A method for preparing a flexible resistance sensor based on silver nanowire material

Abstract

The present invention discloses a method for preparing a flexible resistance sensor based on silver nanowire material. The silver nanowire material is used as the variable resistance material, a PU flexible film is used as the substrate, and the PU flexible film is modified with silicone. Then, the silver nanowire AgNWs material is used as the variable resistance material to prepare the flexible resistance sensor. The combined flexible resistance sensor has the characteristics of high sensitivity and fast response speed, which improves the problems of insufficient flexibility, low sensitivity and poor repeatability of traditional sensors. The preparation method is simple, has low equipment requirements and low cost, and provides a new method and approach for the improvement of flexible film sensors.

Description

Technical Field

[0001] The present invention relates to a method for preparing a flexible resistance sensor, and more specifically, to a method for preparing a flexible resistance sensor based on silver nanowire material, belonging to the technical field of sensors. Background Art

[0002] Flexible sensors are lightweight, bendable, wearable, portable, implantable, and highly sensitive, and are widely used in various fields. They have attracted much attention in the fields of wearable electronics, sports monitoring, health monitoring, and artificial intelligence. The present invention uses a PU flexible film as a substrate, modifies it with silicone, and then uses silver nanowires (AgNWs) as a resistor material to prepare a flexible resistive sensor. According to the existing research results at home and abroad in recent decades, the development of flexible sensors has made great progress, especially in the context of the continuous development of new materials and nanotechnology, which has brought many opportunities to flexible sensors.

[0003] Patent application number 202011097180.1 discloses a flexible composite transparent conductive film comprising a polyethylene terephthalate substrate layer, a blended layer of nanocellulose and silver nanowires, and a graphene oxide layer, all in contact with each other. Nanocellulose, with its three-dimensional porous network structure, serves as a support material for the silver nanowires, allowing them to spread and disperse evenly across the nanocellulose surface, reducing agglomeration. The silver nanowires exhibit excellent film-forming properties and a smooth, uniform surface. Application No. 201711184092.3 provides a highly sensitive electronic skin with a polyvinyl alcohol-silver nanowire / graphene-PDMS sandwich structure. A layer of overlapping and stacked silver nanowire conductive network is formed on the surface of a PET substrate by spray coating. A layer of graphene, a mixture of large and small graphene flakes, is then evenly sprayed and dispersed on the silver nanowire network. This graphene is deposited between the silver nanowire networks or connects adjacent silver nanowires, further enhancing the conductive properties of the conductive network. A polyvinyl alcohol solution is then spin-coated on the surface of the conductive network to serve as the substrate for the electronic skin. Finally, after the polyvinyl alcohol dries, the composite film is separated from the PET film and transferred to an oven. The surface is flipped and a layer of PDMS film is evaporated on the side in contact with the PET, resulting in an electronic skin with a sandwich structure. Application No. 202011077357.1 discloses a flexible electronic skin and its preparation method, belonging to the field of flexible sensor technology. This flexible electronic skin consists of a nanofiber membrane and a conductive coating that partially covers the surface of the nanofiber membrane. The conductive coating is applied to the surface of the nanofiber membrane in a closed or / and non-closed linear pattern. The nanofiber membrane is an elastic polyolefin copolymer nanofiber membrane with a porous structure. While maintaining its excellent tensile / pressure sensing performance, the electronic skin designed in this invention boasts excellent flexibility, breathability, moisture permeability, and thermal regulation properties due to the unique three-dimensional porous structure, elasticity, and infrared transmittance of the polyolefin nanofiber membrane, as well as the partially covered conductive coating. However, the relationship between the deformation of the electronic skin and its resistance is not described. Chinese patent number CN2019111300990.X discloses a multifunctional flexible sensor, its preparation method, and its application. From bottom to top, this functional flexible sensor comprises a bottom flexible substrate, a bottom surface electrode, an intermediate dielectric layer, a conductive electrode, an upper surface electrode, and a top flexible substrate. Among them, microstructure protrusions are designed on the surface of the flexible dielectric layer, and a wire is connected to one end of the upper surface electrode to lead out the electrode, realizing the measurement of temperature, distance and stress, but the metal electrode reduces the flexibility to a certain extent.

