Flexible sensor capable of simultaneously sensing pressure and temperature and preparation method thereof

Abstract

The invention belongs to the technical field of flexible sensors, and particularly relates to a flexible sensor capable of simultaneously sensing pressure and temperature and a preparation method thereof. The sensor sequentially comprises a polyimide film, a pressure sensing layer, a buffer layer, a temperature sensing layer and a polyimide film from top to bottom, the pressure sensing layer is made of a carbon nanotube / graphene / polydimethylsiloxane composite conductive film, polydimethylsiloxane is used as a substrate, and graphene and carbon nanotubes are used as conductive fillers; the temperature sensing layer is made of carbon ink and is printed on the polyimide film through a silk screen; and the buffer layer is made of a polydimethylsiloxane elastomer. The carbon nanomaterial with the negative resistance temperature coefficient is compounded with the polydimethylsiloxane with the thermal expansion effect, so that pressure sensing with the resistance temperature coefficient close to zero is realized; the added graphene can effectively separate the carbon nanotubes and improve the dispersibility of the carbon nanotubes, so that the electrical properties of the composite conductive film are enhanced, the permeation threshold is reduced, and the conductivity is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible sensors, and specifically relates to a flexible sensor that can simultaneously sense pressure and temperature and a preparation method thereof. Background Art

[0002] In recent years, flexible electronics technology, as an emerging technology, has received extensive attention. Flexible sensors manufactured based on this technology have been applied in fields such as electronic skin, health monitoring, and aerospace. Compared with traditional silicon-based sensors, flexible sensors have good flexibility and ductility and can be applied in a variety of complex environments.

[0003] Flexible sensors can generally be used to measure physical quantities such as force, strain, temperature, humidity, flow rate, and light intensity. However, most flexible sensors can only monitor one physical quantity and cannot meet the monitoring requirements of multiple physical quantities. Therefore, developing flexible sensors that can simultaneously monitor multiple physical quantities without signal crosstalk has great practical significance and application potential.

[0004] Carbon nanomaterials are often used to prepare flexible sensors due to their advantages such as good electrical conductivity, high strength, high temperature resistance, corrosion resistance, and low weight. However, carbon nanomaterials are prone to agglomeration due to their large van der Waals forces, resulting in a decrease in electrical conductivity and an increase in the percolation threshold. Therefore, the dispersion of carbon nanomaterials in the composite material determines the conductivity of the composite material. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a flexible sensor that can simultaneously sense pressure and temperature and a preparation method thereof.

[0006] The present invention adopts the following technical solutions to solve the above technical problems:

[0007] A flexible sensor that can simultaneously sense pressure and temperature, which successively comprises a polyimide film, a pressure sensing layer, a buffer layer, a temperature sensing layer, and a polyimide film from top to bottom; characterized in that the pressure sensing layer is made of a carbon nanotube / graphene / polydimethylsiloxane composite conductive film;

[0008] The preparation of the pressure sensing layer includes the following steps:

[0009] First step: Add graphene and carbon nanotubes to a polar solvent according to a mass ratio of 1:1 and perform ultrasonic dispersion; the mass of both graphene and carbon nanotubes is 0.05 - 0.1 g, and the volume of the polar solvent is 50 - 80 ml; the ambient temperature for ultrasonic dispersion is 5 - 15 °C, the power is 1200 W, and intermittent treatment is carried out for 1 - 1.5 h;

[0010] Step 2: Add 5 - 7 g of polydimethylsiloxane main agent into the ultrasonically dispersed solution, and then heat and stir magnetically; when using a heating table for heating, the heating temperature is 100 - 120 °C; when using water bath heating, the heating temperature is 70 - 90 °C; the magnetic stirring speed is 150 - 250 rpm, and the stirring time is 2 - 4 h;

[0011] Step 3: Dropwise add a non-polar solvent and 0.5 - 0.7 g of polydimethylsiloxane curing agent into the mixture obtained in Step 2, and stir magnetically at room temperature; the magnetic stirring speed is 100 - 200 rpm, and the stirring time is 10 - 20 min;

[0012] Step 4: Perform vacuum degassing treatment on the slurry obtained in Step 3 for 5 - 10 min;

[0013] Step 5: Pour the degassed slurry into a mold, and place it in a drying oven for curing to obtain a carbon nanotube / graphene / polydimethylsiloxane composite conductive film; the curing temperature is 60 - 80 °C, and the curing time is 2 - 4 h.

