Flexible pressure sensor layer with integrated mixed microstructure, preparation method and application

Abstract

According to the flexible pressure sensor layer with the integrated mixed microstructure, the preparation method and the application, the integrated flexible pressure sensor layer which is based on MXene / MWCNTs / PDMS and has a micro-dome and a porous structure is obtained through impregnation and integrated forming, and a multi-microstructure sensing layer is formed through the integrated structure. The problem of interface bonding between the micro-pattern layer and the porous layer is effectively solved, the sensor has high sensitivity, wide sensing range, short response time and excellent cycling stability through the synergistic effect of multiple microstructures, the stability of the sensor is improved, and the sensing range of the sensor is widened; besides, the flexible pressure sensor layer of the integrated mixed microstructure can be prepared into a sensor, the sensor can be applied to the field of Morse passwords, information transmission and encryption can be accurately achieved, and the sensor can also be used for monitoring the riding pedaling frequency in real time, optimizing the exercise training scheme and improving the exercise training efficiency. The method has a great application prospect in wearable electronic products.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flexible pressure sensors, and particularly relates to a flexible pressure sensor layer of an integrated mixed microstructure, a preparation method and application. BACKGROUND

[0002] With the development and popularization of the Internet and artificial intelligence, flexible pressure sensors which are light, thin, convenient and excellent in electronic performance have a more and more broad market as core devices of wearable electronic devices. However, most of the current researches still need to make a choice between sensitivity and sensing range, and cannot realize high sensitivity and wide sensing range at the same time.

[0003] Although multiple microstructures are expected to realize high sensitivity and wide sensing range at the same time, due to the unstable physical fitting between the interfaces of the multiple microstructure layers, a large energy loss is easily generated, resulting in signal fluctuation. Therefore, based on this, it is expected to provide an integrated mixed microstructure flexible pressure sensor to improve the signal stability of the sensor. SUMMARY

[0004] The first object of the application is to provide a flexible pressure sensor layer of an integrated mixed microstructure for the signal fluctuation problem caused by the layered structure design of the sensing layer microstructure in the existing flexible pressure sensor.

[0005] To this end, the above object of the application is achieved by the following technical solutions.

[0006] The flexible pressure sensor layer of the integrated mixed microstructure has an upper micro-dome, a lower micro-dome and a porous structure between the two;

[0007] The upper micro-dome and the lower micro-dome are obtained by curing PDMS loaded with MXene and MWCNTs as conductive materials by a template method;

[0008] The porous structure is obtained by filling PDMS loaded with MXene and MWCNTs as conductive materials into a porous material;

[0009] The above PDMS contains a curing agent to integrally cure the upper micro-dome, the porous structure and the lower micro-dome to obtain an integrated mixed microstructure;

[0010] The MXene and the MWCNTs are uniformly dispersed into the surface and the voids of the integrated mixed microstructure.

[0011] The second object of the application is to provide a preparation method of the flexible pressure sensor layer of the integrated mixed microstructure as described above.

[0012] To this end, the above object of the application is achieved by the following technical solutions.

[0013] The preparation method of the flexible pressure sensor layer of the integrated mixed microstructure comprises the following steps:

[0014] S1, MXene and MWCNTs are added to PDMS according to a certain mass ratio, and a curing agent is added and stirred uniformly to obtain an MCP solution;

[0015] The curing agent is preferably hydrogen-containing silicone oil, and the mass fraction of the curing agent in the PDMS is 5% to 20%, preferably 10%.

[0016] S2, the above MCP solution is filled into a clean sponge, and the MCP solution is extruded by a certain pressure to obtain a porous sponge layer loaded with MXene, MWCNTs and PDMS;

[0017] S3, the PDMS is poured into a male mold with a micro-dome array, and after curing, the PDMS female mold is turned to obtain the PDMS female mold, the above MCP solution is poured onto the PDMS female mold to cover the micro-dome array on the PDMS female mold, and the porous sponge layer obtained in step S2 is covered thereon, and then cured and demolded;

[0018] The curing agent is preferably hydrogen-containing silicone oil, and the mass fraction of the curing agent in the PDMS is 5% to 20%, preferably 10%.

