An ultracapacitive off-electric flexible pressure sensor and a preparation method thereof

Abstract

The application discloses a super-capacitive off-electric flexible pressure sensor and a preparation method thereof. The super-capacitive off-electric flexible pressure sensor comprises a first electrode plate, a second electrode plate and a flexible dielectric layer. The first electrode plate and the second electrode plate are oppositely arranged. The first electrode plate comprises a first flexible substrate and a first electrode layer arranged below the first flexible substrate. The second electrode plate comprises a second flexible substrate and a second electrode layer arranged above the second flexible substrate. The flexible dielectric layer is arranged between the first electrode layer and the second electrode layer. The flexible dielectric layer is a bucky gel composite material obtained by embedding an ionic liquid into a physical cross-linking network combined with acidified carbon nanotubes and polyvinylidene fluoride-hexafluoropropylene copolymer. The bucky gel based on a micro-ridge structure is used as the flexible dielectric layer, and the flexible electrode is pressed and bonded, so that the super-capacitive off-electric flexible pressure sensor is prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flexible sensors, in particular to a super-capacitive off-electric flexible pressure sensor and a preparation method thereof. BACKGROUND

[0002] Traditional centralized healthcare services require patients to go to the hospital, which means that the needs of patients cannot be addressed in a timely manner, especially for individuals who need emergency treatment. With the development of technology, the healthcare system needs to obtain physiological signals of the human body more sensitively, more quickly and more comprehensively, so there is an urgent need to improve the sensitivity and portability of flexible electronic devices. Flexible electronics is an emerging technology that has been developed in many fields. Intelligent robots with flexible pressure sensors and wearable sensing devices have greatly promoted the progress of the field of flexible electronic applications, and among them, capacitive flexible pressure sensors have attracted widespread attention due to their simple structure and ultra-high sensitivity.

[0003] The size of the dielectric layer structure and the selection of the active material are important factors in determining the sensitivity and stability of the flexible sensor. The dielectric layer prepared based on the micro-nano structure can change the contact area of the dielectric layer and the electrode when stressed, causing the test capacitance to change rapidly, thereby improving the sensitivity of the corresponding sensor; the preparation of a new type of dielectric layer by compounding active materials in flexible materials can also enable the flexible sensor to maintain relatively high sensitivity during use, improve the dielectric properties of the dielectric layer, and achieve high flexibility within a certain pressure range, thereby meeting the lightweight, miniaturization, and high efficiency goals of flexible sensor design, and realizing functions and performance that existing materials cannot achieve.

[0004] A flexible capacitive sensor based on ion gel is provided in the Chinese patent application publication CN113959603A, published on January 21, 2022. The sensor uses ion gel as the dielectric layer and processes the surface of the dielectric layer by laser ablation / micro-nano machining multi-level structure mold reverse molding. The flexible sensor prepared by the sensor can realize corresponding response to stress changes. The sensor has a certain flexibility, and the structured dielectric layer can improve the sensitivity of the sensor to a certain extent. However, the patent has the following limitations: the ion gel dielectric layer only encapsulates a single ion conductor, which only produces ion / electron interaction at the dielectric layer / electrode interface to form an interfacial double layer, but lacks an electron conductor inside the dielectric layer, thereby limiting the possibility of further improving the sensing performance and expanding the sensing mechanism. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a super-capacitive off-electric flexible pressure sensor to solve the technical problems of the single ion gel cross-linked network, expensive template structure or complex process in the prior art.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is: an ultracapacitor type ionic flexible pressure sensor, comprising a first electrode plate, a second electrode plate and a flexible dielectric layer, the first electrode plate and the second electrode plate are oppositely arranged, the first electrode plate comprises a first flexible substrate and a first electrode layer arranged below the first flexible substrate, the second electrode plate comprises a second flexible substrate and a second electrode layer arranged above the second flexible substrate, the flexible dielectric layer is arranged between the first electrode layer and the second electrode layer, and the flexible dielectric layer is a bucky gel composite material obtained by embedding an ionic liquid into a physical cross-linking network combined with acidized carbon nanotubes and polyvinylidene-hexafluoropropylene copolymer.

