A composite adhesive material and a preparation method of a package-free piezoresistive sensor thereof

Abstract

The present application relates to a kind of encapsulation piezoresistive sensor and the preparation method of composite adhesive material.The preparation method of the composite adhesive material is by the composite material one including nano-conductive material and polymer porous sponge, lower part is loaded in the composite material two including nano-conductive material and PDMS film, then put into vacuum drying oven and with 50-80 ℃ heat preservation 10-60 min, to prepare composite adhesive material.The interface contact between the lower adhesive film and the upper porous sponge of the prepared composite adhesive material is good, with good piezoresistive performance.The encapsulation piezoresistive sensor utilizes composite adhesive material to realize adhesive connection, adopts the structure without introducing external packaging, with higher stability, while having high sensitivity and wide measurement range.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a method for preparing a composite adhesive material, and also to an unencapsulated piezoresistive sensor using the composite adhesive material and its preparation method. Background Technology

[0002] The emerging intelligent applications of flexible wearable pressure sensors in transportation, healthcare, and education have attracted widespread attention. Pressure sensors are typically based on different sensing mechanisms, such as piezoresistive, capacitive, piezoelectric, and triboelectric. Among these, piezoresistive sensors demonstrate great application potential due to their simple structure, large measurement range, and ease of miniaturization and integration.

[0003] Currently, most flexible piezoresistive sensors characterize the pressure by applying external pressure to the sensor and observing the change in the relative resistance of the pressure-sensitive layer. Various high-performance materials, advanced manufacturing methods, and different microstructures are applied to piezoresistive sensors, leading to improvements in sensitivity, detection limit, and stability.

[0004] However, in the fabrication of piezoresistive sensors, external encapsulation structures are commonly introduced for fixation, protection, and to improve sensor stability. Currently, most materials used for external encapsulation are fiber tape, PU tape, or other similar materials, which greatly limits their further applications. Furthermore, simultaneously achieving a piezoresistive sensor that is unencapsulated, highly sensitive, and has a wide measurement range is a major challenge for practical applications. How to obtain a piezoresistive sensor with high sensitivity, a wide measurement range, and no encapsulation has become an important research area. Summary of the Invention

[0005] Based on this, it is necessary to address the technical problem that piezoresistive sensors in the prior art cannot simultaneously possess the characteristics of being unencapsulated, having high sensitivity, and having a wide measurement range. This invention discloses an unencapsulated piezoresistive sensor and a method for preparing a composite adhesive material.

[0006] This invention discloses a method for preparing a composite adhesive material, which includes the following steps:

[0007] The lower layer of composite material one, which contains nano-conductive materials and polymer porous sponge, is loaded into composite material two, which contains nano-conductive materials and PDMS film, and crosslinked. Then, it is placed in a vacuum drying oven and kept at 50-80℃ for 10-60 minutes.

[0008] In one embodiment, the polymer porous sponge in composite material one is selected from any one of PDMS porous sponge, polyurethane porous sponge, polyvinyl alcohol porous sponge, and melamine porous sponge. The nanoconductive materials in composite material one and composite material two are selected from any one of CNTs, silver nanowires, carbon black nanofibers, and graphene.

[0009] In one embodiment, the composite material is a CNT-PDMS porous sponge, and is prepared by loading CNTs onto the PDMS porous sponge.

[0010] In one embodiment, the specific process of loading CNTs onto a PDMS porous sponge is as follows:

[0011] Place the PDMS porous sponge in a 1-10 wt% CNT solution and sonicate it at room temperature for 0.5-1.5 h. Add 0.5 wt% chitosan solution and continue sonicating for another 0.5-1.5 h. Then place it in a vacuum drying oven and dry it at 60-80℃ for 20-120 min.

[0012] In one embodiment, the method for preparing PDMS porous sponge includes the following steps:

[0013] S1.1 Mix PDMS and curing agent at room temperature and stir for 2-5 minutes. Then add 350-500wt% citric acid, stir evenly, compact, and place in a vacuum drying oven and keep at 50-80℃ for 1-7 hours. The mass ratio of PDMS to curing agent is 10:(0.6-1).