[0004] The flexible sensors described in the above patent documents also have the following disadvantages: (1) The flexible sensors can be bent, but their toughness is insufficient, and the bending angle cannot be too large. (2) During the electrode coating process, the high-temperature sputtering of metal particles causes significant damage to the film material itself. Moreover, during subsequent use, the sensor electrodes are prone to falling off, resulting in insufficient sensor response speed, sensitivity, linearity and other indicators. Summary of the Invention

[0005] In order to solve the above-mentioned problems in the prior art, the present invention provides a method for preparing a flexible resistance sensor based on silver nanowire material with technical characteristics such as good sensitivity and repeatability.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A method for preparing a flexible resistance sensor based on silver nanowire material, the preparation method comprising the following steps:

[0008] Step 1) using silver nanowire material as a variable resistor material: mixing polyvinyl pyrrolidone (PVP) with a molecular weight of 58,000 and a molecular weight of 1.3 million in a mass ratio of 1:1 to 2, taking 1.86 g of the above mixture and dissolving it in 100 mL of ethylene glycol (EG), stirring and dissolving, the solution is placed in a three-necked flask, 1 mL of a control agent is dropped into it, and then the stirred AgNO3 / EG solution is added to the three-necked flask at a rate of 25 to 100 mL / h using a peristaltic pump. The heating reaction is continued for 1 hour. After the reaction is completed, a silver nanowire material with a high aspect ratio of more than 1500 is obtained, and the silver nanowire network is used as a variable resistor material;

[0009] Step 2) using a polyurethane (PU) flexible film as a substrate and modifying it with silicone: using polyethylene glycol (PEG-2000) and polypropylene glycol (PPG-2000) in a mass ratio of 1:3 to 3:1 as raw material components of the mixed soft segment, using isophorone diisocyanate (IPDI) as the hard segment component, and the ratio of the soft segment component to the hard segment component is 1:1 to 1.5, and adding 3 mL of a catalyst dibutyltin dilaurate (DBTDL) dropwise, and then adding 5 to 10% by mass of hydroxyalkyl di-terminated polydimethylsiloxane to fully react for 3 hours for modification, and finally removing the organic solvent by distillation under reduced pressure to obtain a silicone-modified polyurethane (Si-PU) film;

[0010] Step 3) The organosilicon-modified polyurethane (Si-PU) film obtained in Step 2) was cut into two 5 cm × 5 cm squares, ultrasonically cleaned with anhydrous ethanol for 10 minutes, dried and placed in a desiccator, and the silver nanowires obtained in Step 1) were centrifuged and dispersed in anhydrous ethanol using a pipette to obtain an AgNWs dispersion, which was ultrasonically treated for 10 minutes to prevent agglomeration.

[0011] Step 4) A flexible resistance sensor is prepared using silver nanowire (AgNWs) material as a variable resistance material: the four sides of the organosilicon-modified polyurethane (Si-PU) film material are glued with transparent tape to reserve positions for electrodes and bonding, and then one side of the two organosilicon-modified polyurethane (Si-PU) film materials is immersed in the AgNWs dispersion prepared in step 3) for 30 minutes so that the surface is evenly covered with AgNWs, the transparent tape is torn off, and the four sides are non-metallized with acetone and anhydrous ethanol; copper sheets are introduced into the upper and lower ends of the treated organosilicon-modified polyurethane (Si-PU) film and fixed with conductive silver glue to serve as lead-out electrodes. Finally, the two organosilicon-modified polyurethane (Si-PU) films are face-to-face bonded and packaged to obtain a flexible thin film resistance sensor, which has a sandwich structure.

[0012] In a preferred embodiment, the control agent in step 1) is any one of copper chloride, ferric chloride, and sodium chloride solutions with a concentration of 3 mmol / L.

[0013] In a preferred embodiment, in step 1), the following steps are performed before adding the control agent to the three-necked flask at a rate of 25 to 100 mL / h: the three-necked flask with 1 mL of the control agent added is placed in an oil bath at 140°C for 1 to 6 hours, 0.51 g of silver nitrate (AgNO3) is weighed and dissolved in 25 mL of ethylene glycol (EG) in a dark place, and the beaker needs to be covered with tin foil during the stirring and dissolving process.

[0014] In a preferred embodiment, after the reaction in step 1) is completed, the obtained gray-green oily liquid is first cooled to room temperature and then placed in a centrifuge tube. Centrifugation is repeated 5-6 times with 500 mL of anhydrous ethanol and then dispersed in an ethanol solution to obtain a silver nanowire material with a high aspect ratio (above 1500).

[0015] In a preferred embodiment, in step 2), before adding 3 mL of the catalyst dibutyltin dilaurate (DBTDL), dehydrated polyethylene glycol (PEG-2000), polypropylene glycol (PPG-2000), and dibutyltin dilaurate (DBTDL) are added to a three-necked flask equipped with a reflux condenser, a stirring device, and a thermometer under nitrogen N2 protection.

