Ultra-flexible piezoresistive solid-liquid mixed wearable sensor and preparation method thereof

Abstract

The invention relates to an ultra-flexible piezoresistive solid-liquid mixed wearable sensor and a preparation method thereof. The sensor is of a five-layer structure and sequentially comprises a copper foil, an electrode, a piezoresistive sensing layer, an electrode and a copper foil from bottom to top. And the piezoresistive sensing layer is specifically a polymer of C3H8O3, a carbon nano tube and PDMS (Polydimethylsiloxane). According to the invention, the co-existence of the solid phase and the liquid phase of the carbon nanotubes and the glycerol ensures that the flexibility of the sensor is enhanced, and the prepared piezoresistive sensor can be used for clicking mouse keys, detecting human little finger joint action signals and identifying a pressure array.

Description

Technical Field

[0001] The invention relates to the technical field of sensor manufacturing, and in particular to the preparation and application of an ultra-flexible piezoresistive solid-liquid hybrid sensor. Background Art

[0002] With the rapid development of electronic skin, intelligent robotic arms, human-computer interaction, wearable devices and other fields, flexible piezoresistive sensors with good sensitivity and conductivity have well met the needs of many of the above fields. Piezoresistive sensors are composed of flexible substrate materials, electrodes and sensing materials. They can generate resistance signals by applying pressure, and can also be converted into voltage signals using external power supplies. They have high-quality and high-sensitivity signal acquisition.

[0003] Among various impressive dielectric materials, polydimethylsiloxane (PDMS) is known for its high electronegativity, flexibility, hydrophobicity and wear resistance, making it the most promising flexible substrate material for flexible piezoresistive sensors. Although 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 interface separation and reduced performance and lifetime. Summary of the invention

[0004] The purpose of the present invention is to provide an ultra-flexible piezoresistive solid-liquid hybrid wearable sensor and a preparation method thereof in view of the limitations of the current technology. The sensor uses propylene glycol (C3H8O3) as a liquid filler, and the high boiling point of C3H8O3 is used to prevent it from easily volatilizing during the preparation process when it is used as a liquid filler of a flexible piezoresistive sensor; the co-existence of the solid and liquid phases of carbon nanotubes and C3H8O3 ensures that the flexibility of the sensor is enhanced, and the prepared piezoresistive sensor can be used for clicking mouse buttons, detecting human little finger joint motion signals, and pressure array recognition.

[0005] The present invention can be implemented through the following technical solutions:

[0006] An ultra-flexible piezoresistive solid-liquid hybrid wearable sensor, the sensor having a five-layer structure, including, from bottom to top, copper foil, electrode, piezoresistive sensing layer, electrode, 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 in the range of 1-1.5 mm; and the thickness of the piezoresistive sensing layer is in the range of 1.5-2 mm.

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

[0010] (1) Preparation steps of electrodes:

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

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

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

[0014] S3: placing in a drying oven and curing at 60-80° C. for 0.5-2.0 h to obtain a silica gel doping layer;

[0015] S4: coating the pure silica gel solution on the silica gel doping layer, and obtaining an electrode after curing;

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

[0017] S1: adding carbon nanotubes to C3H8O3 and dispersing by ultrasonic to obtain a conductive C3H8O3 solution;

[0018] Wherein, 1.2-1.8 g of carbon nanotubes are added to every 20 ml of C3H8O3;

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

[0020] S3: adding a conductive C3H8O3 solution to the PDMS, stirring, and placing in a vacuum device to remove bubbles; wherein the conductive C3H8O3 solution is 8-12% of the mass of the PDMS solution;

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

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

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

[0024] The length and width of the sensor are 18-20 mm × 8-10 mm.

[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, without the generation of three wastes and without causing pollution to the environment; the process is simple and can be used for industrial production without the need for additional new equipment, and the process is rapid and the production speed is fast.

[0027] (2) Mechanical properties test results show that the tensile strength and tensile Young's modulus of the material are 0.06Mpa and 0.0723 respectively; the compressive strength and compressive Young's modulus are 0.0876Mpa and 0.142 respectively. Compared with the traditional PDMS mixed carbon nanotube piezoresistive sensor, its flexibility is improved by about 50 times. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0029] Figure 2 This is a comparison diagram of the force-displacement curve of the sensor in the stretching mode in Example 2;

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

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

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

[0033] Figure 6 This is a schematic diagram of sensor hand motion recognition in Example 6. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0035] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0036] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] Unless otherwise specified, the reagents used in the examples can be purchased from the market.

[0038] Example 1

[0039] S1: Take 5g of the A / B parts of Ecoflex silicone rubber respectively and mix them in a mass ratio of 1:1. The mass after mixing 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 bubbles.

[0040] S2: The rectangular substrate obtained by 3D printing is molded to obtain a rectangular structure of 20mm×10mm×2mm, and a mixture of graphene aqueous solution and Ecoflex silicone rubber is spin-coated on 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 h to obtain a silicone doped layer with a thickness of 1.0 mm.

