CN114993527B - Flexible resistance type pressure sensor based on carbonized electrostatic spinning fibers and preparation - Google Patents
Flexible resistance type pressure sensor based on carbonized electrostatic spinning fibers and preparation Download PDFInfo
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- CN114993527B CN114993527B CN202210607365.5A CN202210607365A CN114993527B CN 114993527 B CN114993527 B CN 114993527B CN 202210607365 A CN202210607365 A CN 202210607365A CN 114993527 B CN114993527 B CN 114993527B
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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
- G01L1/2287—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 constructional details of the strain gauges
- G01L1/2293—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 constructional details of the strain gauges of the semi-conductor type
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
Abstract
The invention discloses a flexible resistance type pressure sensor based on carbonized electrostatic spinning fibers and a preparation method thereof. The sensor is composed of a pressure sensitive layer and upper and lower flexible electrodes. The pressure-sensitive layer uses carbonized polyacrylonitrile electro-spun film to obtain carbon nano-fibers as a conductive framework, and bacterial cellulose nano-materials are filled among the conductive fibers by a dip-coating method to form the flexible film. Compared with nano carbon materials such as graphene, the conductive carbon skeleton reserves the unique 3D network characteristics of the electrospinning process, has better stress transfer characteristics, and the conductivity of the conductive carbon skeleton is adjustable along with the carbonization process. The filling of the bacterial cellulose improves the flexibility and the recovery performance of the film, and the bacterial cellulose is inserted between the carbon fibers, so that the variable conductive path number in the film is further increased. The invention fully utilizes the piezoresistive performance advantage of the carbon nanofiber framework, has easy preparation and low cost, and the prepared sensor has high sensitivity and wide detection range and can realize real-time monitoring on human physiological signals.
Description
Technical Field
The invention belongs to the fields of energy conversion technology, wearable electronic technology, micro-electro-mechanical systems (MEMS), flexible polymer materials and nano materials, and particularly relates to a flexible resistance type pressure sensor based on carbonized electrospun fibers and a preparation method thereof.
Background
The pressure is one of the most common physical quantities in daily life, and the detection of the pressure has very important application value. The traditional rigid pressure sensor is made by utilizing the resistance strain effect of metal or the piezoresistive effect of semiconductor, and the device has the inherent properties of inflexibility and inextensibility, can be only applied to pressure detection of a certain point or a smooth plane, and cannot work in the environment with special surface topography. Especially in the field of biomedical health, such as in the process of detecting physiological signals of human body, such as pulse, blood pressure, respiration, limb movement, etc., such rigid sensors are often limited in application to a great extent due to the defects of incapability of adhering to the surface, large volume, uncomfortable wearing, difficulty in portability, etc.
With the increasing development of flexible electronic technology, the pressure sensor developed and designed by using flexible functional materials can effectively make up for the above defects of the traditional rigid device. The portable wearable flexible pressure sensor can realize real-time detection of stress by converting pressure signals into changes of resistance and capacitance or utilizing piezoelectric effect and triboelectric effect. The resistance-type pressure sensor which changes resistance to reflect the stress size due to increase and decrease of the conductive path in the device has the advantages of easy signal collection, simple structure, capability of detecting static pressure, good temperature stability and the like, and has received wide attention.
At present, the design of the sensitive layer of the flexible resistive pressure sensor is that nano conductive materials such as graphene, carbon nanotubes, silver nanowires, MXene and the like are often dispersed in a flexible polymer material to form a composite material with a variable conductive network inside. On the basis, the application of three-dimensional porous structures such as sponge and aerogel and the like and the method of adding the electrode surface microstructure and the like can effectively improve the stress deformation condition of the sensor and increase the specific surface area of the elastic support body, thereby improving the sensitivity and the measurement range of the sensor. However, such methods are often expensive, complicated in preparation process, and difficult to achieve compatibility of high sensitivity and wide detection range.
