An ultra-flexible piezoresistive solid-liquid hybrid wearable sensor and its fabrication method

Abstract

This invention relates to an ultra-flexible piezoresistive solid-liquid hybrid wearable sensor and its fabrication method. The sensor has a five-layer structure, comprising, from bottom to top, copper foil, electrodes, a piezoresistive sensing layer, electrodes, and copper foil again. Specifically, the piezoresistive sensing layer is a polymer of C3H8O3, carbon nanotubes, and PDMS. The coexistence of the solid and liquid phases of carbon nanotubes and glycerol in this invention enhances the sensor's flexibility. The fabricated piezoresistive sensor can be used for clicking mouse buttons, detecting the movement signals of the little finger joint, and pressure array recognition.

Description

Technical Field

[0001] This invention relates to the field of sensor manufacturing technology, specifically to the preparation and application of an ultra-flexible piezoresistive solid-liquid hybrid sensor. Background Technology

[0002] With the rapid development of fields such as electronic skin, intelligent robotic arms, human-computer interaction, and wearable devices, flexible piezoresistive sensors, with their excellent sensitivity and conductivity, perfectly meet the needs of these fields. Piezoresistive sensors consist of a flexible substrate material, electrodes, and sensing material. They can generate resistance signals by applying pressure or convert them into voltage signals using an external power source, offering high-quality and high-sensitivity signal acquisition.

[0003] Among a variety of impressive dielectric materials, polydimethylsiloxane (PDMS) is renowned for its high electronegativity, flexibility, hydrophobicity, and abrasion resistance, making it the most promising flexible substrate material for flexible piezoresistive sensors. While the performance of flexible piezoresistive sensors can be improved by adding conductive fillers such as carbon nanotubes, Mxene, or silver nanowires, their poor rigidity and deformability during operation can lead to interfacial separation and reduced performance and lifespan. Summary of the Invention

[0004] The purpose of this invention is to address the limitations of current technologies by providing an ultra-flexible piezoresistive solid-liquid hybrid wearable sensor and its fabrication method. This sensor uses glycerol (C3H8O3) as a liquid filler. The high boiling point of C3H8O3 prevents it from easily volatilizing during the fabrication process. The coexistence of carbon nanotubes and the solid-liquid phases of C3H8O3 enhances the sensor's flexibility. The fabricated piezoresistive sensor can be used for applications such as clicking mouse buttons, detecting the movement signals of the little finger joint, and pressure array recognition.

[0005] This invention can be achieved through the following technical solutions:

[0006] An ultra-flexible piezoresistive solid-liquid hybrid wearable sensor has a five-layer structure, including, from bottom to top, copper foil, electrodes, piezoresistive sensing layer, electrodes, and copper foil.

[0007] The piezoresistive sensing layer is specifically a polymer of C3H8O3, carbon nanotubes and PDMS, with a mass ratio of 9-12:1:100-130.

[0008] The thickness of the copper foil is 60–75 μm; the thickness of the electrode layer is 1–1.5 mm; and the thickness of the piezoresistive sensing layer is 1.5–2 mm.

[0009] The method for fabricating the ultra-flexible piezoresistive solid-liquid hybrid wearable sensor includes the following steps:

[0010] (1) Electrode preparation steps:

[0011] S1: Mix the A and B parts of silicone rubber in a 1:1 mass ratio, pour in the graphene aqueous solution, place in a vacuum chamber, remove air bubbles, and obtain the mixed material;

[0012] In this process, 5-15g of silicone rubber is added to every 10ml of graphene aqueous solution; the mass concentration of the graphene aqueous solution is 40%.

[0013] S2: Spin-coating the mixed material onto the substrate;

[0014] S3: Place in a drying oven and cure at 60-80℃ for 0.5-2.0h to obtain a silicone doped layer;

[0015] S4: A pure silica gel solution is coated onto a silica gel doped layer, and after curing, the electrode is obtained.

[0016] (2) Fabrication steps of the piezoresistive sensing layer:

[0017] S1: Carbon nanotubes are added to C3H8O3 and dispersed by ultrasonication to obtain a conductive C3H8O3 solution;

[0018] In this process, 1.2 to 1.8 g of carbon nanotubes are added to every 20 ml of C3H8O3;

[0019] S2: Weigh out components A and B of PDMS and mix them in a mass ratio of 10:1 to obtain a PDMS solution;

[0020] S3: Add conductive C3H8O3 solution to PDMS, stir, and place in a vacuum device to remove air bubbles; wherein, the conductive C3H8O3 solution accounts for 8-12% of the mass of the PDMS solution;

[0021] S4: Spin-coat the sample into the mold and place it in a drying device at 60-80℃ for 2-4 hours;

[0022] S5: Take out the prepared sample, soak it in C3H8O3 to remove unreacted monomers and surface impurities, and let it air dry at room temperature for 12 hours to obtain the piezoresistive sensing layer.

