Deformation sensing film and preparation method and application thereof

Abstract

The invention relates to the technical field of sensing materials, and particularly discloses a deformation sensing film as well as a preparation method and application thereof. The electrochromic friction nanometer generator sequentially comprises a friction nanometer generator layer, an electrochromic hydrogel layer and a liquid metal net transparent electrode layer from bottom to top. The liquid metal ink and the spinning film are utilized, the flexible dot matrix electrode layer is prepared through silk-screen printing, the friction nanometer generator layer and the electrochromic hydrogel layer are combined, the prepared deformation sensing film achieves point-to-point characterization of a surface deformation field, and the skin deformation monitoring precision is high; the visual real-time representation of the skin deformation field is realized, and professional monitoring personnel are not needed; the self-energized feature is achieved, daily wearing is convenient, and the device can be used in the fields of wearable equipment, electronic skin, tactile perception and the like; and the device has the characteristics of high integration level, high conformality, high efficiency and large-area and large-batch preparation.

Description

Technical Field

[0001] The present invention relates to the technical field of sensing materials, and in particular to a deformation sensing film and a preparation method and application thereof. Background Art

[0002] At present, there are mainly the following solutions for posture and skin deformation field perception:

[0003] 1. Resistance sensing scheme: prepare ion-conductive hydrogels, composite graphene foams and other flexible conductive materials. When strain or pressure is applied, the microstructure inside the material changes, thereby changing its resistance. This material is assembled into a resistive sensor, and the voltage change is measured to reflect the deformation size. The main disadvantage is low accuracy, inability to directly characterize the deformation point of the patch, and the need for external power supply and the need to capture electrical signals through an external circuit. The deformation characterization is not real-time and intuitive enough.

[0004] 2. Triboelectric effect and piezoelectric effect scheme: Use triboelectric nanogenerators or piezoelectric nanogenerators, through special electrode structure design, to form a self-powered sensor, based on the generated potential induction motion signal and pressure signal, output electrical signals to reflect skin deformation. The main disadvantage is that the output electrical signal needs to be collected by multiple electrodes, transmitted to the external circuit, amplified, filtered and processed, with a complex structure and high preparation difficulty, and cannot intuitively characterize the skin deformation signal in real time.

[0005] 3. Capacitive sensing solution: Combining bionics, based on the structure of human skin, using pressure sensing micro-elements and flexible electrodes, designing micro-nano pattern scale sensing units, the capacitance changes when under pressure, and the pressure is calculated based on the capacitance increment. The main shortcomings are the complex preparation of micro-nano patterns, the difficulty of assembling multi-level structures, the need for external circuits, and high requirements for data transmission and processing.

[0006] In summary, the existing skin deformation field sensing elements still have problems such as being inconvenient to wear daily, low monitoring accuracy, inability to characterize in real time, high technical requirements for monitoring personnel, and inability to be prepared in large quantities and in high efficiency. Therefore, it is necessary to provide a deformation sensing film and its preparation method and application, so that the deformation sensing film has the characteristics of high integration, high conformality, high efficiency, real-time characterization, and large-area and large-scale preparation. Summary of the invention

[0007] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a deformation sensing film and a preparation method and application thereof, so that the deformation sensing film has the characteristics of high integration, high conformality, high efficiency, real-time characterization and large-area and large-batch preparation.

[0008] A first aspect of the present invention provides a deformation sensing film.

[0009] Specifically, the deformation sensing film includes, from bottom to top, a friction nanogenerator layer, an electrochromic hydrogel layer, and a liquid metal mesh transparent electrode layer.

[0010] Preferably, the friction nanogenerator layer includes, from top to bottom, a flexible dot matrix electrode layer, a first polydimethylsiloxane mold layer, a liquid metal ink layer, and a second polydimethylsiloxane mold layer.

[0011] Preferably, the first polydimethylsiloxane mold layer is concave; and the second polydimethylsiloxane mold layer is concave.