[0014] S1.2. Soak the dried product obtained in step S1.1 in an ethanol solution and sonicate for 8-15 hours to obtain a PDMS porous sponge with a thickness of 0.5-20 mm. Then place it in a vacuum drying oven and dry it at 60-80℃ for 20-80 minutes. Cut the dried product into pieces.

[0015] In one embodiment, composite material two is a CNT-PDMS film, and its preparation method includes the following steps:

[0016] S3.1 Mix PDMS and curing agent at room temperature and stir for 2-5 minutes. Then add CNTs and polyethylene glycol and stir until homogeneous to obtain a PDMS mixed solution. The mass ratio of PDMS to curing agent is 10:(0.6-1), the CNT content is 0.5-5 wt%, and the polyethylene glycol content is 6-10 wt%.

[0017] S3.2 Take a portion of the PDMS mixed solution obtained in step S3.1 and prepare a CNT-PDMS film using a spin coater. The spin coater speed is 900-1500 rpm, the time is 50-90 s, and the thickness of the CNT-PDMS film is 0.5-500 μm.

[0018] In one embodiment, the unencapsulated piezoresistive sensor includes a flexible electrode and a composite adhesive material. The composite adhesive material includes a first composite material and a second composite material. The flexible electrode and the first composite material are cross-linked and fixed together via the second composite material.

[0019] The composite adhesive material is prepared using any of the above-mentioned methods for preparing composite adhesive materials.

[0020] This invention also discloses a method for fabricating an unencapsulated piezoresistive sensor, which includes the following steps:

[0021] S1. Preparation of polymer porous sponge. The polymer porous sponge is a PDMS porous sponge. The PDMS porous sponge is obtained using the method described above for preparing the composite adhesive material.

[0022] S2. Nano-conductive materials are loaded onto the polymer porous sponge obtained in step S1 to prepare composite material one. Composite material one is the same as the composite material one obtained using the aforementioned method for preparing composite adhesive materials.

[0023] S3. Preparation of composite material two. Composite material two is obtained using the method described above for preparing composite adhesive material.

[0024] S4. Composite material one and composite material two are prepared into a composite adhesive material. The composite adhesive material is prepared using the method described above.

[0025] S5. Prepare a flexible electrode on the surface of the substrate material.

[0026] S6. An unencapsulated piezoresistive sensor is fabricated using composite adhesive materials and flexible electrodes.

[0027] In one embodiment, in step S5, the substrate material is selected from any one of PET film, PI film, and fabric; the method for fabricating the flexible electrode is selected from any one of chemical vapor deposition, physical vapor deposition, magnetron sputtering, electrochemical deposition, sol-gel method, inkjet printing, screen printing, and spraying.

[0028] In one embodiment, the specific process of fabricating the unencapsulated piezoresistive sensor by combining a composite adhesive material and a flexible electrode in step S6 is as follows:

[0029] First, the surface of the adhesive film of the composite adhesive material is placed on the surface of the flexible electrode. Then, the electrode signal of the flexible electrode is led out through the conductive adhesive and copper wires to obtain an unencapsulated piezoresistive sensor. The conductive adhesive is selected from either silver paste or encapsulation electrode solder.

[0030] Compared with the prior art, the composite viscous material and its unencapsulated piezoresistive sensor preparation method disclosed in this invention have the following beneficial effects:

[0031] 1. The method for preparing this composite adhesive material involves loading the lower layer of a composite material I containing nano-conductive materials and a porous polymer sponge into a composite material II containing nano-conductive materials and a PDMS film, and then cross-linking and fixing it. This method enables the efficient preparation of a composite adhesive material. Furthermore, the prepared composite adhesive material exhibits good interfacial contact between the lower adhesive film and the upper porous sponge, resulting in excellent piezoresistive properties.