[0023] (3) The upper and lower electrodes and the obtained piezoresistive sensing layer form a multi-layer flexible piezoresistive pressure sensor; copper foil is bonded to the upper and lower contact electrodes respectively to realize the encapsulation of the flexible piezoresistive pressure sensor.

[0024] The sensor measures 18–20 mm in length and 8–10 mm in width.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The production process of this product is green and environmentally friendly, with no waste generated and no pollution to the environment; the process is simple and can be used for industrial production without the need for additional new equipment. The process is rapid and the production speed is fast.

[0027] (2) Mechanical property test results show that the tensile strength and tensile Young's modulus of the material are 0.06 MPa and 0.0723, respectively; the compressive strength and compressive Young's modulus are 0.0876 MPa and 0.142, respectively. Compared with the traditional piezoresistive sensor of PDMS mixed carbon nanotubes, its flexibility is improved by about 50 times. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the sensor fabrication and assembly in Example 1;

[0029] Figure 2 This is a comparison chart of force-displacement curves in the sensor's tensile mode in Example 2;

[0030] Figure 3 This is a comparison diagram of stress-strain curves in the sensor tensile mode of Example 3;

[0031] Figure 4 This is a comparison chart of force-displacement curves in the sensor compression mode of Example 4;

[0032] Figure 5 This is a comparison diagram of stress-strain curves in the sensor compression mode in Example 5;

[0033] Figure 6 This is a schematic diagram of the sensor's hand movement recognition in Example 6. Detailed Implementation

[0034] 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. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0035] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0036] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0037] Unless otherwise specified, all reagents used in the examples are commercially available.

[0038] Example 1

[0039] S1: Take 5g of Ecoflex silicone rubber A and B parts respectively and mix them thoroughly in a mass ratio of 1:1. The mass of the mixture is 10g. Take 10ml of 40% graphene aqueous solution and add it to Ecoflex silicone rubber. Place it in a vacuum box for about 20 minutes to remove air bubbles.

[0040] S2: A rectangular structure of 20mm × 10mm × 2mm is obtained by casting a rectangular substrate obtained through 3D printing. A mixture of graphene aqueous solution and Ecoflex silicone rubber is spin-coated onto the substrate.

[0041] S3: Place the mixture of graphene aqueous solution and Ecoflex silicone rubber in a drying oven and cure at 70°C for 1 hour to obtain a silicone doped layer with a thickness of 1.0 mm.

[0042] S4: The prepared mixed solution of components A and B of pure silicone rubber is injected into the mold at a ratio of 1:1, and the smooth surface of the silicone doped layer is placed on the liquid. It is cured at 70°C for 0.5 hours to obtain a well-bonded silicone doped layer and a flexible substrate, i.e., an electrode; the thickness of the flexible substrate is 0.5 mm.

[0043] S5: Dissolve 1.5g of carbon nanotubes in 20ml of C3H8O3 and ultrasonically disperse for 30min to obtain a uniformly dispersed conductive C3H8O3 solution.

[0044] S6: Weigh 9.1g and 0.9g of PDMS components A and B (Dow Corning DC184) and mix them in a mass ratio of 10:1 to obtain a PDMS mixture.

[0045] S7: Add 1g of conductive C3H8O3 solution (containing 0.087g of carbon nanotubes) obtained in step S5 to 10g of PDMS mixture obtained in step S6, stir magnetically for 30min, and then place it in a vacuum device to remove air bubbles.

[0046] S8: Spin-coat the sample into the mold of the 3D printer and place it in a drying device at 70°C for 3 hours.

[0047] S9: Take out the prepared sample, immerse it in C3H8O3 several times to remove unreacted monomers and surface impurities, and dry it naturally at room temperature for 12 hours to obtain a piezoresistive sensing layer with a thickness of 2.0 mm.

[0048] like Figure 1 As shown, the electrodes (i.e., the upper and lower electrodes) formed by graphene bonded to the Ecoflex silicone rubber substrate obtained in the two steps S4 sandwich a piezoresistive sensing layer doped with conductive C3H8O3 (wherein, the silicone doped layer is bonded to the piezoresistive sensing layer); copper foil (70μm thick) is then bonded to the outside of the upper and lower contact electrodes respectively, forming a multi-layer flexible piezoresistive pressure sensor to realize the encapsulation of the flexible piezoresistive pressure sensor, and to connect wires to measure the sensor performance.

