Capacitive polymer strain sensor, preparation method and application

Abstract

The present invention provides a capacitive polymer strain sensor, preparation method, and application. CN-TiO2 is obtained by modifying TiO2 with 2-cyanoethyltriethoxysilane and then doped into a PVDF-HFP polymer to produce a composite film with a high dielectric constant. Silicone electrodes are coated on both sides of the composite film to produce a capacitive polymer strain sensor with a wide range, high sensitivity, and high resolution. Furthermore, the capacitive polymer strain sensor can be used as a wearable device, attached to human joints, to monitor the body's movement in real time.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and in particular relates to a preparation method and application of a capacitive polymer strain sensor with a large range and high sensitivity. Background Art

[0002] Over the past two decades, flexible, stretchable capacitive sensors, using a combination of various inorganic and organic materials, have experienced rapid development. Due to their unique flexibility and stretchability, they have attracted significant attention for applications in aerospace, automotive, marine environments, robotics, healthcare, and portable electronics. Capacitive sensors consist of a deformable dielectric elastomer sandwiched between two electrode layers, similar to a flat-plate capacitor. When a capacitive sensor is deformed by applied external pressure, the change in thickness of the dielectric elastomer causes a change in capacitance. By determining the relationship between capacitance and deformation, pressure, and displacement, they can be used as strain sensors, pressure sensors, and displacement sensors.

[0003] With the continuous advancement of science and technology, there is a great demand for flexible capacitive sensors with a wide range and high sensitivity. For capacitive sensors, the structure and dielectric constant of the dielectric elastomer in the middle layer determine the sensitivity of the sensor. Dielectric elastomers with a pyramid array structure on the surface or a porous structure inside are prepared by the template method. When the dielectric elastomer is deformed by force, the air phase is reduced, which increases the dielectric constant of the dielectric elastomer, thereby improving the sensitivity of the sensor. However, the preparation process of the pyramid array structure and the porous structure is complicated and the economic cost is high, which is not suitable for large-scale industrial production and application expansion. Therefore, it is extremely important to find a simple and low-cost method to improve the sensitivity of capacitive sensors by increasing the dielectric constant of the dielectric elastomer.

[0004] Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) membranes, prepared by plasticizing them with the plasticizer tri-n-butyl citrate (TBC), exhibit low modulus and high deformation, making them ideal materials for flexible sensors. Improving the dielectric constant of PVDF-HFP membranes is key to developing high-performance flexible capacitive sensors. Summary of the Invention

[0005] To address the challenges of the existing technology, the present invention proposes a capacitive polymer strain sensor with a wide range and high sensitivity, as well as its preparation method and application. CN-TiO2 is obtained by modifying TiO2 with 2-cyanoethyltriethoxysilane. This CN-TiO2 is then doped into a PVDF-HFP membrane to create a composite film with a high dielectric constant. Silicone electrodes are coated on both sides of the composite film to produce a capacitive polymer strain sensor with a wide range, high sensitivity, and high resolution.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A capacitive polymer strain sensor is composed of a CN-TiO2 / PVDF-HFP composite film sandwiched between flexible and stretchable conductive silicone electrodes.

[0008] Furthermore, the capacitive polymer strain sensor has a measuring range of 1-14 mm, a resolution of 0.5 mm, and sensitivities of 1.11 Å / mm and 2.85 Å / mm.

[0009] Furthermore, the CN-TiO2 / PVDF-HFP composite membrane is prepared by solution casting from cyanated titanium dioxide (CN-TiO2), plasticizer tri-n-butyl citrate (TBC) and polymer resin PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene).

[0010] Furthermore, the diameter of the TiO2 nanoparticles in the CN-TiO2 / PVDF-HFP composite film is 5-10 nm, and the content of CN-TiO2 is 2-8 wt%.

[0011] Furthermore, the dielectric constant and dielectric loss of the CN-TiO2 / PVDF-HFP composite film at 40 Hz are 13.50-38.28 and 0.49-1.11, respectively.

[0012] Furthermore, the Young's modulus and elongation at break of the CN-TiO2 / PVDF-HFP composite membrane are 0.06-0.31 MPa and 631-715%, respectively.