[0042] S4: Inject the mixed solution of the prepared A and B components of pure silicone rubber into the mold at a ratio of 1:1, place the smooth surface of the silicone doped layer on the liquid, and cure it in a 70°C environment for 0.5h to obtain a well-combined silicone doped layer and a flexible substrate, i.e., an electrode; the thickness of the flexible substrate is 0.5mm.

[0043] S5: Take 1.5 g of carbon nanotubes and dissolve them in 20 ml of C3H8O3, and perform ultrasonic dispersion treatment for 30 min to obtain a uniformly dispersed conductive C3H8O3 solution.

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

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

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

[0047] S9: Take out the prepared sample, soak it in C3H8O3 for 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 electrode and the lower electrode) composed of the graphene combined with the Ecoflex silicone rubber substrate obtained in the two steps S4 clamp the piezoresistive sensing layer doped with conductive C3H8O3 (wherein the silicone doped layer is bonded to the piezoresistive sensing layer); copper foil (with a thickness of 70 μm) is then bonded to the outer sides of the upper and lower contact electrodes, respectively, to form a flexible piezoresistive pressure sensor with a multi-layer structure, so as to realize the packaging of the flexible piezoresistive pressure sensor, and connect the wires to measure the sensor performance.

[0049] Example 2

[0050] S1: Weigh 1.5 g of carbon nanotubes and dissolve them in 20 ml of C3H8O3. Perform ultrasonic dispersion treatment for 30 min to obtain a uniformly dispersed conductive C3H8O3 solution.

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

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

[0053] S4: Add 1 g of conductive C3H8O3 solution (containing 0.087 g of carbon nanotubes) obtained in step S1 to 10 g of the PDMS mixed solution obtained in step S2, stir magnetically for 30 min, and place in a vacuum device to remove bubbles, which serves as the experimental group.

[0054] S5: The samples of the control group and the experimental group were spin-coated on a 18 mm × 10 mm × 5 mm mold printed by a 3D printer and placed in a drying device at 70 °C for 3 h. The sample size was 18 mm × 10 mm × 5 mm.

[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) in the tensile mode.

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

[0057] Example 3

[0058] S1: Weigh 1.5 g of carbon nanotubes and dissolve them in 20 ml of C3H8O3. Perform ultrasonic dispersion treatment for 30 min to obtain a uniformly dispersed conductive C3H8O3 solution.

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

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

[0061] S4: Add 1 g of conductive C3H8O3 solution (containing 0.087 g of carbon nanotubes) obtained in step S1 to 10 g of the PDMS mixed solution obtained in step S2, stir magnetically for 30 min, and place in a vacuum device to remove bubbles, which serves as the experimental group.

[0062] S5: The samples of the control group and the experimental group were spin-coated on a 18 mm × 10 mm × 5 mm mold printed by a 3D printer and placed in a drying device at 70 °C for 3 h. The sample size was 18 mm × 10 mm × 5 mm.

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

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

[0065] Example 4

[0066] S1: Weigh 1.5 g of carbon nanotubes and dissolve them in 20 ml of C3H8O3. Perform ultrasonic dispersion treatment for 30 min to obtain a uniformly dispersed conductive C3H8O3 solution.

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

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

[0069] S4: Add 1 g of conductive C3H8O3 solution (containing 0.087 g of carbon nanotubes) obtained in step S1 to 10 g of the PDMS mixed solution obtained in step S2, stir magnetically for 30 min, and place in a vacuum device to remove bubbles, which serves as the experimental group.

[0070] S5: The samples of the control group and the experimental group were spin-coated on a 18 mm × 10 mm × 5 mm mold printed by a 3D printer and placed in a drying device at 70 °C for 3 h. The sample size was 18 mm × 10 mm × 5 mm.

[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) using the compression mode.

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

[0073] Example 5

[0074] S1: Weigh 1.5 g of carbon nanotubes and dissolve them in 20 ml of C3H8O3. Perform ultrasonic dispersion treatment for 30 min to obtain a uniformly dispersed conductive C3H8O3 solution.

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

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

[0077] S4: Add 1 g of conductive C3H8O3 solution (containing 0.087 g of carbon nanotubes) obtained in step S1 to 10 g of the PDMS mixed solution obtained in step S2, stir magnetically for 30 min, and place in a vacuum device to remove bubbles, which serves as the experimental group.

[0078] S5: The samples of the control group and the experimental group were spin-coated on a 18 mm × 10 mm × 5 mm mold printed by a 3D printer and placed in a drying device at 70 °C for 3 h. The sample size was 18 mm × 10 mm × 5 mm.

[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) using the compression mode.

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

[0081] Example 6

[0082] S1: Take 5g of the A / B parts of Ecoflex silicone rubber respectively and mix them in a mass ratio of 1:1. The mass after mixing 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 bubbles.

[0083] S2: The rectangular substrate obtained by 3D printing is molded to obtain a rectangular structure of 20mm×10mm×2mm, and a mixture of graphene aqueous solution and Ecoflex silicone rubber is spin-coated on 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 h to obtain a silicone doped layer with a thickness of 1.0 mm.

