Pva / glycerol / biomass carbon sphere flexible composite piezoresistive sensor and preparation method thereof

Abstract

This invention discloses a flexible composite piezoresistive sensor based on PVA / glycerol / biomass carbon spheres and its preparation method. The sensor comprises a flexible substrate and a conductive active layer, the conductive active layer being distributed within the flexible substrate. The flexible substrate is a polyvinyl alcohol / glycerol composite hydrogel system. The conductive active layer comprises biomass-derived carbon nanospheres and poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid, with the biomass-derived carbon nanospheres having a particle size range of 150–200 nm. The mass ratio of the polyvinyl alcohol, biomass-derived carbon nanospheres, and the aqueous solution of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid is 10:1:5, and the amount of glycerol added is 20%–30% of the mass of the polyvinyl alcohol. The surface structure of the flexible composite piezoresistive sensor is a periodically arranged micro-dome array structure. The sensor of this invention possesses advantages such as high sensitivity, wide response range, fast response, excellent mechanical stability, and environmental friendliness.

Description

Technical Field

[0001] This invention belongs to the field of flexible sensor technology, specifically relating to a micro-dome structure flexible piezoresistive sensor based on biomass-derived carbon nanospheres and conductive polymer composite materials, its preparation method, and its application. Background Technology

[0002] With the rapid development of flexible electronics technology, wearable sensors have shown broad application prospects in fields such as human health monitoring, human-computer interaction, intelligent robots, and electronic skin. As one of the core components of wearable systems, flexible pressure sensors can convert external mechanical stimuli into recognizable electrical signals, playing an irreplaceable role in applications such as physiological signal acquisition, motion posture recognition, and tactile feedback. Compared to traditional rigid pressure sensors, flexible pressure sensors must possess excellent pressure sensing performance, good flexibility, mechanical stability, and convenient fabrication processes to meet the precise sensing needs in complex scenarios.

[0003] Among numerous sensing mechanisms, piezoresistive pressure sensors have become a research hotspot due to their advantages such as simple structure, convenient signal readout, fast response speed, and good durability. However, flexible piezoresistive sensors still face challenges in practical applications, such as maintaining high sensitivity while achieving a wide linear detection range, fast response, and long-term stability. Researchers have proposed that constructing micro / nanostructures on flexible substrates is an effective strategy to overcome these performance bottlenecks. By designing regular microarrays such as pyramids, micropillars, and microdome, the effective contact area between the active layer and the electrode can be significantly increased, generating stress concentration and deformation amplification effects under pressure, thereby greatly improving the sensor's sensitivity.

[0004] Polyvinyl alcohol (PVA) has become a preferred substrate material for flexible sensors due to its good flexibility, excellent film-forming properties, good biocompatibility, and low cost. However, pure PVA films suffer from defects such as high brittleness, weak resistance to deformation, and susceptibility to breakage after long-term use, which seriously restricts the expansion of its practical applications.

[0005] Cuttlefish ink-derived carbon nanospheres have the advantages of large specific surface area, excellent electrical conductivity, simple preparation process, and low cost. They are also environmentally friendly and rich in oxygen-containing functional groups on the surface, which can significantly improve interfacial compatibility with polymer matrices. Their nanoscale size helps to form a continuous three-dimensional conductive network.

[0006] Poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) is a typical conductive polymer material with good flexibility, high conductivity and solution processability, making it an ideal conductive component for flexible sensors. However, the single PEDOT:PSS system is prone to filler agglomeration, resulting in uneven distribution of the conductive network, which in turn affects the stability and consistency of sensing performance.

[0007] Currently, simply replacing the elastic conductive material is insufficient to meet the development expectations for high-performance flexible sensors. When the sensor deforms under external force, the spacing of the conductive fillers inside the polymer matrix changes dynamically, causing disorder and reconstruction of the conductive network, which directly affects the overall resistance response characteristics of the composite sensor.