[0049] Example 2

[0050] S1: Weigh 1.5g of carbon nanotubes and dissolve them in 20ml of C3H8O3. Disperse the solution by ultrasonication for 30min to obtain a uniformly dispersed conductive C3H8O3 solution.

[0051] S2: Weigh out 9.1g and 0.9g of two PDMS components A and B (Dow Corning DC184) and mix them in a mass ratio of 10:1 to obtain a PDMS mixture.

[0052] S3: 0.08-0.09 g of carbon nanotubes were directly added to 10 g of PDMS mixture obtained in step S2. After magnetic stirring for 30 min, the mixture was placed in a vacuum device to remove air bubbles. This was used as a control group.

[0053] S4: Add 1g of conductive C3H8O3 solution (containing 0.087g of carbon nanotubes) obtained in step S1 to 10g of PDMS mixture obtained in step S2. After stirring magnetically for 30min, place it in a vacuum device to remove air bubbles. This is used as the experimental group.

[0054] S5: The control group and experimental group samples were spin-coated into 18mm×10mm×5mm molds printed by 3D printers and placed in a drying device at 70℃ for 3 hours. The sample size was 18mm×10mm×5mm.

[0055] S6: The experimental group with added C3H8O3 and the control group without added C3H8O3 were assembled in a universal testing machine (China-UTM-4103) and subjected to tensile testing.

[0056] like Figure 2 As shown, under tensile conditions, when a force of 2N is applied, the experimental group with added conductive C3H8O3 can produce a displacement of 15mm; while the control group without added C3H8O3 can only produce a displacement of 2.1mm under the action of a 2N force.

[0057] Example 3

[0058] S1: Weigh 1.5g of carbon nanotubes and dissolve them in 20ml of C3H8O3. Disperse the solution by ultrasonication for 30min to obtain a uniformly dispersed conductive C3H8O3 solution.

[0059] S2: Weigh out 9.1g and 0.9g of components A and B (Dow Corning DC184) of PDMS and mix them in a mass ratio of 10:1 to obtain a PDMS mixture.

[0060] S3: 0.08-0.09 g of carbon nanotubes were directly added to 10 g of PDMS mixture obtained in step S2. After magnetic stirring for 30 min, the mixture was placed in a vacuum device to remove air bubbles, and this was used as a control group.

[0061] S4: Add 1g of conductive C3H8O3 solution (containing 0.087g of carbon nanotubes) obtained in step S1 to 10g of PDMS mixture obtained in step S2. After stirring magnetically for 30min, place it in a vacuum device to remove air bubbles. This is used as the experimental group.

[0062] S5: The control group and experimental group samples were spin-coated into 18mm×10mm×5mm molds printed by 3D printers and placed in a drying device at 70℃ for 3 hours. The sample size was 18mm×10mm×5mm.

[0063] S6: The experimental group with added C3H8O3 and the control group without added C3H8O3 were both assembled in a universal testing machine (China-UTM-4103) and subjected to tensile mode.

[0064] like Figure 3 As shown, under tensile conditions, the experimental group with added conductive C3H8O3 only required a stress of 0.14 MPa to achieve 100% mechanical strain.

[0065] Example 4

[0066] S1: Weigh 1.5g of carbon nanotubes and dissolve them in 20ml of C3H8O3. Disperse the solution by ultrasonication for 30min to obtain a uniformly dispersed conductive C3H8O3 solution.

[0067] S2: Weigh out 9.1g and 0.9g of components A and B (Dow Corning DC184) of PDMS and mix them in a mass ratio of 10:1 to obtain a PDMS mixture.

[0068] S3: 0.08-0.09 g of carbon nanotubes were directly added to 10 g of PDMS mixture obtained in step S2. After magnetic stirring for 30 min, the mixture was placed in a vacuum device to remove air bubbles, and this was used as a control group.

[0069] S4: Add 1g of conductive C3H8O3 solution (containing 0.087g of carbon nanotubes) obtained in step S1 to 10g of PDMS mixture obtained in step S2. After stirring magnetically for 30min, place it in a vacuum device to remove air bubbles. This is used as the experimental group.

[0070] S5: The control group and experimental group samples were spin-coated into 18mm×10mm×5mm molds printed by 3D printers and placed in a drying device at 70℃ for 3 hours. The sample size was 18mm×10mm×5mm.

