A flexible stress / strain sensor with high sensitivity and wide response range and a preparation method thereof

Abstract

The application discloses a kind of high sensitivity, wide response range flexible stress / strain sensor and preparation method thereof, belong to sensor field, obtain flexible stress / strain sensor with ultrahigh sensitivity, ultra-low detection limit, wide tensile range, fast response time and ultrahigh stability.The flexible stress / strain sensor of the application is sequentially from bottom to top stretchable polymer substrate with screen structure, metal film, metal nanoparticle carbon nanotube composite layer, metal film, polymer protective film;Sensor functional layer is metal film / metal nanoparticle carbon nanotube composite layer / metal film, obtain super-wide range (strain 0.02%~90%) and ultrahigh sensitivity (the highest GF value is 13590), fast response speed (~100ms) and excellent cycle stability (≥18000 times).And applied in human motion detection, human pulse monitoring and sound detection and other scenes, obtain good effect.

Description

Technical Field

[0001] This invention belongs to the field of sensors, and particularly relates to a high-sensitivity, wide-response-range flexible stress / strain sensor and its fabrication method. Background Technology

[0002] Flexible stress / strain sensors are devices that convert stress / strain into measurable electrical signals. These devices have enormous application potential in fields such as electronic skin, human-computer interaction, wearable devices, and medicine. The performance characteristics of these sensors mainly include sensitivity, stretchability, response and recovery time, and stability.

[0003] Commonly used conductive network materials in resistive flexible stress / strain sensors include carbon black (CB), carbon nanotubes (CNTs), graphene, metal nanoparticles, and silver nanowires. Among these, carbon nanotubes (CNTs) possess excellent mechanical properties (high tensile strength, high elastic modulus) and good conductivity. Flexible stress / strain sensors using carbon nanotubes as conductive fillers have a large tensile range but low sensitivity; conversely, sensors using metal nanoparticles as conductive fillers exhibit high sensitivity but a small tensile range. Besides the conductive filler, the performance of flexible stress / strain sensors is also affected by the flexible substrate and electrodes. Research shows that flexible substrates containing specific microstructures have a large specific surface area, which is beneficial for forming complex electrical behaviors of conductive fillers, resulting in higher sensitivity and faster response times. Therefore, developing novel stress / strain sensors with specific microstructures and architectures is an effective way to resolve the contradiction between high sensitivity and a wide tensile range. Summary of the Invention

[0004] This invention provides a flexible stress / strain sensor with high sensitivity and wide response range and its fabrication method, resulting in a flexible stress / strain sensor with ultra-high sensitivity, ultra-low detection limit, wide tensile range, fast response time and ultra-high stability.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A highly sensitive, wide-response-range flexible stress / strain sensor, comprising, from bottom to top, a stretchable polymer substrate with a sieve structure, a sensing functional layer, and a polymer protective film; the sensing functional layer is a metal thin film / metal nanoparticles@carbon nanotube composite layer / metal thin film.

[0007] In the above-described structure, the stretchable polymer substrate with a sieve structure is any one of DragonSkin, silicone rubber, or acrylate elastomer; the metal film is Pt, Au, Cu, Ag, Al, Mg, Fe, Co, Ti, Zn, Ta, Ni, or an alloy thereof, with a thickness of approximately 50-200 nm; the metal nanoparticle@carbon nanotube composite layer has a thickness of approximately 10-50 μm, wherein the metal nanoparticles are Ir, Pt, Au, Ag, Cu, Al, Ti, Zn, Fe, Co, or Ni.

[0008] A method for fabricating a highly sensitive, wide-response-range flexible stress / strain sensor includes the following steps:

[0009] Step 1: After cutting the metal mesh, clean it with deionized water, dry it, and then fix it on the glass slide as a template;

[0010] Step 2: Pour the polymer monomer solution onto the surface of the metal screen, cure it at 40℃-80℃ for 2-24 hours, and then peel it off to obtain a polymer film with a patterned metal screen.