[0007] Further improvement of the technical scheme of the present application is that the first electrode plate and the second electrode plate are both flexible electrode material indium tin oxide / polyethylene terephthalate.

[0008] Further improvement of the technical scheme of the present application is that a preparation method of an ultracapacitor type ionic flexible pressure sensor comprises the following steps:

[0009] Step S1, preparing a flexible dielectric layer:

[0010] Step S1-1, mixing acidized carbon nanotubes and N,N-dimethylformamide according to a mass ratio of 1-4:400, ultrasonic dispersion treatment for 2h to obtain solution A;

[0011] Step S1-2, mixing polyvinylidene-hexafluoropropylene copolymer and N,N-dimethylformamide according to a mass ratio of 1:7, 50℃ water bath stirring treatment for 2h to obtain solution B;

[0012] Step S1-3, mixing solution A and solution B, stirring treatment for 2h to obtain solution C; polyvinylidene-hexafluoropropylene copolymer chains form hydrogen bonds with hydroxyl and carboxyl groups of acidized carbon nanotubes, the hydrogen bonds are formed by fluorine atoms of polyvinylidene-hexafluoropropylene copolymer, hydrogen atoms of acidized carbon nanotubes and oxygen atoms of polyvinylidene-hexafluoropropylene copolymer, and a physical cross-linking double three-dimensional space network is formed through the hydrogen bonds;

[0013] Step S1-4, adding ionic liquid into solution C, 50℃ water bath stirring treatment for 30min to obtain solution D;

[0014] Step S1-5, pouring solution D into a 3D printing template, 50℃ annealing treatment for 6h, peeling off after film formation and cutting into the required shape;

[0015] Step S2, washing the first electrode plate and the second electrode plate with ultrapure water and drying for 1-3h;

[0016] Step S3, placing the flexible dielectric layer between the first electrode plate and the second electrode plate, and performing pressure bonding by polydimethylsiloxane and then heating.

[0017] Further improvement of the technical scheme of the present application is that the preparation method of the acidified carbon nanotube in step S1-1 comprises the following steps:

[0018] Step a, mixing concentrated sulfuric acid and concentrated nitric acid according to a volume ratio of 1:3 to obtain a strong acid solution;

[0019] Step b, adding a certain amount of carbon nanotubes to the strong acid solution, performing ultrasonic dispersion treatment for 1h, performing 120℃ oil bath stirring treatment for 3h, and naturally cooling to room temperature to obtain a mixture;

[0020] Step c, filtering the mixture through a vacuum pump, washing with deionized water for multiple times until the PH of the mixture reaches 7, and drying the obtained acidified carbon nanotube at 80℃ for 12h.

[0021] Further improvement of the technical scheme of the present application is that the ionic liquid in step S1-4 is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide.

[0022] Further improvement of the technical scheme of the present application is that the mass ratio of the acidified carbon nanotube, the polyvinylidene fluoride-hexafluoropropylene copolymer and the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide is 1-4:100:100.

[0023] Further improvement of the technical scheme of the present application is that in step S3, the polydimethylsiloxane glue is applied to each corner of the flexible dielectric layer, then the flexible dielectric layer is placed between the first electrode plate and the second electrode plate with a static film, and after pressure bonding, heating is performed at 60-70℃ for 2-4h.

[0024] Due to the adoption of the above technical scheme, the present application has achieved the following technical progress:

[0025] 1. The flexible sensor provided by the present application has excellent biocompatibility, can be in contact with and attached to the object to be measured for a long time, and can reduce the vibration interference caused by the movement of the object, thereby improving the accuracy and long-term effectiveness of the sensor measurement.

[0026] 2. The present application combines flexible materials and structural engineering to significantly improve the performance of flexible pressure sensors. The 3D printed model is used as a template to form a Bucky gel with uniform micro-ridge structure by reverse film forming, which has the advantages of low cost, reusability and simple process. The Bucky gel based on the micro-ridge structure has good mechanical flexibility, excellent resilience and mechanical stability, and is an excellent material for dielectric layer.