[0013] The method for preparing the capacitive polymer strain sensor of the present invention comprises the following steps:

[0014] (1) TiO2 was ultrasonically dispersed in a solvent with a water-alcohol volume ratio of 1:9, and then dibutyltin dilaurate and 2-cyanoethyltriethoxysilane were added. At 60°C, the hydrolyzed 2-cyanoethyltriethoxysilane reacted with the hydroxyl functional groups on the TiO2 surface to obtain cyanated titanium dioxide (CN-TiO2) after 24 hours of post-reaction treatment.

[0015] (2) Ultrasonic dispersion of cyanated titanium dioxide (CN-TiO2) into N,N-dimethylacetamide was performed, and then TBC and PVDF-HFP were added in sequence under continuous stirring. After continuous stirring at 75°C for 6 hours, the mixture was poured into a glass Petri dish and placed in an oven at 90°C for 24 hours to remove the solvent to obtain a CN-TiO2 / PVDF-HFP composite membrane.

[0016] (3) The conductive silicone electrode was evenly mixed and coated on one side of the CN-TiO2 / PVDF-HFP composite membrane, and then placed in an oven at 70°C for 8 hours. This operation was repeated to complete the coating on the other side to obtain a capacitive polymer strain sensor based on CN-TiO2 / PVDF-HFP.

[0017] Furthermore, in step (1), based on 0.5 g of TiO2 nanoparticles, 0.05 mL of dibutyltin dilaurate and 1 mL of 2-cyanoethyltriethoxysilane are required.

[0018] Furthermore, in step (2), the mass ratio of CN-TiO2 to PVDF-HFP is 0.08:1-0.35:1; and the mass ratio of TBC to PVDF-HFP is 3:1.

[0019] The capacitive polymer strain sensor described in the present invention is a wearable device that is attached to the joints of the human body to monitor the body's movement posture in real time. Specifically, when the capacitive polymer strain sensor is subjected to force and produces displacement in a fixed shape state, the displacement caused by the force can be detected by the change in the capacitance signal. It can be used in electronic skin to detect human movement posture.

[0020] The beneficial effects of the present invention are: the dielectric constant of the PVDF-HFP composite film is significantly improved by doping with CN-TiO2, while the composite film still maintains flexibility and stretchability. Therefore, the capacitive polymer strain sensor based on the CN-TiO2 / PVDF-HFP composite film has the advantages of a wide range, high resolution, and high sensitivity. Specifically:

[0021] (1) The dielectric constant and dielectric loss of CN-TiO2 / PVDF-HFP composite films at 40 Hz ranged from 13.50 to 38.28 and 0.49 to 1.11, respectively, when the content of CN-TiO2 ranged from 2 to 8 wt%. The high dielectric constant of TiO2 itself and the polarization of the cyano groups introduced after modification under an electric field significantly enhanced the dielectric constant of the composite films.

[0022] (2) The Young's modulus and elongation at break of the CN-TiO2 / PVDF-HFP composite film at a content of 2-8 wt% were 0.06-0.31 MPa and 631-715%, respectively. The elastic modulus and elongation at break of the composite film did not change significantly, making it suitable for use in capacitive flexible sensors.

[0023] Capacitive polymer strain sensors based on CN-TiO2 / PVDF-HFP composite films have a range of 1–14 mm, a resolution of 0.5 mm, and sensitivities of 1.11 Å / mm and 2.85 Å / mm. While significantly improving displacement sensing performance, they can also be used to attach electronic skin to human joints for motion monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a structural diagram of the capacitive polymer strain sensor of the present invention.

[0025] Figure 2 This is the Raman spectrum of CN-TiO2 of the present invention.

[0026] Figure 3 1 and 2 are the stress-strain curve and elastic modulus of the composite film of the present invention.

[0027] Figure 4 are the dielectric constant and dielectric loss of the composite film of the present invention.

[0028] Figure 5 is the sensitivity of the capacitive polymer strain sensor of the present invention.

[0029] Figure 6 The capacitive polymer strain sensor of the present invention is used as electronic skin to monitor human body movement posture. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to specific examples. It should be understood that the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention, and that those skilled in the art may make non-essential improvements and adjustments based on the contents of the above invention.