[0014] Furthermore, when using 0.05 g of graphene with a sheet diameter of 10000 nm and a thickness of 4 nm, 0.05 g of carbon nanotubes with a length of 12000 nm and a diameter of 80 nm, 6 g of polydimethylsiloxane main agent, and 0.6 g of polydimethylsiloxane curing agent, the resistance temperature coefficient of the pressure sensing layer is close to zero.

[0015] Furthermore, the polar solvent is selected from isopropyl alcohol, ethanol, propanol, or water, the non-polar solvent is selected from xylene, and the mass of xylene is 8 - 10 g.

[0016] Furthermore, the preparation of the temperature sensing layer includes the following steps:

[0017] Step 1: Mix 5 - 7 g of carbon ink with 0.3 - 0.5 g of screen washing water, and stir magnetically at room temperature; the magnetic stirring speed is 200 - 300 rpm, and the stirring time is 2 - 4 h;

[0018] Step 2: Use a screen printing stencil to print the stirred solution on a polyimide film, and place it in a drying oven for curing to obtain a temperature sensing layer; the curing temperature is 60 - 80 °C, and the curing time is 2 - 4 h.

[0019] Furthermore, the buffer layer is made of polydimethylsiloxane elastomer, and the thickness is 1 - 2 mm.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] The flexible sensor of the present invention realizes pressure sensing with a resistance temperature coefficient close to zero by compounding carbon nanomaterials with a negative resistance temperature coefficient and polydimethylsiloxane with a thermal expansion effect. This is because the volume of polydimethylsiloxane increases after thermal expansion, resulting in a reduction in the conductive path, which compensates for the negative resistance temperature coefficient of the carbon nanomaterial itself. As a one-dimensional nanomaterial, carbon nanotubes are easily agglomerated due to their elongated structure. Therefore, adding graphene can effectively separate carbon nanotubes, improve the dispersion of carbon nanotubes, and thus enhance the electrical properties of the composite conductive film, reduce the permeation threshold and improve the conductivity.

[0022] First, add the carbon nanotubes to a polar solvent for ultrasonic dispersion, then add the polydimethylsiloxane main agent, heat and stir until the polar solvent evaporates, and then add the non-polar solvent and polydimethylsiloxane curing agent. The reason why the carbon nanotubes are not directly added to the non-polar solvent and then treated is that the carbon nanotubes have better dispersibility in polar solvents than in non-polar solvents; and the purpose of adding the polydimethylsiloxane curing agent at the end is to fully mix the carbon nanotubes and the polydimethylsiloxane main agent. Adding the polydimethylsiloxane curing agent in advance will cause the polydimethylsiloxane to cross-link, making the carbon nanotubes and polydimethylsiloxane mixed unevenly. The non-polar solvent can make the resulting slurry more fluid and convenient for pouring into the mold.

[0023] The present invention uses polydimethylsiloxane elastomer as a buffer layer to separate the pressure sensing layer and the temperature sensing layer, thereby preventing the temperature sensing layer from being affected by the pressure sensing layer and causing signal crosstalk. The serpentine-shaped temperature sensing layer is prepared by screen printing, so that the thickness of the temperature sensing layer is thin enough to avoid direct pressure on the temperature sensing layer to the greatest extent. At the same time, the serpentine structure can also resist the resistance change caused by the bending of the sensor to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a side view of the overall structure of the present invention;

[0025] Figure 2 An exploded view of the present invention;

[0026] Figure 3 is a structural diagram of the pressure sensing layer of the present invention;

[0027] Figure 4 It is a structural diagram of the temperature sensing layer of the present invention. DETAILED DESCRIPTION

[0028] Specific embodiments are given below in conjunction with the accompanying drawings. The specific embodiments are only used to introduce the technical solutions of the present invention in detail and are not intended to limit the protection scope of the present application.

[0029] The present invention provides a flexible sensor that can simultaneously sense pressure and temperature. From top to bottom, it includes: a polyimide (PI) film, a pressure sensing layer, a buffer layer, a temperature sensing layer, and a polyimide film. When encapsulating, a flame-retardant adhesive is used to bond each layer, and the electrode materials are conductive silver paste and copper tape.