[0019] The above steps are continuously repeated to cure the other side micro-dome on the porous sponge layer to prepare the flexible pressure sensor layer of the integrated mixed microstructure;

[0020] S4, the flexible pressure sensor layer of the integrated mixed microstructure prepared in step S3 is immersed in a solution containing chitosan for 4 to 10 hours, and then immersed in an aqueous dispersion of MXene and OH-MWCNTs for 4 to 10 hours.

[0021] While the above technical solutions are adopted, the following technical solutions can also be adopted or combined:

[0022] As a preferred technical solution of the present application: in step S1, the mass ratio between MXene and MWCNTs is 1:(3 to 5);

[0023] The mass percentage of the conductive materials MXene and MWCNTs in the PDMS is 3% to 5%.

[0024] As a preferred technical solution of the present application: the PDMS is vinyl-terminated, and the viscosity is 500 to 5000 centipoise, preferably 3500 centipoise.

[0025] As a preferred technical solution of the present application: the curing agent is hydrogen-containing silicone oil; and the mass fraction of the curing agent is 10%.

[0026] As a preferred technical solution of the present application: in step S2, the extrusion pressure is 500N-1000N.

[0027] As a preferred technical solution of the present application: in step S4, the molecular weight of chitosan is 1000g / mol-3000g / mol, and the mass fraction of chitosan in the chitosan solution is 0.1-10%.

[0028] As a preferred technical solution of the present application: in step S4, the molecular weight of chitosan is preferably 1526.5g / mol; and the mass fraction of chitosan in the chitosan solution is preferably 1%.

[0029] As a preferred technical solution of the present application: in step S4, the mass ratio between MXene and OH-MWCNTs is 1:(4-6), and the mass percentage of the conductive material MXene and MWCNTs in water is 1-5%, preferably 2%.

[0030] The third object of the present application is to provide the application of the flexible pressure sensor layer of the integrated mixed microstructure in Morse code information transmission and encryption.

[0031] The present application also has the purpose of providing the application of the flexible pressure sensor layer of the integrated mixed microstructure in cycling cadence monitoring.

[0032] The present application provides an integrated mixed microstructure flexible pressure sensor layer, a preparation method and an application, the integrated mixed microstructure flexible pressure sensor layer has microdome and porous structure, which can overcome the signal fluctuation problem caused by the layered structure design of the sensing layer in the existing flexible pressure sensor; in addition, the preparation method provided by the present application obtains the integrated flexible pressure sensor layer based on MXene / MWCNTs / PDMS with microdome and porous structure through immersion and integral molding, the multiple microstructure sensing layer formed by overall structure effectively solves the interface bonding problem between the micro-pattern layer and the porous layer, and the multiple microstructure synergistic effect makes the sensor have high sensitivity (S=-7.94kPa -1 ), wide sensing range (0-200kPa), fast response time (56ms) and excellent cycle stability (more than 6000 cycles under 6kPa pressure), improves the stability of the sensor and widens the sensing range of the sensor; in addition, the integrated mixed microstructure flexible pressure sensor layer provided by the present application can be prepared into a sensor, and the sensor can be applied to the field of Morse code to accurately realize information transmission and encryption, and can also be used for real-time monitoring of cycling cadence, optimizing the training scheme, and has great application prospect in wearable electronic products. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Figure 8. XRD comparison of Ti3C2T x Figure 9. XRD comparison of MXene and Ti3AlC2.

[0034] Figure 2 Figure 10. SEM images of (a) original PU sponge, (b-d) MPS in Example 2.

[0035] Figure 3 Figure 11. (a) Physical assembled side view of P-MMPS in Example 3, (b) integrated side view of MMPS in Example 4.

[0036] Figure 4 Figure 12. (a) Physical view of MMPS in Example 4, (b-c) surface microdome structure and enlarged view.

[0037] Figure 5 Figure 13. (a) Stress-strain test of MMPS, MPS and original PU sponge in Example 2 and 4, (b) MPS sensor resistance change with pressure, (c) MMPS sensor resistance change with pressure, (d) sensitivity comparison of MPS and MMPS.

[0038] Figure 6 Figure 14. Stability test of MPS, P-MMPS and MMPS in Example 2, 3 and 4 under the same pressure.

[0039] Figure 7 Figure 15. Sensing performance of MMPS sensor in Example 4: (a) IV curve under different pressure, (b) response recovery time, (c) resistance change rate under different pressure, (d) stability test under different compression speed.