[0016] In a preferred embodiment, in step 2), after the modification, triethylamine (TEA) is added dropwise at a neutralization degree of 100% for 15 minutes, and the system temperature is cooled to room temperature. Deionized water containing a defoaming agent is added and emulsified at high speed for 30 minutes. Finally, the organic solvent is removed by distillation under reduced pressure to obtain a silicone-modified polyurethane (Si-PU) emulsion. The obtained silicone-modified polyurethane (Si-PU) emulsion is poured into a PTFE mold and naturally cured at room temperature for 24 hours. It is then placed in a vacuum oven at 50°C and dried for 48 hours. The resulting film is placed in a drying dish to obtain a silicone-modified polyurethane (Si-PU) film.

[0017] In a preferred embodiment, the flexible thin film resistance sensor can reach 13.2 to 54.1 Ω / m 2 .

[0018] In a preferred embodiment, the flexible resistor sensor has a maximum sensitivity GF=21.78 and an average sensitivity GF=9.58.

[0019] In a preferred embodiment, the breaking strength of the silicone-modified polyurethane (Si-PU) film in step 2) is 10.7-14.8 MP, and the breaking elongation is 289.3%-432.5%.

[0020] In a preferred embodiment, in step 3), the silver nanowires are dispersed in anhydrous ethanol using a pipette to obtain AgNWs dispersions with mass concentrations of 5 g / L, 10 g / L, 15 g / L, 20 g / L and 30 g / L.

[0021] Beneficial effects: The present invention improves the problems of insufficient flexibility, low sensitivity and poor repeatability of traditional sensors. The preparation method is simple, has low equipment requirements and low cost, and provides a new method for improving flexible thin film sensors. The flexible thin film sensor prepared by the present invention has good sensitivity and repeatability stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the appearance of the flexible resistance sensor of the present invention.

[0023] Figure 2 This is an electron microscope photograph of the silver nanowire material used in the present invention.

[0024] Figure 3 It is a schematic diagram of the sandwich structure of the flexible resistor sensor.

[0025] Figure 4 This is a graph showing the relationship between the bending angle and resistance value of the AgNWs / Si-PU flexible resistive thin film sensor.

[0026] Figure 5This is the data fitting curve of the bending angle and resistance value of the AgNWs / Si-PU flexible film sensor.

[0027] Figure 6 It is the change of resistance value of AgNWs / Si-PU flexible film sensor during 7 cycles of bending. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings, but the present invention is not limited to the following embodiments.

[0029] like Figure 1-6 The following is a specific embodiment of a method for preparing a flexible resistance sensor based on silver nanowire material. The method includes the following steps:

[0030] Step 1) Using silver nanowire material as variable resistor material: Mix polyvinyl pyrrolidone (PVP) with a molecular weight of 58,000 and a molecular weight of 1.3 million in a mass ratio of 1:1 to 2, take 1.86g of the above mixture and dissolve it in 100mL of ethylene glycol (EG), stir and dissolve it, put the solution into a three-necked flask, drop 1mL of the control agent into it, place the three-necked flask with 1mL of the control agent in an oil bath at 140°C and react for 1 to 6 hours, protect from light, weigh 0.51g of silver nitrate (AgNO3) and dissolve it in 25mL of ethylene glycol. In alcohol (EG), the beaker needs to be covered with tin foil during the stirring and dissolving process, and then the stirred AgNO3 / EG solution is added to the three-necked flask at a rate of 25-100mL / h using a peristaltic pump. The heating reaction is continued for 1 hour. After the reaction is completed, the obtained gray-green oily liquid is first cooled to room temperature and then placed in a centrifuge tube. It is repeatedly centrifuged 5-6 times with 500mL of anhydrous ethanol and then dispersed in the ethanol solution to obtain a silver nanowire material with a high aspect ratio of more than 1500. The silver nanowire network is used as a variable resistor material. The electron microscope photo of the silver nanowire is shown as follows. Figure 2 As shown; the control agent is any one of copper chloride, ferric chloride and sodium chloride solutions with a concentration of 3 mmol / L;

[0031] Step 2) A polyurethane PU flexible film is used as a substrate and modified with silicone: polyethylene glycol (PEG-2000) and polypropylene glycol (PPG-2000) are used in a mass ratio of 1:3 to 3:1 as raw material components of the mixed soft segment, and isophorone diisocyanate (IPDI) is used as the hard segment component. The ratio of the soft segment component to the hard segment component is 1:1 to 1.5. First, under N2 protection, dehydrated polyethylene glycol (PEG-2000), polypropylene glycol (PPG-2000), and dibutyltin dilaurate (DBTDL) are added to a three-necked flask equipped with a reflux condenser, a stirring device, and a thermometer, and 3 mL of catalyst dibutyltin dilaurate (DBTDL) is added dropwise, and then a mass ratio of 5 to 1% is added. 10% hydroxyl bi-terminated polydimethylsiloxane was fully reacted for 3 hours for modification, and triethylamine (TEA) was added dropwise according to the neutralization degree of 100% for neutralization for 15 minutes. After the system temperature dropped to room temperature, deionized water containing a defoamer was added and emulsified at high speed for 30 minutes. Finally, the organic solvent was removed by distillation under reduced pressure to obtain a silicone-modified polyurethane (Si-PU) emulsion. The obtained silicone-modified polyurethane (Si-PU) emulsion was poured into a PTFE mold and naturally cured at room temperature for 24 hours. It was then placed in a vacuum oven at 50°C for 48 hours and the obtained film was placed in a drying dish to obtain a silicone-modified polyurethane (Si-PU) film. Finally, the organic solvent was removed by distillation under reduced pressure to obtain a silicone-modified polyurethane (Si-PU) film.

