CN116715930A - Flexible conductive composite sensor and preparation method and application thereof - Google Patents
Flexible conductive composite sensor and preparation method and application thereof Download PDFInfo
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
- G01L1/22—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/02—Elements
- C08K3/04—Carbon
- C08K3/041—Carbon nanotubes
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K2201/00—Specific properties of additives
- C08K2201/001—Conductive additives
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K2201/00—Specific properties of additives
- C08K2201/011—Nanostructured additives
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- Health & Medical Sciences (AREA)
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Abstract
The invention belongs to the technical field of flexible sensing materials, and particularly relates to a flexible conductive composite sensor and a preparation method and application thereof. The invention slowly adds the water-based elastic polymer emulsion into the alcohol dispersion liquid of the conductive filler, uniformly mixes, rapidly separates out the polymer emulsion due to the demulsification effect of the alcohol, fully and uniformly mixes the polymer emulsion with the conductive filler, and finally obtains the flexible conductive composite material through solidification molding. In the conductive composite material prepared by the process, the carbon nano tubes are uniformly dispersed and are not easy to fall off, and can repeatedly bear deformation such as repeated compression, bending and the like. Meanwhile, the prepared composite material has the characteristics of good stability, reliability and the like, can be prepared into a flexible sensor, can be used for monitoring various micro stresses, has great potential in the aspects of preparing wearable flexible products and medical equipment, and solves the problems of uneven dispersion, poor binding force, complex manufacturing process, poor electric conductivity and the like of the conventional composite material of the flexible sensor.
Description
Technical Field
The invention belongs to the technical field of flexible sensing materials, and particularly relates to a flexible conductive composite sensor and a preparation method and application thereof.
Background
With the development of technology, the requirements and demands of human beings on the sensor are greatly changed, and the sensor is more sensitive, tiny, wider in monitoring range and the like, so that the sensor is pursued. Thus, the flexible sensor is straightforward. Flexible sensors are the product of a combination of technologies in various fields of chemistry, biology, machinery, materials, etc. Meanwhile, with the emerging field of artificial intelligence, the field of robot electronics skin, and the application of medical devices and various monitoring needs, wearable sensing is particularly important for data acquisition.
The structure of the wearable flexible pressure-voltage-change sensor mainly comprises an intermediate layer composite conductive material, an upper surface packaging layer, a lower surface packaging layer and a conductive electrode. The sensitivity, accuracy and stability determine the overall performance of the sensor. However, the flexible pressure change sensor in the present stage has the defects of mixing effect of the composite conductive material, poor stability effect of the conductive material, easy falling of the composite layer material, low fatigue resistance and the like, so that the overall performance of the flexible pressure change sensor is limited to a certain extent, and further application of the flexible pressure change sensor is limited.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a conductive composite material, and a flexible conductive composite sensor is prepared based on the conductive composite material, so that the problems of unstable doping, poor service performance, easy falling off, low conductivity and the like of the conventional flexible sensor are solved.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
the first aspect of the invention provides a preparation method of a conductive composite material, which specifically comprises the following steps: dispersing carbon nanotubes in an alcohol organic solvent to prepare carbon nanotube conductive ink, then dropwise adding aqueous elastic polymer emulsion into the obtained carbon nanotube conductive ink under the stirring action, dropwise adding the aqueous elastic polymer emulsion into the carbon nanotube conductive ink to realize demulsification and self-assembly between the carbon nanotubes and the elastic polymer, and curing and forming after the dropwise adding to obtain the conductive composite material.
In one embodiment, the alcohol organic solvent includes, but is not limited to, ethanol, propanol, isopropanol, butanol. Preferably, the alcohol organic solvent is ethanol, and the mass fraction is 99.7%.
In one embodiment, the carbon nanotubes include hydroxyl-modified carbon nanotubes, carboxyl-modified carbon nanotubes, amino-modified carbon nanotubes.