[0071] S6: The experimental group with added C3H8O3 and the control group without added C3H8O3 were assembled in a universal testing machine (China-UTM-4103) and the compression mode was used.

[0072] like Figure 4 As shown, under compression mode, the experimental group with added conductive C3H8O3 achieved a deformation of 6 mm when a force of 20 N was applied, while the control group without added conductive C3H8O3 had a deformation of less than 2 mm.

[0073] Example 5

[0074] S1: Weigh 1.5g of carbon nanotubes and dissolve them in 20ml of C3H8O3. Disperse the solution by ultrasonication for 30min to obtain a uniformly dispersed conductive C3H8O3 solution.

[0075] S2: Weigh out 9.1g and 0.9g of components A and B (Dow Corning DC184) of PDMS and mix them in a mass ratio of 10:1 to obtain a PDMS mixture.

[0076] S3: 0.08-0.09 g of carbon nanotubes were directly added to 10 g of PDMS mixture obtained in step S2. After magnetic stirring for 30 min, the mixture was placed in a vacuum device to remove air bubbles, and this was used as a control group.

[0077] S4: Add 1g of conductive C3H8O3 solution (containing 0.087g of carbon nanotubes) obtained in step S1 to 10g of PDMS mixture obtained in step S2. After stirring magnetically for 30min, place it in a vacuum device to remove air bubbles. This is used as the experimental group.

[0078] S5: The control group and experimental group samples were spin-coated into 18mm×10mm×5mm molds printed by 3D printers and placed in a drying device at 70℃ for 3 hours. The sample size was 18mm×10mm×5mm.

[0079] S6: The experimental group with added C3H8O3 and the control group without added C3H8O3 were assembled in a universal testing machine (China-UTM-4103) and the compression mode was used.

[0080] like Figure 5 As shown, under compression mode, the experimental group with added conductive C3H8O3 achieved a deformation of 70% at 0.1 MPa, while the control group without added conductive C3H8O3 only achieved a deformation of 40%.

[0081] Example 6

[0082] S1: Take 5g of Ecoflex silicone rubber A and B parts respectively and mix them thoroughly in a mass ratio of 1:1. The mass of the mixture is 10g. Take 10ml of 40% graphene aqueous solution and add it to Ecoflex silicone rubber. Place it in a vacuum box for about 20 minutes to remove air bubbles.

[0083] S2: A rectangular structure of 20mm × 10mm × 2mm is obtained by casting a rectangular substrate obtained through 3D printing. A mixture of graphene aqueous solution and Ecoflex silicone rubber is spin-coated onto the substrate.

[0084] S3: Place the mixture of graphene aqueous solution and Ecoflex silicone rubber in a drying oven and cure at 70°C for 1 hour to obtain a silicone doped layer with a thickness of 1.0 mm.

[0085] S4: The prepared mixed solution of components A and B of pure silicone rubber is injected into the mold at a ratio of 1:1, and the smooth surface of the silicone doped layer is placed on the liquid. It is cured at 70°C for 0.5 hours to obtain a well-bonded silicone doped layer and a flexible substrate, i.e., an electrode; the thickness of the flexible substrate is 0.5 mm.

[0086] S5: Dissolve 1.5g of carbon nanotubes in 20ml of C3H8O3 and ultrasonically disperse for 30min to obtain a uniformly dispersed conductive C3H8O3 solution.

[0087] S6: Weigh 9.1g and 0.9g of PDMS components A and B (Dow Corning DC184) and mix them in a mass ratio of 10:1 to obtain a PDMS mixture.

[0088] S7: Add 1g of conductive C3H8O3 solution (containing 0.087g of carbon nanotubes) obtained in step S5 to 10g of PDMS mixture obtained in step S6, stir magnetically for 30min, and then place in a vacuum device to remove air bubbles.

[0089] S8: Spin-coat the sample into the mold of the 3D printer and place it in a drying device at 70°C for 3 hours.

[0090] S9: Take out the prepared sample, immerse it in C3H8O3 several times to remove unreacted monomers and surface impurities, and let it air dry at room temperature for 12 hours to obtain a piezoresistive sensing layer with a thickness of 2.0 mm.

[0091] S10: The electrodes (i.e., the upper and lower electrodes) formed by graphene bonded to the Ecoflex silicone rubber substrate obtained in the two steps S4 sandwich a piezoresistive sensing layer doped with conductive C3H8O3 (wherein, the silicone doped layer is attached to the piezoresistive sensing layer); copper foil (70μm thick) is then bonded to the outside of the upper and lower contact electrodes respectively, forming a multilayer flexible piezoresistive pressure sensor.