[0032] Step 3) The organosilicon-modified polyurethane (Si-PU) film obtained in Step 2) is cut into two 5 cm × 5 cm squares, ultrasonically cleaned with anhydrous ethanol for 10 minutes, blown dry and placed in a desiccator, the silver nanowires obtained in Step 1) are centrifuged, and then dispersed in anhydrous ethanol using a pipette to obtain an AgNWs dispersion, and ultrasonically treated for 10 minutes to prevent agglomeration; the silver nanowires are dispersed in anhydrous ethanol using a pipette to obtain AgNWs dispersions with mass concentrations of 5 g / L, 10 g / L, 15 g / L, 20 g / L, and 30 g / L;

[0033] Step 4) Silver nanowire (AgNWs) material is used as a variable resistor material to prepare a flexible resistance sensor: the four sides of the organosilicon-modified polyurethane (Si-PU) film material are glued with transparent tape to reserve the position of the electrodes and the bonding, and then one side of the two organosilicon-modified polyurethane (Si-PU) film materials is immersed in the AgNWs dispersion prepared in step 3) for 30 minutes so that the surface is evenly covered with AgNWs, the transparent tape is torn off, and the four sides are non-metallized with acetone and anhydrous ethanol; copper sheets are introduced into the upper and lower ends of the treated organosilicon-modified polyurethane (Si-PU) film and fixed with conductive silver glue as lead-out electrodes, and finally the two organosilicon-modified polyurethane (Si-PU) films are face-to-face bonded and packaged to obtain a flexible thin film resistance sensor. The flexible thin film resistance sensor has a sandwich structure. The flexible thin film sensor with a "sandwich structure" is as shown in FIG. Figure 3 shown.

[0034] In a preferred embodiment, the flexible thin film resistance sensor can reach 13.2 to 54.1 Ω / m 2 The flexible resistor sensor has a maximum sensitivity of GF = 21.78 and an average sensitivity of GF = 9.58. The breaking strength of the silicone-modified polyurethane (Si-PU) film ranges from 10.7 to 14.8 MPa, and the elongation at break ranges from 289.3% to 432.5%.

[0035] When the flexible sensor is bent, Figure 1 The figure shows the appearance of the flexible resistance sensor of the present invention. Theoretically, its resistance value is:

[0036]

[0037] formula Where A is the cross-sectional area of the sensor, and L is the length of the sensor. Assume that the length of the sensor before bending is l and the width is w. When the sensor is bent, the outer radius and inner radius of its extended portion are r and R, respectively. The thickness after bending is d = Rr, and A = d × w. Therefore, the length L of the sensor after bending is:

[0038]

[0039] The total cross-sectional area S after bending is:

[0040]

[0041] Then the volume V of the medium after bending remains unchanged:

[0042]

[0043] Therefore, it can be deduced that:

[0044]

[0045] make is the initial resistance R0, K1 and K2 are constants, so the relationship between R and angle θ is considered to be:

[0046]

[0047] Then the flexible thin film resistance sensor was tested with bending angles of 0°, 30°, 60°, 90°, 120°, 150°, and 180°. The results are as follows: Figure 4 The above measured data can be fitted using analysis software to obtain the following: Figure 5 The results show that the bending angle of the sensor and the resistance output value show a parabolic correlation trend. The relationship between the resistance value Y and the bending angle θ is Y=0.0011θ 2 +0.03θ+35.05. Correlation coefficient R 2 =0.9926. This is basically consistent with the theoretically derived formula (2); combined with Figure 3 and formula The sensitivity GF was calculated (where R0 is the initial resistance, R is the real-time resistance, and ε is the bending strain). The maximum sensitivity GF was 21.78, and the average sensitivity GF was 9.58, meeting the sensitivity requirements of flexible film sensors.

[0048] The sensor prepared by the present invention was subjected to a cyclic bending deformation test, and the results are as follows Figure 6 As shown in the figure, during the bending process, the resistance of the flexible sensor gradually increases. However, during the bending recovery process, the resistance of the flexible sensor gradually decreases. The resistance change of the flexible sensor is basically the same during the seven cycles. The flexible film sensor prepared by the present invention has good sensitivity and repeatability.