In one embodiment, the aqueous elastomeric polymer emulsion comprises an aqueous acrylic emulsion, an aqueous styrene-acrylate emulsion, and an aqueous polyurethane emulsion.
The composite conductive material mainly comprises carbon nanotubes, aqueous elastic polymer emulsion and an alcohol organic solvent; the carbon nano tube has good conductivity, high carrier mobility and large specific surface area, and can well optimize the performance of the material. The carbon nano tube is modified hydroxylation carbon nano tube, and the specific surface area is 250-270m 2 And/g, the pipe diameter is 3-15nm, the pipe length is 15-30um, and the purity of the multi-wall carbon nano-tube is more than 97%. The water-based elastic polymer emulsion belongs to waterproof resin, and has good elasticity, plasticity and stretchability. The nature of the resin itself also determines to some extent the nature of the conductive composite sensor.
The water-based elastic polymer emulsion is slowly added into an alcohol dispersion liquid of a conductive filler (carbon nano tube) and is uniformly mixed, the polymer emulsion is rapidly separated out due to demulsification of alcohol and is fully and uniformly mixed with the conductive filler, and the hydroxylated carbon nano tube and acrylic resin in the composite conductive material are linked through hydrogen bonds (carbonyl oxygen in carboxyl groups and hydroxyl groups form intermolecular or intramolecular interaction), so that the prepared conductive composite material has the characteristics of good stability, reliability and the like, can be used for monitoring various micro stresses, and is used for preparing wearable flexible products and medical equipment.
In one embodiment, the carbon nanotubes comprise 1% -20% by mass of the conductive composite.
In one embodiment, the stirring is magnetic stirring, the stirring speed is gradually increased along with the increase of the dropwise adding amount of the acrylic emulsion, the maximum speed is 1500rpm, and the stirring time is more than 10min. The magnetic stirrer is used for stepless speed regulation, and the rotating speed range is as follows: 0-1500rpm.
In one example, stirring is continued after the addition is completed until a precipitate is formed.
In one embodiment, carbon nanotubes are dispersed in an alcohol organic solvent by ultrasound with a power ratio of 1% -75%, a time of 1-5min, and a frequency of: ultrasonic switch 1-4s and ultrasonic switch 2-8s.
Preferably, in one embodiment, the carbon nanotubes are dispersed in the alcohol organic solvent by ultrasound with a power ratio of 20% for 2min at a frequency of: ultrasonic on for 4s and ultrasonic off for 2s.
In one embodiment, after solidification and molding, the culture dish is pressed into a flat shape with a certain thickness, which is beneficial to subsequent cutting.
In one embodiment, the curing and molding process is performed by pouring the material into a molding die (such as a polytetrafluoroethylene die) for curing, and performing curing by adopting a room natural drying method.
The second aspect of the invention provides a conductive composite material prepared by the preparation method of the first aspect.
A third aspect of the invention provides the use of the conductive composite of the second aspect in the manufacture of a flexible sensor.
A fourth aspect of the invention provides a flexible conductive composite sensor comprising the conductive composite material of the second aspect, a conductive electrode and an encapsulation material.
In one embodiment, the packaging material is prepared from the following main ingredients: curing agent = 10:1 (mass ratio) and the conductive electrode is a copper electrode plate. PDMS is silicon rubber, and has the advantages of high transparency, heat resistance, water resistance and the like. The PDMS is a silicon elastomer sleeve, which is prepared from an agent A (main agent) and an agent B (curing agent) according to a proportion of 10:1, and mixing the materials in proportion.
In one embodiment, the connection between the conductive composite and the conductive electrode is: and curing a layer of conductive silver paste at the contact position of the conductive composite material and the conductive electrode, and then attaching the conductive silver paste, wherein the electrode is cured once by using the conductive silver paste at the attachment position of the composite material, and then attaching the cured wire.
In one embodiment, the conductive composite is encapsulated by applying a PDMS shower coating to the composite followed by a vacuum de-bubbling process.