[0031] Example 1

[0032] Preparation of CN-TiO2

[0033] 0.5 g of TiO2 nanoparticles were ultrasonically dispersed in 100 mL of a 1:9 water / ethanol mixture. 0.05 mL of dibutyltin dilaurate and 1 mL of 2-cyanoethyltriethoxysilane were then added, and the mixture was refluxed at 60°C for 24 hours. The product was then centrifuged and washed with ethanol three times before being placed in a 90°C oven for 24 hours to obtain cyanated titanium dioxide (CN-TiO2).

[0034] Example 2

[0035] Preparation of composite membrane (membrane 1)

[0036] 0.24 g of CN-TiO2 nanoparticles were ultrasonically dispersed in 20 mL of N,N-dimethylacetamide solvent. Then, 3 g of PVDF-HFP powder and 9 g of tri-n-butyl citrate (TBC) were added sequentially. After continuous stirring at 75°C for 6 hours, the mixture was poured into a glass Petri dish and then placed in a 90°C oven for 24 hours to remove the solvent, resulting in CN-TiO2 / PVDF-HFP composite membrane 1.

[0037] Example 3

[0038] Preparation of composite membrane (membrane 2)

[0039] 0.50 g of CN-TiO2 nanoparticles were ultrasonically dispersed in 20 mL of N,N-dimethylacetamide solvent. Then, 3 g of PVDF-HFP powder and 9 g of tri-n-butyl citrate (TBC) were added sequentially. After continuous stirring at 75°C for 6 hours, the mixture was poured into a glass Petri dish and then placed in a 90°C oven for 24 hours to remove the solvent, resulting in CN-TiO2 / PVDF-HFP composite membrane 2.

[0040] Example 4

[0041] Preparation of composite membrane (membrane 3)

[0042] 0.76 g of CN-TiO2 nanoparticles were ultrasonically dispersed in 20 mL of N,N-dimethylacetamide solvent. Then, 3 g of PVDF-HFP powder and 9 g of tri-n-butyl citrate (TBC) were added sequentially. After continuous stirring at 75°C for 6 hours, the mixture was poured into a glass Petri dish and then placed in a 90°C oven for 24 hours to remove the solvent, resulting in CN-TiO2 / PVDF-HFP composite membrane 3.

[0043] Example 5

[0044] Preparation of composite membrane (membrane 4)

[0045] 1.04 g of CN-TiO2 nanoparticles were ultrasonically dispersed in 20 mL of N,N-dimethylacetamide solvent, followed by the addition of 3 g of PVDF-HFP powder and 9 g of tri-n-butyl citrate (TBC). After continuous stirring at 75°C for 6 hours, the mixture was poured into a glass Petri dish and then placed in an oven at 90°C for 24 hours to remove the solvent, resulting in CN-TiO2 / PVDF-HFP composite membrane 4.

[0046] Example 6

[0047] Fabrication of capacitive polymer strain sensors

[0048] Take 1.5 g of each of the two components of the conductive silicone electrode and stir continuously for one hour to mix them evenly. Coat the mixed conductive silicone electrode on one side of the composite membrane and then place it in a 70°C oven for 8 hours. Repeat the above steps to complete the electrode coating on the other side of the composite membrane. The capacitive displacement sensor based on the CN-TiO2 / PVDF-HFP composite membrane is obtained. Its structure is as follows: Figure 1 shown.

[0049] 1. Raman spectra of TiO2 and CN-TiO2

[0050] Figure 2 Medium, 143 cm -1 The signal peak is E g Symmetrical O-Ti-O angle-shifting vibration peaks with the largest intensities at 392, 517, and 640 cm -1 The peaks at 1g , A 1g or B 1g and A 1g The Raman spectrum of CN-TiO2 modified with the cyanosilane coupling agent exhibits two new characteristic peaks, located near 2250 cm-1 and 2918 cm-1, attributed to C≡N and CH, respectively. Furthermore, the characteristic peaks attributed to TiO2 have not disappeared, but their intensities have decreased slightly compared to the unmodified state, indicating that the modification process did not damage the original TiO2 structure. The presence of the characteristic peaks of C≡N and CH in the Raman spectrum of CN-TiO2 indicates that the cyanosilane coupling agent has been successfully modified on the TiO2 surface.