[0027] 3、The flexible sensor provided by the application has a flexible dielectric layer, and 1-ethyl-3-methyl imidazole bis(trifluoromethyl sulfone) imide ([EMIM][TFSI]) is used as an ionic liquid. On one hand, when the electrons on the electrode attract and accumulate counter ions at the interface of the dielectric layer, an interface capacitor is formed, and a double electric layer is constructed; on the other hand, the capacitive sensor increases the interface contact area of the sensor due to the compression change of the micro-ridge structure under pressure, thereby increasing the double electric layer area and improving the sensitivity of the sensor.

[0028] 4、The flexible sensor provided by the application has a flexible dielectric layer, and 1-ethyl-3-methyl imidazole bis(trifluoromethyl sulfone) imide ([EMIM][TFSI]) is used as an ionic liquid. On one hand, when the electrons on the electrode attract and accumulate counter ions at the interface of the dielectric layer, an interface capacitor is formed, and a double electric layer is constructed; on the other hand, the capacitive sensor increases the interface contact area of the sensor due to the compression change of the micro-ridge structure under pressure, thereby increasing the double electric layer area and improving the sensitivity of the sensor.

[0029] 5、The super-capacitive electrostatic flexible pressure sensor provided by the application has a very low detection limit, can detect small objects, and has super-high sensitivity and good linearity in a large range of low pressure, thereby realizing multifunctional measurement of the sensor. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 FIG. 1 is a schematic diagram of the super-capacitive electrostatic flexible pressure sensor of the application;

[0031] Figure 2 FIG. 2 is a schematic diagram of the micro-ridge structure-based PAGU dielectric layer structure of the sensor; Figure 1

[0032] Figure 3 FIG. 5 is an equivalent circuit model diagram of the pressure sensor of the embodiments 1-4 of the application;

[0033] Figure 4 FIG. 6 is a capacitance increment change curve of the pressure sensor of the embodiments 1-4 of the application under a continuously changing pressure;

[0034] Figure 5 FIG. 7 is an application schematic diagram of the pressure sensor of the embodiment 2 of the application applied to a small pressure test;

[0035] Figure 6 FIG. 8 is a cycle test schematic diagram of the pressure sensor of the embodiment 2 of the application;

[0036] Figure 7 FIG. 9 is an application schematic diagram of the pressure sensor of the embodiment 2 of the application applied to human-computer interaction.​

[0037] Wherein, 11-first flexible substrate; 21-first electrode layer; 31-flexible dielectric layer; 22-second electrode layer; 12-second flexible substrate. DETAILED DESCRIPTION

[0038] The application will be further described in detail below in conjunction with examples:

[0039] As Figure 1 shown, a supercapacitive ionic flexible pressure sensor, comprising a first electrode plate, a second electrode plate and a flexible dielectric layer 31, the first electrode plate and the second electrode plate are both flexible electrode material indium tin oxide / polyethylene terephthalate. The first electrode plate and the second electrode plate are oppositely arranged, the first electrode plate comprises a first flexible substrate 11 and a first electrode layer 21 arranged below the first flexible substrate 11, the second electrode plate comprises a second flexible substrate 12 and a second electrode layer 22 arranged above the second flexible substrate 12, the flexible dielectric layer 31 is arranged between the first electrode layer 21 and the second electrode layer 22, the flexible dielectric layer 31 is a bucky gel composite material obtained by embedding ionic liquid into the physical crosslinking network of acidified carbon nanotubes combined with polyvinylidene fluoride-hexafluoropropylene copolymer, and the bucky gel dielectric layer structure based on micro-ridge structure is as shown in Figure 2 .

[0040] A preparation method of a supercapacitive ionic flexible pressure sensor, comprising the following steps:

[0041] Step S1, preparing a flexible dielectric layer 31:

[0042] Step S1-1, mixing acidified carbon nanotubes and N,N-dimethylformamide according to a mass ratio of 1-4:400, ultrasonic dispersion treatment for 2h, to obtain solution A;

[0043] The preparation method of the acidified carbon nanotube comprises the following steps:

[0044] Step a, mixing concentrated sulfuric acid and concentrated nitric acid according to a volume ratio of 1:3 to obtain a strong acid solution;

[0045] Step b, adding a certain amount of carbon nanotubes to the strong acid solution, ultrasonic dispersion treatment for 1h, 120℃ oil bath stirring treatment for 3h, and natural cooling to room temperature to obtain a mixture;

[0046] Step c, filtering the mixture through a vacuum pump, washing with deionized water for multiple times until the PH of the mixture reaches about 7, which is an unclear word, a range can be given, drying the obtained acidified carbon nanotubes at 80℃ for 12h.