[0040] Figure 8 Figure 16. 6000 cycles test of MMPS sensor in Example 4 under 6kPa pressure.

[0041] Figure 9 Figure 17. Application of MMPS sensor in Morse code in Example 5.

[0042] Figure 10 Figure 18. (a-d) Schematic diagram of MMPS sensor for cycling pedal frequency monitoring in Example 6, (e-f) signal capture. DETAILED DESCRIPTION

[0043] The present application is further described in detail by reference to the attached figures and specific examples.

[0044] Example 1

[0045] The MXene nanosheets are preferably obtained by a mild etching method. First, 1 g of LiF powder is dissolved in 20 ml of 9 mol / L hydrochloric acid, and is magnetically stirred for 30 min. 1 g of Ti3AlC2(200 mesh) powder is added within five minutes, and is placed in an oil bath for stirring for 48 h at a temperature of 40°C and a rotation speed of 500 r / min. The solution after the reaction is subjected to centrifugal treatment at a rotation speed of 3500 rpm for 5 min, and the upper solution is discarded. The process is repeated multiple times until the pH of the solution approaches neutrality, and the solution is shaken and used. The solution is subjected to low-temperature ultrasonic treatment for 1 h, and the solution after the ultrasonic treatment is again subjected to centrifugal treatment at a rotation speed of 3500 rpm for 5 min. The upper solution after the centrifugal treatment is retained, and is the MXene nanosheet solution. The water is removed by freeze-drying.

[0046] Figure 1 The (104) crystal face of Ti3AlC2disappears after etching, and the (002) crystal face is shifted to the left, indicating that Al is successfully etched to generate Ti3C2T x MXene.

[0047] Example 2

[0048] (1) The conductive material with a mass ratio of Ti3C2T x :OH-MWCNTs=1:4 is added to PDMS, wherein the total mass of the conductive material is 4% of the mass of the PDMS, and the conductive material is uniformly dispersed in the vinyl-terminated PDMS (3500 centipoise) by magnetic stirring for 15 hours. Subsequently, 10% of the mass of the PDMS of hydrogen-containing silicone oil is added as a curing agent, and stirring is continued for 15 minutes to ensure uniform dispersion, and the solution is named as MCP (MXene, MWCNTs, PDMS) solution.

[0049] (2) The MCP solution is filled into a cleaned PU sponge, and the excess MCP solution is squeezed out by using a universal testing machine at a pressure of 700 N, so as to obtain a PU sponge uniformly covered with a layer of MCP on the skeleton.

[0050] (3) The treated sponge is soaked in a solution containing 1% by mass of CS (chitosan, molecular weight 1526.5 g / mol) for 5 h, so that the surface is positively charged. Then, the conductive material with a mass ratio of Ti3C2T x :OH-MWCNTs=1:5 is prepared into an aqueous dispersion solution with a conductive material concentration of 2 mg / ml, and the obtained sponge with a positively charged surface is soaked in the aqueous dispersion solution for 5 h at room temperature, and is vacuum dried to obtain a sensing layer.

[0051] (4) The sensing layer is linked with copper foil and wires from top to bottom, and is packaged with a polyimide film to obtain a pressure sensor, that is, a MPS (Modified porous sponge) sensor.

[0052] Example 3

[0053] (1) A positive mold plate with a micro-dome structure was prepared using a 3D printing technology. The overall size was 20 mm*20 mm, and the surface micro-dome was a 6*6 array with a diameter of 2.5 mm. Then, the positive mold plate was used as a template, a frame with a size of 20 mm*20 mm*20 mm was placed on the mold, and a mixed solution with a mass ratio of PDMS: hydrogen-containing silicone oil = 10:1 was poured into the frame. After heating and curing, a negative mold plate with a micro-dome structure was obtained by demolding.

[0054] Steps (2) and (3) are the same as steps (2) and (3) in Example 2.

[0055] (4) The negative mold plate was placed in a 20 mm*20 mm*40 mm rectangular hollow frame, positioned 1 mm away from the upper boundary. MCP solution was added to the mold, and the mold was kept flat with the edge of the hollow frame. After curing at room temperature, two separate micro-domes were obtained.