[0032] 2. The unencapsulated piezoresistive sensor fabricated using this method eliminates the need for external encapsulation in each component, overcoming the limitations of existing technologies that require external encapsulation (such as fiber tape, PU tape, etc.) and significantly expanding the application range of piezoresistive sensors. Furthermore, the flexible electrode of this unencapsulated piezoresistive sensor is cross-linked and fixed to the nano-conductive material—polymer porous sponge—through an adhesive nano-conductive material—PDMS film, exhibiting high stability. Attached Figure Description

[0033] Figure 1 This is a schematic flowchart of the preparation method of the composite adhesive material in Embodiment 1 of the present invention;

[0034] Figure 2 This is a schematic diagram of the unencapsulated piezoresistive sensor in Embodiment 3 of the present invention;

[0035] Figure 3 This is a flowchart of the fabrication method of the unencapsulated piezoresistive sensor in Embodiment 4 of the present invention;

[0036] Figure 4 This is the resistance-current response diagram based on an unpackaged piezoresistive sensor in Embodiment 4 of the present invention;

[0037] Figure 5 This is a sensitivity diagram of the unpackaged piezoresistive sensor in Embodiment 4 of the present invention.

[0038] Explanation of main component symbols

[0039] 1. Composite material one; 2. Composite material two; 3. Flexible electrode; 4. Composite adhesive material; 5. Piezoresistive sensor.

[0040] The above description of the main component symbols, together with the accompanying drawings and specific embodiments, provides a more detailed explanation of the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] It should be noted that when a component is said to be "installed on" another component, it can be directly on the other component or it may be in a component that is centered on it. When a component is said to be "set on" another component, it can be directly set on the other component or it may also be in a component that is centered on it. When a component is said to be "fixed to" another component, it can be directly fixed to the other component or it may also be in a component that is centered on it.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] Example 1

[0045] Please see Figure 1 This embodiment provides a method for preparing a composite adhesive material, which includes the following steps:

[0046] The lower layer of composite material one, which contains nano-conductive materials and polymer porous sponge, is loaded onto composite material two, which contains nano-conductive materials and PDMS (i.e., polydimethylsiloxane) film, and crosslinked. Then, it is placed in a vacuum drying oven and kept at 80°C for 15 minutes.

[0047] The polymer porous sponge in composite material one can be selected from any one of the following: PDMS porous sponge, polyurethane porous sponge, polyvinyl alcohol porous sponge, and melamine porous sponge. The nano-conductive materials in composite material one and composite material two can be selected from any one of the following: CNT (i.e., carboxylated multi-walled carbon nanotubes), silver nanowires, carbon black nanofibers, and graphene.

[0048] In this embodiment, composite material one is preferably CNT-PDMS porous sponge. Composite material two is preferably CNT-PDMS film. In actual operation, the lower layer of CNT-PDMS porous sponge is loaded onto CNT-PDMS film and crosslinked. After being placed in a vacuum drying oven and kept at 80°C for 15 minutes, the composite adhesive material can be obtained.

[0049] Example 2

[0050] This embodiment provides a method for preparing a composite adhesive material. Based on Example 1, this method refines the preparation methods for composite material one and composite material two, as well as some of their raw materials. Of course, in other embodiments, composite material one and composite material two can also be directly purchased as existing finished products.

[0051] In this embodiment, the composite material is a CNT-PDMS porous sponge, which can be prepared by loading CNTs onto a PDMS porous sponge. The PDMS porous sponge can be obtained through the following process:

[0052] PDMS and curing agent were stirred at room temperature for 3 minutes. 450 wt% citric acid was added, stirred until homogeneous, and then compacted. The compacted product was placed in a vacuum drying oven and kept at 80°C for 1 hour. The preferred mass ratio of PDMS to curing agent was 10:1. The product after vacuum drying was then immersed in an ethanol solution, ultrasonically treated for 10 hours, and then placed again in a vacuum drying oven and dried at 80°C for 40 minutes to obtain a PDMS porous sponge with a thickness of approximately 4.6 mm, which was then cut into blocks.