[0011] Step 3: Deposit a metal film on the polymer film obtained in Step 2 using magnetron sputtering or vacuum evaporation.

[0012] Step 4: Grow metal nanoparticles on carbon nanotubes using atomic layer deposition, chemical solution methods, or physical vapor deposition methods;

[0013] Step 5: Disperse the metal nanoparticle-carbon nanotube composite material obtained in Step 4 in ethanol at a concentration of 1-5 mg / mL, and then sonicate it for 1 hour to achieve uniform dispersion.

[0014] Step 6: Apply the dispersion evenly to the metal layer from Step 3, and then dry at 40°C for 1 hour;

[0015] Step 7: Use conductive silver paste to attach copper foil to both ends of the film dried in step 6, then magnetron sputter a metal layer, and then coat the surface with a polymer film of the same material as the lower polymer layer as a protective layer, thus obtaining a flexible stress / strain sensor with a complete structure.

[0016] Beneficial effects: This invention provides a high-sensitivity, wide-response-range flexible stress / strain sensor and its fabrication method, obtaining a flexible stress / strain sensor with a composite microstructure and architecture. Specifically, an elastic polymer with a sieve structure serves as the flexible substrate, and a metal thin film / metal nanoparticle@carbon nanotube composite layer / metal thin film composite structure and architecture are used as the sensing functional layer. This results in an ultra-wide measurement range (strain 0.02%–90%), ultra-high sensitivity (maximum GF value of 13590), fast response speed (~100ms), and excellent cycle stability (≥18000 cycles). Furthermore, it has achieved good results in applications such as human motion detection, human pulse monitoring, and sound detection. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the flexible strain sensor in an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the fabrication process of the flexible strain sensor in Embodiment 1 of the present invention;

[0019] Figure 3 The images shown are, in order: a copper mesh, a copper mesh patterned dragon scale armor film in this embodiment of the invention, a magnetron sputtered platinum film, and a drop-coated carbon nanotube;

[0020] Figure 4 TEM image of the iridium nanoparticle-modified carbon nanotube composite material prepared in an embodiment of the present invention;

[0021] Figure 5 The dynamic response curve of the flexible strain sensor prepared according to an embodiment of the present invention;

[0022] Figure 6 The sensitivity curve of the flexible strain sensor prepared according to an embodiment of the present invention;

[0023] Figure 7 The response and recovery time curves of the flexible strain sensor prepared according to an embodiment of the present invention are shown.

[0024] Figure 8 Cyclic stability curve of the flexible strain sensor prepared according to an embodiment of the present invention;

[0025] Figure 9 The flexible strain sensor prepared according to an embodiment of the present invention is used for human pulse monitoring to obtain the ΔR / R0-t curve;

[0026] Figure 10 The ΔR / R0-t curve of the flexible strain sensor prepared according to an embodiment of the present invention for human motion detection;

[0027] Figure 11The ΔR / R0-t curve of the flexible strain sensor prepared for sound detection in an embodiment of the present invention is shown. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0029] Example 1

[0030] like Figure 1 As shown, a high-sensitivity, wide-response-range flexible stress / strain sensor structure, from bottom to top, is a sieve structure: dragon scale armor / Pt metal layer / Ir nanoparticles@carbon nanotubes / Pt metal layer / dragon scale armor stress / strain sensor.

[0031] like Figure 2 As shown, a method for fabricating a highly sensitive, wide-response-range flexible stress / strain sensor includes the following steps:

[0032] 1) Clean the copper mesh with deionized water, dry it, and then fix it on the glass slide as a template;

[0033] 2) Mix components A and B of the dragon scale armor in a 1:1 mass ratio, stir with a stirring rod for 5 minutes, pour it onto the surface of the copper mesh, wait for the surface to self-level, place it in an oven at 40℃ for 3 hours, peel it off after curing, and then cut it into 10mm×20mm×0.5mm dimensions.