[0030] The pressure sensing layer is made of a carbon nanotube / graphene / polydimethylsiloxane composite conductive film. Polydimethylsiloxane (PDMS) is used as the substrate, and graphene and carbon nanotubes with a negative temperature coefficient of resistance are used as conductive fillers. The pressure signal is monitored by the way that the pressure direction is perpendicular to the conduction path; the mass ratio of graphene to carbon nanotubes is 1:1; the sheet diameter of graphene is 10000 nm, and the thickness is 3 - 4 nm; the length of carbon nanotubes is 12000 nm, and the diameter is 80 nm.

[0031] The temperature sensing layer is made of carbon ink and is screen-printed onto the polyimide film. In this embodiment, the temperature sensing layer has a serpentine structure.

[0032] The buffer layer is made of a polydimethylsiloxane elastomer to ensure that the temperature sensing layer is not affected by the pressure sensing layer.

[0033] The preparation of the pressure sensing layer includes the following steps:

[0034] The first step: Add graphene and carbon nanotubes to a polar solvent according to a mass ratio of 1:1 and perform ultrasonic treatment;

[0035] Among them, the mass of both graphene and carbon nanotubes is 0.05 - 0.1 g, and the volume of the polar solvent is 50 - 80 ml; the polar solvent is selected from isopropanol, ethanol, propanol, water, etc.; the sheet diameter of graphene is 10000 nm, and the thickness is 3 - 4 nm; the length of carbon nanotubes is 12000 nm, and the diameter is 80 nm; the ambient temperature of ultrasonic treatment is 5 - 15 °C, the ultrasonic power is 1200 W, and it is continuously treated for 1 - 1.5 h in the form of ultrasonic treatment for 1 - 2 s and pause for 3 - 4 s;

[0036] The second step: Add 5 - 7 g of polydimethylsiloxane main agent to the solution after ultrasonic treatment, and perform heating and magnetic stirring to evaporate the polar solvent; when using a heating table for heating, the heating temperature is 100 - 120 °C; when using water bath heating, the heating temperature is 70 - 90 °C; the magnetic stirring speed is 150 - 250 rpm, and the stirring time is 2 - 4 h;

[0037] When using 0.05 g of graphene with a sheet diameter of 10000 nm and a thickness of 4 nm, 0.05 g of carbon nanotubes with a length of 12000 nm and a diameter of 80 nm, 6 g of polydimethylsiloxane main agent, and 0.6 g of polydimethylsiloxane curing agent, the temperature coefficient of resistance of the pressure sensing layer is close to zero;

[0038] Step 3: After the polar solvent has completely evaporated, add a non-polar solvent and a polydimethylsiloxane curing agent, and perform magnetic stirring at room temperature;

[0039] The non-polar solvent is xylene, and the mass of xylene is 8 - 10 g. The non-polar solvent is used to ensure the fluidity of the polydimethylsiloxane main agent; the mass of the polydimethylsiloxane curing agent is 0.5 - 0.7 g; the magnetic stirring speed is 100 - 200 rpm, and the stirring time is 10 - 20 min;

[0040] Step 4: Perform vacuum degassing on the slurry obtained in Step 3; the vacuum degassing time is 5 - 10 min;

[0041] Step 5: Pour the degassed slurry into a polytetrafluoroethylene (PTFE) mold, and place it in an oven for curing to obtain a carbon nanotube / graphene / polydimethylsiloxane composite conductive film; use a laser cutter to cut the carbon nanotube / graphene / polydimethylsiloxane composite conductive film; use conductive silver paste and copper tape to externally connect electrodes, and the electrodes are adhered to a polyimide film;

[0042] Among them, the curing temperature is 60 - 80 °C, the curing time is 2 - 4 h, and the thickness of the carbon nanotube / graphene / polydimethylsiloxane composite conductive film is 0.3 - 0.5 mm.

[0043] The preparation of the temperature sensing layer includes the following steps:

[0044] Step 1: Mix 5 - 7 g of carbon ink with 0.3 - 0.5 g of screen washing water, and perform magnetic stirring at room temperature;

[0045] Among them, the magnetic stirring speed is 200 - 300 rpm, and the stirring time is 2 - 4 h;

[0046] Step 2: Use a screen printing stencil to print the stirred solution on a polyimide film, and place it in an oven for curing to obtain a temperature sensing layer;

[0047] Among them, the curing temperature is 60 - 80 °C, and the curing time is 2 - 4 h.