Compared with the conductive material commonly used by the flexible resistance type pressure sensor, the three-dimensional self-supporting conductive carbon skeleton material obtained by the electrostatic spinning and high-temperature carbonization of the polymer solution has simple preparation process and low production cost, and has a three-dimensional porous structure. In addition, compared with two-dimensional materials such as graphene, the nano-fibers can effectively transfer stress, can be quickly recovered after external force is removed, and is a good candidate material suitable for designing a resistance-type pressure sensor. And the controllability of the spinning, carbonization and subsequent treatment processes can also enable the structural characteristics of the carbonized nanofiber material to be flexibly adjusted, so that the sensor can give consideration to key sensing parameters such as sensitivity, detection range, linearity and the like in the design process.
Disclosure of Invention
The invention provides a flexible resistance type pressure sensor based on carbonized electrostatic spinning nano fibers and a preparation method thereof. The sensor is simple in preparation process, good in biological adaptability, flexible and wearable, high in sensitivity and wide in detection range, and can be used for detecting physiological signals of a human body in real time.
In order to realize the purpose, the technical scheme of the invention is as follows:
a flexible resistance type pressure sensor based on carbonized electrospun fibers comprises a pressure-sensitive film and two flexible electrodes respectively attached to the upper surface and the lower surface of the pressure-sensitive film; the pressure-sensitive film takes a carbon nanofiber structure obtained by carbonizing a polymer electrostatic spinning film as a conductive framework, and a fibrous one-dimensional nano material is filled among carbon nanofibers in a dip-coating mode to form a composite flexible film; and after the stable contact between the electrodes and the sensitive film is ensured, the whole device is packaged and fixed, and the upper flexible electrode and the lower flexible electrode are respectively provided with a bonding lead at one side for measuring external working voltage and output signals.
As a preferable mode, in order to ensure that the polymer fiber does not have melting phenomenon in the subsequent heat treatment process so as to cause the collapse of the fiber structure, the polymer electrostatic spinning film nanofiber is subjected to pre-oxidation treatment before carbonization, and the pre-oxidation treatment is carried out at the temperature of 230-280 ℃ in the air atmosphere, so that the linear long molecular chain structure in the polymer fiber is subjected to cyclization and crosslinking to form the ladder-shaped macromolecular structure with thermal stability.
As a preferred mode, after the pre-oxidation treatment, the polymer electrostatic spinning film nanofiber is carbonized at high temperature under the nitrogen atmosphere of 700-900 ℃, non-carbon atoms are removed, a carbon network conductive framework is obtained, in order to enhance the mechanical property of the film, the carbon network conductive framework is compounded with the fibrous one-dimensional nano material through a dip-coating method, a stable conductive network formed by the polymer material inserted between the conductive carbon nanofibers is realized, and meanwhile, the number of the variable conductive paths of the film is further increased.
Preferably, the nanofiber membrane obtained by electrostatic spinning has a three-dimensional network structure, the contact condition between internal fibers is remarkably changed after the nanofiber membrane is pressed, and the nanofiber membrane is suitable for designing a high-sensitivity piezoresistive sensor. Different from other methods of doping conductive materials by taking a spinning film as a template, the method directly prepares the nano carbon fiber material with good conductivity and capable of keeping a spinning fiber structure by a high-temperature carbonization electrostatic spinning film process, and prepares the flexible piezoresistive sensor by taking the nano carbon fiber material as a framework. The structure taking the conductive carbon skeleton as the main body can realize more effective stress transfer, and has good conductive uniformity and conductive phase dispersibility.
Preferably, the composite flexible film comprises conductive carbon nanofibers and non-conductive fibrous one-dimensional nanomaterials, and the working performance of the device is adjusted by adjusting the amount of the fibrous one-dimensional nanomaterials added. The working performance of the device is directly influenced by the amount of the added insulating phase, and on one hand, if the amount of the added fibrous one-dimensional nano material is too small, the effects of supporting protection and improving sensitivity cannot be achieved; on the other hand, if an excessive amount of fibrous one-dimensional nanomaterial is added, the insulating phase will be caused to occupy the conductive contact sites between the carbon fibers, and the conductive path will remain blocked after the compression.
