Piezoresistive flexible sensor

Abstract

The invention provides a piezoresistive flexible sensor, and belongs to the field of sensors. The preparation method of the piezoresistive flexible sensor provided by the invention comprises the following steps: impregnating foamed plastic in a solution at least containing a conductive polymer, and drying to obtain conductive foam; at least two electrodes are arranged on any surface of the conductive foam, the piezoresistive flexible sensor is obtained, and the conductive polymer is polybenzodifuran diketone. The piezoresistive flexible sensor provided by the invention has the advantages of high sensitivity, wide detection range, quick response and recovery, light flexible structure, simple and mature preparation process and the like.

Description

Technical Field

[0001] This invention relates to the field of sensors, and more specifically to a piezoresistive flexible sensor. Background Technology

[0002] With the rapid development of the Internet of Things (IoT), Artificial Intelligence (AI), wearable devices, soft robots, and human-computer interaction technologies, traditional rigid and bulky sensors can no longer meet the needs of new application scenarios. The market has generated a huge demand for flexible sensors that can adapt to complex curved surfaces, are stretchable, and lightweight.

[0003] Piezoresistive pressure sensors operate based on the piezoresistive effect. When certain materials are subjected to mechanical stress (such as compression or tension), their resistivity changes. By measuring this change in resistance, the applied pressure can be accurately deduced. Sensors based on this effect have become the mainstream research choice due to their simple structure, convenient signal processing, and fast response speed. However, traditional piezoresistive sensors face the challenge of becoming more flexible. Traditional piezoresistive materials, such as single-crystal silicon, while possessing high sensitivity (high gauge factor), are primarily rigid and brittle, unable to withstand large deformations, and therefore unsuitable for flexible applications.

[0004] The key to developing flexible piezoresistive sensors lies in structural design. Porous structures (such as sponges and foams) possess extremely high compressibility, ultralight weight, and a huge specific surface area. When compressed, their internal framework undergoes extensive bending, contact, and separation, leading to an exponential change in the number of conductive pathways. This sensing mechanism, dominated by "contact resistance" rather than changes in "intrinsic resistance" caused by material deformation, can deliver ultra-high sensitivity and an extremely wide detection range. Imbuing the conductive properties onto a three-dimensional porous insulating substrate is a crucial technological step in realizing such sensors. Current technologies primarily employ template methods, such as using sugar cubes or salt granules as templates, filling the conductive composite material, and then dissolving and removing the template. This method offers good controllability but is cumbersome and difficult to fabricate on a large scale. Summary of the Invention

[0005] This invention is made to solve the above-mentioned problems, and aims to provide a piezoresistive flexible sensor with advantages such as simple preparation method, low density, and high sensitivity.

[0006] This invention provides a piezoresistive flexible sensor, characterized by the following steps in its fabrication method: The foam plastic is impregnated in a solution containing at least a conductive polymer and then dried to obtain conductive foam. By placing at least two electrodes on any surface of the conductive foam, a piezoresistive flexible sensor is obtained. The conductive polymer is polybenzodifurandione.

[0007] The piezoresistive flexible sensor provided by the present invention may also have the following feature: wherein the solvent of the solution is DMSO.

[0008] The piezoresistive flexible sensor provided by the present invention may also have the following feature: wherein the number-average molecular weight of the polybenzodifuran diketone is between 100,000 and 500,000 Daltons.

[0009] The piezoresistive flexible sensor provided by the present invention may also have the following feature: wherein the foam plastic has a pore size of 20μm-200μm, preferably, the foam plastic has a pore size of 100μm.

[0010] The piezoresistive flexible sensor provided by the present invention may also have the following feature: wherein the foam plastic is selected from any one of polyurethane foam plastic, polystyrene foam plastic, polyvinyl chloride foam plastic or melamine foam plastic.

[0011] The piezoresistive flexible sensor provided by the present invention may also have the following feature: wherein the solution further contains conductive filler.

[0012] The piezoresistive flexible sensor provided by the present invention may also have the following feature: wherein the filler is selected from any one or more of silver nanowires, single-walled carbon nanotubes, multi-walled carbon nanotubes, single-layer MXene, multi-layer MXene, or graphene.