[0034] 3) A Pt layer was deposited on a copper mesh patterned dragon scale methyl substrate using a magnetron sputtering instrument. The sputtering current was 30 mA, the sputtering time was 900 s, and the thickness was 140 nm.

[0035] 4) Ir NPs (nanoparticles) were grown on CNTs (carbon nanotubes) using atomic layer deposition (ALD). The specific growth conditions were as follows: the chamber growth temperature was 310℃; the precursors were iridium acetylacetone (Ir(C5H7O2)3, source temperature 200℃) and oxygen (O2, room temperature); the deposition pulse cycles were 8s Ir(C5H7O2)3 pulse followed by a 25s cleaning pulse, 8s O2 pulse, and a 25s cleaning pulse; the cleaning gas and carrier gas were both high-purity nitrogen (N2, 99.999%); the partial pressure and flow rate of oxygen were 1.1 hPa and 50 sccm, respectively; and the number of growth cycles was 200.

[0036] 5) The deposited CNTs were dispersed in anhydrous ethanol at a concentration of 2 mg / mL, and after magnetic stirring for 5 min, they were placed in an ultrasonic bath and sonicated for 1 h to obtain a uniformly dispersed Ir NPs@CNTs ethanol solution.

[0037] 6) The Ir NPs@CNTs dispersion was uniformly drop-coated onto the Pt layer of the dragon scale armor / Pt film in step 3) above, and then heated at 40°C for 30 min. This step was repeated three times until the drop coating was uniform.

[0038] 7) Use conductive silver paste to attach copper foil to both ends of the thin film CNTs layer in step 6) above, place it in a fume hood for 30 minutes to cure it, and then repeat step 3) to deposit a layer of platinum on it, and then wrap a layer of dragon scale armor protective layer on the surface to obtain a flexible stress / strain sensor with high sensitivity and wide response range.

[0039] Figure 3 These are SEM images of the morphology of each layer of the aforementioned sensor. Figure 3 (1) The copper mesh texture structure is displayed; Figure 3 (2) The copper mesh structure is a dragon scale methyl base. The image shows a nearly regularly arranged square structure with a distance of 41.6 μm between the squares. Figure 3 (3) The surface structure of the patterned copper mesh after magnetron sputtering of platinum is shown, indicating that platinum is deposited relatively uniformly on the dragon scale methyl substrate; Figure 3 (4) The surface morphology after drop-coating Ir NPs@CNTs shows that carbon nanotubes have been uniformly distributed on platinum.

[0040] Figure 4 The image shows a TEM image of carbon nanotubes modified with Ir nanoparticles. The deposition cycle was 200 cycles. It can be seen that the Ir nanoparticles are about 15 nm in diameter and are uniformly dispersed around the carbon nanotubes.

[0041] The electrical performance of the sensor was tested using an electrochemical workstation and a stepper motor. Figure 5 The relative resistance change of the sensor was measured when it was stretched from 0.02% to 98%. It was found that the relative resistance value increased to varying degrees with the increase of strain, and the minimum detection limit was 0.02%, which means that the sensor is very sensitive to extremely small deformations. Figure 6 The sensor sensitivity curve shows that the sensor sensitivity can be roughly divided into two segments. When the strain is less than 55%, the sensor sensitivity is 214.9. When the strain is greater than 55%, the sensor sensitivity surges to 13589.9, and the maximum strain is 98%. Both segments have very good linearity, indicating that the sensor has very good sensitivity and a very wide tensile range. Figure 7 The image shows the response and recovery time curves of the sensor under 0.1% strain. The sensor's response time is 134.4 ms when stress is applied, and its recovery time is 208 ms when stress is removed, exhibiting very fast response and recovery times. Figure 8As shown, after more than 18,000 stretch-recovery cycles, the current shift of the sensor is only about 9.7%, which indicates that the sensor has good stability.