[0049] The present invention will be further described in detail below with reference to actual drawings and examples using determined process parameters. These examples are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Various embodiments of the present invention may also be combined arbitrarily, and their inventive concepts are consistent with the present invention and should also be considered as the disclosure of the present invention.

[0050] Example 1

[0051] Polyvinylpyrrolidone (PVP) with a molecular weight of 58,000 and that of 1.3 million were mixed in a mass ratio of 1:1.8. 1.86 g of the above mixture was dissolved in 100 mL of ethylene glycol (EG). After stirring and dissolving, the solution was poured into a three-necked flask and 1 mL of a control agent (3 mmol / L copper chloride solution) was dropped into it.

[0052] The three-necked flask was placed in an oil bath at 140°C for 4 hours. 0.51 g of silver nitrate (AgNO3) was weighed and dissolved in 25 mL of ethylene glycol (EG) in a dark place. The beaker needed to be covered with tin foil during the stirring and dissolving process. The stirred AgNO3 / EG solution was then added to the three-necked flask at a rate of 75 mL / h using a peristaltic pump. The heating reaction was continued for 1 hour. After the reaction was completed, the obtained gray-green oily liquid was cooled to room temperature and placed in a centrifuge tube. It was centrifuged 5 times with 500 mL of anhydrous ethanol and then dispersed in an ethanol solution.

[0053] Polyethylene glycol (PEG-2000) and polypropylene glycol (PPG-2000) in a mass ratio of 1:3 are used as the raw materials of the mixed soft segment, and isophorone diisocyanate (IPDI) is used as the raw material of the hard segment. The ratio of the soft segment to the hard segment is 1:1.2. Under nitrogen protection, dehydrated PEG-2000, PPG-2000, and DBTDL were added to a three-necked flask equipped with a reflux condenser, a stirrer, and a thermometer. 3 mL of the catalyst dibutyltin dilaurate (DBTDL) was added dropwise. The reaction was maintained at 70°C for 1 h, then the temperature was raised to 80°C for another 2 h. The -NCO and -OH contents in the system were then determined by di-n-butylamine titration to maintain a soft segment to hard segment ratio of 1:1.2. 1-4-Butanediol (BDO) and 2-bis(hydroxymethyl)propionic acid (DMPA) were added for chain extension. After the reaction was continued for 2 h, 7.5% by mass of hydroxyalkyl di-terminated polydimethylsiloxane was added and fully reacted for 3 h for modification. Triethylamine (TEA) was then added dropwise to neutralize the system for 15 min until the neutralization degree reached 100%. After the system temperature dropped to room temperature, deionized water containing a defoamer was added and emulsified with high-speed stirring for 30 minutes. Finally, the organic solvent was removed by vacuum distillation to obtain a silicone-modified polyurethane emulsion (Si-PU). The resulting polyurethane Si-PU emulsion was poured into a PTFE mold and naturally cured at room temperature for 24 hours. It was then dried in a vacuum oven at 50°C for 48 hours. The resulting film was placed in a drying dish.

[0054] The Si-PU film prepared under the aforementioned conditions was cut into two 5 cm x 5 cm squares. After ultrasonic cleaning with anhydrous ethanol for 10 minutes, it was air-dried and placed in a desiccator for later use. The silver nanowires prepared above were centrifuged and then dispersed in anhydrous ethanol using a pipette to obtain a 30 g / L AgNW dispersion. The dispersion was then ultrasonically treated for 10 minutes.

[0055] The preparation process of the flexible thin film sensor: The treated Si-PU material is glued to the four sides with transparent tape to reserve the position of electrodes and bonding. Then, one side of the two Si-PU materials is immersed in the prepared AgNWs dispersion for 30 minutes so that the surface is evenly covered with AgNWs; the soaked Si-PU film is placed in a ventilated place to dry in the shade for 30 minutes, and then the transparent tape is torn off. The four sides are non-metallized with acetone and anhydrous ethanol; copper sheets are introduced into the upper and lower ends of the treated Si-PU film and fixed with conductive silver glue as lead-out electrodes. Finally, the two Si-PU films are face-to-face bonded and encapsulated to obtain a "sandwich structure" flexible thin film sensor.

[0056] Example 2

[0057] Polyvinylpyrrolidone (PVP) with a molecular weight of 58,000 and that of 1.3 million were mixed in a mass ratio of 1:1.6. 1.86 g of the above mixture was dissolved in 100 mL of ethylene glycol (EG). After stirring and dissolving, the solution was poured into a three-necked flask and 1 mL of a control agent was dropped into it. The control agent used was a 3 mmol / L ferric chloride (FeCl3) solution.

