A piezoelectric composite material with piezoelectric particles oriented and arranged at a high filling amount and a preparation method thereof

Abstract

A piezoelectric composite material with oriented arrangement of piezoelectric particles at high filling amounts and a preparation method thereof belong to the field of flexible piezoelectric composite materials. Using BCZT@Cu heterojunction powder as the piezoelectric phase and PDMS as the matrix, a BCZT@Cu / PDMS piezoelectric composite material with a microstructure of oriented arrangement of piezoelectric particles at high filling amounts is prepared by combining dielectrophoresis technology. Due to the additional dielectrophoretic force provided by the attached Cu nanoparticles, the BCZT@Cu powder can still achieve good oriented arrangement in the PDMS matrix at a higher filling amount. Thus, while retaining the good flexibility of the piezoelectric composite material, its 33 g and sensitivity are further improved.

Description

Technical Field

[0001] The present invention belongs to the field of flexible piezoelectric composites, and particularly relates to a BCZT@Cu / PDMS composite material in which piezoelectric particles can still maintain an oriented arrangement microstructure at a high filling amount and a preparation method thereof. Background Art

[0002] With the rapid development of wearable electronic devices and bio-integrated devices, various sports monitoring bracelets, watches, etc. applied to human health monitoring have emerged one after another, providing assistance for preventive monitoring and early diagnosis confirmation of diseases in a non-invasive and convenient manner. At present, most of the commercial devices on the market for obtaining human motion information are based on optical or electromagnetic systems, accelerometers, and inertial sensors. However, due to the inherent flexibility and ductility of biological tissues, these sensing devices with rigid structures cannot closely fit the human skin or joint parts to ensure the accuracy of data; on the other hand, most of these rigid-structured electronic devices are powered by batteries and need to be charged frequently, which is neither comfortable nor convenient in practical applications. In summary, developing a self-powered flexible stress / strain sensor is a research topic with important scientific value and social and economic benefits.

[0003] The flexible piezoelectric composite material based on dielectrophoresis technology is prepared by compounding piezoelectric particles with a polymer. Under the action of dielectrophoretic force, the internal piezoelectric particles are oriented along the direction of the applied force, and can efficiently convert the received stress signal into an electrical signal, with a higher piezoelectric voltage coefficient (g 33 ), and has important application prospects in the field of flexible sensing. However, with the further increase of the filling amount of piezoelectric particles, the effect of this oriented arrangement weakens, and its g 33 value also decreases accordingly.

[0004] In the present invention, we synthesized BCZT@Cu heterojunction powder by attaching Cu nanoparticles to the surface of barium calcium zirconate titanate (BCZT) powder, and used dielectrophoresis technology to compound it with polydimethylsiloxane (PDMS) to prepare a BCZT@Cu / PDMS piezoelectric composite material in which piezoelectric particles still have an oriented arrangement characteristic at a high filling amount. The modified Cu nanoparticles have excellent electrical conductivity and the ability to distort the electric field, and will provide an additional dielectrophoretic force to help BCZT@Cu maintain an oriented arrangement microstructure at a higher filling amount, so it has an ultra-high g 33 (720×10 -3 Vm / N), which is about 12 times that of the g 33 of the BCZT / PDMS piezoelectric composite material at the same filling amount; in addition, this material also has an ultra-high sensitivity (2.8V / kPa) and a Young's modulus (1.12MPa) similar to that of human skin. Summary of the Invention

[0005] The present invention provides a flexible piezoelectric composite material in which piezoelectric particles can still maintain an oriented arrangement microstructure at a high filling amount and a preparation method thereof. Using BCZT@Cu heterojunction powder as the piezoelectric phase and PDMS as the matrix, a BCZT@Cu / PDMS piezoelectric composite material with an oriented arrangement microstructure at a high filling amount is prepared by combining dielectrophoresis technology. Due to the additional dielectrophoretic force provided by the attached Cu nanoparticles, the BCZT@Cu powder can still achieve good oriented arrangement in the PDMS matrix at a higher filling amount. Thus, while retaining the good flexibility of the piezoelectric composite material, its 33 g and

[0006] A piezoelectric composite material in which piezoelectric particles can still maintain an oriented arrangement microstructure at a high filling amount, characterized in that the composite material is formed by attaching Cu nanoparticles to the surface of BCZT piezoelectric particles to form BCZT@Cu as the piezoelectric phase, using PDMS as the matrix, and using dielectrophoresis technology to compound BCZT@Cu with polydimethylsiloxane (PDMS) and promoting the formation of an oriented arrangement microstructure during the dielectrophoresis process.