[0047] Step S1-2, polyvinylidene fluoride-hexafluoropropylene copolymer and N,N-dimethylformamide were mixed in a mass ratio of 1:7, treated with 50℃ water bath stirring for 2h, to obtain solution B;

[0048] Step S1-3, solution A and solution B were mixed, stirred for 2h to obtain solution C; the polyvinylidene fluoride-hexafluoropropylene copolymer chain and the hydroxyl and carboxyl of the acidified carbon nanotube formed a hydrogen bond, the hydrogen bond was formed by the fluorine atom of the polyvinylidene fluoride-hexafluoropropylene copolymer, the hydrogen atom on the hydroxyl and carboxyl of the acidified carbon nanotube, the hydrogen atom of the polyvinylidene fluoride-hexafluoropropylene copolymer, and the oxygen atom on the hydroxyl and carboxyl of the acidified carbon nanotube, and a physically cross-linked double three-dimensional space network was formed through the hydrogen bond;

[0049] Step S1-4, 1-ethyl-3-methyl imidazole bis(trifluoromethylsulfonyl) imide was selected as an ionic liquid, the ionic liquid was added to solution C, and 50℃ water bath stirring treatment was carried out for 30min to obtain solution D, the mass ratio of acidified carbon nanotube, polyvinylidene fluoride-hexafluoropropylene copolymer and 1-ethyl-3-methyl imidazole bis(trifluoromethylsulfonyl) imide was 1-4:100:100;

[0050] Step S1-5, solution D was poured into a 3D printing template, and annealing treatment was carried out at 50℃ for 6h, and after film formation, it was peeled off and cut into the required shape;

[0051] Step S2, the first electrode plate and the second electrode plate were washed with ultrapure water and then dried for 1-3h;

[0052] Step S3, the flexible dielectric layer 31 was placed between the first electrode plate and the second electrode plate, and pressure bonding was carried out through polydimethylsiloxane, and then heating was carried out. Specifically, polydimethylsiloxane glue was applied to each corner of the flexible dielectric layer 31, then the flexible dielectric layer 31 was placed between the first electrode plate and the second electrode plate with static film, pressure bonding was carried out, and then heating was carried out at 60-70℃ for 2-4h.

[0053] The present application realizes the preparation of the supercapacitive ionic flexible pressure sensor by pressure bonding the flexible electrode with the flexible dielectric layer based on the micro-ridge structure Bucky gel. Since under the bias voltage, the interfacial double layer and the dielectric layer micro-capacitance generated by the micro-ridge structure Bucky gel also increase with the increase of pressure, the sensor has super-high sensitivity and extremely low detection limit.

[0054] Example 1

[0055] The preparation method of the supercapacitive ionic flexible pressure sensor comprises:

[0056] Step S1, preparing a flexible dielectric layer 31

[0057] Step S1-1, 5 mg acidified MWCNTs were first mixed with 2 g N,N-dimethylformamide DMF, ultrasonic dispersion for 2 h to obtain solution A;

[0058] Step S1-2, 0.5 g P(VDF-HFP) particles were placed in a beaker at the same time, 3.5 g DMF was added, and stirring was carried out at 50℃ water bath for 2 h to make it completely dissolved to obtain solution B;

[0059] Step S1-3, then solution A and solution B were mixed and stirred for 2 h to obtain solution C; P(VDF-HFP) chains and the hydroxyl and carboxyl groups of the acidified MWCNTs bundle formed hydrogen bonds, which were mainly formed by the fluorine atoms of P(VDF-HFP) and the hydrogen atoms on the hydroxyl and carboxyl groups of the acidified MWCNTs, and the hydrogen atoms of P(VDF-HFP) and the oxygen atoms on the hydroxyl and carboxyl groups of the acidified MWCNTs. Through hydrogen bonds, a physically cross-linked double three-dimensional space network was formed.