[0053] Further, the specific process for loading CNTs onto the prepared PDMS porous sponge can be as follows: 0.5 mL of acetic acid and 0.25 g of chitosan are placed in a beaker containing 49.5 mL of deionized water and stirred for 30 min to obtain a 0.5 wt% chitosan solution for later use. The prepared PDMS porous sponge is mixed with 10 mL of a 10 wt% CNT dispersion and ultrasonically treated for 1 h. Then, 2.5 mL of a 0.5 wt% chitosan solution is added, and ultrasonic treatment is continued for another 1 h to fill the sponge pores. Finally, the ultrasonically treated product is placed in a vacuum drying oven and dried at 80 °C for 40 min to obtain the target product: CNT-PDMS porous sponge, i.e., composite material one.

[0054] In this embodiment, the second composite material is a CNT-PDMS film, which can be prepared as follows: weigh 1g of PDMS and 0.1g of curing agent, mix and stir in a plastic petri dish at room temperature for 4min, then add 0.055g of CNT and 0.088g of polyethylene glycol, and stir evenly to obtain a PDMS mixed solution; using an existing spin coater, drop a portion of the PDMS mixed solution onto a smooth flat plate, and spin coat at 1000rpm for 60s to obtain a CNT-PDMS film with a thickness of 150μm.

[0055] After preparing the CNT-PDMS porous sponge and the CNT-PDMS film, the lower part of the CNT-porous sponge is loaded onto the CNT-PDMS film and crosslinked. The composite adhesive material is obtained by keeping it at 80°C for 15 minutes in a vacuum drying oven.

[0056] Example 3

[0057] This embodiment provides an unencapsulated piezoresistive sensor 5, which includes: a flexible electrode 3 and a composite adhesive material 4.

[0058] Please see Figure 2 The composite adhesive material 4 includes: composite material 1 and composite material 2. Figure 2 From top to bottom, the components are: composite material 1, composite material 2, and flexible electrode 3. The composite adhesive material 4 can be prepared using the method described in Example 2.

[0059] In this embodiment, the flexible electrode 3 and the composite material 1 are cross-linked and fixed through the composite material 2.

[0060] Example 4

[0061] Please see Figure 3 This embodiment provides a method for fabricating an unpackaged piezoresistive sensor, which can be used to fabricate the unpackaged piezoresistive sensor in Embodiment 3. The fabrication method includes the following steps:

[0062] S1. Preparation of PDMS porous sponge: PDMS and curing agent are mixed and stirred at room temperature for 3 min, 450 wt% citric acid is added and stirred evenly and compacted, and then kept at 80℃ for 1 h; wherein the mass ratio of PDMS to curing agent is 10:1; the above product is soaked in ethanol solution, sonicated for 10 h, and dried in a vacuum drying oven at 80℃ for 40 min to obtain PDMS porous sponge with a thickness of about 4.6 mm, and cut into blocks.

[0063] S2. Preparation of CNT-PDMS porous sponge: 0.5 ml of acetic acid and 0.25 g of chitosan were placed in a beaker containing 49.5 ml of deionized water and stirred for 30 min to obtain a 0.5 wt% chitosan solution for later use; the above PDMS porous sponge was mixed with 10 ml of 10 wt% CNT dispersion and sonicated for 1 h. 2.5 ml of 0.5 wt% chitosan solution was added and sonicated for another 1 h to fill the sponge pores. The solution was then placed in a vacuum drying oven and dried at 80 °C for 40 min.

[0064] S3, Preparation of CNT-PDMS film: Weigh 1g of PDMS and 0.1g of curing agent and mix them in a plastic petri dish at room temperature for 4min. Then add 0.055g of CNT and 0.088g of polyethylene glycol and stir evenly to obtain a PDMS mixed solution. Using the existing spin coater, drop part of the PDMS mixed solution onto a smooth flat plate and hold it at 1000rpm for 60s to obtain a thickness of 150μm.