[0007] The chemical formula of the above piezoelectric composite material: xBCZT@Cu / PDMS, where the value of x is 0–60 vol% and not 0, preferably 1–60 vol%, and x refers to the content of Cu / PDMS.

[0008] The particle size range of BCZT piezoelectric particles is 0.1–20 μm, preferably the average particle size is 0.95 μm; the diameter range of Cu nanoparticles is 0.01–10 μm, preferably the average particle size is 120 nm; among them, the volume ratio of Cu:BCZT is preferably 4:100.

[0009] The preparation method of the above flexible composite material is as follows:

[0010] 1) Use the molten salt method to prepare BCZT particles, and attach Cu nanoparticles to its surface by the liquid-phase reduction method to synthesize BCZT@Cu heterojunction powder;

[0011] 2) Weigh BCZT powder according to the chemical formula xBCZT@Cu / PDMS;

[0012] 3) In order to reduce the viscosity of the slurry, first mix BCZT@Cu, PDMS and a small amount of dispersant (preferably n-hexane) evenly to obtain slurry A, and then mix slurry A with a curing agent evenly to obtain slurry B. The mass ratio of PDMS:curing agent is preferably 10:1.

[0013] 4) After mixing evenly, in order to remove the dispersant and tiny air bubbles in Slurry B, place Slurry B into a vacuum device and slowly reduce the pressure in the chamber to 3–4 Pa, lasting for at least 15 min;

[0014] 5) Slowly pour the vacuum-treated Slurry B onto a metal electrode plate. There is a clamping plate mold frame on the metal electrode plate, so that the slurry stands and spreads flatly in the clamping plate mold frame, and fills the mold to form a film. Use another metal electrode plate parallel to the metal electrode plate to clamp and fix the clamping plate mold frame; The surface of the other metal electrode plate is parallel to and in contact with the slurry film, and finally a structure of metal electrode plate / film / metal electrode plate is formed; In order to prevent the slurry from being broken down in the alternating electric field, a 0.05-mm-thick polyimide tape is pasted on each surface of the two metal electrode plates that contact the film;

[0015] 6) Connect the above two metal electrode plates to an AC voltage source through wires for dielectrophoresis treatment;

[0016] 7) To ensure that the sample is completely cured and the internal structure is maintained, place it in an oven at 70 °C for heat preservation for 12 h, then take it out of the oven, peel off the metal plate and the mold frame, and a flaky sample can be obtained.

[0017] 8) Place the sample in silicone oil and apply a DC electric field for polarization. The polarization voltage is set to 150 kV / cm, the polarization temperature is 60 °C, and the polarization time is 5 h.

[0018] Further parameters for the dielectrophoresis treatment in step 6): The dielectrophoresis AC electric field value is 1–10 kV / cm, the AC electric field frequency is 1–800 Hz, and the AC electric field duration is 0.5–24 h.

[0019] The composite material of the present invention is used for flexible stress / strain sensing.

[0020] The present invention has the following main advantages compared with the prior art:

[0021] First, metal nanoparticles are modified on the surface of the piezoelectric particles, thus significantly enhancing the dielectrophoresis effect and enabling the piezoelectric composite material to still maintain the microscopic morphology of oriented arrangement at high filling amounts;

[0022] Second, since the electromechanical conversion performance mainly comes from the piezoelectric phase and its microscopic distribution, the piezoelectric composite material with oriented arrangement at high filling amounts can further improve the electromechanical conversion performance of the piezoelectric composite material;

[0023] Third, the BCZT@Cu / PDMS piezoelectric composite material in the present invention has a Young's modulus (1.12 MPa) similar to that of human skin, which is difficult to achieve for 3-3 type or 2-2 type piezoelectric composite materials.

[0024] Therefore, in the present invention, by modifying the surface of piezoelectric particles with metal nanoparticles, the dielectrophoresis effect is enhanced, enabling the piezoelectric composite material to maintain a microstructure with a good orientation distribution even at a higher filling amount, thereby significantly improving its 33 g value; in addition, this material has a Young's modulus similar to that of human skin, can closely adhere to the skin surface, making the test data more accurate and improving the wearing comfort. Brief Description of the Drawings

[0025] Figure 1 Scanning electron microscope photograph of the BCZT@Cu heterojunction powder used in the present invention.

[0026] Figure 2 Schematic diagram of pouring the slurry into the dielectrophoresis mold.

[0027] Figure 3 (a) Scanning electron microscope photograph of the dielectrophoresis-treated BCZT@Cu / PDMS flexible piezoelectric composite material sample, where the filling amount of BCZT@Cu powder is 6–25 vol%; three-dimensional X-ray microscope test results of the (b) BCZT@Cu / PDMS composite material and (c) BCZT / PDMS composite material samples treated by dielectrophoresis.