[0058] The three-necked flask was placed in an oil bath at 140°C for 4 hours. 0.51 g of silver nitrate (AgNO3) was weighed and dissolved in 25 mL of ethylene glycol (EG) in a dark place. The beaker needed to be covered with tin foil during the stirring and dissolving process. After that, the stirred AgNO3 / EG solution was added to the three-necked flask at a rate of 100 mL / h using a peristaltic pump. The heating reaction was continued for 1 hour. After the reaction was completed, the obtained gray-green oily liquid was cooled to room temperature and placed in a centrifuge tube. After repeated centrifugation 5 times with 500 mL of anhydrous ethanol, it was dispersed in an ethanol solution.

[0059] Polyethylene glycol (PEG-2000) and polypropylene glycol (PPG-2000) in a mass ratio of 1:1 are used as the raw materials of the mixed soft segment, and isophorone diisocyanate (IPDI) is used as the raw material of the hard segment. The ratio of the soft segment to the hard segment is 1:1.3. Under nitrogen protection, dehydrated PEG-2000, PPG-2000, and DBTDL were added to a three-necked flask equipped with a reflux condenser, a stirrer, and a thermometer. 3 mL of the catalyst dibutyltin dilaurate (DBTDL) was added dropwise. After the reaction was maintained at 70°C for 1 h, the temperature was raised to 80°C and the reaction was continued for another 2 h. The -NCO and -OH contents in the system were then determined by di-n-butylamine titration to maintain a ratio of 1:1.3 between the soft segment and the hard segment. 1-4-Butanediol (BDO) and 2-bis(hydroxymethyl)propionic acid (DMPA) were added for chain extension. After the reaction was continued for 2 h, 5% by mass of hydroxyalkyl di-terminated polydimethylsiloxane was added and fully reacted for 3 h for modification. Triethylamine (TEA) was then added dropwise to neutralize the system for 15 min, with the neutralization degree reaching 100%. After the system temperature dropped to room temperature, deionized water containing a defoamer was added and emulsified with high-speed stirring for 30 minutes. Finally, the organic solvent was removed by vacuum distillation to obtain a silicone-modified polyurethane emulsion (Si-PU). The resulting polyurethane Si-PU emulsion was poured into a PTFE mold and naturally cured at room temperature for 24 hours. It was then dried in a vacuum oven at 50°C for 48 hours. The resulting film was placed in a drying dish.

[0060] The Si-PU film prepared under the aforementioned conditions was cut into two 5 cm x 5 cm squares. After ultrasonic cleaning with anhydrous ethanol for 10 minutes, it was air-dried and placed in a desiccator for later use. The silver nanowires prepared above were centrifuged and then dispersed in anhydrous ethanol using a pipette to obtain a 20 g / L AgNW dispersion. The dispersion was then ultrasonically treated for 10 minutes.

[0061] The preparation process of the flexible thin film sensor: The treated Si-PU material is glued to the four sides with transparent tape to reserve the position of electrodes and bonding. Then, one side of the two Si-PU materials is immersed in the prepared AgNWs dispersion for 30 minutes so that the surface is evenly covered with AgNWs; the soaked Si-PU film is placed in a ventilated place to dry in the shade for 30 minutes, and then the transparent tape is torn off. The four sides are non-metallized with acetone and anhydrous ethanol; copper sheets are introduced into the upper and lower ends of the treated Si-PU film and fixed with conductive silver glue as lead-out electrodes. Finally, the two Si-PU films are face-to-face bonded and encapsulated to obtain a "sandwich structure" flexible thin film sensor.

[0062] Example 3

[0063] Polyvinylpyrrolidone (PVP) with a molecular weight of 58,000 and that of 1.3 million were mixed in a mass ratio of 1:1.4. 1.86 g of the above mixture was dissolved in 100 mL of ethylene glycol (EG). After stirring to dissolve, the solution was poured into a three-necked flask and 1 mL of a control agent was dropped into it. The control agent used was a 3 mmol / L sodium chloride (NaCl) solution.

[0064] Place the above three-necked flask in an oil bath at 140°C for 4 hours, weigh 0.51g of silver nitrate (AgNO3) and dissolve it in 25mL of ethylene glycol (EG) in the dark. During the stirring and dissolving process, the beaker needs to be covered with tin foil. Then, the evenly stirred AgNO3 / EG solution is added to the three-necked flask at a rate of 50mL / h using a peristaltic pump, and the heating reaction is continued for 1 hour. After the reaction is completed, the obtained gray-green oily liquid is cooled to room temperature and placed in a centrifuge tube. It is centrifuged 5 times with 500mL of anhydrous ethanol and then dispersed in the ethanol solution.