[0013] The piezoresistive flexible sensor provided by the present invention may also have the following feature: wherein the filler is a silver nanowire with a diameter of 20nm-200nm and a length of 5μm-50μm.

[0014] The piezoresistive flexible sensor provided by the present invention may also have the following feature: wherein, in a solution containing at least a conductive polymer, the concentration of the conductive polymer is 0.5-7.5 mg / mL.

[0015] The piezoresistive flexible sensor provided by this invention may also have the following feature: the drying process is carried out at a temperature of 80-100°C for 4-8 hours. Preferably, the drying process is carried out at a temperature of 80°C for 4 hours.

[0016] The role and effect of invention According to the piezoresistive flexible sensor of the present invention, because foam plastic is used as the sensor frame, on the one hand, when pressure is applied, the foam skeleton bends and deforms, causing the previously non-contacting internal beams coated with conductive material to come into contact with each other, or increasing the contact area between already contacting beams. This instantly creates a large number of new conductive paths, resulting in a sharp drop in resistivity. This change in contact resistance is far more significant than the change in resistance caused by the deformation of the material itself, therefore the sensor is extremely sensitive to even small pressure changes. On the other hand, using foam plastic as the matrix results in a very low overall density of the sensor (0.0050 g / cm³). 3 -0.0070g / cm 3 This material is ideal for applications with stringent weight requirements, such as wearable devices, aerospace, and robotics. The foam matrix provides the sensor with excellent flexibility, allowing it to easily conform to various curved or even irregular surfaces (such as human joints or robotic fingers) without affecting its performance. Furthermore, the sensor's performance can be easily customized by adjusting the concentration of the conductive polymer solution and changing the added conductive fillers, thereby altering the coating thickness and conductivity, and adjusting the sensor's sensitivity and detection range to meet the needs of different applications.

[0017] Furthermore, because the preparation method utilizes an "immersion-drying" process, which is a very simple, mature, and flexible fabrication technique, compared to micro / nano fabrication (such as photolithography, sputtering, and evaporation), electrochemical deposition, and laser direct writing, the "immersion-drying" process does not require expensive equipment or demanding clean environments, significantly lowering the technological barrier. This process is also naturally suitable for large-scale production, facilitating industrial manufacturing. Immersion can adapt to the processing needs of almost all shapes and can efficiently complete the processing and manufacturing of various irregularly shaped parts and customized products. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the sensor structure described in Examples 1-2.

[0019] Figure 2 This is a scanning electron microscope image of the Mel-PBFDO-AgNWs sample from Example 2.

[0020] Figure 3 This is a signal diagram generated by compressing the Mel-PBFDO-AgNWs sample at a frequency of 0.25Hz under different deformations in Example 2.

[0021] Figure 4 The image shows the IV curve of the Mel-PBFDO-AgNWs sample in Example 2.

[0022] Figure 5The response time is the value of the Mel-PBFDO-AgNWs sample in Example 2.

[0023] Figure 6 The signal diagrams are generated by the Mel-PBFDO-2.5, Mel-PBFDO-5.0, and Mel-PBFDO-7.5 samples in Example 1 under 30% compressive deformation.

[0024] Figure 7 This is a signal diagram generated by Mel-PBFDO-2.5 in Example 1 during 1000 cycles of 20% deformation compression.

[0025] Figure 8 The image shown is of Mel-PBFDO-2.5 in Example 1. Detailed Implementation

[0026] To make the technical means, creative features, objectives and effects of this invention easy to understand, the invention will be specifically described below in conjunction with embodiments and accompanying drawings.

[0027] The sources of the raw materials used in the following embodiments are shown in the table below.

[0028]

[0029] In the following examples and raw material preparation methods, unless otherwise stated, all water mentioned is deionized water.