[0042] Several practical applications of the sensor were studied using an electrochemical workstation. Figure 9 The response curves of the above sensors to the tiny deformation of the human pulse show the response pattern of the sensors to the human pulse, and can clearly distinguish the pulse's impact wave (P-wave), heavy impact wave (D-wave), and tidal wave (T-wave). Figure 10 (1), (2), (3), and (4) are the ΔR / R0-t curves of the above sensors for elbow joint, finger joint, swallowing, and blinking actions, respectively. It can be found that the larger the angle of elbow joint and finger joint movement, the higher the peak value of the sensor response. At the same time, the sensor has different response peak shapes for swallowing and smiling actions. Figure 11 The curves are ΔR / R0-t for the sensor's response to the machine's sound, where (1) and (2) represent Chinese sounds, and (3) and (4) represent English sounds. It was found that the sensor responds regularly to different sounds and has different peak shapes.

[0043] Example 2

[0044] like Figure 1 As shown, a flexible stress / strain sensor with high sensitivity and wide response range has a structure from bottom to top consisting of a sieve structure of silicone rubber (polydimethylsiloxane, PDMS) / Au metal layer / Pt nanoparticles@carbon nanotubes / Au metal layer / PDMS.

[0045] like Figure 2 As shown, a method for fabricating a highly sensitive, wide-response-range flexible stress / strain sensor includes the following steps:

[0046] 1) Clean the stainless steel wire mesh with deionized water, dry it, and then fix it on the glass slide as a template;

[0047] 2) Mix PDMS monomer and curing agent at a mass ratio of 10:1, stir magnetically for 20 minutes to make them evenly mixed, then place them in a vacuum for 30 minutes to remove air bubbles, then pour them onto the surface of stainless steel wire mesh, let them stand at room temperature for 10 minutes to allow the surface to self-level, then cure at 50℃ for 24 hours, then peel them off and cut them into 10mm×20mm×0.5mm sizes;

[0048] 3) An Au layer was deposited on a copper mesh patterned PDMS substrate using a magnetron sputtering apparatus, with a sputtering thickness of 50 nm;

[0049] 4) Pt NPs were grown on CNTs using atomic layer deposition (ALD). The specific growth conditions were as follows: the chamber growth temperature was 300℃; the precursors were an organic platinum source (MeCpPtMe3, source temperature 70℃) and oxygen (O2, room temperature); the deposition pulse cycles were 2s MeCpPtMe3 pulse, 5s nitrogen purging pulse, 5s O2 pulse, and 10s nitrogen purging pulse; the purging gas and carrier gas were both high-purity nitrogen (N2, 99.999%); the partial pressure and flow rate of oxygen were 1.1 hPa and 50 sccm, respectively; and the number of growth cycles was 180.

[0050] 5) The deposited CNTs were dispersed in anhydrous ethanol at a concentration of 3 mg / mL, and after magnetic stirring for 5 min, they were placed in an ultrasonic bath and sonicated for 1 h to obtain a uniformly dispersed Pt NPs@CNTs ethanol solution.

[0051] 6) The Pt NPs@CNTs dispersion was uniformly drop-coated onto the Au layer of the PDMS / Au film in step 3) above, and then heated at 40°C for 30 min. This step was repeated three times until the drop coating was uniform.

[0052] 7) Use conductive silver paste to attach copper foil to both ends of the thin film CNTs layer in step 6) above, place it in a fume hood for 30 minutes to cure it, and repeat step 3) to deposit a layer of Au on it. Then wrap a layer of PDMS protective layer on the surface to obtain a flexible stress / strain sensor with high sensitivity and wide range.

[0053] Example 3

[0054] like Figure 1 As shown, a high-sensitivity, wide-response-range flexible stress / strain sensor structure, from bottom to top, is a sieve structure of acrylate elastomer (styrene-butadiene-styrene block copolymer, SBS) / Ag metal layer / Au nanoparticles@carbon nanotubes / Ag metal layer / SBS.

