Flow polarization process for improving polarization efficiency of ceramic / polymer-based piezoelectric composite material

Abstract

The invention relates to a flow polarization process for improving the polarization efficiency of a ceramic / polymer-based piezoelectric composite material, and belongs to the technical field of flexible piezoelectric composite materials. Piezoelectric nanorods selected by the composite material are consistent in electric dipole orientation under a mesoscale (can be prepared by a molten salt method, a hydrothermal method or an electrostatic spinning method), a thermosetting polymer is used as a matrix (such as polydimethylsiloxane, thermosetting epoxy resin and the like), and polarity orientation of piezoelectric filler in the polymer matrix is regulated and controlled by means of electrophoresis, so that the piezoelectric composite material is obtained. The orientation of the electric dipoles of the material is consistent under the macroscopic scale, the material is firstly polarized and then molded, and the polarization efficiency of the material is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of flexible piezoelectric composite material technology, and relates to a "fluid polarization" process for improving the polarization efficiency of ceramic / polymer-based piezoelectric composite materials. Background Technology

[0002] Ceramic / polymer composite piezoelectric materials combine the piezoelectricity of ceramics with the flexibility of polymers, making them ideal materials for developing next-generation human-machine interface flexible sensors.

[0003] However, there is a severe mismatch in the electrical properties between the ceramic phase and the polymer phase, and commonly used piezoelectric ceramic fillers such as lead zirconate titanate ( Barium calcium zirconate titanate and potassium sodium niobate, among others, exhibit relatively high dielectric constant and low resistivity (ε). r ≈ 1000–4000, ρ = 10 10 -10 12 Ω·cm), while commonly used polymer matrices such as polydimethylsiloxane (PDMS), epoxy resins, and polyimides exhibit relatively low dielectric constant and high resistance (ε). r = 2.5–3.5, ρ = 10 14 -10 17 The high polarization field (Ω·cm) makes it difficult for the applied polarization electric field to effectively act on the ceramic filler. Even after high-temperature, high-field polarization treatment, it is still difficult to fully utilize the piezoelectric properties of the piezoelectric ceramic filler. To address this bottleneck, researchers have attempted to improve the connectivity of the composite material to enhance polarization efficiency by increasing the filler content or constructing ceramic skeletons (such as 1-3, 2-2, or 3-3 types). However, these strategies often come at the cost of sacrificing the mechanical properties of the material, thus limiting the application scope and further industrial development of piezoelectric composite materials and related devices.

[0004] Therefore, developing a new polarization strategy to overcome the limitations of low polarization efficiency on the electromechanical conversion performance of piezoelectric composite materials is a research topic with significant scientific value and socio-economic benefits. Summary of the Invention

[0005] In view of this, in order to solve the problem that the existing technology cannot effectively apply an external polarization electric field to ceramic fillers, and that even after polarization treatment at high temperature and strong electric field, it is still difficult to fully exert the piezoelectric properties of piezoelectric ceramic fillers, the present invention provides a "fluid polarization" process for improving the polarization efficiency of ceramic / polymer-based piezoelectric composite materials. This process changes the traditional preparation sequence of ceramic / polymer piezoelectric composite materials, realizing the material is polarized first and then formed, thus breaking through the limitation of low polarization efficiency on the piezoelectric properties of composite piezoelectric materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A "fluid polarization" process for improving the polarization efficiency of ceramic / polymer-based piezoelectric composites is disclosed. The piezoelectric nanorods selected for this composite material have uniform electric dipole orientation at the mesoscale (which can be prepared by molten salt method, hydrothermal method or electrospinning method). A thermosetting polymer is used as the matrix (e.g. polydimethylsiloxane, thermosetting epoxy resin, etc.). The polar orientation of the piezoelectric ceramic filler in the polymer matrix is ​​controlled by electrophoresis, so that the electric dipoles of the material are uniformly oriented at the macroscale. This achieves pre-polarization followed by molding of the material, which significantly improves the polarization efficiency of the material.

[0008] Furthermore, the electric fields used in electrophoresis are DC and AC electric fields applied sequentially, with field strengths of 0.1–100 kV / cm and durations of 0.1–24 h, and AC field frequencies of 0.1–1000 Hz. By first polarizing the material with an electric field and then forming it, the electric dipoles of the material are oriented from mesoscopic to macroscopic, achieving the effect of polarization of the material in a flowing state.