[0065] Polyethylene glycol (PEG-2000) and polypropylene glycol (PPG-2000) with a mass ratio of 3:1 are used as the raw materials of the mixed soft segment, and isophorone diisocyanate (IPDI) is used as the raw material of the hard segment. The ratio of soft segment to hard segment is 1:1.5. Under nitrogen protection, dehydrated PEG-2000, PPG-2000, and DBTDL were added to a three-necked flask equipped with a reflux condenser, a stirrer, and a thermometer. 3 mL of the catalyst dibutyltin dilaurate (DBTDL) was added dropwise. After the reaction was maintained at 70°C for 1 h, the temperature was raised to 80°C and the reaction was continued for another 2 h. The -NCO and -OH contents in the system were then determined by di-n-butylamine titration to maintain a ratio of soft segment to hard segment of 1:1.5. 1-4-Butanediol (BDO) and 2-bis(hydroxymethyl)propionic acid (DMPA) were added for chain extension. After the reaction was continued for 2 h, 10% by mass of hydroxyalkyl di-terminated polydimethylsiloxane was added and fully reacted for 3 h for modification. Triethylamine (TEA) was then added dropwise to neutralize the system for 15 min, with the neutralization degree reaching 100%. After the system temperature dropped to room temperature, deionized water containing a defoamer was added and emulsified with high-speed stirring for 30 minutes. Finally, the organic solvent was removed by vacuum distillation to obtain a silicone-modified polyurethane emulsion (Si-PU). The resulting polyurethane Si-PU emulsion was poured into a PTFE mold and naturally cured at room temperature for 24 hours. It was then dried in a vacuum oven at 50°C for 48 hours. The resulting film was placed in a drying dish.

[0066] The Si-PU film prepared under the aforementioned conditions was cut into two 5 cm x 5 cm squares. After ultrasonic cleaning with anhydrous ethanol for 10 minutes, it was air-dried and placed in a desiccator for later use. The silver nanowires prepared above were centrifuged and then dispersed in anhydrous ethanol using a pipette to obtain a 30 g / L AgNW dispersion. The dispersion was then ultrasonically treated for 10 minutes.

[0067] The preparation process of the flexible thin film sensor: The treated Si-PU material is glued to the four sides with transparent tape to reserve the position of electrodes and bonding. Then, one side of the two Si-PU materials is immersed in the prepared AgNWs dispersion for 30 minutes so that the surface is evenly covered with AgNWs; the soaked Si-PU film is placed in a ventilated place to dry in the shade for 30 minutes, and then the transparent tape is torn off. The four sides are non-metallized with acetone and anhydrous ethanol; copper sheets are introduced into the upper and lower ends of the treated Si-PU film and fixed with conductive silver glue as lead-out electrodes. Finally, the two Si-PU films are face-to-face bonded and encapsulated to obtain a "sandwich structure" flexible thin film sensor.

[0068] The present invention also includes forming other specific embodiments by using other numerical values within the process parameter range.

[0069] Comparative Example 1

[0070] Compared with Example 1, the concentration of the prepared AgNWs ethanol solution was 15 g / l, and the other steps remained unchanged.

[0071] Comparative Example 2

[0072] Compared with Example 1, the concentration of the prepared AgNWs alcohol solution was 10 g / l, and the other steps remained unchanged.

[0073] Comparative Example 3

[0074] Compared with Example 3, the concentration of the prepared AgNWs alcohol solution was 5 g / l, and the other steps remained unchanged.

[0075] Table 1:

[0076]

[0077] It can be seen from Table 1 that as the concentration of AgNWs dispersed in the ethanol solution increases, the square resistance decreases. In summary, it can be seen that the flexible thin film sensor prepared by the present invention has good sensitivity and repeatability.