[0008] Therefore, exploring flexible sensing material systems that combine excellent electrical properties and structural designability, and developing efficient and low-cost microstructure construction strategies, is of great significance for promoting the development of flexible piezoresistive sensors towards high performance and multifunctionality. Summary of the Invention

[0009] The purpose of this invention is to provide a flexible composite piezoresistive sensor with a microdome structure (PVA / glycerol / biomass carbon spheres) and its preparation method. This sensor has the advantages of high sensitivity, wide response range, fast response, excellent mechanical stability and environmental friendliness.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A flexible composite piezoresistive sensor based on PVA / glycerol / biomass carbon spheres includes a flexible substrate and a conductive active layer, wherein the conductive active layer is distributed within the flexible substrate; wherein: the flexible substrate is a polyvinyl alcohol / glycerol composite hydrogel system; the conductive active layer comprises biomass-derived carbon nanospheres and poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid, and the particle size range of the biomass-derived carbon nanospheres is 150–200 nm, and the poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid is an aqueous solution with a concentration of 1.0–1.3 wt%; wherein the mass ratio of polyvinyl alcohol, biomass-derived carbon nanospheres, and the aqueous solution of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid is 10:1:5, and the amount of glycerol added is 20%–30% of the mass of polyvinyl alcohol; the surface structure of the flexible composite piezoresistive sensor is a periodically arranged microdome array structure.

[0012] In this invention, the flexible substrate is a polyvinyl alcohol / glycerol composite hydrogel system. By utilizing glycerol to disrupt the hydrogen bonds between PVA molecules, the flexibility and mechanical stability of the flexible substrate film can be significantly improved. Furthermore, the amount of glycerol added is limited to 20% to 30% of the mass of polyvinyl alcohol, allowing glycerol molecules to insert between PVA chains, thereby disrupting some of the strong hydrogen bonds between PVA molecules and forming a dynamic hydrogen bond network. This not only compensates for the rigidity caused by the high carbon filler content but also enables the sensor to maintain high conductivity while achieving an elongation at break of 380%.

[0013] This invention introduces biomass-derived carbon nanospheres with a specific particle size range (150-200 nm) into the conductive active layer, forming a "dual conductive network" with PEDOT:PSS. Experimental data shows that when the carbon nanosphere particle size is too large (>200 nm), particle sedimentation leads to uneven distribution, and when the particle size is too small (<150 nm), quantum size effect leads to decreased conductivity. Through the synergistic effect of biomass-derived carbon nanospheres with a specific particle size and PEDOT:PSS, this invention achieves a composite material conductivity of 0.0181 S / m, which is significantly higher than existing similar products, and no agglomeration phenomenon is observed.

[0014] This invention also specifies that the mass ratio of polyvinyl alcohol, biomass-derived carbon nanospheres, and poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid aqueous solution is 10:1:5. In the preparation process, by controlling the mass ratio of the three components, the mechanical flexibility and film-forming properties of the flexible matrix are maintained while ensuring good conductivity of the composite material, avoiding brittleness or film-forming difficulties caused by excessive conductive filler. Biomass-derived carbon nanospheres serve as the conductive reinforcing phase, poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid as the conductive polymer matrix, and polyvinyl alcohol as the film-forming matrix and dispersant. At this ratio, the three components form a stable blend system, preventing carbon nanosphere aggregation and ensuring a uniform microstructure of the composite material. This ratio helps optimize the interfacial bonding between carbon nanospheres and poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid, while utilizing the hydrogen bonding between the hydroxyl groups of polyvinyl alcohol and the sulfonic acid groups in poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid enhances the compatibility and interfacial stability between the components.