[0060] Step S1-4, [EMIM][TFSI] was added to solution C, and 50℃ water bath was stirred vigorously for 30 min to obtain solution D; acidified MWCNTs can orient imidazole ions on its π-electron surface through strong “cation-π” interaction, and P(VDF-HFP) can form non-covalent bonds with [EMIM][TFSI]. This molecular ordering will trigger the aggregation of surrounding ions, thereby connecting adjacent P(VDF-HFP) chains and acidified MWCNTs bundles with each other.

[0061] Step S2, pour solution 4 into a 3D printing template, place it on a heating platform and anneal at 50℃ for 6 h, then peel off and cut into 2×2×0.1 cm size after film formation to obtain the corresponding flexible dielectric layer M1.

[0062] Step S3, after the flexible electrode ITO / PET was washed with ultrapure water, the dielectric layer M1 was prepared into a sensor, 4 g of polydimethylsiloxane PDMS and 0.4 g of PDMS B glue with trade name Dow Corning Sylgard 184 curing agent were doped to prepare 3 ml of PDMS glue, then a small amount of PDMS glue was applied to each corner of the dielectric layer M1, and the dielectric layer M1 was placed between the first electrode plate and the second electrode plate. Heat in a 65℃ air drying oven for 3 hours to make a sensor.

[0063] Examples 2-4

[0064] The differences between Examples 2-4 and Example 1 are that in Example 2, 10 mg of acidized MWCNTs are added in step S1-1, and the obtained flexible dielectric layer 31 is flexible dielectric layer M2; in Example 3, 15 mg of acidized MWCNTs are added in step S1-1, and the obtained flexible dielectric layer 31 is flexible dielectric layer M3; and in Example 4, 20 mg of acidized MWCNTs are added in step S1-1, and the obtained flexible dielectric layer 31 is flexible dielectric layer M4.

[0065] The super-capacitive flexible pressure sensor prepared in Examples 1-4 can be simplified as a capacitor element, as shown in the figure, which is composed of a double-layer capacitor on the dielectric / electrode interface, a micro-capacitor in the dielectric layer, and a bulk resistance in series. Figure 3

[0066] The super-capacitive flexible pressure sensor provided in Examples 1-4 mainly measures the physical quantity of capacitance, which is related to the contact area of the sensor dielectric layer, the electrode spacing, and the effective dielectric constant. The relative size of the change in capacitance under pressure is the sensitivity of the sensor, and the formula for measuring the sensitivity of the capacitive sensor is

[0067] Figure 4 The capacitance increment change curve of the sensor under changing pressure shows the capacitance increment change of the pressure sensor prepared by the flexible dielectric layers M1, M2, M3, and M4 in the examples under the process of pressure from 0 to 12 kPa. Through calculation, it is known that the sensitivity of the sensors prepared in Examples 1-4 in the range of 0-3.625 kPa is 33.464 kPa -1 , 70.783 kPa -1 , 25.386 kPa -1 , and 17.706 kPa -1 .

[0068] Figure 5 The figure is a schematic diagram of the application of the pressure sensor of Example 2 in micro-pressure testing, which shows the capacitance increment obtained by loading or unloading a polyurethane sponge with a pressure of about 0.2 Pa on the sensor prepared by the flexible dielectric layer M2. From the experimental data graph, it can be clearly seen that the sensor can distinguish the weight of the sponge and determine the detection limit of the sensor.

[0069] Figure 6 The figure is a schematic diagram of the cyclic test of the pressure sensor of Example 2, which shows the repeated use of the sensor prepared by the flexible dielectric layer M2. The sensor is subjected to multiple tests of capacitance increment under different pressures, and the actual capacitance increment is observed to remain relatively flat, indicating that the sensor can be recycled to a certain extent.