As a preferred mode, after the sensor is subjected to external pressure, the interior of the composite flexible film deforms, contact sites among the carbon nanofibers increase, and an effective conductive path between the surface of the composite flexible film and the flexible electrode also increases, so that the resistance of the device is obviously reduced; when the pressure is removed, the device is quickly recovered and the resistance value is reduced due to the mechanical property of the carbon nano fiber and the elasticity of the fibrous one-dimensional nano material.
Preferably, the device flexible electrode is a metal planar electrode evaporated or printed on the flexible substrate layer, and the material of the device flexible electrode is aluminum, copper, silver or gold. And/or the flexible substrate layer is selected from one of polyimide, polydimethylsiloxane, polyethylene terephthalate and polyethylene naphthalate.
Preferably, the raw material for electrospinning the polymer thin film is selected from one or a composite material consisting of two or more materials selected from polyacrylonitrile, polyimide, polyvinylpyrrolidone and lignin materials. The selected polymer material is required to have good filamentation and thermal stability, and avoid the hot melting phenomenon which can cause the collapse of the spinning structure in the subsequent high-temperature treatment process.
Preferably, the fibrous one-dimensional nanomaterial is selected from one of bacterial cellulose, silk fibroin and nanofiber crystals. The fibrous materials with the characteristic of large length-diameter ratio can be effectively inserted among the carbon nanofibers to form a stable composite film, thereby being beneficial to stress conduction.
As a preferred mode, one of a polyurethane adhesive tape, a polyimide adhesive tape and a polyethylene adhesive tape is selected for the whole device packaging method for sealing and fixing.
The invention also provides a preparation method of the flexible resistance type pressure sensor based on the carbonized electrospun fiber, which comprises the following steps:
(1) Cutting a flexible substrate layer film with the length and width of 2-3 cm and the thickness of 100-300 um, ultrasonically cleaning the film by ultrapure water and absolute ethyl alcohol, and drying the film;
(2) Printing a layer of rectangular silver electrode on a flexible substrate layer film by using conductive silver paste through a screen printing technology, and bonding a lead wire on one side of the electrode by using the silver paste after drying to serve as an upper flexible electrode and a lower flexible electrode;
(3) Weighing 1-1.2 g of polyacrylonitrile powder, dissolving the polyacrylonitrile powder in 8.8-9 g of N, N-dimethylformamide solution, magnetically stirring for 8-12 h under the condition of 35-50 ℃ water bath, and preparing spinning precursor solution with the mass fraction of 10-12 wt%;
(4) Putting the spinning precursor solution into an injector, setting electrostatic spinning voltage at 18-20 kV, setting the distance between a needle tip collector and the injector at 12-15 cm, setting the pushing speed of a pushing pump at 8-12 uL/min, setting the environmental temperature at 40-50 ℃, receiving spinning fibers through aluminum foil, and spinning for 2-4 h to obtain a spinning film which is white in macroscopic appearance;
(5) Drying the obtained film in a drying oven for a period of time to fully volatilize the residual organic solvent;
(6) The spinning film is taken off from the aluminum foil, and is clamped by two titanium nets and is put into a tube furnace for heat treatment; raising the temperature to 230-280 ℃ in the air atmosphere, and keeping the temperature for 1-3 h for pre-oxidation to obtain a film with a brownish yellow surface;
(7) Continuously introducing nitrogen as protective gas after the pre-oxidation stage is finished, then keeping the temperature rise rate of 2-3 ℃/min, slowly raising the temperature to 700-900 ℃, carbonizing for 2-3 h, and then cooling along with the furnace to obtain a pure black carbon fiber film;
(8) Preparing bacterial cellulose water dispersion with the mass fraction of 0.3-0.5 wt%, soaking the carbon fiber film in the water dispersion for 30-60 min, taking out the carbon fiber film, repeatedly soaking for 2-3 times, and placing the film on a heating table at 40-50 ℃ to dry excessive moisture to obtain a pressure-sensitive film;
(9) And tightly attaching the obtained pressure-sensitive film to the printed silver electrode, and sealing and fixing the pressure-sensitive film by using an adhesive tape to finally obtain the flexible resistance type pressure sensor based on the carbonized electrostatic spinning fibers.