[0048] The preparation of the buffer layer includes the following steps:

[0049] Step 1: Mix the polydimethylsiloxane main agent and the curing agent in a mass ratio of 10:1, and perform magnetic stirring; the magnetic stirring speed is 150 - 200 rpm, and the stirring time is 5 - 15 min;

[0050] Step 2: Perform vacuum degassing on the stirred polydimethylsiloxane; the vacuum degassing time is 5 - 10 min;

[0051] Step 3: Pour the defoamed polydimethylsiloxane into a polytetrafluoroethylene mold and place it in a drying oven for curing to obtain a polydimethylsiloxane elastomer; the curing temperature is 80 °C, the curing time is 2 h, and the thickness of the polydimethylsiloxane elastomer is 1 - 2 mm;

[0052] Step 4: Use a laser cutter to cut the polydimethylsiloxane elastomer into squares with side lengths of 1 - 2 cm to obtain a buffer layer.

[0053] A preparation method of a flexible sensor for simultaneously sensing pressure and temperature includes the following steps:

[0054] S1: Use a laser cutter to cut out two square polyimide films with side lengths of 50 mm and a thickness of 0.2 mm, and clean the polyimide films with absolute ethanol and deionized water;

[0055] S2: Use tape to attach the two polyimide films under the screen printing stencil for printing electrodes, and scrape the conductive silver paste through the mesh holes; after scraping, tear off the polyimide film printed with the conductive silver paste and cure it at room temperature;

[0056] S3: Add 0.05 g of graphene with a particle size of 10000 nm and a thickness of 4 nm, and 0.05 g of carbon nanotubes with a length of 12000 nm and a diameter of 80 nm to 50 ml of isopropanol, and perform ultrasonic treatment at an ambient temperature of 10 °C. The power of the ultrasonic disperser is 1200 W, and it is continuously treated in the form of ultrasonic treatment for 2 s and pause for 3 s for 1 h;

[0057] S4: Add 6 g of polydimethylsiloxane main agent to the ultrasonically treated solution, and perform water bath heating and magnetic stirring to volatilize the isopropanol; the temperature of the water bath heating is 90 °C, the rotation speed of the magnetic stirring is 200 rpm, and the magnetic stirring time is 2 h;

[0058] S5: Drop 0.6 g of polydimethylsiloxane curing agent and 8 g of xylene into the viscous slurry mixed with graphene, carbon nanotubes, polydimethylsiloxane main agent and a small amount of isopropanol, and perform magnetic stirring at room temperature; the rotation speed of the magnetic stirring is 150 rpm, and the stirring time is 10 min; put the stirred viscous slurry into a vacuum defoamer for defoaming for 10 min;

[0059] S6: Pour the defoamed slurry into a cylindrical polytetrafluoroethylene mold with a diameter of 5 cm and a depth of 5 mm, and the volume of the slurry is 40% of the total volume of the mold; place the mold filled with the slurry in a drying oven at 80 °C for curing for 2 h to obtain a carbon nanotube / graphene / polydimethylsiloxane composite conductive film with a thickness of 0.3 mm;

[0060] S7: Use a laser cutting machine to cut the carbon nanotube / graphene / polydimethylsiloxane composite conductive film into a square with a side length of 1 cm, and clean it with absolute ethanol and deionized water; paste the carbon nanotube / graphene / polydimethylsiloxane composite conductive film on one piece of polyimide film printed with conductive silver paste with a flame retardant adhesive, then drop a small amount of conductive silver paste at both ends of the carbon nanotube / graphene / polydimethylsiloxane composite conductive film, then stick on copper tape, and then drop a small amount of conductive silver paste to connect the copper tape to the carbon nanotube / graphene / polydimethylsiloxane composite conductive film; put the polyimide film adhered with the carbon nanotube / graphene / polydimethylsiloxane composite conductive film into an oven at 80 °C and cure for 1 h;

[0061] S8: Mix 3 g of polydimethylsiloxane main agent and 0.3 g of curing agent, and perform magnetic stirring at room temperature. The magnetic stirring speed is 200 rpm, and the stirring time is 10 min; put the stirred polydimethylsiloxane into a vacuum degassing machine for degassing for 10 min, pour the degassed polydimethylsiloxane into a cylindrical polytetrafluoroethylene mold with a diameter of 5 cm and a depth of 5 mm. The volume of polydimethylsiloxane is about 40% of the total volume of the mold; put the mold filled with polydimethylsiloxane into an oven and cure at 80 °C for 2 h to obtain a polydimethylsiloxane elastomer with a thickness of 2 mm; use a laser cutting machine to cut the polydimethylsiloxane elastomer into a square with a side length of 1 cm, and clean it with absolute ethanol and deionized water to obtain a buffer layer;