[0056] (5) The two micro-domes were sequentially soaked in a solution containing 1% CS (chitosan, molecular weight 1526.5 g / mol) for 5 hours to make the surface positively charged. Then, according to the mass ratio of Ti3C2T x :OH-MWCNTs = 1:5, a water-based dispersion solution with a conductive substance concentration of 2 mg / ml was prepared, and the above-mentioned substance was soaked in it for 5 hours. After vacuum drying at room temperature, a micro-dome sensing layer was obtained.

[0057] (6) The micro-dome sensing layer was placed on the upper and lower surfaces of the MPS sensing layer, with the micro-dome facing outward, and physical attachment was performed.

[0058] Step (7) is the same as step (4) in Example 2, and a P-MMPS (Physical attach-MMPS) sensor is obtained.

[0059] Example 4

[0060] Step (1) is the same as step (1) in Example 3.

[0061] (2) The negative mold plate was placed in a 20 mm*20 mm*40 mm rectangular hollow frame, positioned 1 mm away from the upper boundary. MCP solution was added to the mold, and the mold was kept flat with the edge of the hollow frame. Then, the MPS obtained in the previous step was placed on the surface, and the mold was gently pressed to partially immerse the MPS in the MCP solution. After curing at room temperature, a single micro-dome structure sponge was demolded, and then another layer of micro-dome structure was constructed on the opposite side to form a one-piece sponge with double-layer micro-dome.

[0062] Steps (3) and (4) are the same as steps (3) and (4) in Example 2.

[0063] The MMPS (Micro-dome Modifiedporous sponge) sensor was obtained.

[0064] Discussion of Results:

[0065] 1) Morphological analysis:

[0066] like Figure 2 As shown in (a)-(c), the roughness of the sponge skeleton after MCP treatment is significantly increased compared to the untreated original sponge skeleton, proving that MCP successfully adheres to the surface of the sponge skeleton. Figure 2 (d) shows the uniform distribution of MXene and MWCNTs on the skeleton.

[0067] Figure 3 (a) and (b) are side-view comparison images of P-MMPS and MMPS. Compared with the integrated structure of MMPS, the physical bonding structure of P-MMPS has a significant problem of weak interface bonding, which will affect the stability of the sensing signal. Figure 4 This is a physical image of the MMPS sensing layer, showing the upper microdome, porous sponge, and lower microdome from top to bottom. The individual microdome structure exhibits a layered structure, which facilitates a gradient increase in contact area with pressure.

[0068] 2) Performance Evaluation:

[0069] Pressure is applied to the pressure sensor connected to a universal compressor, and the resistance change is monitored in real time by a digital multimeter.

[0070] Figure 5 In the middle (a), the stress-strain tests of the original PU, MPS and MMPS are shown. Under the same displacement conditions, the mechanical strength of MMPS is significantly improved. Figure 5 Figures (b)-(d) show the sensitivity and sensing range tests of the MPS and MMPS sensors. The MPS sensor exhibits: S1 = -8.4 kPa. -1 (0-10kPa), S2=-0.8kPa -1 (10-30kPa), S3=-0.1kPa -1 (30-75 kPa), the MMPS sensor exhibits S1 = -7.94 kPa. -1 (0-10kPa), S2=-0.12kPa -1 (10-75kPa), S3=-0.02kPa -1 (75-150kPa) indicates that while maintaining similar sensitivity, the resistance change of MMPS is significantly improved, thus further expanding the sensing range (from 75kPa to 200kPa). Figure 6For the cycle stability test of P-MMPS, MPS and MMPS sensors under 10 kPa pressure, the integrated structure of MMPS highlights more stable resistance changes compared to P-MMPS. Compared with MPS, the microstructure of MMPS enables it to perceive small pressure changes, and the resistance changes are gentle. Figure 7 Fig. 5(a) is the IV curve of the MMPS sensor under different pressures, indicating good ohmic characteristics of the sensor. Figure 7 Fig. 5(b) is the response recovery time of the MMPS sensor, which has excellent response (56 ms) and recovery (85 ms) times. Figure 7 Fig. 5(c) is the stability test of the MMPS sensor under different pressures, indicating that the sensor can accurately respond to continuous pressure changes. Figure 7 Fig. 5(d) is the stability test of the MMPS sensor under different compression speeds. Figure 8 Fig. 5(e) is the long-term cycle stability test of the MMPS sensor, and the curves remain highly reproducible after 6000 cycles, demonstrating the excellent dynamic pressure monitoring capability and cycle stability of the sensor.

[0071] Example 5

[0072] The MXene / MWCNTs / PDMS-based integrated flexible pressure sensor (MMPS sensor) with micro-dome and porous structure in Example 4 was applied to the field of Morse code, and the results are shown in Fig. 6. Figure 9 As shown in Fig. 6, point pressure and continuous pressure were applied to the sensor to realize point-line patterns to correspond to the point-line in Morse code. Figure 9 Fig. 6(b) is HELLO; and Fig. 6(c) is ZSTU.

[0073] Example 6

[0074] The MXene / MWCNTs / PDMS-based integrated flexible pressure sensor (MMPS sensor) with micro-dome and porous structure in Example 4 was applied to the field of Morse code, and the results are shown in Fig. 6. Figure 10 Figs. 6(a)-(b) are schematic diagrams of the sensor monitoring mode. Figure 10 Fig. 6(c) is the actual monitoring mode. Figure 10 Figs. 6(d)-(e) are simulated cycling sensor recording data, which can effectively monitor the cycling pedal frequency pressure and interval, and optimize the cycling training program.

[0075] The above specific embodiments are used to explain and illustrate the present application, rather than limit the present application. Any modifications, equivalent replacements, improvements, etc. made to the present application within the spirit and scope of the present application and the claims and protection scope fall within the protection scope of the present application.

Claims

1. A flexible pressure sensor layer of an integrated hybrid microstructure, characterized by: The flexible pressure sensor layer has an upper micro-dome, a lower micro-dome, and a porous structure therebetween; The upper micro-dome and the lower micro-dome are obtained by template method using PDMS loaded with MXene and MWCNTs as conductive materials; The porous structure is obtained by filling the PDMS loaded with MXene and MWCNTs as conductive materials into a porous material; The above-mentioned PDMS contains a curing agent to integrally cure the upper micro-dome, the porous structure, and the lower micro-dome to obtain an integrated mixed microstructure; MXene and MWCNTs are uniformly dispersed on the surface and in the voids of the integrated mixed microstructure.

2. The method of claim 1, wherein: The method comprises the following steps: S1, adding MXene and MWCNTs to PDMS according to a certain mass ratio, adding a curing agent, and stirring uniformly to obtain an MCP solution; S2, filling the MCP solution into a clean sponge, and extruding the MCP solution under a certain pressure to obtain a porous sponge layer loaded with MXene, MWCNTs, and PDMS; S3, pouring the PDMS into a positive mold with a micro-dome array, inverting the mold after curing to obtain a PDMS negative mold, pouring the MCP solution onto the PDMS negative mold to cover the micro-dome array on the PDMS negative mold, and then covering the porous sponge layer obtained in step S2, and then curing and demolding; Continue to repeat the above steps to cure the other side micro-dome on the porous sponge layer to obtain a flexible pressure sensor layer of an integrated mixed microstructure; S4, immersing the flexible pressure sensor layer of the integrated mixed microstructure prepared in step S3 in a solution containing chitosan for 4-10 hours, and then immersing in an aqueous dispersion of MXene and OH-MWCNTs for 4-10 hours.

3. The method of claim 2, wherein: In step S1, the mass ratio of MXene to MWCNTs is 1:(3-5); The mass percentage of the conductive materials MXene and MWCNTs in the PDMS is 3%-5%.

4. The method of claim 2 or 3, wherein: The PDMS is vinyl-terminated and has a viscosity of 500-5000 centipoise.

5. The method of claim 2, wherein: The curing agent is hydrogen-containing silicone oil, and the mass fraction of the curing agent is 5-20%.

6. The method of claim 2, wherein: In step S2, the extrusion pressure is 500-1000 N.

7. The method of claim 2, wherein: In step S4, the molecular weight of chitosan is 1000-3000 g / mol, and the mass fraction of chitosan in the chitosan solution is 0.1-10%.

8. The method of claim 2, wherein: In step S4, the mass ratio of MXene to OH-MWCNTs is 1:(4-6), and the mass percentage of the conductive materials MXene and MWCNTs in water is 1-5%.

9. The application of the flexible pressure sensor layer of the integrated mixed microstructure in Morse code information transmission and encryption according to claim 1.

10. The application of the flexible pressure sensor layer of the integrated mixed microstructure in cycling pedal frequency monitoring according to claim 1.

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