[0085] S4: Inject the mixed solution of the prepared A and B components of pure silicone rubber into the mold at a ratio of 1:1, place the smooth surface of the silicone doped layer on the liquid, and cure it in a 70°C environment for 0.5h to obtain a well-combined silicone doped layer and a flexible substrate, i.e., an electrode; the thickness of the flexible substrate is 0.5mm.

[0086] S5: Take 1.5 g of carbon nanotubes and dissolve them in 20 ml of C3H8O3, and perform ultrasonic dispersion treatment for 30 min to obtain a uniformly dispersed conductive C3H8O3 solution.

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

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

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

[0090] S9: Take out the prepared sample, soak it in C3H8O3 for 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.

[0091] S10: The electrodes (i.e., upper and lower electrodes) formed by the Ecoflex silicone rubber substrate obtained in step S4 sandwich the piezoresistive sensing layer doped with conductive C3H8O3 (wherein the silicone doped layer is bonded to the piezoresistive sensing layer); copper foil (thickness of 70 μm) is then bonded to the outer sides of the upper and lower contact electrodes, respectively, to form a multi-layered flexible piezoresistive pressure sensor.

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

[0093] like Figure 6As shown in the figure, the resistance change waveform represents the resistance change of the sensors on the index finger, middle finger, ring finger, little finger, and thumb from left to right. When the gesture changes, each finger presents a different combination of numerical changes: when showing the gesture of the number "1", only the index finger remains straight, and 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 produce resistance changes; when showing the gestures of the numbers "3", "6", and "8", the pressure sensor can also quickly and accurately generate corresponding resistance responses.

[0094] In summary, this technical solution designs an ultra-flexible piezoresistive solid-liquid hybrid pressure sensor. Graphene aqueous solution is combined with silicone rubber to prepare an electrode with excellent conductive properties, and PDMS, carbon nanotubes, and conductive C3H8O3 are mixed to prepare a solid-liquid hybrid flexible piezoresistive pressure sensor, whose tensile and compressive properties are about 50 times that of the piezoresistive sensor without the addition of conductive C3H8O3, which improves its flexibility; it is verified that the sensor can adapt to various complex usage scenarios with its good flexibility, and has broad application prospects in the future in the fields of human-computer interaction, wearable devices, and motion status monitoring.

[0095] The above is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

[0096] Matters not covered by the present invention are known technologies.

Claims

1. An ultra-flexible piezoresistive solid-liquid hybrid wearable sensor, which has a five-layer structure, including, from bottom to top, copper foil, electrode, piezoresistive sensing layer, electrode, and copper foil; The piezoresistive sensing layer is specifically a polymer of C3H8O3, carbon nanotubes and PDMS, with a mass ratio of 9-12:1:100-130.

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

3. The method for preparing the ultra-flexible piezoresistive solid-liquid hybrid wearable sensor according to claim 1, comprising the following steps: (1) Preparation steps of electrodes: S1: Mix the two parts A / B of silicone rubber in a mass ratio of 1:1, pour into the graphene aqueous solution, place in a vacuum box, remove bubbles, and obtain a mixed material; Wherein, 5 to 15 g of silicone rubber is added to every 10 ml of graphene aqueous solution; the mass concentration of the graphene aqueous solution is 40%; S2: Spin coating the mixed material on the substrate; S3: placing in a drying oven and curing at 60-80° C. for 0.5-2.0 h to obtain a silica gel doping layer; S4: coating the pure silica gel solution on the silica gel doping layer, and obtaining an electrode after curing; (2) Preparation steps of piezoresistive sensing layer: S1: adding carbon nanotubes to C3H8O3 and dispersing by ultrasonic to obtain a conductive C3H8O3 solution; Wherein, 1.2-1.8 g of carbon nanotubes are added to every 20 ml of C3H8O3; S2: Weigh the A / B components of PDMS and mix them in a mass ratio of 10 to 1 to obtain a PDMS solution; S3: adding a conductive C3H8O3 solution to the PDMS, stirring, and placing in a vacuum device to remove bubbles; wherein the conductive C3H8O3 solution is 8-12% of the mass of the PDMS solution; S4: Spin-coat the sample in the mold and place it in a drying device at 60-80°C for 2-4h; S5: taking out the prepared sample, soaking it in C3H8O3 to remove unreacted monomers and surface impurities, and drying it naturally at room temperature to obtain a piezoresistive sensing layer; (3) The upper and lower electrodes clamp the piezoresistive sensing layer to form a flexible piezoresistive pressure sensor with a multi-layer structure; copper foil is bonded to the upper and lower electrodes respectively to realize the packaging of the flexible piezoresistive pressure sensor.

4. The method for preparing the ultra-flexible piezoresistive solid-liquid hybrid wearable sensor as described in claim 1, wherein the length and width of the sensor are 18-20 mm×8-10 mm.

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