[0062] S9: Mix 5 g of carbon ink and 0.35 g of screen washing water, and perform magnetic stirring at room temperature. The magnetic stirrer speed is 200 rpm, and the stirring time is 3 h; use tape to attach another piece of polyimide film printed with conductive silver paste under the silk screen plate printed with a snake pattern, scrape the mesh holes with a small amount of carbon ink, then tear off the polyimide film printed with the snake pattern and carbon ink, stick on copper tape at both ends of the polyimide film, and then drop a small amount of conductive silver paste to connect the copper tape to the carbon ink; put the polyimide film adhered with carbon ink into an oven and cure at 80 °C for 2 h;

[0063] S10: Use a flame retardant adhesive to paste the buffer layer in the center of the temperature sensing layer with a snake structure, put it into an oven at 80 °C and cure for 30 min and then take it out, use a flame retardant adhesive to paste the pressure sensing layer on the buffer layer, and put it into an oven at 80 °C and cure for 30 min and then take it out to obtain a flexible sensor that can simultaneously sense pressure and temperature.

[0064] The parts not described in the present invention are applicable to the prior art.

Claims

1. A flexible sensor for simultaneously sensing pressure and temperature, comprising, from top to bottom, a polyimide film, a pressure sensing layer, a buffer layer, a temperature sensing layer and a polyimide film; characterized in that: The pressure sensing layer is made of a carbon nanotube / graphene / polydimethylsiloxane composite conductive film; The preparation of the pressure sensing layer comprises the following steps: Step 1: adding graphene and carbon nanotubes into a polar solvent in a mass ratio of 1:1 and performing ultrasonic dispersion; the mass of graphene and carbon nanotubes is 0.05-0.1g, the volume of the polar solvent is 50-80ml; the ambient temperature of ultrasonic dispersion is 5-15°C, the power is 1200W, and the intermittent treatment is 1-1.5h; Step 2: Add 5-7g of polydimethylsiloxane main agent to the solution after ultrasonic dispersion, and heat and magnetically stir; when heating on a heating table, the heating temperature is 100-120°C; when heating in a water bath, the heating temperature is 70-90°C; the magnetic stirring speed is 150-250rpm, and the stirring time is 2-4h; Step 3: Add a non-polar solvent and 0.5-0.7 g of polydimethylsiloxane curing agent to the mixture obtained in the second step, and perform magnetic stirring at room temperature; the magnetic stirring speed is 100-200 rpm, and the stirring time is 10-20 min; Step 4: vacuum degassing the slurry obtained in step 3 for 5 to 10 minutes; Step 5: Pour the deaerated slurry into a mold and place it in a drying oven for curing to obtain a carbon nanotube / graphene / polydimethylsiloxane composite conductive film; the curing temperature is 60 to 80° C. and the curing time is 2 to 4 hours.

2. The flexible sensor for simultaneously sensing pressure and temperature according to claim 1, characterized in that: When 0.05 g of graphene with a sheet diameter of 10,000 nm and a thickness of 4 nm, 0.05 g of carbon nanotubes with a length of 12,000 nm and a diameter of 80 nm, 6 g of polydimethylsiloxane as a main agent and 0.6 g of polydimethylsiloxane as a curing agent are used, the resistance temperature coefficient of the pressure sensing layer is close to zero.

3. The flexible sensor for simultaneously sensing pressure and temperature according to claim 1 or 2, characterized in that: The polar solvent is selected from isopropanol, ethanol, propanol or water, and the non-polar solvent is selected from xylene, and the mass of xylene is 8-10g.

4. The flexible sensor for simultaneously sensing pressure and temperature according to claim 1, characterized in that: The preparation of the temperature sensing layer comprises the following steps: Step 1: Mix 5-7g of carbon ink with 0.3-0.5g of screen washing water and stir magnetically at room temperature; the magnetic stirring speed is 200-300rpm and the stirring time is 2-4h; Step 2: Print the stirred solution on the polyimide film using a screen printing plate, and put it into a drying oven for curing to obtain a temperature sensing layer; the curing temperature is 60 to 80° C., and the curing time is 2 to 4 hours.

5. The flexible sensor for simultaneously sensing pressure and temperature according to claim 1, characterized in that: The buffer layer is made of polydimethylsiloxane elastomer and has a thickness of 1 to 2 mm.

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