The invention has the beneficial effects that: compared with the prior art, the flexible pressure sensor provided by the invention does not need other complicated structural designs, the carbon fiber framework with good piezoresistive performance is obtained through a high-temperature carbonization process after electrostatic spinning, and the mechanical property of the film is enhanced by compounding the bacterial cellulose material. After the sensor is pressed and deformed, the structural characteristics of the material cause that abundant conductive contact site changes occur inside the film and between the film and an electrode interface, so that the sensor has higher sensitivity. Meanwhile, the device provided by the invention has the advantages of low manufacturing cost, batch production, light weight and no biological harm, and can be attached to the skin of a human body for real-time physiological health signal detection.
Drawings
FIG. 1 is a schematic structural diagram of a pressure sensor of the present invention;
FIG. 2 is a flow chart of a process for making the pressure sensor of the present invention;
FIG. 3 is a diagram of a piezoresistive sensing mechanism of the pressure sensor of the present invention;
FIG. 4 is a surface topography of a pressure sensitive film prepared according to the present invention, wherein (a) is an SEM image of a carbon nanofiber conductive framework; (b) Is SEM picture of the composite film of the carbonized fiber material and the fibrous one-dimensional nano material;
FIG. 5 is a voltage-current graph of a pressure sensor of the present invention under various pressure conditions;
fig. 6 is a graph of the sensitivity of the pressure sensor of the present invention.
1 is an upper electrode, 2 is a pressure-sensitive film, and 3 is a lower electrode.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Example 1:
a flexible resistance type pressure sensor based on carbonized electrospun fibers comprises a pressure-sensitive film and two flexible electrodes respectively attached to the upper surface and the lower surface of the pressure-sensitive film; the pressure-sensitive film takes a carbon nanofiber structure obtained by carbonizing a polymer electrostatic spinning film as a conductive framework, and a fibrous one-dimensional nano material is filled among carbon nanofibers in a dip-coating mode to form a composite flexible film; and after the stable contact between the electrodes and the sensitive film is ensured, the whole device is packaged and fixed, and the upper flexible electrode and the lower flexible electrode are respectively provided with a bonding lead at one side for measuring external working voltage and output signals.
In order to ensure that the polymer fiber does not melt in the subsequent heat treatment process, the polymer electrostatic spinning film nanofiber is subjected to preoxidation treatment before carbonization, and the preoxidation treatment is carried out at 230-280 ℃ in air atmosphere, so that the linear long molecular chain structure in the polymer fiber is cyclized and crosslinked to form a trapezoidal macromolecular structure with thermal stability.
After the preoxidation treatment, the polymer electrostatic spinning film nano-fiber is carbonized at high temperature under the nitrogen atmosphere of 700-900 ℃, non-carbon atoms are removed, a carbon network conductive framework is obtained, in order to enhance the mechanical property of the film, the carbon network conductive framework is compounded with a bacterial cellulose material through a dip-coating method, the polymer material is inserted among the conductive nano-carbon fibers to form a stable conductive network, and meanwhile, the number of the variable conductive paths of the film is further increased.
Preferably, the nanofiber membrane obtained by electrostatic spinning has a three-dimensional network structure, the contact condition between internal fibers is remarkably changed after the nanofiber membrane is pressed, and the nanofiber membrane is suitable for designing a high-sensitivity piezoresistive sensor. Different from other methods of doping conductive materials by taking a spinning film as a template, the method directly prepares the nano carbon fiber material with good conductivity and capable of keeping a spinning fiber structure by a high-temperature carbonization electrostatic spinning film process, and prepares the flexible piezoresistive sensor by taking the nano carbon fiber material as a framework. The structure taking the conductive carbon skeleton as the main body can realize more effective stress transfer and has good conductive uniformity and conductive phase dispersibility.
