Disclosure of Invention
The invention provides a preparation method of a pressure sensor, aiming at solving the technical problems that the protective layer of the existing pressure sensor is easy to fall off, so that the protection of a nano silver wire is lost, the nano silver wire is easy to be oxidized and the like.
In order to achieve the above object, the present invention provides a method for manufacturing a pressure sensor, comprising the steps of:
s1, preparing a nano silver wire by using ethylene glycol and polyvinyl pyrrole silver nitrate through a reduction method;
s2, preparing a thermoplastic polyurethane electrospun membrane;
s3, transferring the nano silver wires to a thermoplastic polyurethane electrospun membrane to form a composite membrane;
and S4, allowing the polydimethylsiloxane solution to penetrate through the gaps of the thermoplastic polyurethane electrospun membrane and diffuse on the surface of the composite membrane, and curing at high temperature to form the pressure sensor in which the polydimethylsiloxane and the thermoplastic polyurethane electrospun membrane coat the nano-silver wire in the middle.
As a further preferable technical solution of the present invention, in the step S1, the method for preparing the silver nanowire from the ethylene glycol and the polyvinylpyrrolidone silver nitrate by the reduction method specifically includes the following steps:
20 ml of ethylene glycol, 0.204 g of silver nitrate and 0.3996g of polyvinyl pyrrole are simultaneously added into a container to form a mixed solution;
stirring the mixed solution for 1 hour in a dark environment to completely dissolve silver nitrate and polyvinyl pyrrole, adding 10 microliter of sodium chloride into the completely dissolved solution, and stirring for 10 minutes again;
placing the solution added with the sodium chloride in an oil bath under a vacuum environment, controlling the temperature, heating at 170 ℃ for 30 minutes to cool the solution to room temperature in air, and adding sufficient acetone into the solution;
the solution to which sufficient acetone was added was centrifuged at 5000 rpm for 10 minutes and washed three times with ethanol to remove excess polyvinylpyrrolidone glycol to obtain 4.0 mg of dispersed silver nanowires per ml of ethanol.
As a further preferred technical solution of the present invention, in step S2, the method for preparing the thermoplastic polyurethane electrospun membrane specifically includes the following steps:
adding 25 mass percent of thermoplastic polyurethane elastomer into a mixture of N-dimethylformamide and tetrahydrofuran to obtain a thermoplastic polyurethane solution, wherein the volume ratio of the mixture to the thermoplastic polyurethane elastomer is 1: 1;
adding a thermoplastic polyurethane solution into a plastic injector with a metal nozzle, wherein the metal nozzle of the plastic injector and a rotating cylinder of the plastic injector are respectively used as an electrode, and the distance between the two electrodes is 12 cm;
the thermoplastic polyurethane solution was injected into the aluminum foil using a high voltage of 21 kv at both electrodes of the plastic syringe to obtain a thermoplastic polyurethane electrospun film.
As a further preferred technical scheme of the invention, when the plastic injector injects the thermoplastic polyurethane solution, two plastic injectors are adopted for simultaneous injection, and the total extrusion speed of the two plastic injectors is 12 milliliters per hour.
As a further preferable technical scheme of the invention, when the plastic injector injects the thermoplastic polyurethane solution, the aluminum foil is placed in an electrostatic spinning box, the environmental temperature of the electrostatic spinning box is 25 ℃, and the relative humidity is 64%.
As a further preferred embodiment of the present invention, in step S3, the method for transferring the nano silver wires to the thermoplastic polyurethane electrospun film to form the composite film specifically includes:
uniformly dripping 5 ml of ethanol dispersed with nano silver wires on a thermoplastic polyurethane electrospun membrane with the thickness of 5 x 5cm ^ 2, filtering the ethanol in gaps and holes of the thermoplastic polyurethane electrospun membrane, and separating the nano silver wires on the surface of the thermoplastic polyurethane electrospun membrane to form a composite membrane with the thickness of 3 x 1cm ^ 2.
As a further preferred embodiment of the present invention, the method further comprises the following steps after the step S3 and before the step S4:
and sticking the two ends of the composite film by adopting silver paste.
In a further preferred embodiment of the present invention, in step S4, the polydimethylsiloxane solution is diffused on the surface of the composite membrane at a speed of 500 rpm.
In a further preferred embodiment of the present invention, the composite film dispersed with polydimethylsiloxane is cured at 80 ℃ for 1 hour to obtain a pressure sensor.
As a further preferable technical scheme of the invention, the content of the nano silver wire in each pressure sensor is 2.4 mg.