[0030] The polybenzodifurandione (PBFDO) solution used in the following examples was prepared with reference to the papers Synthesis and Characterization of n-Doped Poly(benzodifurandione) (n-PBDF) Derivatives via Aromatic Substitution (Macromolecules, 2024. 57(22): p. 10717-10724) and Solvent-promoted synthesis of n-type high-conductivity poly(benzodifurandione) (PBFDO) via DMSO / Ac2O: an efficient, purification-free approach (Science China-Chemistry, 2025: p. 8), and the reaction formula is as follows:

[0031] Specifically, the steps include the following: Step 1: Add 108g (1mol) of p-benzoquinone and 1000ml of 95% ethanol to a 2L flask. Heat to 40°C with stirring. When the p-benzoquinone is mostly dissolved, add 112g (1mol) of ethyl cyanoquinone and continue stirring until completely dissolved. This is reaction solution A. Add 60ml of ethyl cyanoquinone, 200ml of ethanol, and 50ml of 28% ammonia to a 2L round-bottom three-necked flask equipped with a mechanical stirrer, a 500ml dropping funnel, and a 250ml dropping funnel, and room temperature circulating water. Add 90% of the total amount of reaction solution A to the dropping funnel. Add the remaining reaction solution A to the dropping funnel when it is empty. Add 200ml of 28% ammonia to the 250ml dropping funnel. Strictly avoid contact between reaction solution A and ammonia before adding it to the 2L flask. Adjust the flow rate of the dropping funnel to evenly inject the reaction solution into the flask over 45 minutes. It is best to complete the addition of ammonia when 90% of reaction solution A has been added. After adding all the liquid, continue stirring for 1 hour and refrigerate for 4 hours. Then filter the reaction solution to obtain a purple-red precipitate. Wash it three times with ethanol, collect it and dry it to obtain 62.8 g of P1 (yield 54.1%).

[0032] Step Two: Add 72g of P1 to a 2L flask equipped with a reflux condenser, add 420ml of concentrated hydrochloric acid and 380ml of water, and stir and heat to dissolve. Reflux the mixture at 80°C for 2 hours, then raise the temperature to 110°C and react under vigorous reflux for 20 hours. Add 360ml of water and 12g of activated carbon, stir and boil for 3 minutes, then filter while hot. Discard the filter cake, refrigerate the filtrate for 4 hours, and filter again to obtain 23.6g of white precipitate, which is P2 (yield 48.2%).

[0033] Step 3: 7.24 g of P2, 380 ml of anhydrous toluene, and 76 ml of acetic anhydride were added to a round-bottom flask equipped with a reflux condenser. The mixture was heated to 100°C with stirring and reacted for 5 h. The solvent was then removed by rotary evaporation. The crude sample was recrystallized from boiling ethyl acetate to obtain 2.31 g of P3 (yield 38.0%).

[0034] Step Four: Weigh 1.5g of P3 monomer and add it to 200ml of DMSO. Vacuum the solution for 10 minutes, purge with nitrogen for 10 minutes, and repeat this cycle 3 times. Heat the solution to 100 degrees Celsius and add 1.21g of acetic anhydride using a syringe. React for about 20-30 minutes until the solution viscosity remains essentially unchanged. Then add another 1.21g of acetic anhydride using a syringe and continue the reaction at 100 degrees Celsius for 30 minutes. Finally, cool the solution to room temperature. This is the PBFDO solution used in this invention.

[0035] The PBFDO solution prepared by the above method can be used directly in the examples, or it can be used after being diluted with DMSO.

[0036] The silver nanowire dispersions (AgNWs dispersions) used in the following examples were synthesized in-house using a polyol method. The size range of the silver nanowires was 90 nm-100 nm in diameter and 15 μm-50 μm in length. The preparation method is as follows: Take a 500ml three-necked flask and add 1.67g PVP-K90, 9.6mg NaCl, and 220ml ethylene glycol sequentially. Heat to 130°C with magnetic stirring. Dissolve 0.849g silver nitrate in 30ml ethylene glycol and add it dropwise to the reaction solution. Maintain the temperature at 130°C and react for 6 hours. After cooling the solution, centrifuge at 8k r / min for 5 minutes, discard the supernatant, collect the precipitate, wash twice with ethanol, and disperse it in dimethyl sulfoxide to prepare a 1mg / mL AgNWs dispersion, which is the AgNWs dispersion used in this invention.