[0051] 2. The mechanical properties of the prepared composite films 1 to 4 were tested by a universal tensile machine. The stress-strain curves and Young's modulus were as follows: Figure 3 As the CN-TiO2 content increases, the modulus of the CN-TiO2 / PVDF-HFP composite film increases continuously, the tensile strength increases, and the elongation at break decreases. The detailed data are shown in Table 1.

[0052] Table 1. Mechanical properties, dielectric constants, and breakdown strengths of composite films 1–4

[0053]

[0054] 3. The prepared composite membranes 1~4 were heated to 40~10 7 Hz tested the dielectric constant, dielectric loss and conductivity using an impedance analyzer, and the results are as follows Figure 4As shown in Table 1, the dielectric constant and dielectric loss increase with increasing frequency, while the conductivity decreases. In addition, the dielectric loss, dielectric constant and conductivity of the composite film increase with increasing CN-TiO2 content. The dielectric constants of different contents at 10 kHz are recorded in Table 1.

[0055] Four, Figure 6 Capacitive polymer strain sensors are used as electronic skin to monitor the bending state of the finger, wrist, and elbow joints. Because the dielectric layer of the capacitive polymer strain sensor can deform by over 600%, and its high dielectric constant enhances sensitivity, it can accurately detect changes in capacitance at the joints during large movements.

[0056] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A capacitive polymer strain sensor as a wearable electronic skin, characterized by: The capacitive polymer strain sensor is a wearable device that is attached to the joints of the human body to monitor the body's movement posture in real time. When a force is applied to a fixed shape and the sensor is displaced, the displacement caused by the force is detected by the change in the capacitance signal. This allows the sensor to be used as an electronic skin to detect the body's movement posture. The capacitive polymer strain sensor consists of a CN-TiO2 / TBC / PVDF-HFP composite film sandwiched between flexible and stretchable conductive silicone electrodes; The dielectric constant of the CN-TiO2 / TBC / PVDF-HFP composite film at 40 Hz is 38.28; The Young's modulus and elongation at break of the CN-TiO2 / TBC / PVDF-HFP composite membrane are 0.31 MPa and 715%, respectively; The preparation method of the capacitive polymer strain sensor comprises the following steps: (1) TiO2 was ultrasonically dispersed in a solvent with a water-alcohol volume ratio of 1:9, and then dibutyltin dilaurate and 2-cyanoethyltriethoxysilane were added. At 60°C, the hydrolyzed 2-cyanoethyltriethoxysilane reacted with the hydroxyl functional groups on the TiO2 surface to obtain cyanated titanium dioxide (CN-TiO2) after 24 hours of post-reaction treatment. (2) Ultrasonic dispersion of cyanated titanium dioxide (CN-TiO2) into N,N-dimethylacetamide was performed, and then tributyl citrate (TBC) and PVDF-HFP were added in sequence under continuous stirring. After continuous stirring at 75°C for 6 hours, the mixture was poured into a glass Petri dish and placed in an oven at 90°C for 24 hours to remove the solvent to obtain a CN-TiO2 / PVDF-HFP / TBC composite membrane. (3) The conductive silicone electrode was evenly mixed and coated on one side of the CN-TiO2 / TBC / PVDF-HFP composite membrane, and then placed in an oven at 70°C for 8 hours. This operation was repeated to complete the coating on the other side to obtain a capacitive polymer strain sensor based on the CN-TiO2 / TBC / PVDF-HFP composite membrane; In the step (2), the mass ratio of CN-TiO2 to PVDF-HFP is 0.35:1; the mass ratio of TBC to PVDF-HFP is 3:1; The capacitive polymer strain sensor has a measuring range of 1-14 mm, a resolution of 0.5 mm, and sensitivities of 1.11 / mm and 2.85 / mm.

2. The capacitive polymer strain sensor as wearable electronic skin according to claim 1, characterized in that: The diameter of the TiO2 nanoparticles in the CN-TiO2 / TBC / PVDF-HFP composite membrane is 5-10 nm, and the content of CN-TiO2 is 8 wt%.

3. The capacitive polymer strain sensor as wearable electronic skin according to claim 1, characterized in that: In step (1), based on 0.5 g of TiO2 nanoparticles, 0.05 mL of dibutyltin dilaurate and 1 mL of 2-cyanoethyltriethoxysilane are required.

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