Compared with the prior art, the invention has the beneficial effects that:
the invention discloses a preparation method of a flexible conductive composite material, which comprises the steps of slowly adding aqueous elastic polymer emulsion into alcohol dispersion liquid of conductive filler (carbon nano tube), uniformly mixing, rapidly separating out the polymer emulsion due to demulsification effect of alcohol, fully and uniformly mixing with the conductive filler, and finally curing and forming to obtain the flexible conductive composite material. In the conductive composite material prepared by the process, the carbon nano tube is uniformly dispersed in the polymer matrix and is not easy to fall off, and the conductive composite material can repeatedly bear deformation such as repeated compression, bending and the like. Meanwhile, the prepared composite material has the characteristics of good stability, reliability and the like, can be prepared into a flexible sensor, can be used for monitoring various micro stresses, has great potential in the aspects of preparing wearable flexible products and medical equipment, and solves the problems of unstable composite material, poor binding force, complex manufacturing process, poor electric conductivity and the like existing in the flexible sensor at present. In addition, the invention also simplifies complex and complicated process steps, saves cost in manufacturing and improves production efficiency.
Drawings
FIG. 1 is a schematic diagram of the preparation of a carbon nanotube/acrylic composite;
FIG. 2 is a flow chart showing the preparation of the carbon nanotube/acrylic composite material according to example 1;
FIG. 3 is a scanning electron microscope image of the carbon nanotube/acrylic resin composite material with a carbon nanotube content of 5%,10% and 20% provided in example 1;
FIG. 4 is a schematic structural diagram of a flexible stress-strain sensor device provided in example 2;
in FIG. 4, a 1-carbon nanotube/acrylic composite conductive material, a 2-conductive silver paste and electrode, a 3-Polydimethylsiloxane (PDMS) encapsulation layer, a 4-wire;
FIG. 5 is a graph showing the resistivity of the carbon nanotube/acrylic resin composite material at different carbon nanotube contents as provided in example 1;
FIG. 6 is a graph showing tensile stress-strain curves of carbon nanotube/acrylic composites at different carbon nanotube contents provided in example 1;
FIG. 7 is a plot of resistivity versus strain for a carbon nanotube/acrylic composite conductive material having 10% carbon nanotube content provided in example 1 when stretched;
FIG. 8 is a graph showing the results of monitoring the water surface fluctuation signal by the carbon nanotube/acrylic resin flexible composite sensor device with 10% carbon nanotube content provided in example 2;
FIG. 9 is a graph showing the signal monitoring results of the carbon nanotube/acrylic flexible composite sensor device of example 2 under the condition of simulating different flow rates at 10% carbon nanotube content;
FIG. 10 is a plot of resistivity versus time for the carbon nanotube/acrylic composite conductive material at different bend angles for the 10% carbon nanotube content provided in example 2;
fig. 11 is a plot of the resistivity of the carbon nanotube/acrylic resin composite conductive material at 10% carbon nanotube content provided in example 2 versus the number of stretches over repeated stretches.
Detailed Description
In order to better demonstrate the advantageous properties and features of the present invention, a further description of specific embodiments of the invention follows. The description of these embodiments is provided to assist understanding of the present invention, but is not intended to limit the present invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The experimental methods in the following examples, unless otherwise specified, are conventional, and the experimental materials used in the following examples, unless otherwise specified, are commercially available.