[0015] As a further explanation of the present invention, the dome radius of the microdome array is 0.4–0.6 mm, and the center-to-center distance between adjacent domes is 1.2–1.5 mm. The PVA / glycerol / carbon spheres / PEDOT:PSS system of the present invention has a specific Young's modulus, enabling it to resonate with the microdome array of the above-mentioned geometric parameters. When subjected to minute pressure, the microdome structure of the present invention undergoes a 'collapse-contact' abrupt change, achieving a pressure of 44.092 kPa through the combined dual conductive network of the material. -1 Its ultra-high sensitivity.

[0016] As a further explanation of the present invention, the biomass-derived carbon nanospheres are prepared by high-temperature carbonization of squid ink. As a natural biological raw material, squid ink-derived carbon nanospheres (CNPs) have advantages such as uniform particle size, large specific surface area, excellent electrical conductivity, simple preparation process, and environmental friendliness.

[0017] As a further illustration of the present invention, the flexible composite piezoresistive sensor has a sensitivity greater than 40 kPa in the pressure range of 0–5.6 kPa. -1The response time is less than 90ms. This invention combines the sensing mechanism with a targeted design of the microstructure of conductive active materials. By introducing special configurations and regulating the arrangement of conductive fillers, the sensitivity of the sensor is significantly improved.

[0018] This invention also provides a method for preparing the PVA / glycerol / biomass carbon sphere flexible composite piezoresistive sensor as described above, characterized by comprising the following steps:

[0019] Step 1: The bio-based carbon material is subjected to acid washing, centrifugation, drying, and high-temperature carbonization to obtain biomass-derived carbon nanospheres;

[0020] Step 2: Add polyvinyl alcohol to deionized water and heat and stir at 85-95°C until completely dissolved. Then add the biomass-derived carbon nanospheres, poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid and glycerol in sequence. After ultrasonic dispersion and magnetic stirring, a uniform composite solution is formed.

[0021] Step 3: The composite solution obtained in Step 2 is cast into a mold with a micro-dome array structure and dried at 75-85℃ for 6-10 hours. After demolding, a composite flexible film with a micro-dome array is obtained.

[0022] (4) The electrode is encapsulated on the composite flexible film obtained in step three to obtain a PVA / glycerol / biomass carbon ball flexible composite piezoresistive sensor.

[0023] The method of the present invention is further described in that, in step one, the bio-based carbon material is squid ink, the high-temperature carbonization temperature is 900°C, the heating rate is 5°C / min, the carbonization time is 2h, and the protective atmosphere is nitrogen.

[0024] The method of the present invention is further described in step three, wherein the dome radius of the microdome array of the composite flexible film is 0.4 to 0.6 mm, and the center-to-center distance between adjacent domes is 1.2 to 1.5 mm.

[0025] The PVA / glycerol / biomass carbon ball flexible composite piezoresistive sensor described in this invention is applied in human motion monitoring, Morse code recognition, touch screen handwriting input, and motion signal classification and recognition combined with machine learning algorithms.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. Synergistic effect of conductive materials: Compared with the simple PEDOT:PSS / PVA system or biomass carbon ball / PVA system in the prior art, the conductive active layer of the present invention introduces squid ink-derived carbon nanospheres with a particle size of 150-200nm. The carbon nanospheres with a specific particle size (150-200nm) form a "dual conductive network" with PEDOT:PSS, exerting a synergistic effect, so that the electrical conductivity of the composite material reaches 0.0181 S / m, which is significantly higher than that of similar materials in the prior art, and no agglomeration phenomenon is observed.

[0028] 2. Improved Mechanical Properties of the Substrate: The flexible substrate of this invention is a polyvinyl alcohol / glycerol composite hydrogel system. Glycerol disrupts the hydrogen bonds between PVA molecules, significantly improving the flexibility and mechanical stability of the flexible substrate film. Simultaneously, the introduction of a high proportion of carbon nanospheres (PVA:carbon nanospheres = 10:1) in this invention typically hinders polymer chain movement, making the material brittle. Therefore, this application specifies that by limiting the amount of glycerol added to 25% of the PVA mass, glycerol molecules insert between PVA chains, disrupting the strong hydrogen bonds between PVA molecules and forming a dynamic hydrogen bond network. This not only compensates for the rigidity caused by the high carbon filler content but also enables the sensor to maintain high conductivity while achieving an elongation at break of 380%.