Preferably, the composite flexible film comprises conductive carbon nanofibers and non-conductive fibrous one-dimensional nanomaterials, and the working performance of the device is adjusted by adjusting the amount of the fibrous one-dimensional nanomaterials added. The working performance of the device is directly influenced by the amount of the added insulating phase, and on one hand, if the amount of the added fibrous one-dimensional nano material is too small, the effects of supporting protection and improving sensitivity cannot be achieved; on the other hand, if an excessive amount of fibrous one-dimensional nanomaterial is added, the insulating phase will occupy the conductive contact sites between the carbon fibers, and the conductive paths will remain blocked after compression.
After the sensor is subjected to external pressure, the interior of the composite flexible film deforms, contact sites among the carbon nanofibers are increased, and effective conductive paths between the surface of the composite flexible film and the flexible electrodes are increased, so that the resistance of the device is obviously reduced; when the pressure is removed, the device is quickly recovered and the resistance value is reduced due to the mechanical property of the carbon nano fiber and the elasticity of the fibrous one-dimensional nano material.
The flexible electrode of the device is a metal plane electrode which is evaporated or printed on a flexible substrate layer, and the material of the flexible electrode is aluminum, copper, silver or gold. And/or the flexible substrate layer is selected from one of polyimide, polydimethylsiloxane, polyethylene terephthalate and polyethylene naphthalate.
The raw material of the polymer electrostatic spinning film is selected from one or a composite material consisting of more than two materials of polyacrylonitrile, polyimide, polyvinylpyrrolidone and lignin materials. The selected polymer material is required to have good filamentation and thermal stability, and avoid the hot melting phenomenon which can cause the collapse of the spinning structure in the subsequent high-temperature treatment process.
The fibrous one-dimensional nano material is selected from one of bacterial cellulose, silk fibroin and nano fiber crystal. The fibrous materials with the characteristic of large length-diameter ratio can effectively penetrate among the carbon nanofibers to form a stable composite film, thereby being beneficial to stress conduction.
The whole device packaging method adopts one of polyurethane adhesive tape, polyimide adhesive tape and polyethylene adhesive tape for sealing and fixing.
As shown in fig. 4 (b), the obtained pressure-sensitive film comprises conductive carbon nanofibers and non-conductive fibrous one-dimensional nanomaterials, the carbon nanofiber material maintains the fibrous structure obtained by electrospinning, but the fiber diameter is reduced to some extent, which is caused by the large amount of non-carbon elements in the polymer molecules under the high temperature condition. The network framework structure has a large specific surface area, and the fibrous distribution ensures that the structure is beneficial to internal conduction of stress, and contact sites among fibers can be greatly changed when the structure is subjected to compression deformation.
In addition, the resulting carbon nanofiber material exhibits excellent electrical conductivity, and the higher the temperature selected at the time of carbonization, the stronger the electrical conductivity. This is because non-carbon elements are removed from the polymer material during carbonization, and carbon atoms are spatially rearranged to form amorphous carbon. However, this amorphous carbon still has a graphite-like layered crystal structure except that the crystal grains are very small, and hexagonal ring sheets of carbon atoms are randomly overlapped in the crystal grains. With the increase of the carbonization temperature, the amorphous carbon crystal grains absorb energy and begin to move violently, so that the smaller crystal grains are fused after colliding with each other, and the carbon atom hexagonal ring sheet layers which are randomly overlapped in the tiny crystal grains are changed into a space-ordered overlapped crystal structure, namely, a graphitization process begins to occur, thereby obtaining stronger electric conductivity. Therefore, the higher the carbonization temperature, the higher the conductivity of the carbonized material.
Example 2:
the embodiment provides a preparation method capable of directly obtaining a carbonized nanofiber material, which comprises the following steps:
(1) Cutting a flexible substrate layer film with the length and width of 2cm and the thickness of 100um, ultrasonically cleaning the flexible substrate layer film by ultrapure water and absolute ethyl alcohol, and drying the flexible substrate layer film;
(2) Printing a layer of rectangular silver electrode on a flexible substrate layer film by using conductive silver paste through a screen printing technology, and bonding a lead wire on one side of the electrode by using the silver paste after drying to serve as an upper flexible electrode and a lower flexible electrode;
(3) Weighing 1g of polyacrylonitrile powder, dissolving the polyacrylonitrile powder in 8.8g of N, N-dimethylformamide solution, and magnetically stirring for 8 hours at the temperature of 35 ℃ under the condition of water bath to prepare spinning precursor solution with the mass fraction of 10 wt%;
(4) Putting the spinning precursor solution into an injector, setting electrostatic spinning voltage at 18kV, setting the distance between a needle tip collector and the injector at 12cm, setting the pushing speed of a pushing pump at 8uL/min, setting the ambient temperature at 40 ℃, receiving spinning fibers through an aluminum foil, and spinning for 2 hours to obtain a spinning film which is white in macroscopic appearance;
(5) Drying the obtained film in a drying oven for a period of time to fully volatilize the residual organic solvent;
(6) The spinning film is taken off from the aluminum foil, and is clamped by two titanium nets and is put into a tube furnace for heat treatment; raising the temperature to 230 ℃ in the air atmosphere, keeping the temperature for 1h, and carrying out pre-oxidation to obtain a film with a brownish yellow surface;
(7) Continuously introducing nitrogen as protective gas after the pre-oxidation stage is finished, then keeping the heating rate of 2 ℃/min, slowly heating to 700 ℃, continuously carbonizing for 2h, and then cooling along with a furnace to obtain a pure black carbon fiber film;
(8) Preparing a fibrous one-dimensional nano material water dispersion liquid with the mass fraction of 0.3wt%, soaking a carbon fiber film in the fibrous one-dimensional nano material water dispersion liquid for 30min, taking out the carbon fiber film, repeatedly soaking for 3 times, and placing the film on a heating table at 40 ℃ to dry excessive moisture to obtain a pressure-sensitive film;
(9) And tightly attaching the obtained pressure-sensitive film to the printed silver electrode, and sealing and fixing the pressure-sensitive film by using an adhesive tape to finally obtain the flexible resistance type pressure sensor based on the carbonized electrostatic spinning fibers.
Example 3:
the embodiment provides a preparation method of a flexible resistance-type pressure sensor based on a carbonized nanofiber material, which comprises the following steps:
(1) Cutting a polyimide film with the length and width of 3cm and the thickness of 300um, ultrasonically cleaning the polyimide film by ultrapure water and absolute ethyl alcohol, and drying the polyimide film;
(2) Printing a rectangular silver electrode with the size of 1cm x 1.5cm and the thickness of 100-500 um on a flexible substrate layer film by using a screen printing technology, drying, and bonding a lead on one side of the electrode by using silver paste to serve as an upper flexible electrode and a lower flexible electrode;
(3) Weighing 1.2g of polyacrylonitrile powder, dissolving the polyacrylonitrile powder in 9g of N, N-dimethylformamide solution, and magnetically stirring for 12 hours at 50 ℃ under a water bath condition to prepare a spinning precursor solution with the mass fraction of 12 wt%;
(4) Putting the spinning precursor solution into an injector, setting electrostatic spinning voltage to be 20kV, setting the distance between a needle tip collector and the injector to be 15cm, setting the pushing speed of a pushing pump to be 12uL/min, setting the ambient temperature to be 50 ℃, receiving spinning fibers through an aluminum foil, and spinning for 4 hours to obtain a spinning film which is white in macroscopic appearance;
(5) Drying the obtained film in a drying oven for a period of time to fully volatilize the residual organic solvent;
(6) Taking off the spinning film from the aluminum foil, clamping the spinning film by adopting two titanium nets, and putting the spinning film into a tube furnace for heat treatment; heating to 280 ℃ in air atmosphere, and keeping for 3h for pre-oxidation to obtain a film with a brownish yellow surface;
(7) Continuously introducing nitrogen as protective gas after the pre-oxidation stage is finished, then keeping the heating rate of 3 ℃/min, slowly heating to 900 ℃, carbonizing for 3 hours, and then cooling along with a furnace to obtain a pure black carbon fiber film;
(8) Preparing a bacterial cellulose water dispersion with the mass fraction of 0.5wt%, soaking a carbon fiber film in the bacterial cellulose water dispersion for 60min, taking out the carbon fiber film, repeatedly soaking for 3 times, and placing the film on a heating table at 50 ℃ to dry excessive moisture to obtain a pressure-sensitive film;
(9) And tightly attaching the obtained pressure-sensitive film to the printed silver electrode, and sealing and fixing by using a 3M medical adhesive tape to finally obtain the flexible resistance type pressure sensor based on the carbonized electrospun fiber.