[0037] Example 1 Piezoresistive flexible sensor without conductive filler This embodiment provides a piezoresistive flexible sensor without conductive filler, and the fabrication method includes the following steps: Take three pieces of melamine foam, each measuring 1cm x 1cm x 0.5cm (length x width x height), and immerse them respectively in PBFDO solutions of different concentrations (2.5mg / ml, 5.0mg / ml, and 7.5mg / ml) at 30°C. Stir for 10 minutes, remove, and place in a forced-air drying oven at 80°C to remove the solvent. Then, attach copper foil electrodes to both sides of the foam (e.g., ...). Figure 1 As shown in the figure, tactile sensor samples (Mel-PBFDO-2.5, Mel-PBFDO-5.0, Mel-PBFDO-7.5) can be obtained. The bulk density of the Mel-PBFDO-2.5 sample is 0.0052 g / cm³. 3 The bulk density of the Mel-PBFDO-5.0 sample was 0.0060 g / cm³, and the density of the foam portion of the Mel-PBFDO-7.5 sample was 0.0070 g / cm³. 3 .

[0038] The morphology of the Mel-PBFDO-AgNWs sample under a scanning electron microscope is shown in the figure below. Figure 2 As shown.

[0039] Example 2 The PBFDO solution was first diluted to 1 mg / mL with DMSO, and then mixed with an equal volume of 1 mg / mL AgNWs dispersion to obtain the PBFDO-AgNMs solution. Melamine foam was cut into 1 cm x 1 cm x 0.5 cm pieces (length x width x height), and immersed in the PBFDO-AgNMs solution (PBFDO and AgNWs concentrations were both 0.5 mg / mL) at 30°C. After stirring for 10 minutes, the foam was removed and dried in a forced-air oven at 80°C to remove the solvent. Copper foil electrodes were then attached to both sides of the foam to obtain the tactile sensor sample (Mel-PBFDO-AgNWs). The density of the foam portion of the Mel-PBFDO-AgNWs sample was 0.0056 g / cm³. 3 .

[0040] Comparison Example Yue Li et al. (Li, Y., L. Yang, SH Deng, H. Huang, YY Wang, ZP Xiong, SM Feng, SQ Wang, T. Li, T. Zhang, A machine learning-assisted multifunctional tactile sensor for smart prosthetics. Infomat, 2023. 5(9): p.12.) prepared a sensor with the same pressure sensing function using PEDOT-PSS aqueous dispersion by impregnation with foam. It has the same structure, equivalent sensitivity, and additional temperature sensing function as the sensor described in this application. The advantage of the sensor described in this application is its wider detection range. The sensor described in that paper exhibits a large resistance change under 1N pressure (equivalent to 10kPa), but a very small resistance change under subsequent 2N-5N pressure (20kPa-50kPa); while the sensor described in this application... Figure 5 It is understood that the sensor described in this application can continuously change its resistance when subjected to greater pressure, and has a wider pressure detection range than the sample described in the paper.

[0041] Zhaoyang Chen et al. (Chen, ZY, S. Liu, PY Kang, YL Wang, H. Liu, CT Liu, CY Shen, Decoupled Temperature-Pressure Sensing System for DeepLearning Assisted Human-Machine Interaction. Advanced Functional Materials, 2024. 34(52): p. 12.) prepared a pressure-sensing sensor by impregnating foam using a PEDOT-PSS aqueous dispersion combined with a single-walled carbon nanotube dispersion. It exhibits similar pressure-sensing performance to the Mel-PBFDO-AgNWs sensor described in this application. Although the materials are different, both can achieve pressure response over a wide range and possess fast response speed and fatigue resistance.