[0055] like Figure 2 As shown, a method for fabricating a highly sensitive, wide-response-range flexible stress / strain sensor includes the following steps:

[0056] 1) Clean the copper mesh with deionized water, dry it, and then fix it on the glass slide as a template;

[0057] 2) SBS monomers styrene and butadiene are polymerized using butyllithium as an initiator, cyclohexane as a solvent, and a small amount of tetrahydrofuran as an activator. The ratio of styrene to butadiene is controlled to be (0.3-0.4):(0.7-0.6). The polymer solution is poured onto the surface of a copper mesh, left to stand until the surface self-levels, and cured at 75°C for 20 hours. The mesh is then peeled off and cut into 10mm×20mm×0.5mm sizes.

[0058] 3) An Ag metal layer with a thickness of 100 nm was deposited on a copper mesh patterned SBS substrate using a magnetron sputtering apparatus;

[0059] 4) The pH of the mixed solution of tetrachloroauric acid (HAuCl4) and polyethyleneimine (bPEI) was adjusted to 9.5 using 0.5 mol / L NaOH solution. The mixture was then stirred at room temperature for 2 min, and then placed in a 95℃ oil bath and stirred for 35 min. After centrifugation, a dispersion of Au nanoparticles was obtained. The CNTs were dispersed in ethanol and sonicated for 3 h. The mixture was then mixed with the above Au nanoparticle dispersion and sonicated for 1 h. The solution was then dried to obtain Au nanoparticle-modified CNTs.

[0060] 5) The deposited CNTs were dispersed in anhydrous ethanol at a concentration of 1.5 mg / mL, and after magnetic stirring for 5 min, they were placed in an ultrasonic bath and sonicated for 1 h to obtain a uniformly dispersed Au NPs@CNTs ethanol solution.

[0061] 6) The Au NPs@CNTs dispersion was uniformly drop-coated onto the Ag layer of the SBS / Ag film in step 3) above, and then heated at 60°C for 30 min. This step was repeated three times until the coating was uniform.

[0062] 7) Use conductive silver paste to attach copper foil to both ends of the thin film CNTs layer in step 6) above, place it in a fume hood for 30 minutes to cure it, and then repeat step 3) to deposit a layer of Ag on it, and then wrap a layer of SBS protective layer on the surface. The high-sensitivity, wide-range flexible stress / strain sensor is thus prepared.

[0063] Example 4

[0064] like Figure 1 As shown, the structure of a highly sensitive, wide-response-range flexible stress / strain sensor, from bottom to top, is a sieve structure: dragon scale armor / Al metal layer / FePt nanoparticles@carbon nanotubes / Al metal layer / dragon scale armor.

[0065] like Figure 2 As shown, a method for fabricating a highly sensitive, wide-response-range flexible stress / strain sensor includes the following steps:

[0066] 1) Clean the aluminum mesh with deionized water, dry it, and then fix it on the glass slide as a template;

[0067] 2) Mix components A and B of the Dragon Scale Armor in a 1:1 mass ratio, stir with a stirring rod for 5 minutes, pour it onto the surface of the aluminum mesh, and after the surface self-levels, place it in an oven at 40°C for 3 hours to cure. After curing, peel it off and cut it into 10mm×20mm×0.5mm sizes.

[0068] 3) An Al metal layer was deposited on an aluminum mesh patterned dragon scale methyl substrate using a vacuum evaporation apparatus. The Al film thickness was 200 nm.