[0012] Preferably, the electrochromic hydrogel layer comprises polyvinyl alcohol, ethyl viologen dibromide, potassium ferrocyanide, potassium ferrocyanide, and sodium tetraborate.

[0013] Preferably, the liquid metal mesh transparent electrode layer comprises thermoplastic polyurethane.

[0014] A second aspect of the present invention provides a method for preparing a deformation sensing film.

[0015] Specifically, the following steps are included:

[0016] (1) mixing a gallium-based alloy with a solvent and stirring the mixture ultrasonically to obtain a liquid metal ink;

[0017] (2) using an electrospinning process to prepare a spinning membrane from a thermoplastic polyurethane solution, printing a circuit pattern on the spinning membrane using liquid metal ink, drying and curing the membrane, and hammering the membrane to obtain a flexible dot matrix electrode layer;

[0018] (3) pouring the polydimethylsiloxane solution into the concave mold, drying and curing, removing the cured polydimethylsiloxane to obtain a polydimethylsiloxane mold layer, stacking and bonding two polydimethylsiloxane mold layers, pasting a conductive copper tape, and then injecting the liquid metal ink obtained in step (1) into the cavity between the two polydimethylsiloxane mold layers, gluing the flexible dot matrix electrode layer obtained in step (2) onto the first polydimethylsiloxane mold layer, drying and curing, and obtaining a friction nanogenerator layer;

[0019] (4) photolithography of a friction nanogenerator layer pattern on a silicon wafer, covering it with a polydimethylsiloxane solution, vacuum treating it, removing bubbles, drying and curing it to form a thin film, removing the thin film, coating the liquid metal ink obtained in step (1) on the pattern of the thin film, drying and curing it, washing it, immersing it with a thermoplastic polyurethane solution, drying and curing it, and transferring the liquid metal mesh transparent electrode to obtain a liquid metal mesh transparent electrode layer;

[0020] (5) gluing a gap frame on the flexible dot matrix electrode layer of the friction nanogenerator layer obtained in step (3), filling the gap frame with electrochromic hydrogel, and then gluing the liquid metal mesh transparent electrode glue layer obtained in step (4) on the gap frame to obtain a deformation sensing film.

[0021] Preferably, the drying and curing temperature is 75-85° C. and the time is 10-20 min.

[0022] More preferably, the drying and curing temperature is 80-85° C. and the time is 15-20 min.

[0023] More preferably, the drying and curing temperature is 80° C. and the time is 15 minutes.

[0024] Preferably, in step (1), the gallium-based alloy includes at least one of a gallium-indium alloy and a gallium-indium-tin alloy.

[0025] Further preferably, in step (1), the gallium-based alloy is a gallium-indium alloy.

[0026] Preferably, in step (2), the circuit pattern is square.

[0027] Preferably, in step (3), the stacking and bonding method comprises the following steps:

[0028] The concave surface of the second polydimethylsiloxane mold layer is facing upwards, and the polydimethylsiloxane solution is used to coat the periphery of the second polydimethylsiloxane mold layer. Then, the concave surface of the first polydimethylsiloxane mold layer is facing downwards for stacking and bonding.

[0029] Preferably, in step (5), the method for preparing the electrochromic hydrogel comprises the following steps:

[0030] Ethyl viologen dibromide, potassium ferrocyanide and potassium ferrocyanide are added to a polyvinyl alcohol solution, and then mixed with a sodium tetraborate solution and stirred to prepare an electrochromic hydrogel.