[0042] However, the sulfonic acid groups inherent in the PEDOT-PSS polymer inevitably result in a certain degree of hygroscopicity. This is evident in the paper "Through Ring-Opening Reactions To Weaken the Hygroscopicity of PEDOT:PSS Films with Improved Stability of Silicon Hybrid Solar Cells" (Liu, Y., Q. Geng, Z. Wang, Z. Liu, Z. Gao, X. Sun, Y. Li, M. Li, Through Ring-Opening Reactions To Weaken the Hygroscopicity of PEDOT:PSS Films with Improved Stability of Silicon Hybrid Solar Cells. ACS Applied Materials & Interfaces, 2025. 17(45): p. 62022-62031.), and fl-fl interaction-driven in situgrowth of covalent organic framework membranes for enhanced PEDOT:PSS interfaces in pin perovskite solar cells" (Ma, MR, YG Jing, L. Liu, C. Wang, N. Zhang, This characteristic has been confirmed in multiple publications, including SP Wen, GS Zhu, fl-fl interaction-driven in situ growth of covalent organic framework membranes for enhanced PEDOT:PSS interfaces in p-in perovskite solar cells. Chemical Engineering Journal, 2025. 519. , and this characteristic is limited by its intrinsic structure. With current theoretical basis, it can only be controlled to a certain extent. When used in such sensors, its performance will fluctuate due to the influence of humidity in the air, affecting the sensing performance.PBFDO has a highly hydrophobic structure, is insoluble in water, and cannot be dispersed in water without special treatment. Therefore, sensors made using PBFDO are far less affected by humidity in the air than sensors made using PEDOT-PSS polymer.

[0043] Test Example 1 The lower surface of the Mel-PBFDO-AgNWs was fixed to the lower surface of the sample tray of a dynamic mechanical property tester (TA Instruments ElectroForce 3220, USA). A digital source meter (Keithley 2602B) was used to connect the electrodes at both ends of the sample to collect the resistance change of the sample under dynamic pressure. The sample was compressed by 0.5 mm (10% deformation), 1.5 mm (30% deformation), 2.5 mm (50% deformation), and 3.5 mm (70% deformation) at a frequency of 1.0 Hz using the dynamic mechanical property tester, and the real-time resistance of the sample was measured.

[0044] Test results are as follows Figure 3 As shown in the figure. The test results demonstrate that the piezoresistive flexible pressure sensor Mel-PBFDO-AgNWs described in this invention has excellent performance and can generate a stable signal over a wide detection range.

[0045] Test Example 2 The lower surface of the Mel-PBFDO-AgNWs was fixed to the lower surface of the sample tray of a dynamic mechanical property tester (TA Instruments ElectroForce 3220, USA). A digital source meter (Keithley 2602B) was used to connect the electrodes at both ends of the sample, and the IV curve of the sample was collected under a fixed pressure. The sample was compressed by 0.5 mm (10% deformation) using the dynamic mechanical property tester. While maintaining the sample deformation, the voltage of the sample was scanned using the digital source meter, and the current value during the voltage scan was recorded to obtain the IV curve of the sample.

[0046] Test results are as follows Figure 4 As shown, the test results prove that the piezoresistive flexible pressure sensor Mel-PBFDO-AgNWs described in this invention does not exhibit capacitance or other characteristics when compressed, but only resistive characteristics, and can work under different voltages.

[0047] Test Example 3 The lower surface of the Mel-PBFDO-AgNWs was fixed to the lower surface of the sample tray of a dynamic mechanical property tester (TA Instruments ElectroForce 3220, USA). A digital source meter (Keithley 2602B) was used to connect the electrodes at both ends of the sample, and IV curves of the sample were collected under a fixed pressure. The sample was compressed to 3.5 mm (70% deformation) using the dynamic mechanical property tester, and the resistance change of the sample during compression was recorded using the digital source meter. Then, the pressure was removed, and the resistance change of the sample during recovery was recorded using the digital source meter.

[0048] Test results are as follows Figure 5 As shown, the test results demonstrate that the piezoresistive flexible pressure sensor Mel-PBFDO-AgNWs described in this invention has a short response time and high sensitivity.

[0049] Test Example 4 The lower surfaces of Mel-PBFDO-2.5, Mel-PBFDO-5.0, and Mel-PBFDO-7.5 samples were fixed to the lower surface of the sample pan of a dynamic mechanical property tester (TA Instruments ElectroForce 3220, USA). A digital source meter (Keithley 2602B) was connected to the electrodes at both ends of the sample to collect the resistance changes of the sample under dynamic pressure. The samples were compressed by 1.5 mm (30% deformation) at a frequency of 1.0 Hz using the dynamic mechanical property tester in a sinusoidal cyclic manner, and the real-time resistance of the sample was measured.