[0069] 4) Preparation of FePt nanoparticles using a chemical solution synthesis method. The most commonly used "alcohololysis method" was employed, dissolving platinum acetylacetonate and iron pentacarbonyl in diphenyl ether, using oleic acid as a surfactant and amine oleate as a stabilizer. The reaction was carried out at 220–250°C under nitrogen protection to form FePt nanoparticles with uniform particle size and good monodispersity. After water-soluble treatment of the FePt nanocrystals, a certain amount of pretreated carbon nanotubes was added, and the mixture was ultrasonically dispersed for 4 hours. Under capillary adsorption, carbon nanotubes loaded with FePt nanoparticles were prepared.

[0070] 5) The FePt nanoparticle-loaded CNTs were dispersed in anhydrous ethanol at a concentration of 5 mg / mL. After magnetic stirring for 5 min, the mixture was placed in an ultrasonic bath and sonicated for 1 h to obtain a uniformly dispersed FePt NPs@CNTs ethanol solution.

[0071] 6) The FePt NPs@CNTs ethanol solution was uniformly drop-coated onto the Al layer of the dragon scale armor / Al film in step 3) above, and then heated at 80°C for 30 min. This step was repeated three times until the drop coating was uniform.

[0072] 7) Use conductive silver paste to attach copper foil to both ends of the thin film CNTs layer in step 6) above, place it in a fume hood for 30 minutes to cure it, and then repeat step 3) to deposit a layer of Al on it, and then wrap a layer of dragon scale armor protective layer on the surface to obtain a flexible stress / strain sensor with high sensitivity and wide range.

[0073] This invention has many specific applications. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A high-sensitivity, wide-response-range flexible stress / strain sensor, characterized in that, The sensor, from bottom to top, consists of a stretchable polymer substrate with a sieve structure, a sensing functional layer, and a polymer protective film. The stretchable polymer substrate with the sieve structure is a polymer film with a patterned metal sieve obtained by pouring a polymer monomer solution onto the surface of a metal sieve, curing it at 40℃-80℃ for 2-24 hours, and then peeling it off. The sensing functional layer is a metal film / metal nanoparticle@carbon nanotube composite layer / metal film, with the metal film having a thickness of 50-200nm and the metal nanoparticle@carbon nanotube composite layer having a thickness of 10-50µm. The electrodes in the sensor are copper foil.

2. The high-sensitivity, wide-response-range flexible stress / strain sensor according to claim 1, characterized in that, The metal thin film is Pt, Au, Cu, Ag, Al, Mg, Fe, Co, Ti, Zn, Ta, Ni or an alloy thereof.

3. The high-sensitivity, wide-response-range flexible stress / strain sensor according to claim 1, characterized in that, The metal nanoparticles are Ir, Pt, Au, Ag, Cu, Al, Ti, Zn, Fe, Co, or Ni.

4. The high-sensitivity, wide-response-range flexible stress / strain sensor according to claim 1, characterized in that, The method for preparing the sensor includes the following steps: Step 1: After cutting the metal mesh, clean it with deionized water, dry it, and then fix it on the glass slide as a template; Step 2: Pour the polymer monomer solution onto the surface of the metal screen, cure it at 40℃-80℃ for 2-24 hours, and then peel it off to obtain a polymer film with a patterned metal screen. Step 3: Deposit a metal film on the polymer film obtained in Step 2 using magnetron sputtering or vacuum evaporation. Step 4: Grow metal nanoparticles on carbon nanotubes using atomic layer deposition, chemical solution methods, or physical vapor deposition methods; Step 5: Disperse the metal nanoparticle-carbon nanotube composite material obtained in Step 4 in ethanol at a concentration of 1-5 mg / mL, and then sonicate it for 1 hour to achieve uniform dispersion. Step 6: Apply the dispersion evenly to the metal layer from Step 3, and then dry at 40°C for 1 hour; Step 7: Use conductive silver paste to attach the copper foil to both ends of the film dried in step 6, then repeat step 3 to deposit a metal layer on it, and then coat the surface with a polymer film of the same material as the lower polymer layer as a protective layer, thus obtaining a flexible stress / strain sensor with a complete structure.

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