The preparation method of the pressure sensor can achieve the following beneficial effects:
the preparation method of the pressure sensor comprises the following steps: s1, preparing a nano silver wire by using ethylene glycol and polyvinyl pyrrole silver nitrate through a reduction method; s2, preparing a thermoplastic polyurethane electrospun membrane; s3, transferring the nano silver wires to a thermoplastic polyurethane electrospun membrane to form a composite membrane; s4, allowing a polydimethylsiloxane solution to penetrate through gaps of the thermoplastic polyurethane electrospun membrane and diffuse on the surface of the composite membrane, and curing at high temperature to form a pressure sensor with the polydimethylsiloxane and the thermoplastic polyurethane electrospun membrane wrapping the nano silver wire in the middle, so that the pressure sensor prepared by the invention has a sandwich structure, can better isolate the nano silver wire from air, and transfers the nano silver wire to the thermoplastic polyurethane electrospun membrane with stronger adhesiveness, thereby overcoming the defects that the nano silver wire is easy to oxidize and has poor stability, and the pressure sensor prepared by the invention is difficult to oxidize and has better stability.
Detailed Description
The invention will be further described with reference to the accompanying drawings and specific embodiments. In the preferred embodiments, the terms "upper", "lower", "left", "right", "middle" and "a" are used for clarity of description only, and are not used to limit the scope of the invention, and the relative relationship between the terms and the terms is not changed or modified substantially without changing the technical content of the invention.
In the aspects of electronic skin, intelligent textiles, structural health monitoring and the like, because the protective layer of the silver nanowire is easy to fall off, the protection of the silver nanowire is lost, and the silver nanowire is easy to oxidize, so that the use performance of the electronic skin, the intelligent textiles and structural health monitoring equipment is influenced.
In the present invention, the materials and corresponding chemical formulas are as follows:
the chemical molecular formula of the nano silver wire is AgNWs;
the chemical molecular formula of the silver nitrate is AgNO3;
The chemical formula of polyvinyl pyrrole is: PVP);
the chemical formula of the thermoplastic polyurethane elastomer is as follows: a TPU;
the chemical formula of the sodium chloride is NaCl;
the chemical formula of the polydimethylsiloxane is PDMS;
the chemical formula of N-dimethylformamide is DMF).
As shown in fig. 2, the method for manufacturing the pressure sensor includes the following steps:
step S1, preparing a nano silver wire by using ethylene glycol and polyvinyl pyrrole silver nitrate through a reduction method;
step S2, preparing a thermoplastic polyurethane electrospun membrane;
step S3, transferring the nano silver wires to a thermoplastic polyurethane electrospun membrane to form a composite membrane;
and step S4, allowing the polydimethylsiloxane solution to penetrate through the gaps of the thermoplastic polyurethane electrospun membrane and diffuse on the surface of the composite membrane, and curing at high temperature to form the pressure sensor in which the polydimethylsiloxane and the thermoplastic polyurethane electrospun membrane coat the nano-silver wire in the middle.
In specific implementation, as shown in fig. 3, the method for preparing the nano silver wire by using the ethylene glycol and the polyvinylpyrrolidone silver nitrate through the reduction method in the step S1 specifically includes the following steps:
step S11, adding 20 ml of ethylene glycol, 0.204 g of silver nitrate and 0.3996g of polyvinyl pyrrole into a container at the same time to form a mixed solution; preferably, the container selected in step S11 is a three-necked flask, which facilitates better mixing, although in practice it may be other containers known in the art.
Step S12, stirring the mixed solution for 1 hour in a dark environment to completely dissolve silver nitrate and polyvinyl pyrrole, adding 10 microliter of sodium chloride into the completely dissolved solution, and stirring for 10 minutes again;
step S13, placing the above solution added with sodium chloride in an oil bath under vacuum environment, and heating at 170 ℃ for 30 minutes while controlling the temperature, so that the solution is cooled to room temperature in air, and adding sufficient acetone (about 200m1) to the solution;
in step S14, the solution with sufficient acetone added was centrifuged at 5000 rpm for 10 minutes and washed three times with ethanol to remove excess polyvinylpyrrolidone glycol to obtain 4.0 mg of silver nanowires dispersed in ethanol per ml.
In step S13, the sufficient amount of acetone is used to mean that the mixed solution of ethylene glycol can be completely diluted.