[0009] Furthermore, the electric field strength of both the DC and AC electric fields is 10 kV / cm, the duration of both electric fields is 0.5 h, and the frequency of the AC electric field is 250 Hz.

[0010] Furthermore, the piezoelectric ceramic filler is one or more of lead zirconate titanate, barium calcium zirconate titanate, or potassium sodium niobate, and the thermosetting polymer is one or more of polydimethylsiloxane, epoxy resin, or polyimide.

[0011] The "fluid polarization" process for improving the polarization efficiency of ceramic / polymer-based piezoelectric composites includes the following steps:

[0012] S1. Weigh the piezoelectric filler and polymer according to the proportion and mix them evenly to obtain the piezoelectric filler-polymer slurry;

[0013] S2. Place the slurry obtained in step S1 into a defoaming device to remove tiny air bubbles from the slurry.

[0014] S3. Slowly inject the slurry obtained in step S2 into the groove consisting of two metal plates and a plastic partition. The two metal plates are connected to a voltage source through wires.

[0015] S4. Apply a DC electric field of 0.1–100 kV / cm for 0.1–24 h and an AC electric field of 0.1–100 kV / cm for 0.1–1000 Hz for 0.1–24 h to the slurry in step S3 using a voltage source.

[0016] S5. To ensure that the slurry is completely cured and to maintain the spatial distribution of the piezoelectric filler in the polymer matrix, the slurry in step S4 is placed in an oven at 70~90℃ and kept at that temperature for 10~15 hours. After that, it is taken out of the oven and the metal electrode plate and plastic separator are peeled off to obtain a sheet sample.

[0017] S6. Plasma treatment is performed on both sides of the sheet sample obtained in step S5, and stretchable silver paste is coated on them. After curing, a flexible piezoelectric composite material sample is obtained.

[0018] Furthermore, the content of S1 piezoelectric filler in the step is 0–60 vol% and not 0, and the morphology of the piezoelectric filler is one-dimensional particles or two-dimensional nanorods / wires with a diameter range of 0.01–10 μm and a length range of 1–100 μm.

[0019] Furthermore, in step S1, the content of the piezoelectric filler is 5–20 vol%, and the piezoelectric filler is a two-dimensional nanorod / wire with an average diameter of 0.5 μm and an average length of 10 μm.

[0020] Furthermore, in step S4, a DC electric field of 10 kV / cm for 30 min and an AC electric field of 10 kV / cm for 250 Hz for 30 min are applied to the slurry in step S3 by a voltage source.

[0021] Flexible piezoelectric composite materials are prepared using the "fluid polarization" process described above, which is used to improve the polarization efficiency of ceramic / polymer-based piezoelectric composite materials.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. The "fluid polarization" process disclosed in this invention for improving the polarization efficiency of ceramic / polymer-based piezoelectric composite materials controls the polar orientation of piezoelectric fillers in the polymer matrix by applying an external electric field when the material is still in an uncured state, i.e., polarization before molding, so that the piezoelectric composite material has good piezoelectric properties after curing.

[0024] 2. The "fluid polarization" process disclosed in this invention for improving the polarization efficiency of ceramic / polymer-based piezoelectric composite materials is effective because the piezoelectric filler and the polymer matrix have vastly different electrical properties, making it difficult for the material to achieve sufficient polarization even after high-temperature and strong electric field polarization treatment. However, based on the "fluid polarization" process, the material can achieve good polarization at room temperature and with a small electric field, thus improving the polarization efficiency.

[0025] 3. The "fluid polarization" process disclosed in this invention for improving the polarization efficiency of ceramic / polymer-based piezoelectric composite materials produces piezoelectric composite materials that, while possessing high piezoelectric properties, also have a Young's modulus (1.12 MPa) similar to that of human skin. This is difficult to achieve with 2-2 or 3-3 type piezoelectric composite materials, providing a feasible technical solution for the development of a new generation of human-machine interaction flexible sensors.

[0026] 4. The "fluid polarization" process disclosed in this invention for improving the polarization efficiency of ceramic / polymer-based piezoelectric composite materials can only control the distribution of internal fillers in materials prepared by AC electrophoresis, and the prepared materials still need to be artificially polarized to acquire piezoelectricity. However, by using DC electrophoresis and AC power, in-situ polarization is achieved, and the materials prepared by this method acquire piezoelectricity upon molding.