[0065] S4. Preparation of composite adhesive material: The lower part of the CNT / PDMS porous sponge is loaded into the CNT / PDMS film and crosslinked, and then kept at 80℃ for 15 minutes in a vacuum drying oven.

[0066] S5. Fabrication of the flexible electrode: A flexible electrode is fabricated on the surface of a PI film using magnetron sputtering. In this embodiment, PI (polyimide) can be used as the substrate material for the flexible electrode. In other embodiments, any one of PET (polyethylene terephthalate) film or fabric can also be used. Alternatively, the flexible electrode can be fabricated using any one of the following methods: chemical vapor deposition, physical vapor deposition, magnetron sputtering, electrochemical deposition, sol-gel method, inkjet printing, screen printing, and spray coating.

[0067] S6. Fabrication of an unencapsulated piezoresistive sensor: The adhesive surface of the above-mentioned adhesive composite material is placed on the surface of a flexible electrode. The electrode can then be led out using silver paste and copper wires to obtain an unencapsulated piezoresistive sensor. In other embodiments, the silver paste can be replaced with encapsulation electrode solder.

[0068] It should be noted that there is no requirement for the order of steps S4 and S5, and they can be performed simultaneously.

[0069] To verify the performance of the unpackaged piezoresistive sensor prepared by the above method, this embodiment also conducted experiments using the unpackaged piezoresistive sensor.

[0070] Please see Figure 4 and Figure 5 , Figure 4 and Figure 5The figures show the resistance-current response and sensitivity of the unpackaged piezoresistive sensor described above. As can be seen from the figures, this unpackaged piezoresistive sensor exhibits a wide measurement range and high sensitivity.

[0071] In summary, compared with the prior art, the fabrication method of the unpackaged piezoresistive sensor provided in this embodiment has the following advantages:

[0072] 1. This preparation method rapidly produces a composite adhesive material by loading the lower layer of a composite material I containing nano-conductive materials and a porous polymer sponge onto a composite material II containing nano-conductive materials and a PDMS film. Furthermore, the prepared composite adhesive material exhibits good interfacial contact between the lower adhesive film and the upper porous sponge, resulting in excellent piezoresistive properties.

[0073] 2. The unencapsulated piezoresistive sensor fabricated using this method eliminates the need for external encapsulation for each component, overcoming the limitations of existing technologies that require external encapsulation (such as fiber tape, PU tape, etc.) and greatly expanding the application range of piezoresistive sensors. Furthermore, the flexible electrodes of this unencapsulated piezoresistive sensor are cross-linked and fixed to the nano-conductive material—polymer porous sponge—through an adhesive nano-conductive material—PDMS film, exhibiting high stability.

[0074] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0075] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for preparing a composite adhesive material, characterized in that, It includes the following steps: The lower part of composite material one, which contains nano-conductive materials and polymer porous sponge, is loaded into composite material two, which contains nano-conductive materials and PDMS film, and crosslinked. Then, it is placed in a vacuum drying oven and kept at 50-80℃ for 10-60 minutes. The polymer porous sponge in composite material one is selected from any one of PDMS porous sponge, polyurethane porous sponge, polyvinyl alcohol porous sponge, and melamine porous sponge; the nano-conductive materials in composite material one and composite material two are selected from any one of CNT, silver nanowires, nano-carbon black, and graphene.

2. The method for preparing the composite adhesive material according to claim 1, characterized in that, The composite material is a CNT-PDMS porous sponge, which is prepared by loading CNTs onto the PDMS porous sponge.

3. The method for preparing the composite adhesive material according to claim 2, characterized in that, The specific process of loading CNTs onto PDMS porous sponge is as follows: Place the PDMS porous sponge in a 1-10 wt% CNT solution and sonicate it at room temperature for 0.5-1.5 h. Add 0.5 wt% chitosan solution and continue sonicating for another 0.5-1.5 h. Then place it in a vacuum drying oven and dry it at 60-80℃ for 20-120 min.