In a specific implementation, as shown in fig. 4, the method for preparing the thermoplastic polyurethane electrospun membrane in step S2 specifically includes the following steps:
step S21, adding 25% by mass of thermoplastic polyurethane elastomer into a mixture of N-dimethylformamide and tetrahydrofuran to obtain a thermoplastic polyurethane solution, wherein the volume ratio of the mixture to the thermoplastic polyurethane elastomer is 1: 1;
step S22, adding a thermoplastic polyurethane solution into a plastic injector with a metal nozzle, wherein the metal nozzle of the plastic injector and a rotating cylinder of the plastic injector are respectively used as an electrode, and the distance between the two electrodes is 12 cm;
and step S23, injecting the thermoplastic polyurethane solution into the aluminum foil by adopting high voltage of 21 kilovolts on two electrodes of the plastic injector to obtain the thermoplastic polyurethane electrospun membrane.
In a specific implementation, when the plastic syringe injects the thermoplastic polyurethane solution, two plastic syringes may be used for simultaneous injection, with a total extrusion rate of 12 milliliters per hour. Of course, in the specific implementation, the number of the plastic syringes and the extrusion speed of the plastic syringes can be specifically selected according to the needs. In addition, when the plastic syringe injected the thermoplastic polyurethane solution, the aluminum foil was placed in an electrospinning box having an ambient temperature of 25 degrees celsius and a relative humidity of 64%.
In a specific implementation, in step S3, the method for transferring the nano silver wires to the thermoplastic polyurethane electrospun film to form the composite film specifically includes:
uniformly dripping 5 ml of ethanol dispersed with nano silver wires on a thermoplastic polyurethane electrospun membrane with the thickness of 5 x 5cm ^ 2, filtering the ethanol in gaps and holes of the thermoplastic polyurethane electrospun membrane, separating the nano silver wires on the surface of the thermoplastic polyurethane electrospun membrane to form a composite membrane with the thickness of 3 x 1cm ^ 2, and sticking two ends of the composite membrane with silver paste.
In this embodiment, in step S4, preferably, in order to better ensure the performance of the pressure sensor prepared by the present invention, the polydimethylsiloxane solution is diffused on the surface of the composite membrane at a speed of 500 rpm, and the composite membrane diffused with polydimethylsiloxane is cured at 80 ℃ for 1 hour to obtain the pressure sensor, although in this embodiment, other specific values of the diffusion speed and temperature may also be used.
Preferably, the amount of silver nanowires in each pressure sensor is 2.4 mg, although other specific amounts of silver nanowires are possible in specific implementations.
As shown in fig. 5, the pressure sensor of the present invention has a sandwich structure in which silver nanowires are coated with an electrospun film of polydimethylsiloxane and thermoplastic polyurethane, and the structure better isolates the silver nanowires from air, so that the pressure sensor of the present invention solves the problem that the silver nanowires are easily oxidized and have poor stability compared to the conventional pressure sensor of fig. 1, i.e., the pressure sensor of the present invention has good conductivity, good sensing ability, good oxidation resistance, and good stability compared to the conventional pressure sensor, thereby enabling it to accurately detect bending deformation.
The pressure sensor prepared by the preparation method is applied to the tests of stability, durability, oxidation resistance, bending response characteristic and the like, and the test results are as follows:
(1) stability testing
The relative resistivities were 0.03, 0.1, 0.16, 0.22 and 0.29 respectively and the tension control was 1%, 2%, 3%, 4% and 5% respectively by tensile release, the results showing that the sensor was still stable under alternating strain conditions.
(2) Testing durability
Cycling tests with 1%, 2%, 5% and 10% showed good stability and repeatability after 1600 cycles (with 2% applied pressure), indicating good durability in practical applications.
(3) Testing of Oxidation resistance
The linear current-voltage characteristic is applied to various pressure sensors with strain within the range of 0-10%, excellent ohmic behavior is displayed, and the self-formed sandwich structure can protect the nano silver wire from being oxidized.
To test for its antioxidant properties, one or more pressure sensor specimens were placed at room temperature and recorded daily for 30 days. The resistance of the pressure sensor is almost unchanged, exhibiting a surprising conductivity (50 cm-1) and durability.
(4) Bending response characteristics of test sensors
Continuous bending angle measurements were taken on the sensor and the results of the tests showed that the degree of bending in the range of 0-80% increases linearly with respect to the increase in resistivity, which is critical for pressure sensor applications, which can accurately detect bending deformation.
Although specific embodiments of the present invention have been described above, it will be appreciated by those skilled in the art that these are merely examples and that many variations or modifications may be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims.