Polyethyleneimine carbon nanotube composite sponge pressure sensor and preparation method thereof

Abstract

The invention discloses a polyethyleneimine carbon nanotube composite sponge pressure sensor and a preparation method thereof.The preparation method is simple in process and economical in material, by introducing a polyethyleneimine middle layer, the agglomeration phenomenon of conductive material carbon nanotubes is improved, uniform distribution and firm combination of the carbon nanotubes on the surface of a three-dimensional framework are facilitated, and the pressure sensor has good application prospects. Therefore, the structural stability of the sensor under the cyclic load is improved, and the cyclic stability in performance is ensured. According to the polyethyleneimine-carbon nanotube composite sponge pressure sensor prepared by the method, the sensitivity and the pressure measurement range of the flexible pressure sensor are improved, and high sensitivity, wide pressure range and good cycling stability are shown; the problems of insufficient binding force, uneven distribution and the like of the carbon nanotube conductive particles and the elastic substrate in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to a pressure sensor and a preparation method thereof, in particular to a polyethyleneimine carbon nanotube composite sponge pressure sensor and a preparation method thereof, belonging to the technical field of flexible pressure sensors. Background Art

[0002] Conductive porous sponge is a promising piezoresistive pressure sensing material, which has rich sensing space and dense sensing paths in three-dimensional space, can effectively improve sensitivity and sensing range, and the sponge is light in texture and soft on the surface, suitable for human body surface application scenarios.

[0003] The preparation methods of conductive porous sponges include template method, freeze-drying method, dip-coating method, etc. The dip-coating method is a simple, economical and efficient process. In this process, the conductive material enters the porous structure in solution form and is fixed on the insulating elastic three-dimensional polymer skeleton. During the dipping process, the binding effect between the conductive material and the substrate is random and difficult to control, often resulting in poor interfacial bonding strength between the two, and it is impossible to maintain a stable framework for efficient electron transport and load transfer during long-term use, thus causing a decline in sensing performance. Therefore, various polymer adhesives are used to improve the interfacial adhesion ability between the conductive material and the polymer surface, and the composite strategy of conductive particles and polymer macromolecules is also an inevitable trend in the development of piezoresistive sensing composite materials.

[0004] Regarding the research on carbon nanotube conductive sponges, there are already performance improvement schemes for optimizing porous substrate pressure sensors by doping polymer materials, which can suppress the thermoelectric effect and reduce errors. This scheme reduces the conductivity of the composite conductive sponge and has limited effect on improving sensitivity, and fails to effectively improve the hysteresis phenomenon of the porous structure matrix.

[0005] The invention patent with the application number CN202010980505.4 discloses a preparation method of a pressure sensor based on a composite sponge porous structure, which claims to protect a preparation method of a polyurethane porous sponge material with uniform and variable pore size. The preparation process of this patent takes a long time, and although the three-dimensional wrinkled structure formed on the surface after the polyurethane porous sponge is compounded with polypyrrole improves the sensitivity in the small pressure range, the output data will deviate after multiple cycles.

[0006] In view of the above problems, it is necessary to conduct in-depth research on the preparation method of sponge pressure sensors to optimize their performance such as structure and cycle stability. Summary of the Invention

[0007] To solve the deficiencies of the prior art, the purpose of the present invention is to provide a polyethyleneimine-carbon nanotube composite sponge pressure sensor and its preparation method, so as to obtain a composite conductive sponge sensor with uniform distribution of conductive substances and strong interfacial bonding force of materials. This sensor can exhibit high sensitivity, a wide pressure range, and good cyclic stability, overcoming the problems of insufficient bonding force and uneven distribution between carbon nanotube conductive particles and elastic substrates in the prior art.

[0008] To achieve the above objectives, the present invention adopts the following technical solutions:

[0009] A preparation method of a polyethyleneimine-carbon nanotube composite sponge pressure sensor, comprising the following steps:

[0010] S1. Ultrasonically clean and dry the melamine sponge with absolute ethanol and deionized water;

[0011] S2. Prepare an aqueous solution of polyethyleneimine and an aqueous solution of carboxylated carbon nanotubes respectively;

[0012] S3. Immerse the melamine sponge in the aqueous solution of polyethyleneimine, wash it with deionized water, and place it in an oven to dry;

[0013] S4. Then immerse the melamine sponge in the carboxylated carbon nanotube solution for a period of time and then dry it;

[0014] S5. Repeat the above two impregnation processes of S3 and S4 multiple times;

[0015] S6. Dry it. After completion of the connection, a polyethyleneimine-carbon nanotube composite sponge pressure sensor is obtained.

[0016] Preferably, dissolve polyethyleneimine particles in deionized water, put them into an ultrasonic cleaner and ultrasonically oscillate for several minutes to fully dissolve polyethyleneimine, and obtain an aqueous solution of polyethyleneimine with a certain concentration.

[0017] Preferably, the mass percentage concentration of the aforementioned aqueous solution of polyethyleneimine is 1%.

[0018] Preferably, dilute the carboxylated carbon nanotube solution to obtain an aqueous solution of carboxylated carbon nanotubes with a certain concentration.

[0019] More preferably, the concentration of the aforementioned aqueous solution of carboxylated carbon nanotubes is 1 - 5 mg / mL.

[0020] Further preferably, in the aforementioned step S3, the environmental temperature during impregnation is 60 - 90 °C.

[0021] Even more preferably, in the aforementioned steps S3 and S4, the impregnation process is carried out in a vacuum environment, so as to ensure that the solution fully penetrates into the inner pores and the surface of the framework, precipitate the air in the pores to form a low pressure, and promote the uniform distribution of the solution.

[0022] Further preferably, in the foregoing step S5, the number of repetitions of the impregnation process is more than 5 times.

[0023] Further preferably, the connection in the foregoing step S5 is as follows: Fix and encapsulate the conductive carbon cloth at both ends of the large area of the piezoresistive layer, fix the carbon cloth at the four vertices of the end face of the piezoresistive layer with cotton thread, embed wires inside the carbon cloth, and at the same time ensure that the contact area between the carbon cloth and the piezoresistive layer is slightly smaller than the end face of the pressure-sensitive layer to avoid short-circuit caused by the interconnection of the carbon cloth during use. Finally, a polyethyleneimine-carbon nanotube composite sponge pressure sensor is prepared.

[0024] The present invention also claims to protect a polyethyleneimine-carbon nanotube composite sponge pressure sensor prepared by the foregoing method.

[0025] The beneficial effects of the present invention are as follows:

[0026] (1) The sensor preparation method of the present invention has a simple process and economical materials. By introducing a polyethyleneimine intermediate layer, the agglomeration phenomenon of the conductive material carbon nanotubes is improved, which helps the uniform distribution and firm combination of carbon nanotubes on the surface of the three-dimensional skeleton, thereby enhancing the structural stability of the sensor under cyclic loading and ensuring the cyclic stability in performance.

[0027] (2) The polyethyleneimine-carbon nanotube composite sponge pressure sensor prepared by the method of the present invention improves the sensitivity and pressure measurement range of the flexible pressure sensor. Description of the Drawings

[0028] Figure 1 is a schematic flow chart of preparing a conductive sponge pressure sensor in the present invention;

[0029] Figure 2 is a microscopic morphology comparison diagram of the sponge internal structure of the product of Example 5 and Comparative Example 1 of the present invention after 100 pressure cycles;

[0030] Figure 3 is the sensitivity curves of the products of Example 5 and Comparative Example 1 of the present invention before and after 1000 pressure cycles;

[0031] Figure 4 is the Raman spectra of the composite sponge Example 5 prepared according to the preparation method of the present invention, the sponge of Comparative Example 1 coated only with carbon nanotubes, the sponge of Comparative Example 2 coated only with polyethyleneimine, and the clean sponge;

[0032] Figure 5 is the sensitivity curves of the conductive composite sponge pressure sensors with different concentrations prepared according to the preparation method of the present invention (Examples 1 to 5 and Comparative Example 1);

[0033] Figure 6It is the optimal sensitivity curve diagram obtained by the preparation method of the present invention (Example 5);

[0034] Figure 7 It is the cyclic test diagram of the conductive composite sponge pressure sensor prepared according to the present invention (Example 5). Detailed implementation manners

[0035] The present invention will be specifically introduced below in conjunction with the accompanying drawings and specific embodiments.

[0036] The carboxylated multi-walled carbon nanotube dispersion (CNTs) used in the present invention was purchased from Jiangsu Xianfeng Nano Materials Science Co., Ltd., with the specification of XFWPMC-M09 (1.7 g / mL); polyethylenimine (PEI) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with the specification of E107078.

[0037] Example 1

[0038] In this example, a conductive composite material was synthesized using a 1% mass concentration of polyethylenimine solution and a 1 mg / mL carbon nanotube solution to prepare a conductive composite sponge pressure sensor. The process is as Figure 1 shown, and the specific steps are as follows:

[0039] S1. Weigh 0.1 g of polyethylenimine particles and dissolve them in 100 ml of deionized water. Place them in an ultrasonic cleaner and ultrasonically oscillate for 30 minutes to fully dissolve the polyethylenimine, obtaining a 1% polyethylenimine aqueous solution;

[0040] S2. Weigh 5 g of carboxylated carbon nanotube aqueous solution and add 97.06 ml of deionized water to dilute it to 1 mg / mL;

[0041] S3. First, place a 10 mm×10 mm×3 mm melamine sponge in the polyethylenimine aqueous solution, place it in an oven at 80 °C for 2 h, take it out and wash it in deionized water for 2 min, and then place it in the oven to dry; then place the melamine sponge in a 5 mg / ml carboxylated carbon nanotube aqueous solution and place it in a vacuum environment for 2 h, take it out and dry it;

[0042] S4. Repeat the impregnation and drying processes in step S3 more than 5 times to obtain the polyethylenimine-carbon nanotube composite sponge pressure sensor of Example 1.

[0043] Example 2

[0044] The method and steps of this example are basically the same as those of Example 1, except that the concentration of the prepared carboxylated carbon nanotube aqueous solution is 2 mg / mL: weigh 10 g of carboxylated carbon nanotube aqueous solution and add 94.12 ml of deionized water.

[0045] Example 3

[0046] This example is basically the same as the method and steps of Example 1, except that the concentration of the carboxylated carbon nanotube aqueous solution configured is 3 mg / mL: Weigh 15 g of the carboxylated carbon nanotube aqueous solution and add 91.18 ml of deionized water.

[0047] Example 4

[0048] This example is basically the same as the method and steps of Example 1, except that the concentration of the carboxylated carbon nanotube aqueous solution configured is 4 mg / mL: Weigh 20 g of the carboxylated carbon nanotube aqueous solution and add 88.24 ml of deionized water.

[0049] Example 5

[0050] This example is basically the same as the method and steps of Example 1, except that the concentration of the carboxylated carbon nanotube aqueous solution configured is 5 mg / mL: Weigh 25 g of the carboxylated carbon nanotube aqueous solution and add 85.3 ml of deionized water.

[0051] Comparative Example 1

[0052] This comparative example prepares a conductive sponge pressure sensor impregnated only in a 5 mg / mL carbon nanotube solution.

[0053] The specific process is as follows: Directly place the washed 10 mm × 10 mm × 3 mm melamine sponge into a 5 mg / mL carboxylated carbon nanotube solution and keep it under vacuum for 10 h, and finally dry it to obtain the carbon nanotube sponge pressure sensor of Comparative Example 1.

[0054] Comparative Example 2

[0055] This comparative example prepares a conductive sponge pressure sensor impregnated only in a 1% polyethyleneimine solution.

[0056] The specific process is as follows: Directly place the washed 10 mm × 10 mm × 3 mm melamine sponge into a 1% polyethyleneimine solution, heat it at 80 °C for 2 h, and finally dry it to obtain the polyethyleneimine sponge pressure sensor of Comparative Example 2.

[0057] Apply 100 pressure cycles to the products of Example 5 and Comparative Example 1 respectively, and the microscopic morphologies of the sponge skeletons of the two products are as Figure 2 shown. It can be Figure 2 seen that the carbon nanotube conductive layer is firmly coated on the composite sponge skeleton containing the PEI intermediate layer in Example 5, while the carbon nanotubes on the sponge skeleton without PEI in Comparative Example 1 show the phenomena of shedding and displacement.

[0058] Apply 1000 pressure cycles to the products of Example 5 and Comparative Example 1 respectively, and compare the sensitivity curves of the two samples before and after cycling. As Figure 3 shown, it is observed that the sensitivity of the PEI-containing sensor in Example 5 is generally higher than that of the product in Comparative Example 1, that is, the presence of PEI improves the sensitivity of pressure sensing. Moreover, after cycling, the sensitivity of the product in Comparative Example 1 changes from 0.139 to 0.175, with a change rate of 25.89%; while after cycling, the sensitivity of the PEI / CNT / sponge in Example 1 changes from 0.913 to 1.052, with a change rate of 15.22%, and the sensitivity change rate is reduced by 41.21% compared with Comparative Example 1. It can be seen that in the sensor product of this example, the presence of the PEI layer reduces the change rate of the sensor sensitivity and improves the working stability of the sensor.

[0059] At the same time, we also observed that the sensitivity curves of pressurization and depressurization of this structural sensor do not coincide. Generally, the change curve during the depressurization process is above the pressurization curve. Hysteresis phenomena are common in porous structures, and the value of the hysteresis amount is obtained by calculation using the formula: where A unloading and A loading represent the areas under the depressurization curve and the pressurization curve respectively.

[0060] Accordingly, we obtained that the hysteresis amount value of the sensor in Example 5 is 25%, and the hysteresis amount value of the sensor in Comparative Example 1 is 36.7%. It can be seen that the PEI intermediate layer reduces the hysteresis amount of the sponge pressure sensor.

[0061] Perform Raman spectroscopy tests on Example 5, Comparative Example 1, Comparative Example 2, and clean sponge respectively. Figure 4 The Raman spectrum characteristic diagrams of each product are shown. From the black line 1 (sponge), it can be seen that the characteristic peaks of the untreated melamine sponge are mainly distributed at 756, 970, 1440, 2960 cm -1 positions, and there are also some small peaks. In the red line 3 (PEI / sponge), PEI is coated on the three-dimensional skeleton inside the sponge, and the spectral energy density shows an upward trend with the increase of displacement. It can be seen that small peaks appear near the displacements of 977 and 2950 cm -1 , indicating that the distribution of PEI is relatively uniform and the coating thickness is large. The blue line 2 (CNTs / sponge) is the spectrum diagram of carbon nanotubes directly coating the sponge. It is similar to the spectrum shape of line 1, and all the characteristic peaks of the melamine sponge can be observed. The difference lies in the intensity relationship between the peak at 1440 cm -1 and the peaks on both sides (1348, 1580 cm -1 ). The peaks on both sides correspond to the D peak and G peak of carbon nanotubes respectively. In line 1, the peak at 1440 cm -1 is higher than the peaks on both sides, while in line 3, the peak at 1440 cm -1The peak is between the two side peaks, and the characteristics of the carbon nanotubes are more obvious. I D / I G It is often used to characterize the structural integrity and crystal quality of carbon nanotubes, and the calculated value is 1.06. The green line 4 (PEI / CNTs / sponge of Example 5) is the overall spectrum of the PEI / CNTs / sponge sample. The overall trend is similar to that of PEI / sponge, and at the same time, two characteristic peaks are added, located at 1350 and 1600 cm -1 respectively. These two characteristic peaks correspond to the D peak and G peak of carbon nanotubes, and the calculated I D / I G is 0.83, which is lower than the above value, indicating that the dispersion of carbon nanotubes is improved, the degree of disorder is reduced, and the degree of graphitization is increased. Under the bonding action of PEI on the three-dimensional skeleton, they are arranged orderly and distributed evenly. This verifies that PEI has the effect of enhancing the binding force between the three-dimensional skeleton and the conductive particles.

[0062] The sensitivity tests were carried out on the products of Examples 1-5 and Comparative Example 1 to obtain the curves of the current change rate output under different pressures. The overall trends of these 6 sensors are the same. The current change rate first rises gently with the increase of pressure, and then the rising trend accelerates until the maximum value of the pressure range. The difference lies in the rising rate of the curve after 10 kPa. The sensitivity is calculated according to the slope in the current change rate-pressure change curve: where I represents the real-time current, I0 represents the initial current, and P represents the input pressure.

[0063] According to the above formula, it is calculated that the sensor of Example 5 has the highest sensitivity. As Figure 6 shown, in the linear range of 0-20 kPa of this sensor, the sensitivity is 0.59 kPa -1 and in the pressure range greater than 20 kPa, the sensitivity is 1.34 kPa -1 .

[0064] Furthermore, after the sensor of Example 5 is subjected to 8000 cycles of cyclic loading and unloading, as Figure 7 shown, the resistance amplitude hardly changes significantly, and the resistance change waveforms are observed at the beginning and end of the cycle respectively, and there is no obvious change in the waveforms, indicating the good repeatability, stability and durability of the pressure sensor prepared by the present invention.

[0065] In summary, the sensor preparation method of the present invention has a simple process and economical materials. By introducing a polyethyleneimine intermediate layer, the agglomeration phenomenon of the conductive material carbon nanotubes is improved, which helps the uniform distribution and firm combination of carbon nanotubes on the surface of the three-dimensional skeleton, thereby improving the structural stability of the sensor under cyclic loading, ensuring the cyclic stability in performance. The detection shows that this composite sponge pressure sensor improves the sensitivity and pressure measurement range of the flexible pressure sensor.

[0066] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and all technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A preparation method of a polyethyleneimine carbon nanotube composite sponge pressure sensor, characterized in that, It includes the following steps: S1. Ultrasonically clean the melamine sponge with absolute ethanol and deionized water and then dry it. S2. Prepare an aqueous solution of polyethyleneimine and an aqueous solution of carboxylated carbon nanotubes respectively. S3. Immerse the melamine sponge in the aqueous solution of polyethyleneimine, wash it with deionized water, and place it in an oven to dry. S4. Then immerse the melamine sponge in the carboxylated carbon nanotube solution for a period of time and then dry it. S5. Repeat the above two impregnation processes of S3 and S4 multiple times. S6. Dry it. After completion of the connection, a polyethyleneimine-carbon nanotube composite sponge pressure sensor is obtained.

2. The preparation method of a polyethyleneimine carbon nanotube composite sponge pressure sensor according to claim 1, wherein, Dissolve the polyethyleneimine particles in deionized water, put them into an ultrasonic cleaner and ultrasonically oscillate for several minutes to fully dissolve the polyethyleneimine, and obtain an aqueous solution of polyethyleneimine with a certain concentration.

3. The preparation method of a polyethyleneimine carbon nanotube composite sponge pressure sensor according to claim 2, characterized in that, The mass percentage concentration of the aqueous solution of polyethyleneimine is 1%.

4. The preparation method of a polyethyleneimine carbon nanotube composite sponge pressure sensor according to claim 1, characterized in that, Dilute the carboxylated carbon nanotube solution to obtain an aqueous solution of carboxylated carbon nanotubes with a certain concentration.

5. The preparation method of a polyethyleneimine-carbon nanotube composite sponge pressure sensor according to claim 4, wherein, The concentration of the aqueous solution of carboxylated carbon nanotubes is 1 - 5 mg / mL.

6. The preparation method of a polyethyleneimine carbon nanotube composite sponge pressure sensor according to claim 1, wherein, In the step S3, the environmental temperature during impregnation is 60 - 90 °C.

7. The preparation method of a polyethyleneimine carbon nanotube composite sponge pressure sensor according to claim 1, characterized in that, In the steps S3 and S4, the impregnation process is carried out in a vacuum environment.

8. The preparation method of a polyethyleneimine carbon nanotube composite sponge pressure sensor according to claim 1, characterized in that, In the step S5, the number of repetitions of the impregnation process is more than 5 times.

9. The preparation method of a polyethyleneimine carbon nanotube composite sponge pressure sensor according to any one of claims 1 to 8, characterized in that, The connection in the step S5 is as follows: Fix and encapsulate the conductive carbon cloth at both ends of the piezoresistive layer on a large area, fix the carbon cloth at the four vertices of the end face of the piezoresistive layer with cotton threads, embed wires inside the carbon cloth, and at the same time ensure that the contact area between the carbon cloth and the piezoresistive layer is slightly smaller than the end face of the pressure-sensitive layer. Finally, a polyethyleneimine-carbon nanotube composite sponge pressure sensor is prepared.

10. A polyethyleneimine carbon nanotube composite sponge pressure sensor, characterized in that, It is prepared by the method according to any one of claims 1 - 9.

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