[0029] 3. Ultra-high sensitivity achieved through synergistic material system and microstructure design: The sensitivity enhancement effect of the microstructure is highly dependent on the modulus of the material; the PVA / glycerol / carbon spheres / PEDOT:PSS system of this invention has a specific Young's modulus, which resonates with the geometric parameters of the microdome array; when subjected to minute pressure, the microdome structure of this invention undergoes a 'collapse-contact' abrupt change, and combined with the material's dual conductive network, a pressure of 44.092 kPa is achieved. -1 Its ultra-high sensitivity. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the fabrication process of a flexible composite piezoresistive sensor according to an embodiment of the present invention.

[0031] Figure 2 This is a structural and characterization diagram of a flexible composite piezoresistive sensor according to an embodiment of the present invention; wherein:

[0032] (a) is a digital photograph of the macroscopic morphology of the thin film under bending, torsion, and stretching conditions;

[0033] (b) is a scanning electron microscope image of a thin film surface with a microdome structure;

[0034] (c) is a magnified scanning electron microscope image of a single microdome structure and its corresponding elemental distribution map;

[0035] (d) is a scanning electron microscope image of the top of the microdome structure;

[0036] (e) is a cross-sectional scanning electron microscope image of the microdome structure;

[0037] (f) is a scanning electron microscope image and energy dispersive spectroscopy analysis of squid ink-derived carbon nanospheres;

[0038] (g) is a scanning electron microscope image of the surface of a thin film without microdome structures.

[0039] Figure 3 This is a material characterization diagram of a flexible composite piezoresistive sensor according to an embodiment of the present invention; wherein:

[0040] (a) is the X-ray diffraction spectrum;

[0041] (b) is the Fourier transform infrared spectrum;

[0042] (c) is the Raman spectrum;

[0043] (d) is the full spectrum of X-ray photoelectron energy;

[0044] (e) is the high-resolution C 1s spectrum;

[0045] (f) is the O 1s high-resolution spectrum.

[0046] Figure 4 A comparison chart showing the sensing mechanism and mechanical properties of different piezoresistive sensors; where:

[0047] (a) Comparison of sensitivity curves for different thin films;

[0048] (b) Comparison of response-recovery characteristics of different thin films;

[0049] (c) Comparison of conductivity of different thin films;

[0050] (d) shows the tensile stress-strain curves of different films;

[0051] (e) Comparison of elongation at break and tensile strength of different films;

[0052] (f) Comparison of toughness and elastic modulus of different films;

[0053] (g) is a schematic diagram of the piezoresistive sensing mechanism of the microdome structure composite film.

[0054] Figure 5 This is a pressure sensing performance diagram of a flexible composite piezoresistive sensor according to an embodiment of the present invention; wherein:

[0055] (a) is the sensitivity curve;

[0056] (b) shows the current-time response curves under different pressures;

[0057] (c) shows the current-time response curve under gradient pressure;

[0058] (d) represents response time and recovery time;

[0059] (e) shows the current-time response curves at different frequencies;

[0060] (f) is the long-term stability test during the cyclic loading-unloading process;

[0061] (g) Comparison with the sensor performance reported in the literature.

[0062] Figure 6 This is a diagram illustrating the application of a flexible composite piezoresistive sensor according to an embodiment of the present invention in Morse code recognition and touchscreen handwriting; wherein:

[0063] (a) is a table of Morse code encoding rules;

[0064] (b)-(f) are the real-time current response curves of the sensor to the Morse code signals “OK”, “NO”, “SOS”, “YES” and “SENSOR”, respectively.

[0065] (g)-(i) represent the application of sensors in touchscreen handwriting input.