[0028] Figure 4 (a) Stress / strain curves and (b) Young's moduli of pure PDMS, randomly and oriented BCZT@Cu / PDMS composite materials.

[0029] Figure 5 Piezoelectric voltage constant (d 33 ) of BCZT@Cu / PDMS composite materials with different filling amounts. Detailed Embodiments

[0030] The following further clarifies the substantial features and remarkable advantages of the present invention through examples. It should be noted that the present invention is by no means limited to the stated examples.

[0031] Prepare BCZT particles by the molten salt method, and use the liquid-phase reduction method to attach Cu nanoparticles on its surface to synthesize BCZT@Cu heterojunction powder as the piezoelectric phase. Take PDMS as the matrix, weigh and mix them in a certain volume ratio to obtain a mixed slurry. After removing the bubbles from the mixed slurry, pour it into a template and apply an alternating electric field. Since the attached Cu nanoparticles provide an additional dielectrophoretic force, BCZT@Cu can still maintain a good dielectrophoresis effect at a higher filling ratio, realizing the preparation of a piezoelectric composite material with an orientation distribution at a high filling ratio. After the assembly of electrodes and polarization treatment, the flexible stress / strain sensor can be obtained.

[0032] Example 1:

[0033] 1) Weigh the raw materials according to the chemical formula xBCZT@Cu / PDMS, where x = 6 vol.%;

[0034] 2) Mix the BCZT@Cu powder, dispersant (n - hexane) and PDMS evenly to obtain slurry A, where the mass ratio of the dispersant to PDMS is preferably 1:5;

[0035] 3) Mix slurry A with the curing agent evenly to obtain slurry B, where the mass ratio of the curing agent to PDMS is preferably 1:10;

[0036] 4) After mixing evenly, in order to remove the dispersant and tiny air bubbles in slurry B, put slurry B into a vacuum device, slowly reduce the pressure in the cavity to 3 - 4 Pa, and keep it for 15 min;

[0037] 5) Slowly pour the vacuum - treated slurry B onto the surface of the metal electrode plate and let it stand for 3 min. The thickness of the clamping die frame on the metal electrode is 0.2 mm. After it spreads flat and fills the die, use another metal electrode plate to clamp and fix it, serving as the experimental group. In order to prevent the slurry from being broken down in the alternating electric field, a 0.05 - mm - thick polyimide tape is pasted on each side of the two metal plates that contact the slurry;

[0038] 6) Repeat the above steps to obtain a die with slurry, serving as the control group;

[0039] 7) Connect the two metal electrode plates of the experimental group to an AC voltage source through wires, where the AC electric field value is 20 kV / cm, the AC electric field frequency is 250 Hz, and the AC electric field duration is 6 h; The control group is not subjected to electrophoresis treatment and is left standing for 6 h;

[0040] 8) Put the experimental group and the control group into an oven at 70 °C for heat preservation for 12 h, then take them out of the oven, peel off the metal plates and the die frames, and the sheet - like samples of the experimental group and the control group can be obtained.

[0041] 9) Put the samples of the experimental group and the control group into silicone oil and apply a DC electric field for polarization. The polarization voltage is set to 150 kV / cm, the polarization temperature is 60 °C, and the polarization time is 5 h. Cut the samples into thin slices of 2 cm × 2 cm × 0.02 cm, and paste copper - foil tapes on the surfaces of the samples as electrodes, and a flexible stress / strain sensor is obtained.

[0042] Example 2:

[0043] Weigh the raw materials according to the chemical formula xBCZT@Cu / PDMS, where x = 8 vol.%; Others are the same as in Example 1.

[0044] Example 3:

[0045] Weigh the raw materials according to the chemical formula xBCZT@Cu / PDMS, where x = 10 vol.%; the others are the same as in Example 1.

[0046] Example 4:

[0047] Weigh the raw materials according to the chemical formula xBCZT@Cu / PDMS, where x = 12 vol.%; the others are the same as in Example 1.

[0048] Example 5:

[0049] Weigh the raw materials according to the chemical formula xBCZT@Cu / PDMS, where x = 14 vol.%; the others are the same as in Example 1.

[0050] Example 6:

[0051] Weigh the raw materials according to the chemical formula xBCZT@Cu / PDMS, where x = 16 vol.%; the others are the same as in Example 1.

[0052] Example 7:

[0053] Weigh the raw materials according to the chemical formula xBCZT@Cu / PDMS, where x = 18 vol.%; the others are the same as in Example 1.