[0027] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0029] Figure 1 The "fluid polarization" preparation process is shown in the example.

[0030] Figure 2 The image shows the XRD pattern of the PbTiO3 / PDMS prepared in the examples; Figure 2 (a) XRD pattern of PbTiO3 / PDMS composite material prepared by applying only an alternating current field; Figure 2 (b) XRD patterns of PbTiO3 / PDMS composite materials prepared by applying DC and AC electric fields sequentially;

[0031] Figure 3 The d of PbTiO3 / PDMS prepared in the examples 33 Comparison chart of values ​​and mechanical properties; Figure 3 (a) Preparation of PbTiO3 / PDMS by applying only an AC electric field and by applying a DC electric field followed by an AC electric field sequentially. 33 A comparison chart of values. Figure 3 (b) Comparison of mechanical properties of PbTiO3 / PDMS prepared by applying only an AC electric field and by applying DC and AC electric fields sequentially. Detailed Implementation

[0032] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0033] In this invention, the "fluid polarization" process improves the polarization efficiency by using an external electric field to control the polar orientation of piezoelectric fillers in a polymer matrix while the material is still in an uncured state. This results in piezoelectric composite materials having excellent piezoelectric properties after curing. Furthermore, the piezoelectric composite materials prepared using this process also exhibit mechanical flexibility far superior to 2-2 or 3-3 type piezoelectric composite materials, providing a feasible technical solution for the development of a new generation of human-machine interface flexible sensors.

[0034] Example 1

[0035] The "fluid polarization" process used to improve the polarization efficiency of ceramic / polymer-based piezoelectric composites is as follows:

[0036] S1. Weigh and mix the raw materials according to the chemical formula xPbTiO3 / PDMS to obtain xPbTiO3-PDMS slurry, where x = 5 vol.

[0037] S2. Place the slurry obtained in step S1 into a defoaming device to remove tiny air bubbles from the slurry.

[0038] S3. Slowly inject the slurry obtained in step S2 into the groove consisting of two metal plates and a plastic partition. The two plates are connected to a voltage source via wires.

[0039] S4. Apply a DC electric field of 10 kV / cm for 30 min and an AC electric field of 10 kV / cm, 250 Hz for 30 min to the slurry obtained in step S3 through a voltage source.

[0040] S5. To ensure complete curing and maintain the spatial distribution of the piezoelectric filler in the polymer matrix, the experimental group and the control group were placed in an oven at 70 ℃ for 12 h. After that, they were taken out of the oven, and the metal electrode plate and plastic separator were peeled off to obtain sheet samples.

[0041] S6. Plasma surface treatment is performed on both sides of the sheet sample obtained in step S5, and stretchable silver paste is coated on it. After curing, further testing can be carried out.

[0042] Comparative Example 1

[0043] The difference between Comparative Example 1 and Example 1 is that in step S4, an AC electric field of 10 kV / cm, 250 Hz, and 30 min is applied to the slurry obtained in step S3 by a voltage source.

[0044] Example 2

[0045] The difference between Example 2 and Example 1 is that in step S1, the raw materials are weighed according to the chemical formula xPbTiO3 / PDMS, where x = 8 vol.%.

[0046] Comparative Example 2

[0047] The difference between Comparative Example 2 and Example 2 is that in step S4, an AC electric field of 10 kV / cm, 250 Hz, and 30 min is applied to the slurry obtained in step S3 by a voltage source.

[0048] Example 3

[0049] The difference between Example 3 and Example 1 is that in step S1, the raw materials are weighed according to the chemical formula xPbTiO3 / PDMS, where x = 10 vol.%.

[0050] Comparative Example 3

[0051] The difference between Comparative Example 3 and Example 3 is that in step S4, an AC electric field of 10 kV / cm, 250 Hz, and 30 min is applied to the slurry obtained in step S3 by a voltage source.

[0052] Example 4

[0053] The difference between Example 4 and Example 1 is that in step S1, the raw materials are weighed according to the chemical formula xPbTiO3 / PDMS, where x = 13 vol.%.