[0066] Figure 7 This is a diagram illustrating the application of a flexible piezoresistive sensor according to an embodiment of the present invention in human motion monitoring; wherein:

[0067] (a)-(h) are the current-time response curves of the sensor in wrist, finger, different angles of finger bending, elbow, neck bending, knee bending, ankle bending and stepping movements, respectively.

[0068] (i) shows the current-time response curves for clicking and double-clicking the mouse.

[0069] Figure 8 This is a diagram showing the results of human motion recognition and classification using a flexible composite piezoresistive sensor combined with machine learning according to an embodiment of the present invention; wherein:

[0070] (a) is the real-time current response signal of the sensor to the movement of multiple parts of the human body;

[0071] (b) is a schematic diagram of the support vector machine classification model;

[0072] (c) is a schematic diagram of the working principle of the support vector machine classifier;

[0073] (d) is the confusion matrix of the classification results on the test set;

[0074] (e) is the confusion matrix of the classification results of the training set;

[0075] (f) Visualization results of feature clustering from principal component analysis;

[0076] (g) is the receiver operating characteristic curve.

[0077] Symbol explanations in the figure: CNPs: Carbon Nanospheres; PEDOT:PSS: Poly(3,4-ethylenedioxythiophene): Polystyrene sulfonic acid; PVA: Polyvinyl alcohol; SEM: Scanning electron microscope; FTIR: Fourier transform infrared spectroscopy; XRD: X-ray diffraction; XPS: X-ray photoelectron spectroscopy; SVM: Support vector machine; PCA: Principal component analysis; ROC: Receiver operating characteristic curve; AUC: Area under the curve. Detailed Implementation

[0078] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0079] Example 1:

[0080] (I) Preparation of biomass-derived carbon nanospheres

[0081] Take 50g of squid ink (food grade, purchased from Qingdao Xinjian Aquatic Products Co., Ltd., China) and disperse it in a mixed solution of 170mL deionized water and 30mL hydrochloric acid. Stir magnetically for 6 hours until a uniformly dispersed suspension is formed. Then, wash with deionized water and ethanol alternately and centrifuge to purify until the system reaches neutrality. Place the obtained product in a 60℃ oven to dry for 12 hours, grind it thoroughly, and transfer it to a tube furnace. Under a nitrogen atmosphere (flow rate 50mL / min), heat it to 900℃ at a heating rate of 5℃ / min and carbonize it at this temperature for 2 hours. After the tube furnace cools naturally to room temperature, remove the black product and grind it thoroughly to obtain squid ink-derived carbon nanospheres, which are then sealed and stored for later use.

[0082] The prepared carbon nanospheres are regular spherical with a diameter of about 170 nm and a relatively rough surface. The X-ray diffraction pattern shows a broadened diffuse peak near 2θ=25°, which is attributed to the (002) plane feature of amorphous carbon, indicating that it is mainly an amorphous structure.

[0083] (II) Preparation of composite solutions

[0084] Weigh 2.0 g of polyvinyl alcohol (molecular weight 1750±50) and add it to 20 mL of deionized water. Stir magnetically in a 90℃ oil bath for 1 h until a transparent and homogeneous polyvinyl alcohol aqueous solution is formed. Then add 0.2 g of the carbon nanospheres prepared above, ultrasonically disperse for 30 min, and magnetically stir for 30 min to obtain a homogeneous composite solution. Slowly add 1 g of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid aqueous solution (concentration 1.0–1.3 wt%, pH 1000) dropwise at room temperature, and stir magnetically for 1 h. Then add 0.5 g of glycerol (purity ≥99.5%), and continue stirring for 30 min to completely disperse the glycerol, obtaining a homogeneous composite solution.