4. The method for preparing the composite adhesive material according to claim 3, characterized in that, The preparation method of the PDMS porous sponge includes the following steps: S1.1 Mix PDMS and curing agent at room temperature and stir for 2-5 minutes. Then add 350-500wt% citric acid, stir evenly, compact, and place in a vacuum drying oven and keep at 50-80℃ for 1-7 hours. The mass ratio of PDMS to curing agent is 10:(0.6-1). S1.

2. Soak the dried product obtained in step S1.1 in an ethanol solution and sonicate for 8-15 hours to obtain a PDMS porous sponge with a thickness of 0.5-20 mm. Then place it in a vacuum drying oven and dry it at 60-80℃ for 20-80 minutes. Cut the dried product into pieces.

5. The method for preparing the composite adhesive material according to claim 1, characterized in that, The second composite material is a CNT-PDMS film, and its preparation method includes the following steps: S3.1 Mix PDMS and curing agent at room temperature and stir for 2-5 minutes. Then add CNTs and polyethylene glycol and stir until homogeneous to obtain a PDMS mixed solution. The mass ratio of PDMS to curing agent is 10:(0.6-1), the CNT content is 0.5-5 wt%, and the polyethylene glycol content is 6-10 wt%. S3.2 Take a portion of the PDMS mixed solution obtained in step S3.1 and prepare a CNT-PDMS film using a spin coater; wherein the spin coater speed is 900-1500 rpm, the time is 50-90 s, and the thickness of the CNT-PDMS film is 0.5-500 μm.

6. A piezoresistive sensor without encapsulation, characterized in that, The unencapsulated piezoresistive sensor includes flexible electrodes and a composite adhesive material; The composite adhesive material includes: composite material one and composite material two; the flexible electrode and composite material one are cross-linked and fixed through composite material two; The composite adhesive material is prepared by the method for preparing composite adhesive materials as described in any one of claims 1 to 5.

7. A method for fabricating an unencapsulated piezoresistive sensor, characterized in that, It includes the following steps: S1. Prepare a polymer porous sponge; wherein the polymer porous sponge is a PDMS porous sponge; the PDMS porous sponge is the PDMS porous sponge obtained in the preparation method of the composite adhesive material as described in claim 4; S2. Loading nano-conductive materials onto the polymer porous sponge obtained in step S1 to prepare composite material one; wherein, the composite material one is the composite material one obtained in the preparation method of the composite adhesive material as described in claim 2 or 3; S3. Prepare composite material two; wherein, the composite material two is the composite material two obtained in the preparation method of the composite adhesive material as described in claim 5; S4. Prepare a composite adhesive material from the first composite material and the second composite material; wherein the composite adhesive material is prepared by the method for preparing a composite adhesive material as described in claim 1; S5. Prepare flexible electrodes on the surface of the substrate material; S6. An unencapsulated piezoresistive sensor is fabricated using the composite adhesive material and the flexible electrode.

8. The method for fabricating an unencapsulated piezoresistive sensor according to claim 7, characterized in that, In step S5, The substrate material is selected from any one of PET film, PI film, and fabric; And / or, The flexible electrode is fabricated using any one of the following methods: chemical vapor deposition, physical vapor deposition, magnetron sputtering, electrochemical deposition, sol-gel method, inkjet printing, screen printing, and spraying.

9. The method for fabricating an unencapsulated piezoresistive sensor according to claim 7, characterized in that, In step S6, the specific process of fabricating the unencapsulated piezoresistive sensor using the composite adhesive material and the flexible electrode is as follows: First, the adhesive film surface of the composite adhesive material is placed on the surface of the flexible electrode. Then, the electrode signal of the flexible electrode is led out through a conductive adhesive and copper wires to obtain the unencapsulated piezoresistive sensor.

10. The method for fabricating an unencapsulated piezoresistive sensor according to claim 9, characterized in that, The conductive adhesive is selected from either silver paste or encapsulation electrode solder.

Images