Example 1 preparation method of Flexible conductive composite Material
The flexible conductive composite material is a carbon nanotube/acrylic resin conductive composite material, as shown in fig. 2, and the preparation method comprises the following steps:
(1) Preparation of carbon nanotube conductive ink: weighing carbon nanotubes (hydroxylated, available from New Material Co., ltd., specific surface area of 250-270 m) of specific mass (0.279 g 5%, 0.589g 10%, 1.325g 20%) 2 3-15nm pipe diameter, 15-30um pipe length, multi-wall carbon nano-tube purity greater than 97%) in plastic cup, dropwise adding 20mL absolute ethanol (99.7%, 46.07 (MW)) into the plastic cup, shaking, dispersing for 2min with ultrasonic disperser, ultrasonic power ratio of 20%, ultrasonic on for 4s, and ultrasonic off for 2s;
(2) A magnetic stirrer (IKA HS-7 digital) was adjusted to room temperature and preheated (experimental stirring temperature was consistent with room temperature), and a quantitative amount of 10g of aqueous acrylic emulsion (309, shandong junwu new material science and technology company) was weighed for use;
(3) Placing the dispersed carbon nanotube conductive ink on a magnetic stirrer, and adding a magnetic rotor into the magnetic stirrer to enable the magnetic stirrer to stably run at a low rotation speed of 500rpm;
(4) Adding acrylic emulsion dropwise into the carbon nanotube conductive ink, observing the rotation speed condition of a magnetic rotor in the solution, and slowly increasing the rotation speed of a magnetic stirrer along with the increase of the amount of the dropwise added acrylic emulsion (ensuring that the magnetic rotor can smoothly rotate in the mixed solution in the experimental process), wherein the maximum rotation speed reaches 1500rpm;
(5) After all the acrylic emulsion is added dropwise, stirring is continued for 30min until precipitation is achieved;
(6) After stirring, placing the obtained liquid composite conductive material into a specific polytetrafluoroethylene mold (square groove mold, shape 80-80-10mm, inner groove 70-70-1 mm), and naturally solidifying and molding at room temperature for 2 days;
(7) Demolding and cutting into long-strip conductive composite material with specific size (20-10-1 mm).
Morphology features of the resulting conductive composite were observed using SEM. FIG. 3 is a scanning electron microscope image of the carbon nanotube/acrylic resin composite material prepared in example 1. As can be seen from fig. 3, the carbon nanotubes are distributed in the carbon nanotube/acrylic resin composite material, and as the content of the carbon nanotubes increases, a large number of pores are formed in the composite material, and the carbon nanotubes in the composite material are uniformly dispersed to form a conductive network with stable structure.
Example 2 preparation of Flexible composite sensor device
Cutting the carbon nano tube/acrylic resin composite material prepared in the embodiment 1 into a specific size and shape, coating conductive silver glue on the upper and lower surfaces of the two ends of the carbon nano tube/acrylic resin composite material to fix copper electrode plates, and then attaching a curing wire.
PDMS silicone rubber (DOWSIL is purchased) is carried out on the carbon nano tube/acrylic resin composite material with the electrode fixed by adopting a surface packaging mode of the composite conductive material TM The silicon elastomer kit is formed by encapsulating an agent A (main agent) and an agent B (curing agent), mixing and stirring the main agent and the curing agent in a mass ratio of 10:1 for 10min, and then vacuum removing bubbles from the carbon nano tube/acrylic resin composite material with the fixed electrode and the stirred PDMS silicon rubber together, wherein the bubble removing time is 2h. And then the composite material with the bubbles removed is placed into an oven, so that PDMS silicone rubber on the surface of the carbon nanotube/acrylic resin composite material is cured, the temperature of the oven is 80 ℃, and the curing time is 12 hours.
Fig. 4 is a schematic structural diagram of a flexible stress-strain sensor device prepared in this embodiment. As shown in fig. 4, the structure of the manufactured flexible stress-strain sensing device mainly comprises a carbon nanotube/acrylic resin composite conductive material 1, a conductive silver paste and electrode 2, a Polydimethylsiloxane (PDMS) packaging layer 3 and a wire 4.