[0078] Finally, it should be noted that the present invention is not limited to the above embodiments and may be subject to many variations. All variations that can be directly derived or imagined by a person skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a flexible resistance sensor based on silver nanowire material, characterized in that The preparation method comprises the following steps: Step 1) Mix polyvinyl pyrrolidone (PVP) with a molecular weight of 58,000 and a molecular weight of 1.3 million in a mass ratio of 1:1-2, take 1.86g of the above mixture and dissolve it in 100mL of ethylene glycol (EG), stir and dissolve it, put the solution into a three-necked flask, drop 1mL of a control agent into it, and then add the stirred AgNO3 / EG solution into the three-necked flask at a rate of 25-100mL / h using a peristaltic pump. Continue heating and reacting for 1 hour. After the reaction is completed, a silver nanowire material with a high aspect ratio of more than 1500 is obtained, and the silver nanowire material is used as a variable resistor material; Step 2) using polyethylene glycol PEG-2000 and polypropylene glycol PPG-2000 in a mass ratio of 1:3 to 3:1 as raw material components of the mixed soft segment, using isophorone diisocyanate (IPDI) as the hard segment component, and the ratio of the soft segment component to the hard segment component is 1:1-1.5, and adding 3 mL of dibutyltin dilaurate (DBTDL) as a catalyst dropwise, and then adding 5-10% by mass of hydroxyalkyl di-terminated polydimethylsiloxane to fully react for 3 hours for modification, and finally removing the organic solvent by vacuum distillation to obtain a silicone-modified polyurethane (Si-PU) film; Step 3) The silicone-modified polyurethane (Si-PU) film obtained in Step 2) was cut into two 5 cm × 5 cm squares, ultrasonically cleaned with anhydrous ethanol for 10 minutes, dried, and placed in a desiccator. The silver nanowires obtained in Step 1) were centrifuged and dispersed in anhydrous ethanol using a pipette to obtain an AgNWs dispersion, which was ultrasonically treated for 10 minutes to prevent agglomeration. Step 4) Use scotch tape to tape the four sides of the silicone-modified polyurethane (Si-PU) film material to reserve positions for electrodes and bonding. Then, soak one side of each silicone-modified polyurethane (Si-PU) film material in the AgNWs dispersion prepared in step 3) for 30 minutes to evenly cover the surface with AgNWs. Remove the scotch tape, and demetallize the four sides with acetone and anhydrous ethanol. Introduce copper sheets at the upper and lower ends of the treated silicone-modified polyurethane (Si-PU) film and fix them with conductive silver glue to serve as lead electrodes. Finally, the two silicone-modified polyurethane (Si-PU) films are face-to-face bonded and encapsulated to obtain a flexible resistive sensor with a sandwich structure. The control agent in step 1) is any one of copper chloride, ferric chloride, and sodium chloride solutions with a concentration of 3 mmol / L; In step 1), before adding the control agent to the three-necked flask at a rate of 25-100 mL / h, the following steps are performed: the three-necked flask with 1 mL of the control agent added is placed in an oil bath at 140°C for 1-6 hours. 0.51 g of AgNO3 is weighed and dissolved in 25 mL of ethylene glycol (EG) in the dark. The beaker needs to be covered with tin foil during the stirring and dissolution process. After the reaction in step 1) is completed, the obtained gray-green oily liquid is first cooled to room temperature and then placed in a centrifuge tube. Centrifugation is repeated 5-6 times with 500 mL of anhydrous ethanol and then dispersed in an ethanol solution to obtain a silver nanowire material with a high aspect ratio of more than 1500.

2. The method for preparing a flexible resistance sensor based on silver nanowire material according to claim 1, characterized in that: In step 2), before adding 3 mL of the catalyst dibutyltin dilaurate (DBTDL), dehydrated polyethylene glycol PEG-2000, polypropylene glycol PPG-2000, and dibutyltin dilaurate (DBTDL) were added to a three-necked flask equipped with a reflux condenser, a stirrer, and a thermometer under nitrogen protection.

3. The method for preparing a flexible resistance sensor based on silver nanowire material according to claim 1, characterized in that: In step 2), after modification, triethylamine (TEA) is added dropwise at a neutralization degree of 100% for neutralization for 15 minutes. After the system temperature drops to room temperature, deionized water containing a defoaming agent is added and emulsified at high speed for 30 minutes. Finally, the organic solvent is removed by distillation under reduced pressure to obtain a silicone-modified polyurethane (Si-PU) emulsion. The obtained silicone-modified polyurethane (Si-PU) emulsion is poured into a PTFE mold and naturally cured at room temperature for 24 hours. It is then placed in a vacuum oven at 50°C and dried for 48 hours. The obtained film is placed in a drying dish to obtain a silicone-modified polyurethane (Si-PU) film.

4. The method for preparing a flexible resistance sensor based on silver nanowire material according to claim 1, characterized in that: Flexible resistance sensor can reach 13.2~54.1Ω / m 2 .

5. The method for preparing a flexible resistance sensor based on silver nanowire material according to claim 1, characterized in that: The maximum sensitivity of the flexible resistance sensor is GF=21.78, and the average sensitivity is GF=9.

58.

6. The method for preparing a flexible resistance sensor based on silver nanowire material according to claim 1, characterized in that: The breaking strength of the silicone-modified polyurethane (Si-PU) film in step 2) is 10.7-14.8 MPa, and the breaking elongation is 289.3%-432.5%.

7. The method for preparing a flexible resistance sensor based on silver nanowire material according to claim 1, characterized in that: In step 3), the silver nanowires were dispersed in anhydrous ethanol using a pipette to obtain an AgNWs dispersion with a mass concentration of 5 g / L, 10 g / L, 15 g / L, 20 g / L or 30 g / L.

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