The flexible pressure sensor provided by the invention does not need other complex structural designs, fully utilizes the excellent physical and chemical properties of the carbonized electrostatic spinning fiber, and retains the three-dimensional porous network structure brought by electrostatic spinning. After the sensor is pressed and deformed, the structural characteristics of the material can cause more obvious conductive contact point change, and the working sensitivity of the sensor is improved to a great extent. The addition of the bacterial cellulose or other flexible materials ensures that the composite film has enough flexibility, and simultaneously, the bacterial cellulose or other flexible materials are also used as fillers to be inserted between the conductive carbon fibers, so that the resistance change space of the composite film is further expanded, and the sensor is ensured to have quick recovery time.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (10)
1. The utility model provides a flexible resistance-type pressure sensor based on carbonization electrostatic spinning fibre which characterized in that: comprises a pressure-sensitive film and two flexible electrodes respectively attached to the upper and lower surfaces of the pressure-sensitive film; the pressure-sensitive film takes a carbon nanofiber structure obtained by carbonizing a polymer electrostatic spinning film as a conductive framework, and a fibrous one-dimensional nano material is filled among carbon nanofibers in a dip-coating mode to form a composite flexible film; and after the stable contact between the electrodes and the sensitive film is ensured, the whole device is packaged and fixed, and the upper flexible electrode and the lower flexible electrode are respectively provided with a bonding lead at one side for measuring external working voltage and output signals.
2. The carbonized electrospun fiber-based flexible resistive pressure sensor of claim 1, wherein: the polymer electrostatic spinning film nano-fiber is subjected to pre-oxidation treatment before carbonization, the pre-oxidation treatment is carried out at 230-280 ℃ in air atmosphere, the linear long molecular chain structure in the polymer fiber is subjected to cyclization and crosslinking, a trapezoidal macromolecular structure with thermal stability is formed, and the polymer fiber is not subjected to melting phenomenon in the subsequent heat treatment process.
3. The flexible resistive pressure sensor based on carbonized electrospun fibers of claim 2 wherein: after the preoxidation treatment, the polymer electrostatic spinning film nano-fiber is carbonized at high temperature under the nitrogen atmosphere of 700-900 ℃, non-carbon atoms are removed to obtain a carbon network conductive framework, and then the carbon network conductive framework is compounded with the fibrous one-dimensional nano-material through a dip-coating method, so that a stable conductive network formed by the polymer material inserted among the conductive carbon nano-fibers is realized, and the number of the conductive paths of the film, which can be changed, is further increased.
4. The flexible resistive pressure sensor based on carbonized electrospun fibers of claim 1 wherein: the composite flexible film comprises conductive carbon nano-fibers and non-conductive fibrous one-dimensional nano-materials, and the working performance of the device is adjusted by adjusting the amount of the added fibrous one-dimensional nano-materials.