Experimental example 1 characterization of Flexible conductive composite and sexual composite sensing device
FIG. 1 is a schematic diagram of the preparation of a carbon nanotube/acrylic composite. The acrylic emulsion is an oil-in-water emulsion system composed of acrylic monomer, emulsifier, stabilizer, water and the like, and the surface of the emulsion contains a very small amount of carboxyl exposed outside. The absolute ethyl alcohol has stronger hydrophilicity, can reduce interfacial tension between an oil phase and a water phase, and damages the stability of an emulsion system. And after demulsification, the high polymer acrylic resin is released, a large number of carboxyl groups are exposed, and physical adsorption is formed by hydrogen bonding action on the hydroxylated multiwall carbon nanotubes, so that the hydroxylated multiwall carbon nanotubes uniformly dispersed in the absolute ethanol solution are adsorbed and fixed. Meanwhile, because the molecular weight of the high molecular polymer acrylic acid is larger, strong intermolecular interaction forces exist among molecules, such as van der Waals force, electrostatic action, hydrogen bonding action and the like, the high molecular polymer acrylic acid has certain viscosity, and acrylic acid molecules are gathered together after demulsification, so that the stability of the inside of the composite material is enhanced.
For the composite material prepared in example 1, the resistances of the composite materials with different carbon nanotube contents were measured using a multimeter, and the corresponding resistivities were calculated. FIG. 5 is a graph showing the change in resistivity of the carbon nanotube/acrylic composite at different carbon nanotube contents. As can be seen from fig. 5, as the content of the carbon nanotubes increases, the resistivity of the composite material decreases, and a small amount of carbon nanotubes doped can change the insulation property of the polymer acrylic resin material itself.
A peel force release force tester was used to apply a tensile force to the composite material prepared in example 1, while a multimeter was used to measure the resistance of the sensor. FIG. 6 is a graph showing tensile stress-strain curves of carbon nanotube/acrylic composites at different carbon nanotube contents. As can be seen from fig. 6, the doped carbon nanotubes can change the brittleness and plasticity of the acrylic resin material, and as the content of the doped carbon nanotubes increases, the composite material exhibits a tendency to decrease in plasticity, bearing stress and increasing brittleness of the material. The reason is that the addition of the carbon nanotubes changes the internal structure of the acrylic resin itself, so that interstitial voids are formed inside the structure, resulting in a decrease in the plasticity of the acrylic resin during the stretching process. Meanwhile, the hydrogen bond adsorption effect among the carbon nanotubes enables the composite material to bear larger acting force than the original acting force, so that the brittleness of the composite material is gradually displayed due to the increase of the content of the carbon nanotubes.
A peel force release force tester was used to apply a tensile force to the composite material prepared in example 1, while a multimeter was used to measure the resistance change of the sensor. FIG. 7 is a graph showing the resistivity-strain curve of a carbon nanotube/acrylic composite conductive material stretched at a carbon nanotube content of 10%. As can be seen from fig. 7, as the tensile strain of the carbon nanotube/acrylic composite material increases, the resistance thereof also shows a phenomenon of gradually increasing. The original conductive network path is formed in the composite material when the composite material is solidified and dried, but the original conductive network path is destroyed along with the increase of the tensile stress acted on the composite material, so that the phenomenon of resistance increase occurs.
The sensor device prepared in example 2 was attached to the inner wall of a beaker in a vertical direction (the sensor was in a long strip shape, the electrodes were located at both ends, one of the electrodes was very close to the bottom of the beaker, and the other was very close to the top of the beaker), and the change in resistance signal of the sensor device prepared in example 2 was monitored by dropping water into the beaker and shaking the beaker by using a multimeter. Fig. 8 is a signal monitoring of the carbon nanotube/acrylic resin flexible composite sensor device for water surface fluctuation at 10% carbon nanotube content provided in example 2. (figures a-c are respectively the resistance signals of the drop of water at different positions (the liquid level is controlled at the upper, middle and lower ends of the sensor), and figures d-f are respectively the resistance signals of the fluctuation of the liquid level after shaking the beaker once at different positions (the liquid level is controlled at the upper, middle and lower ends of the sensor)), the sensor prepared from the composite material is sensitive correspondingly, and the fluctuation of the liquid level at different positions can be monitored.