[0054] Example 8:

[0055] Weigh the raw materials according to the chemical formula xBCZT@Cu / PDMS, where x = 20 vol.%; the others are the same as in Example 1.

[0056] Example 9:

[0057] Weigh the raw materials according to the chemical formula xBCZT@Cu / PDMS, where x = 25 vol.%; the others are the same as in Example 1.

[0058] Take the flexible stress / strain sensor samples prepared in the experimental groups of Examples 1–9 and the control group, and conduct electromechanical tests through the actuator. The force application method is parallel to the sample thickness direction, the pre-tightening force is 35 kPa, the applied pressure peak-to-peak value is 22 kPa, and the frequency is 100 Hz. The test results obtained are shown in Table 1.

[0059] Table 1 Performance comparison table of the above examples

[0060]

Claims

1. A piezoelectric composite material with piezoelectric particles oriented and arranged at a high filling amount, characterized in that, The composite material is BCZT piezoelectric particles with Cu nanoparticles attached to their surfaces to form BCZT@Cu as the piezoelectric phase, and PDMS as the matrix. The BCZT@Cu and polydimethylsiloxane (PDMS) are compounded using dielectrophoresis technology, and the formation of an oriented microstructure is promoted during the dielectrophoresis process. The chemical composition of the composite material is: xBCZT@Cu / PDMS, where the value of x is 0–60 vol%, and x is not 0.

2. The piezoelectric composite material with piezoelectric particles oriented and arranged at a high filling amount according to claim 1, wherein, The particle size range of BCZT piezoelectric particles is 0.1–20 μm, the diameter range of Cu nanoparticles is 0.01–10 μm, and the volume ratio of the attached Cu particles to BCZT particles ranges from 0.1–20:

100.

3. A piezoelectric composite material with piezoelectric particles oriented and arranged at a high filling amount according to claim 1, characterized in that, The average particle size of BCZT piezoelectric particles is 0.95 μm; the average particle size of Cu nanoparticles is 120 nm.

4. A method for preparing a piezoelectric composite material in which piezoelectric particles are oriented and arranged at a high filling amount according to any one of claims 1 to 3, characterized in that, It includes the following steps: 1) Prepare BCZT particles using the molten salt method, and attach Cu nanoparticles to their surfaces through the liquid phase reduction method to synthesize BCZT@Cu heterojunction powder; 2) Weigh BCZT powder according to the chemical formula xBCZT@Cu / PDMS; 3) To reduce the viscosity of the slurry, first mix BCZT@Cu, PDMS, and a dispersant evenly to obtain slurry A, and then mix slurry A with a curing agent evenly to obtain slurry B; 4) After mixing evenly, to remove the dispersant and tiny air bubbles in slurry B, put slurry B into a vacuum device, slowly reduce the pressure in the chamber to 3–4 Pa, and keep it for at least 15 min; 5) Slowly pour the vacuum-treated slurry B onto a metal electrode plate. There is a clamping plate mold frame on the metal electrode plate, so that the slurry stands still and spreads flat in the clamping plate mold frame, and fill the mold to form a film. Use another metal electrode plate parallel to the metal electrode plate to clamp and fix the clamping plate mold frame; the surface of the other metal electrode plate is parallel to and in contact with the slurry film, and finally a metal electrode plate / film / metal electrode plate structure is formed; to prevent the slurry from being broken down in the alternating electric field, a 0.05-mm-thick polyimide tape is pasted on each surface of the two metal electrode plates in contact with the film; 6) Connect the above two metal electrode plates to an AC voltage source through wires for dielectrophoresis treatment; 7) To ensure that the sample is completely cured and the internal structure is maintained, put it into an oven at 70 °C for heat preservation for 12 h, then take it out of the oven, peel off the metal plate and the mold frame, and a sheet-like sample can be obtained; 8) Put the sample into silicone oil and apply a DC electric field for polarization. The polarization voltage is set to 150 kV / cm, the polarization temperature is 60 °C, and the polarization time is 5 h.

5. The method according to claim 4, characterized in that, In step 3), the dispersant is n-hexane, and the mass ratio of PDMS to the curing agent is 10:

1.

6. The method according to claim 4, characterized in that The parameters of the dielectrophoresis treatment in step 6): the value of the electrophoretic AC electric field is 1–10 kV / cm, the AC electric field frequency is 1–800 Hz, and the AC electric field duration is 0.5–24 h.

7. Use of a piezoelectric composite material with oriented arrangement of piezoelectric particles under high filling amount according to any one of claims 1–3 for flexible stress / strain sensing.

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