[0031] A third aspect of the present invention provides an application of a deformation sensing film in the fields of wearable devices, electronic skin, and tactile perception.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The present invention utilizes liquid metal ink and spinning membrane to prepare a flexible dot matrix electrode layer by screen printing, and combines the friction nanogenerator layer and the electrochromic hydrogel layer to obtain a deformation sensing film that realizes point-to-point characterization of the surface deformation field, and has high precision in monitoring skin deformation. It realizes intuitive real-time characterization of the skin deformation field without the need for professional monitoring personnel. It has the characteristics of self-power supply, is easy to wear in daily life, and can be used in wearable devices, electronic skin, tactile perception and other fields. It also has the characteristics of high integration, high conformality, high efficiency, and can be prepared over a large area and in large quantities. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a structural diagram of the deformation sensing film of Example 1 of the present invention;

[0035] Figure 2 This is a flow chart of the preparation of the friction nanogenerator layer in Example 1 of the present invention;

[0036] Figure 3 This is a working principle diagram of the deformation sensing film in Example 1 of the present invention;

[0037] Figure 4 This is a graph showing the joint flexion and extension intuitively represented by the electrochromic deformation sensing film of Example 1 of the present invention;

[0038] Figure 5 This is a microscopic morphology analysis diagram of the flexible dot matrix electrode prepared in Example 1 of the present invention under a scanning electron microscope. DETAILED DESCRIPTION

[0039] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0040] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0041] Example 1

[0042] A deformation sensing film and a preparation method thereof.

[0043] like Figure 1 As shown, the deformation sensing film is composed of a friction nanogenerator layer, an electrochromic hydrogel layer, and a liquid metal mesh transparent electrode layer from bottom to top; wherein the friction nanogenerator layer is composed of a flexible dot matrix electrode layer, a first polydimethylsiloxane mold layer, a liquid metal ink layer, and a second polydimethylsiloxane mold layer from top to bottom.

[0044] The steps of the preparation method are as follows:

[0045] (1) 3.8 g of gallium-indium alloy was mixed with 1100 μL of n-decanol in a centrifuge tube and stirred in a water bath with ultrasonic waves for 5 min to prepare a liquid metal ink;

[0046] (2) Thermoplastic polyurethane (TPU) was dissolved in dimethylformamide solution at room temperature and stirred to obtain TPU solution. 7 ml of TPU solution was taken and the TPU solution was made into a spinning membrane on tin foil using an electrostatic spinning process. A circuit pattern (square) was printed on the spinning membrane using a screen printing ink mold using liquid metal ink. The spinning membrane with the patterned liquid metal ink was then placed in an oven at 80°C for drying and curing, and physically beaten to sinter the liquid metal particles to conduct. Due to the fiber structure of the spinning membrane, the liquid metal ink penetrated and sintered to form a dense flexible dot matrix electrode layer;

[0047] (3) Use a simple 3-D printing mold (the overall shape is a concave platform, the same size as the flexible dot matrix electrode, and there is a convex platform at the bottom), pour the polydimethylsiloxane (PDMS) solution into the concave mold, place it in an 80°C oven for drying and curing for 15 minutes, remove the cured PMDS to obtain a PMDS mold layer, take two PMDS mold layers for stacking and bonding, that is, the concave surface of the second PMDS mold layer faces upward, use the PMDS solution to coat the four sides of the second PMDS mold layer, and then stack and bond the concave surface of the first PMDS mold layer facing downward. Paste the conductive copper tape, guide it out and connect it to the liquid metal mesh transparent electrode layer, then inject the liquid metal ink obtained in step (1) into the cavity between the two PDMS mold layers (use a syringe to push in the liquid metal ink and another to extract the air), glue the flexible dot matrix electrode layer obtained in step (2) to the first PDMS mold layer, place it in an 80°C oven for drying and curing for 15 minutes, and obtain the friction nanogenerator layer. The preparation flow chart is as follows: Figure 2 As shown;

[0048] (4) Photolithography of the friction nanogenerator layer pattern on the silicon wafer, spin coating the silicon wafer with PDMS solution to cover the pattern, placing the treated silicon wafer in a vacuum pump for vacuum treatment, evacuating the PDMS solution to completely penetrate the pattern on the silicon wafer, and removing bubbles, taking out the silicon wafer and drying and curing it in an oven at 80°C for 15 minutes to form a thin film, removing the thin film, retaining the patterned portion of the thin film, placing the thin film on a glass slide with the pattern facing upward, coating the liquid metal ink obtained in step (1) on the pattern of the thin film, placing it in an oven at 80°C for drying and curing for 15 minutes, cleaning the surface with a plasma cleaner, immersing it in a TPU solution, placing it in an oven at 80°C for drying and curing for 15 minutes, completing the transfer of the liquid metal mesh transparent electrode, and removing the TPU film with tweezers to obtain a liquid metal mesh transparent electrode layer;