[0050] Test results are as follows Figure 6 As shown, the test results prove that the piezoresistive flexible pressure sensors Mel-PBFDO-2.5, Mel-PBFDO-5.0, and Mel-PBFDO-7.5 described in this invention have excellent performance, among which Mel-PBFDO-2.5 has better performance than Mel-PBFDO-5.0 and Mel-PBFDO-7.5.

[0051] Test Example 5 The lower surface of the Mel-PBFDO-2.5 sample was fixed to the lower surface of the sample tray of a dynamic mechanical property tester (TA Instruments ElectroForce 3220, USA). A digital source meter (Keithley 2602B) was used to connect the electrodes at both ends of the sample to collect the resistance change of the sample under dynamic pressure. The sample was compressed by 1.0 mm (20% deformation) at a frequency of 1.0 Hz using the dynamic mechanical property tester in a sinusoidal wave cycle of 1000 times, and the real-time resistance of the sample was measured.

[0052] Test results are as follows Figure 7As shown in the figure. The test results demonstrate that the piezoresistive flexible pressure sensor Mel-PBFDO-2.5 described in this invention has good fatigue performance and can still maintain a stable signal output after 1k cycles.

[0053] The role and effect of the embodiments According to the piezoresistive flexible sensor described in Examples 1-2, because foam plastic is used as the sensor frame and PBFDO solution is used as the conductive polymer solution, the sensor structure provided in the above embodiments can simultaneously cover the detection of both small and large pressures (3kPa-70kPa). Under small pressure, the beams begin to contact, generating a signal; as the pressure increases, more and more internal pores are compressed, the contact points and contact area continue to increase, and the resistance continues to change until the foam is completely compacted. This gradual compression process gives the sensor a very wide dynamic response range; on the other hand, suitable foam plastic can quickly deform and generate a signal when subjected to pressure, and can quickly rebound to its original shape after the external force is removed, causing the conductive network to break or return to its original state, thereby achieving rapid signal recovery and enabling real-time monitoring of pressure signals.

[0054] The above embodiments are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention.

Claims

1. A piezoresistive flexible sensor, characterized in that, The preparation method includes the following steps: The foam plastic is impregnated in a solution containing at least a conductive polymer and then dried to obtain conductive foam. By placing at least two electrodes on any surface of the conductive foam, a piezoresistive flexible sensor is obtained. The conductive polymer is polybenzodifurandione.

2. The piezoresistive flexible sensor according to claim 1, characterized in that: in, The solvent for the solution is DMSO.

3. The piezoresistive flexible sensor according to claim 1, characterized in that: in, The number-average molecular weight of the polybenzodifuran diketone is between 100,000 and 500,000 Daltons.

4. The piezoresistive flexible sensor according to claim 1, characterized in that: in, The foam plastic has a pore size of 20μm-200μm.

5. The piezoresistive flexible sensor according to claim 1, characterized in that: in, The foam plastic is selected from any one of polyurethane foam plastic, polystyrene foam plastic, polyvinyl chloride foam plastic or melamine foam plastic.

6. The piezoresistive flexible sensor according to claim 1, characterized in that: in, The solution also contains conductive filler.

7. The piezoresistive flexible sensor according to claim 6, characterized in that: in, The filler is selected from any one or more of silver nanowires, single-walled carbon nanotubes, multi-walled carbon nanotubes, single-layer MXene, multi-layer MXene, or graphene.

8. The piezoresistive flexible sensor according to claim 6, characterized in that: in, The filler is a silver nanowire with a diameter of 20nm-200nm and a length of 5μm-50μm.

9. The piezoresistive flexible sensor according to claim 1, characterized in that: in, In solutions containing at least the conductive polymer, the concentration of the conductive polymer is 0.5-7.5 mg / mL.

10. The piezoresistive flexible sensor according to claim 1, characterized in that: in, The drying process takes place at a temperature of 80-100℃ for 4-8 hours.

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