of F-pGN, and the mixture was ultrasonically broken up for 30 s; 1 g of PDMS liquid component A was added, and the mixture was magnetically stirred for 30 minutes to disperse the F-pGN evenly; the solvent was removed by drying in a vacuum oven at 50 °C for 3 h; PDMS curing agent (PDMS component B) was added, and the mixture was stirred on a magnetic stirrer for 30 minutes; the uncured composite material was spin-coated onto a polytetrafluoroethylene mold at 600 rpm using a spin coater, and then cured in an oven at 80 °C for 1 h to obtain a piezoelectric film (F-pGN / PDMS film) with an F-pGN content of 3 wt.% and dimensions of 20*30*0.5 mm.

[0054] Compared to Example 5, Example 6 is an unpolarized F-pGN / PDMS thin film. The piezoelectric coefficient d of the unpolarized F-pGN / PDMS thin film is... 33 It is 10.7 pC / N.

[0055] Table 1: Peak output voltage of piezoelectric devices based on various F-pGN / PDMS films

[0056]

Claims

1. The application of a three-dimensional porous carbon material as a piezoelectric material in the fabrication of flexible piezoelectric devices, characterized in that, Specifically, the flexible piezoelectric device uses a three-dimensional porous carbon nanopiezoelectric composite material modified with PDMS as the central layer, and metal electrode layers are adhered above and below the central layer. The flexible piezoelectric device is encapsulated with a flexible insulating film. The above-mentioned flexible piezoelectric device is fabricated using the following method, with the specific steps as follows: (1) Add anhydrous ethanol to the porous carbon material, ultrasonically crush it, vacuum dry it to remove the solvent, then add PDMS liquid component A to it, stir it thoroughly to make the porous carbon material disperse evenly; add PDMS curing agent to it, stir it thoroughly, and spin coat the uncured composite material onto the polytetrafluoroethylene mold with a spin coater, and cure it at high temperature to obtain a composite piezoelectric film; wherein, the amount of porous carbon material added is 3% of the mass of PDMS; the composite piezoelectric film is polarized; the oil bath polarization method is used, wherein the oil bath temperature is 60~65℃; the applied voltage is 2kV~10kV, and the polarization time is 3600s; (2) Positive and negative electrodes are respectively set on the upper and lower surfaces of the composite piezoelectric film, and then a flexible insulating film is used for insulating encapsulation; wherein the copper wires connected to the positive and negative electrodes extend out of the flexible insulating film and are electrically connected to the external device. The three-dimensional porous carbon material was prepared by the following method, with the specific steps as follows: (1.1) An aromatic compound containing both nitro and amino groups is mixed with concentrated sulfuric acid and heated to a molten state at high temperature; the aromatic compound containing both nitro and amino groups is 2,6-difluoro-4-p-nitroaniline; (1.2) After becoming molten, the temperature is raised again to cause the molten liquid to expand rapidly and form carbon foam; (1.3) Vacuum filtration method: The obtained porous carbon material is repeatedly washed with water and ethanol until the washing liquid is neutral. After washing, it is dried to obtain three-dimensional porous carbon material.

2. The application of the three-dimensional porous carbon material as a piezoelectric material in the preparation of flexible piezoelectric devices according to claim 1, in step (1.1), the mass ratio of the aromatic compound containing both nitro and amino groups to concentrated sulfuric acid is 0.8~1.5:

1.

3. The application of the three-dimensional porous carbon material as a piezoelectric material in the preparation of flexible piezoelectric devices according to claim 1, wherein in step (1.1), the temperature for heating to the molten state is 190℃~210℃.

4. The application of the three-dimensional porous carbon material as a piezoelectric material in the preparation of flexible piezoelectric devices according to claim 1, in step (1.2), the heating temperature of the secondary heating is 210℃~500℃, and the heating rate is 5℃ / s.

5. The application of the three-dimensional porous carbon material according to claim 1 as a piezoelectric material in the fabrication of flexible piezoelectric devices, characterized in that: The piezoelectric composite material uses three-dimensional porous carbon material as the piezoelectric material, and PDMS is filled in the pores of the porous carbon material. PDMS serves as the supporting structure of the three-dimensional carbon skeleton.

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