[0049] (5) Dissolve 4g of polyvinyl alcohol (PVA) in 96mL of distilled water and stir at 90℃ for 2h until it is evenly dissolved. Add 20mmol / L of ethyl viologen dibromide and a 1:1 mixture of potassium ferrocyanide and potassium ferrocyanide to the PVA solution to make their concentrations 0.8mmol / L respectively, and continue to stir until the solution is evenly mixed. Prepare a 4% sodium tetraborate solution, dissolve 4g of sodium tetraborate in 96mL of distilled water, and stir at room temperature until it is completely dissolved. Mix the PVA solution and the sodium tetraborate solution in a volume ratio of 1:4 and stir rapidly until a uniform gel-like substance is formed, which is the electrochromic hydrogel. A PDMS solution is used to glue a gap frame on top of the flexible lattice electrode layer of the friction nanogenerator layer obtained in step (3). The gap frame is made by drying and curing the PDMS solution. The electrochromic hydrogel is filled in the gap frame and smoothed with a coating scraper. The liquid metal mesh transparent electrode layer obtained in step (4) is then glued on top of the gap frame with a PDMS solution to obtain a deformation sensing film.

[0050] like Figure 3 As shown, the working principle of the deformation sensing film prepared in Example 1 of the present invention is as follows:

[0051] S1, the assembled deformation sensing film is attached to the skin. S2, when skin deformation occurs, the flexible dot matrix electrode and the upper PDMS layer are triboelectrically charged, making the PDMS negatively charged. At the same time, the friction between the skin and the lower PDMS layer further promotes the negative charge of the PDMS. S3, the liquid metal graphite encapsulated inside is induced to generate positive charge, and the electrons are transmitted to the top liquid metal mesh transparent electrode along the conductive copper tape. S4, the top liquid metal mesh transparent electrode is negatively charged, and a potential difference is formed between the frictionally charged part and the flexible dot matrix electrode, driving the electrochromic hydrogel to locally change color and characterize the deformation field. S5, when the deformation is restored and the flexible dot matrix electrode approaches the PDMS layer, the induced positive charge on the liquid metal graphite on the flexible electrode will also decrease, and the free electrons will flow back from the top liquid metal mesh transparent electrode to the liquid metal graphite. The electric field is weakened to disappear, and the color of the electrochromic hydrogel is restored.

[0052] Compared with the existing resistance sensing scheme, triboelectric effect and piezoelectric effect scheme, and capacitive sensing scheme, the existing schemes all require external circuits to transmit the electrical signals collected by the sensor to the external circuits by wired / wireless means, and then analyze the measurement results. The equipment is complex and limited by the receiving equipment, and it is not real-time. For example, in the resistance sensing scheme, an oscilloscope and a power supply are directly used to measure the voltage-current relationship of the sensor, and then analyze it; in the triboelectric effect and piezoelectric effect schemes, in order to improve the spatial accuracy, each unit is derived using a wire, and the structure is complex. Although no external power supply is required, an oscilloscope is also required for characterization and analysis. Compared with the prior art, the present invention can achieve self-power supply, does not require an external circuit, and can work continuously in a wireless and passive manner.

[0053] like Figure 4 As shown, the deformation sensing film prepared in Example 1 is attached to a human joint that is not flexed or extended. When the joint flexes or extends, the deformation sensing film is stretched and deformed. Figure 4 In the A region, the tensile deformation around the deformation sensing film is small, and the potential generated by the friction nanogenerator layer is low, so the color change of the electrochromic hydrogel is not obvious. In the B region, the tensile deformation in the middle of the deformation sensing film is large, and the potential generated by the friction nanogenerator layer is high, so the color change of the electrochromic hydrogel is more obvious.