5. The flexible resistive pressure sensor based on carbonized electrospun fibers of claim 1 wherein: after the sensor is subjected to external pressure, the interior of the composite flexible film deforms, contact sites among the carbon nanofibers are increased, and effective conductive paths between the surface of the composite flexible film and the flexible electrodes are increased, so that the resistance of the device is obviously reduced; when the pressure is removed, the device is quickly recovered and the resistance value is reduced due to the mechanical property of the carbon nano fiber and the elasticity of the fibrous one-dimensional nano material.
6. The flexible resistive pressure sensor based on carbonized electrospun fibers of claim 1 wherein: the flexible electrode of the device is a metal plane electrode which is evaporated or printed on the flexible substrate layer and is made of aluminum, copper, silver or gold; and/or the flexible substrate layer is selected from one of polyimide, polydimethylsiloxane, polyethylene terephthalate and polyethylene naphthalate.
7. The flexible resistive pressure sensor based on carbonized electrospun fibers of claim 1 wherein: the raw material of the polymer electrostatic spinning film is selected from one or a composite material consisting of more than two materials of polyacrylonitrile, polyimide, polyvinylpyrrolidone and lignin materials.
8. The flexible resistive pressure sensor based on carbonized electrospun fibers of claim 1 wherein: the fibrous one-dimensional nano material is selected from one of bacterial cellulose, silk fibroin and nano fiber crystal.
9. The flexible resistive pressure sensor based on carbonized electrospun fibers of claim 1 wherein: the whole device packaging method adopts one of polyurethane adhesive tape, polyimide adhesive tape and polyethylene adhesive tape for sealing and fixing.
10. A method of making a carbonized electrospun fiber based flexible resistive pressure sensor according to any of claims 1 to 9 comprising the steps of:
(1) Cutting a flexible substrate layer film with the length and width of 2-3 cm and the thickness of 100-300 um, ultrasonically cleaning the film by ultrapure water and absolute ethyl alcohol, and drying the film;
(2) Printing a layer of rectangular silver electrode on a flexible substrate layer film by using conductive silver paste through a screen printing technology, and bonding a lead on one side of the electrode by using the silver paste after drying to serve as an upper flexible electrode and a lower flexible electrode;
(3) Weighing 1-1.2 g of polyacrylonitrile powder, dissolving the polyacrylonitrile powder in 8.8-9 g of N, N-dimethylformamide solution, magnetically stirring for 8-12 h under the condition of 35-50 ℃ water bath, and preparing a spinning precursor solution with the mass fraction of 10-12 wt%;
(4) Putting the spinning precursor solution into an injector, setting electrostatic spinning voltage at 18-20 kV, setting the distance between a needle tip collector and the injector at 12-15 cm, setting the pushing speed of a pushing pump at 8-12 uL/min, setting the environmental temperature at 40-50 ℃, receiving spinning fibers through aluminum foil, and spinning for 2-4 h to obtain a spinning film which is white in macroscopic appearance;
(5) Drying the obtained film in a drying oven for a period of time to fully volatilize the residual organic solvent;
(6) The spinning film is taken off from the aluminum foil, and is clamped by two titanium nets and is put into a tube furnace for heat treatment; raising the temperature to 230-280 ℃ in the air atmosphere, and keeping the temperature for 1-3 h for pre-oxidation to obtain a film with a brownish yellow surface;
(7) Continuously introducing nitrogen as protective gas after the pre-oxidation stage is finished, then keeping the heating rate of 2-3 ℃/min, slowly heating to 700-900 ℃, carbonizing for 2-3 h, and then cooling along with the furnace to obtain a pure black carbon fiber film;
(8) Preparing bacterial cellulose water dispersion with the mass fraction of 0.3-0.5 wt%, soaking the carbon fiber film in the water dispersion for 30-60 min, taking out the carbon fiber film, repeatedly soaking for 2-3 times, and placing the film on a heating table at 40-50 ℃ to dry excessive moisture to obtain a pressure-sensitive film;
(9) And tightly attaching the obtained pressure-sensitive film to the printed silver electrode, and sealing and fixing the pressure-sensitive film by using an adhesive tape to finally obtain the flexible resistance type pressure sensor based on the carbonized electrostatic spinning fibers.
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