[0085] (III) Preparation of microdome-structured composite films

[0086] The composite solution was cast into a polytetrafluoroethylene mold with a microdome array structure, wherein the radius of the microdome array is 0.5 mm and the center-to-center distance between adjacent domes is 1.3 mm. The film was dried in an 80°C forced-air drying oven for 8 hours. After the film was fully formed, it was gently peeled off from the mold surface to obtain a flexible composite film of carbon nanospheres / poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid / polyvinyl alcohol / glycerol with a microdome structure.

[0087] (iv) Sensor assembly

[0088] Conductive electrodes are led out from both ends of the above-mentioned composite flexible film. Conductive silver paste and copper foil are used as electrode materials, and after encapsulation, a flexible piezoresistive sensor is obtained.

[0089] (v) Performance Testing

[0090] (1) Microstructure characterization: The microstructure of the film surface and cross-section was observed using field emission scanning electron microscopy. The results showed that a regularly arranged array of microdomes was successfully constructed on the film surface, with a dome radius of 500 μm, forming a periodic microstructure. The carbon nanospheres were uniformly distributed in the matrix and together with poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid, they formed a three-dimensional conductive network.

[0091] (2) Mechanical property testing: The mechanical properties of the film were tested using a universal tensile testing machine at a tensile rate of 5 mm / min. The test results showed that the tensile strength of the prepared composite flexible film was 5.47 MPa, the elongation at break was 380%, the toughness was 12.8 MJ / m³, and the elastic modulus was 18.6 MPa.

[0092] (3) Electrical performance test: The volume resistivity of the thin film was tested using a four-probe tester at a voltage of 10V. The results showed that the conductivity of the composite thin film with the microdome structure was 0.0181 S / m.

[0093] (4) Piezoresistive sensing performance test: The sensor was placed on a universal testing machine, and different pressures were applied. The changes in the current signal were recorded. The results showed:

[0094] Sensitivity: 44.092 kPa in the range of 0–5.6 kPa. -1 ;

[0095] Response range: 0~123.2kPa;

[0096] Response time: 88ms;

[0097] Recovery time: 88ms;

[0098] Cyclic stability: After 7000 load-unload cycle tests, the current response amplitude did not show significant attenuation.

[0099] (5) Application performance testing:

[0100] Morse code recognition: The sensor can accurately capture the difference in the duration of finger pressure and successfully recognize Morse code signals for words such as "OK", "NO", "SOS", "YES" and "SENSOR".

[0101] Touchscreen handwriting: The sensor successfully enabled handwriting input on the electronic screen.

[0102] Human motion monitoring: The sensor is attached to the wrist, fingers, elbow, neck, knee, ankle and other parts of the body. It can record the current response signal during the bending and extension of the joint in real time, and can distinguish different angles such as 30°, 60° and 90° of finger bending.

[0103] Mouse operation recognition: The sensor can clearly distinguish between single-click and double-click mouse operations.

[0104] (6) Machine Learning Classification and Recognition: Five types of human motion signals, including finger bending, wrist rotation, elbow bending, knee bending, and ankle rotation, were collected and classified using a support vector machine model. The results showed that the classification accuracy on the training set was 98.7%, and the classification accuracy on the test set was 98.28%. Principal component analysis and feature clustering visualization showed that the data points of different motion categories exhibited a clear cluster distribution, and the area under the receiver operating characteristic curve was close to 1, indicating that the classification model has excellent discriminative ability.

[0105] Comparative Example 1:

[0106] The difference from Example 1 is that glycerin was not added. The specific steps are as follows:

[0107] Weigh 2.0 g of polyvinyl alcohol and add it to 20 mL of deionized water. Stir in an oil bath at 90 °C for 1 h until completely dissolved. Add 0.2 g of carbon nanospheres, sonicate for 30 min, and stir magnetically for 30 min. Add 1 g of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid aqueous solution dropwise and stir for 1 h. Cast the composite solution into a microdome structure mold, dry at 80 °C for 8 h, and obtain the composite film after demolding.