[0054] Comparative Example 4

[0055] The difference between Comparative Example 4 and Example 4 is that in step S4, an AC electric field of 10 kV / cm, 250 Hz, and 30 min is applied to the slurry obtained in step S3 by a voltage source.

[0056] Example 5

[0057] The difference between Example 5 and Example 1 is that in step S1, the raw materials are weighed according to the chemical formula xPbTiO3 / PDMS, where x = 15 vol.%.

[0058] Comparative Example 5

[0059] The difference between Comparative Example 5 and Example 5 is that in step S4, an AC electric field of 10 kV / cm, 250 Hz, and 30 min is applied to the slurry obtained in step S3 by a voltage source.

[0060] Example 6

[0061] The difference between Example 6 and Example 1 is that in step S1, the raw materials are weighed according to the chemical formula xPbTiO3 / PDMS, where x = 18 vol.%.

[0062] Comparative Example 6

[0063] The difference between Comparative Example 6 and Example 6 is that in step S4, an AC electric field of 10 kV / cm, 250 Hz, and 30 min is applied to the slurry obtained in step S3 by a voltage source.

[0064] Example 7

[0065] The difference between Example 7 and Example 1 is that in step S1, the raw materials are weighed according to the chemical formula xPbTiO3 / PDMS, where x = 20 vol.%.

[0066] Comparative Example 7

[0067] The difference between Comparative Example 7 and Example 7 is that in step S4, an AC electric field of 10 kV / cm, 250 Hz, and 30 min is applied to the slurry obtained in step S3 by a voltage source.

[0068] Take the flexible stress / strain sensor samples prepared in Examples 1–7 and Comparative Examples 1–7, and examine their d 33 The values ​​were tested, and the test results are shown in Table 1.

[0069] Table 1: Performance Comparison of the Above Embodiments;

[0070]

[0071] The comparison between the examples and the comparative examples shows that the examples, through the "fluid polarization" process of polarization followed by molding, enable PbTiO3 / PDMS materials to obtain a higher d33 after treatment at room temperature and with a small electric field. For example, Example 7 can achieve (34 pC / N), which is about 7.5 times the d33 value obtained by conventional polarization of PbTiO3 / PDMS of the same composition in Comparative Example 7.

[0072] This "fluid polarization" process, used to improve the polarization efficiency of ceramic / polymer-based piezoelectric composites, employs a molten salt method to prepare PbTiO3 nanorods with mesoscopically oriented electric dipoles as piezoelectric fillers. PDMS is used as the matrix, and while the PDMS matrix remains in a fluid state, an external electric field is applied to control the spatial distribution and polar orientation of the PbTiO3 nanorods within the matrix. The nanorods are weighed, mixed, and defoamed according to a specific ratio to obtain a slurry. This slurry is then poured into an electrophoretic template, and specific DC and AC electric fields are applied sequentially to control the spatial distribution and polar orientation of the PbTiO3 nanorods within the matrix. This achieves a macroscopic orientation of the material's electric dipoles, resulting in a material with excellent piezoelectricity immediately after curing, without the need for an additional artificial polarization process.