[0070] Figure 7 ​Fig. 1 is a schematic diagram of application of the pressure sensor of the present application in human-computer interaction, showing that the sensor prepared by the flexible dielectric layer M2 is fixed on the fingertip of a mechanical hand, and the mechanical hand repeatedly touches the human finger to perform touch tests of different degrees. As can be seen from the figure, when the mechanical hand touches the finger with different pressures, the sensor can realize the change of different capacitance increments, indicating the test condition of the sensor under different pressure conditions.

Claims

1. An ultracapacitive off-electrically flexible pressure sensor, characterized by: The flexible dielectric layer is prepared by embedding an ionic liquid into a physical cross-linking network of acidified carbon nanotubes combined with a polyvinylidene-hexafluoropropylene copolymer to obtain a bucky gel composite material. The preparation method of the supercapacitive flexible pressure sensor includes the following steps: Step S1, preparing a flexible dielectric layer: Step S1-1, mixing acidified carbon nanotubes and N,N-dimethylformamide according to a mass ratio of 1-4:400, ultrasonic dispersion treatment for 2h to obtain solution A; Step S1-2, mixing polyvinylidene-hexafluoropropylene copolymer and N,N-dimethylformamide according to a mass ratio of 1:7, 50℃ water bath stirring treatment for 2h to obtain solution B; Step S1-3, mixing solution A and solution B, stirring treatment for 2h to obtain solution C; the polyvinylidene-hexafluoropropylene copolymer chain forms hydrogen bonds with the hydroxyl and carboxyl groups of the acidified carbon nanotubes, the hydrogen bonds are formed by the fluorine atoms of the polyvinylidene-hexafluoropropylene copolymer, the hydrogen atoms of the hydroxyl and carboxyl groups of the acidified carbon nanotubes, the hydrogen atoms of the polyvinylidene-hexafluoropropylene copolymer, and the oxygen atoms of the hydroxyl and carboxyl groups of the acidified carbon nanotubes, and a physical cross-linking double three-dimensional space network is formed through the hydrogen bonds; Step S1-4, adding an ionic liquid to solution C, 50℃ water bath vigorous stirring treatment for 30min to obtain solution D; Step S1-5, pouring solution D into a 3D printing template, 50℃ annealing treatment for 6h, peeling off after film formation and cutting into the required shape; Step S2, washing the first electrode plate and the second electrode plate with ultrapure water and drying for 1-3h; Step S3, placing the flexible dielectric layer between the first electrode plate and the second electrode plate, and then performing pressure bonding through polydimethylsiloxane and heating.

2. The ultracapacitive off-electric flexible pressure sensor according to claim 1, wherein: The first electrode plate and the second electrode plate are both flexible electrode material indium tin oxide / polyethylene terephthalate.

3. The ultracapacitive off-electric flexible pressure sensor according to claim 1, wherein: The preparation method of the acidified carbon nanotubes in step S1-1 includes the following steps: Step a, mixing concentrated sulfuric acid and concentrated nitric acid according to a volume ratio of 1:3 to obtain a strong acid solution; Step b, adding a certain amount of carbon nanotubes to the strong acid solution, ultrasonic dispersion treatment for 1h, 120℃ oil bath stirring treatment for 3h, and natural cooling to room temperature to obtain a mixture; Step c, filtering the mixture through a vacuum pump and washing with deionized water multiple times until the PH of the mixture reaches 7, and drying the obtained acidified carbon nanotubes at 80℃ for 12h.

4. The supercapacitive off-the-shelf flexible pressure sensor of claim 1, wherein: The ionic liquid in step S1-4 is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide.

5. The supercapacitive off-the-shelf flexible pressure sensor of claim 1, wherein: The mass ratio of the acidified carbon nanotube, polyvinylidene fluoride-hexafluoropropylene copolymer and 1-ethyl-3-methyl imidazole bis(trifluoromethylsulfonyl) imide is 1-4:100:

100.

6. The ultracapacitive off-electric flexible pressure sensor according to claim 5, wherein: The step S3 is to spot the polydimethylsiloxane glue on each corner of the flexible dielectric layer, and then place the flexible dielectric layer between the first electrode plate and the second electrode plate with the electrostatic film, and then perform pressure bonding, and then heat at 60-70℃ for 2-4h.

Images