[0108] Performance test results show:

[0109] Tensile strength: 3.82 MPa, elongation at break: 120%;

[0110] The film is brittle and cracks appear after repeated bending.

[0111] The sensor's current response significantly decreased after 500 cycles of loading;

[0112] Sensitivity: 28.6 kPa -1 Response range: 0~80kPa.

[0113] Compared with Example 1, the sensor without glycerol showed significantly reduced flexibility and long-term stability, indicating that glycerol plays an important role in improving the mechanical properties of the thin film and the stability of the sensor.

[0114] Comparative Example 2:

[0115] The difference from Example 1 is that the microdome structure was not introduced, and a flat polytetrafluoroethylene mold was used for molding. The specific steps are as follows:

[0116] The composite solution was prepared according to the method in Example 1. The solution was cast into a flat polytetrafluoroethylene mold, dried at 80°C for 8 hours, and a flat composite film was obtained after demolding.

[0117] Performance test results show:

[0118] Sensitivity: 12.3 kPa -1 ;

[0119] Response range: 0~40kPa;

[0120] Response time: 125ms, recovery time: 132ms;

[0121] The current response began to decay after 3000 cycles of loading.

[0122] Compared with Example 1, the sensor without the microdome structure showed significantly worse sensitivity, response range, response speed and cycle stability, indicating that the microdome structure plays a key role in improving the overall performance of the sensor.

[0123] Comparative Example 3:

[0124] The difference from Example 1 lies in the mass ratio of carbon nanospheres to poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid. In this comparative example, the amount of carbon nanospheres added is 0.1g, and the amount of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid aqueous solution added is 1g, with a mass ratio of 1:10.

[0125] Performance test results show:

[0126] Electrical conductivity: 0.0092 S / m;

[0127] Sensitivity: 28.5 kPa -1 ;

[0128] Response range: 0~95kPa;

[0129] Tensile strength: 4.56 MPa, elongation at break: 325%.

[0130] Compared to Example 1, the change in the proportion of conductive filler affected the density and continuity of the conductive network, resulting in a decrease in electrical and sensing performance, but it was still better than a single conductive system.

[0131] Technical Effect Comparison Table:

[0132] Table 1. Comparison of key performance characteristics of Embodiment 1 of the present invention with existing technologies.

[0133] Performance indicators Example 1 Typical values ​​of existing technologies Comparison and explanation <![CDATA[Sensitivity (kPa -1 ).]]> 44.092 5～30 The sensitivity of this invention is significantly superior to that of existing technologies, especially in the low-pressure region. Response range (kPa) 0～123.2 0～50 This invention has a wider response range and is suitable for a wider range of application scenarios. Response time (ms) 88 100～200 This invention offers a faster response time, meeting the needs of real-time monitoring. Recovery time (ms) 88 100～200 This invention offers faster recovery speed and superior dynamic response performance. Tensile strength (MPa) 5.47 2～4 This invention has higher mechanical strength and better structural stability. Elongation at break (%) 380 100～250 This invention offers superior flexibility and adaptability to complex deformation environments. Cyclic stability (times) >7000 1000～5000 This invention offers superior long-term stability and a longer service life. Electrical conductivity (S / m) 0.0181 0.001～0.01 This invention offers superior conductivity and stronger signal output. Machine learning classification accuracy (%) 98.28 — This invention achieves high-precision intelligent classification and recognition for the first time.