[0092] S11: Secure the sensor to your finger using insulating tape, and use an impedance analyzer (e4990A) to measure the sensor resistance change in real time. Set the impedance analyzer's measurement frequency to 20Hz to ensure the measured resistance is within a stable DC range.

[0093] like Figure 6As shown, the resistance change waveforms from left to right represent the resistance changes of the sensors on the index finger, middle finger, ring finger, little finger, and thumb, respectively. When the gesture changes, each finger exhibits different combinations of numerical changes: when the gesture for the number "1" is displayed, only the index finger remains straight, while the other fingers are bent. The resistance of the sensor on the index finger does not change, while the sensors on the other fingers all show resistance changes; when the gestures for the numbers "3", "6", and "8" are displayed, the pressure sensors can also quickly and accurately produce corresponding resistance responses.

[0094] In summary, this technical solution designs an ultra-flexible piezoresistive solid-liquid hybrid pressure sensor. Electrodes with excellent conductivity are prepared by combining graphene aqueous solution with silicone rubber. A flexible piezoresistive pressure sensor with solid-liquid hybrid structure is prepared by mixing PDMS, carbon nanotubes, and conductive C3H8O3. The tensile and compressive properties are approximately 50 times that of the piezoresistive sensor without conductive C3H8O3, significantly improving its flexibility. This demonstrates that the sensor, with its excellent flexibility, can adapt to various complex application scenarios and has broad application prospects in future fields such as human-computer interaction, wearable devices, and motion monitoring.

[0095] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0096] Matters not covered in this invention are common knowledge.

Claims

1. An ultra-flexible piezoresistive solid-liquid hybrid wearable sensor, characterized in that, The sensor has a five-layer structure, including, from bottom to top, copper foil, electrodes, piezoresistive sensing layer, electrodes, and copper foil; The piezoresistive sensing layer is specifically a polymer of C3H8O3, carbon nanotubes, and PDMS; The method for fabricating the ultra-flexible piezoresistive solid-liquid hybrid wearable sensor includes the following steps: (1) Electrode preparation steps: S1: Mix the A and B parts of silicone rubber in a 1:1 mass ratio to obtain a pure silicone solution, pour it into a graphene aqueous solution, place it in a vacuum chamber, remove air bubbles, and obtain a mixed material; In this process, 5-15g of silicone rubber is added to every 10ml of graphene aqueous solution; the mass concentration of the graphene aqueous solution is 40%. S2: Spin-coat the mixed material onto the substrate; S3: Place in a drying oven and cure at 60~80℃ for 0.5~2.0h to obtain a silicone doped layer; S4: A pure silica gel solution is coated onto a silica gel doped layer, and the electrode is obtained after curing. (2) Preparation steps of the piezoresistive sensing layer: S5: Carbon nanotubes are added to C3H8O3 and ultrasonically dispersed to obtain a conductive C3H8O3 solution; In this process, 1.2~1.8g of carbon nanotubes are added to every 20ml of C3H8O3; S6: Weigh out components A and B of PDMS and mix them in a mass ratio of 10:1 to obtain a PDMS solution; S7: Add the conductive C3H8O3 solution to the PDMS solution, stir, and then place it in a vacuum device to remove air bubbles; wherein, the conductive C3H8O3 solution accounts for 8~12% of the PDMS solution mass; S8: Spin-coat the sample into the mold and place it in a drying device at 60~80℃ for 2~4 hours; S9: Take out the prepared sample, immerse it in C3H8O3 to remove unreacted monomers and surface impurities, and let it dry naturally at room temperature to obtain the piezoresistive sensing layer. (3) The two electrodes are respectively used as the upper electrode and the lower electrode, and the piezoresistive sensing layer is sandwiched to form a multi-layer structure of ultra-flexible piezoresistive solid-liquid hybrid wearable sensor; copper foil is respectively bonded to the upper electrode and the lower electrode to realize the encapsulation of ultra-flexible piezoresistive solid-liquid hybrid wearable sensor.

2. The ultra-flexible piezoresistive solid-liquid hybrid wearable sensor as described in claim 1, characterized in that, The thickness of the copper foil is 60μm~75μm; the thickness of the electrode ranges from 1 to 1.5mm; and the thickness of the piezoresistive sensing layer ranges from 1.5 to 2mm.

3. The ultra-flexible piezoresistive solid-liquid hybrid wearable sensor as described in claim 1, characterized in that, The sensor measures 18~20mm in length and 8~10mm in width.

Images