[0073] Due to the anisotropy of ferroelectric materials, tetragonal PbTiO3 nanorods growing along the spontaneous polarization direction can be synthesized via the molten salt method, with their electric dipoles exhibiting uniform orientation at the mesoscale. After the addition of a curing agent, the PbTiO3-PDMS suspension remains in a flowable state for a considerable period. Therefore, applying a DC electric field of only 10 kV / cm to the suspension is sufficient to cause the positive polarity side of the PbTiO3 nanorods to be attracted to the negative electrode, and vice versa, resulting in directional torsion and movement, achieving a macroscopic orientation of the material's electric dipoles. Subsequently, applying an AC electric field of 10 kV / cm to the PbTiO3-PDMS suspension utilizes the high dielectric properties of PbTiO3 to encourage the nanorods to move closer together, forming "end-to-end" particle chains, which are uniformly distributed within the PDMS matrix until the matrix is ​​completely solidified, ultimately achieving multi-scale synergistic orientation of the material's electric dipoles, such as... Figure 1 As shown in the figure. XRD test results show that the composite material prepared by "DC electrophoresis + AC electrophoresis" exhibits a higher peak than the composite material prepared by "AC electrophoresis only", which provides experimental evidence for the above theoretical analysis (see Figure 2 More importantly, the PbTiO3 / PDMS prepared by "AC electrophoresis only" maintained a maximum dg even after treatment under polarization conditions of 80 °C and 200 kV / cm for 5 h. 33 The value is only 4.5 pC / N; while based on the "fluid polarization" process, PbTiO3 / PDMS material, after being treated at room temperature and in a small electric field (10 kV / cm) for 30 min, can achieve a higher d value immediately upon molding. 33 = 34 pC / N, while maintaining good mechanical properties (Young's modulus approximately 2.1 MPa, elongation at break approximately 71%), such as Figure 3 As shown.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A "fluid polarization" process for improving the polarization efficiency of ceramic / polymer-based piezoelectric composites, characterized in that, The piezoelectric nanorods selected for this composite material have consistent electric dipole orientation at the mesoscale. Using a thermosetting polymer as the matrix, the polar orientation of the piezoelectric ceramic filler in the polymer matrix is ​​controlled by electrophoresis technology, so that the electric dipoles of the material are consistent at the macroscale, realizing the material's pre-polarization and subsequent molding, thereby improving the material's polarization efficiency.

2. The "fluid polarization" process as described in claim 1, characterized in that, The electric fields used in electrophoresis are DC and AC electric fields applied sequentially, with electric field strengths of 0.1–100 kV / cm and durations of 0.1–24 h, and AC electric field frequencies of 0.1–1000 Hz.

3. The "fluid polarization" process as described in claim 2, characterized in that, The electric field strength of both the DC and AC electric fields is 10 kV / cm, the duration of both electric fields is 0.5 h, and the frequency of the AC electric field is 250 Hz.

4. The "fluid polarization" process as described in claim 1, characterized in that, The piezoelectric ceramic filler is one or more of lead zirconate titanate, barium calcium zirconate titanate, or potassium sodium niobate, and the thermosetting polymer is one or more of polydimethylsiloxane, epoxy resin, or polyimide.

5. The "fluid polarization" process as described in any one of claims 1 to 4, characterized in that, Specifically, the steps include the following: S1. Weigh the piezoelectric filler and polymer according to the proportion and mix them evenly to obtain the piezoelectric filler-polymer slurry; S2. Place the slurry obtained in step S1 into a defoaming device to remove tiny air bubbles from the slurry. S3. Slowly inject the slurry obtained in step S2 into the groove consisting of two metal plates and a plastic partition. The two metal plates are connected to a voltage source through wires. S4. Apply a DC electric field of 0.1–100 kV / cm for 0.1–24 h and an AC electric field of 0.1–100 kV / cm for 0.1–1000 Hz for 0.1–24 h to the slurry in step S3 using a voltage source. S5. To ensure that the slurry is completely cured and to maintain the spatial distribution of the piezoelectric filler in the polymer matrix, the slurry in step S4 is placed in an oven at 70~90 ℃ and kept at that temperature for 10~15 h. After that, it is taken out of the oven and the metal electrode plate and plastic separator are peeled off to obtain a sheet sample. S6. Plasma treatment is performed on both sides of the sheet sample obtained in step S5, and stretchable silver paste is coated on them. After curing, a flexible piezoelectric composite material sample is obtained.

6. The "fluid polarization" process as described in claim 5, characterized in that, In step S1, the content of piezoelectric filler is 0–60 vol% and not 0. The morphology of piezoelectric filler is one-dimensional particles or two-dimensional nanorods / wires with a diameter range of 0.01–10 μm and a length range of 1–100 μm.

7. The "fluid polarization" process as described in claim 5, characterized in that, In step S1, the piezoelectric filler content is 5–20 vol%, and the piezoelectric filler is a two-dimensional nanorod / wire with an average diameter of 0.5 μm and an average length of 10 μm.

8. The "fluid polarization" process as described in claim 5, characterized in that, In step S4, a DC electric field of 10 kV / cm for 30 min and an AC electric field of 10 kV / cm for 250 Hz for 30 min are applied to the slurry in step S3 by a voltage source.

9. A flexible piezoelectric composite material prepared by the "fluid polarization" process described in claim 5 for improving the polarization efficiency of ceramic / polymer-based piezoelectric composite materials.

Images