[0134] Table 2 Performance Comparison of Example 1 of the Invention and Comparative Examples 1-3

[0135] Performance indicators Example 1 (Microdome + Glycerin) Comparative Example 1 (Glycerin-free) Comparative Example 2 (without microdome) Comparative Example 3 (Different packing ratios) <![CDATA[Sensitivity (kPa -1 )]]> 44.092 28.6 12.3 28.5 Response range (kPa) 0～123.2 0～80 0～40 0～95 Response / Recovery Time (ms) 88 / 88 105 / 110 125 / 132 95 / 98 Tensile strength (MPa) 5.47 3.82 5.12 4.56 Elongation at break (%) 380 120 365 325 Electrical conductivity (S / m) 0.0181 0.0152 0.0168 0.0092 Cyclic stability (times) >7000 500 3000 5500

[0136] Obviously, the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description; it is neither necessary nor possible to exhaustively list all possible implementations; however, obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A flexible composite piezoresistive sensor for PVA / glycerol / biomass carbon spheres, comprising a flexible substrate and a conductive active layer, wherein the conductive active layer is distributed in the flexible substrate; characterized in that: The flexible substrate is a polyvinyl alcohol / glycerol composite hydrogel system; the conductive active layer comprises biomass-derived carbon nanospheres and poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid, wherein the particle size of the biomass-derived carbon nanospheres ranges from 150 to 200 nm, and the poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid is an aqueous solution with a concentration of 1.0 to 1.3 wt%; wherein the mass ratio of polyvinyl alcohol, biomass-derived carbon nanospheres, and poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid aqueous solution is 10:1:5, and the amount of glycerol added is 20% to 30% of the mass of polyvinyl alcohol; the surface structure of the flexible composite piezoresistive sensor is a periodically arranged microdome array structure.

2. The PVA / glycerol / biomass carbon sphere flexible composite piezoresistive sensor according to claim 1, characterized in that: The dome radius of the microdome array is 0.4–0.6 mm, and the center-to-center distance between adjacent domes is 1.2–1.5 mm.

3. The PVA / glycerol / biomass carbon sphere flexible composite piezoresistive sensor according to claim 1, characterized in that: The biomass-derived carbon nanospheres are prepared by high-temperature carbonization of squid ink.

4. The PVA / glycerol / biomass carbon sphere flexible composite piezoresistive sensor according to claim 1, characterized in that: The flexible composite piezoresistive sensor has a sensitivity greater than 40 kPa in the pressure range of 0–5.6 kPa. -1 The response time is less than 90ms.

5. A method for preparing a flexible composite piezoresistive sensor of PVA / glycerol / biomass carbon spheres as described in claim 1, characterized in that... Includes the following steps: Step 1: The bio-based carbon material is subjected to acid washing, centrifugation, drying, and high-temperature carbonization to obtain biomass-derived carbon nanospheres; Step 2: Add polyvinyl alcohol to deionized water and heat and stir at 85-95°C until completely dissolved. Then, add the biomass-derived carbon nanospheres obtained in Step 1, poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid aqueous solution and glycerol in sequence. After ultrasonic dispersion and magnetic stirring, a uniform composite solution is formed. Step 3: The composite solution obtained in Step 2 is cast into a mold with a micro-dome array structure and dried at 75-85℃ for 6-10 hours. After demolding, a composite flexible film with a micro-dome array is obtained. (4) The electrode is encapsulated on the composite flexible film obtained in step three to obtain a PVA / glycerol / biomass carbon ball flexible composite piezoresistive sensor.

6. The method for preparing the PVA / glycerol / biomass carbon sphere flexible composite piezoresistive sensor according to claim 5, characterized in that: In step one, the bio-based carbon material is squid ink, the high-temperature carbonization temperature is 900℃, the heating rate is 5℃ / min, the carbonization time is 2h, and the protective atmosphere is nitrogen.

7. The method for preparing the PVA / glycerol / biomass carbon sphere flexible composite piezoresistive sensor according to claim 5, characterized in that: In step three, the dome radius of the microdome array of the composite flexible film is 0.4 to 0.6 mm, and the center-to-center distance between adjacent domes is 1.2 to 1.5 mm.

8. The application of the PVA / glycerol / biomass carbon ball flexible composite piezoresistive sensor as described in claim 1 in human motion monitoring, Morse code recognition, touch screen handwriting input, and motion signal classification and recognition combined with machine learning algorithms.

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