The sensor device prepared in example 2 was attached to the bottom wall of the beaker, near the bottom of the beaker, and the electrodes at the two ends of the sensor were maintained at the same level. The beaker was filled with water over the sensor and a magnetic rotor was added. Different rotational speeds of the magnetic rotor were controlled on the magnetic rotor platform at normal temperature, and the resistance signal change of the sensor device prepared in example 2 was monitored using a multimeter. Fig. 9 is a signal monitoring of the carbon nanotube/acrylic flexible composite sensor device provided in example 2 at 10% carbon nanotube content simulating different flow rates. Graphs a-c are resistance signal data at 500rpm, 750rpm, 1000rpm, respectively. The faster the rotation speed of the magnetic rotor is observed through image data, the more wave peaks of the obtained wave form are, and the actual rotation speed of the rotor can be calculated according to the wave form number in unit time and is 420rpm, 756rpm and 972rpm respectively, which are matched with the set rotation speed value of the rotor, which shows that the sensor device prepared in the embodiment 2 can well identify different flow rates of liquid.
The sensor device prepared in example 2 was subjected to bending deformation using a multimeter, and the resistance change of the sensor was measured. FIG. 10 is a graph showing the resistivity of the carbon nanotube/acrylic composite conductive material at 10% carbon nanotube content versus time at different bend angles. As can be seen from fig. 10, the sensor made of the carbon nanotube/acrylic resin composite conductive material can detect the resistance change under different bending degrees, the composite material has rapid response, and the sensor can be used for detecting signals of different motion states of the human body part based on the excellent characteristics.
A cyclic pulling force was applied to the sensor device prepared in example 2 using a linear motor control device, while a resistance change of the sensor was measured using a multimeter. FIG. 11 is a graph showing the resistivity of a carbon nanotube/acrylic composite conductive material at 10% carbon nanotube content versus the number of stretches over multiple iterations. As can be seen from fig. 11, the sensor made of the carbon nanotube/acrylic resin composite conductive material shows stable response and sensitivity after tens of thousands of cyclic tensile tests, and has good material stability and fatigue stretch resistance.
The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, and yet fall within the scope of the invention.
Claims (10)
1. A process for preparing the electrically conductive composite material includes such steps as dispersing carbon nanotubes in organic alcohol solvent to obtain electrically conductive ink, adding aqueous elastic polymer emulsion dropwise to said electrically conductive ink, and solidifying.
2. The method of claim 1, wherein the alcohol organic solvent comprises ethanol, propanol, isopropanol, butanol.
3. The method for preparing a conductive composite material according to claim 1, wherein the carbon nanotubes comprise hydroxyl-modified carbon nanotubes, carboxyl-modified carbon nanotubes, amino-modified carbon nanotubes.
4. The method for preparing a conductive composite material according to claim 1, wherein the mass ratio of the carbon nanotubes in the conductive composite material is 1% -20%.
5. The method of claim 1, wherein the aqueous elastic polymer emulsion comprises an aqueous acrylic emulsion, an aqueous styrene-acrylate emulsion, and an aqueous polyurethane emulsion.
6. The method for preparing a conductive composite material according to claim 1, wherein the stirring is magnetic stirring, the stirring speed is gradually increased along with the increase of the dropwise addition amount of the acrylic emulsion, the highest speed is 1500rpm, and the stirring time is more than 10min.
7. A conductive composite prepared by the method of any one of claims 1-6.
8. Use of the conductive composite of claim 7 for the preparation of a flexible sensor.
9. A flexible conductive composite sensor comprising the conductive composite of claim 7, a conductive electrode, and an encapsulation material.
10. The flexible conductive composite sensor of claim 9, wherein the encapsulation material is a base material: curing agent = 10:1, wherein the conductive electrode is a copper electrode plate.
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