[0054] In the prior art, it is necessary to export the electrical signal to an external circuit for analysis and characterization after processing, which is not intuitive enough and requires professional operation. For example, in the resistance sensing scheme, the pressure and strain are characterized by measuring the current change caused by pressure and the resistance change caused by strain through an external oscilloscope. In the triboelectric effect and piezoelectric effect schemes, the deformation is converted into voltage and current by a friction nanogenerator and a piezoelectric nanogenerator, and then exported to the outside and recorded and characterized by an oscilloscope after passing through a current preamplifier. In the capacitive sensing scheme, carbon nanotubes are used to form a microcapacitor array, and the pressure is measured by measuring the relative change of capacitance. In the present invention, the deformation field can be converted into an electric field, and then converted into a color field through an electrochromic material, which can be characterized in real time and intuitively.

[0055] like Figure 5 As shown in the figure, the flexible dot matrix electrode is subjected to microscopic morphology analysis under a scanning electron microscope. The present invention uses liquid metal ink and spinning membrane to print and efficiently prepare flexible dot matrix electrodes, which can achieve point-to-point accurate characterization. The resistance sensing scheme in the prior art uses the resistance characteristics of flexible materials for characterization, and has low spatial accuracy. The triboelectric effect and piezoelectric effect schemes and capacitive sensing schemes use micro components to achieve higher spatial accuracy, but the circuits are complex and difficult to prepare.

[0056] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution obtained by any modification, equivalent replacement, improvement, etc. made by a person skilled in the art based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall be within the scope of protection determined by the claims.

Claims

1. A deformation sensing film, characterized in that: From bottom to top, it includes a friction nanogenerator layer, an electrochromic hydrogel layer, and a liquid metal mesh transparent electrode layer.

2. The deformation sensing film according to claim 1, characterized in that: The friction nanogenerator layer includes, from top to bottom, a flexible dot matrix electrode layer, a first polydimethylsiloxane mold layer, a liquid metal ink layer, and a second polydimethylsiloxane mold layer.

3. The deformation sensing film according to claim 2, characterized in that: The first polydimethylsiloxane mold layer is concave; the second polydimethylsiloxane mold layer is concave.

4. The method for preparing the deformation sensing film according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) mixing a gallium-based alloy with a solvent and stirring the mixture ultrasonically to obtain a liquid metal ink; (2) using an electrospinning process to prepare a spinning membrane from a thermoplastic polyurethane solution, printing a circuit pattern on the spinning membrane using liquid metal ink, drying and curing the membrane, and hammering the membrane to obtain a flexible dot matrix electrode layer; (3) pouring the polydimethylsiloxane solution into the concave mold, drying and curing, removing the cured polydimethylsiloxane to obtain a polydimethylsiloxane mold layer, stacking and bonding two polydimethylsiloxane mold layers, pasting a conductive copper tape, and then injecting the liquid metal ink obtained in step (1) into the cavity between the two polydimethylsiloxane mold layers, gluing the flexible dot matrix electrode layer obtained in step (2) onto the first polydimethylsiloxane mold layer, drying and curing, and obtaining a friction nanogenerator layer; (4) photolithography of a friction nanogenerator layer pattern on a silicon wafer, covering it with a polydimethylsiloxane solution, vacuum treating it, removing bubbles, drying and curing it to form a thin film, removing the thin film, coating the liquid metal ink obtained in step (1) on the pattern of the thin film, drying and curing it, washing it, immersing it with a thermoplastic polyurethane solution, drying and curing it, and transferring the liquid metal mesh transparent electrode to obtain a liquid metal mesh transparent electrode layer; (5) gluing a gap frame on the flexible dot matrix electrode layer of the friction nanogenerator layer obtained in step (3), filling the gap frame with electrochromic hydrogel, and then gluing the liquid metal mesh transparent electrode layer obtained in step (4) on the gap frame to obtain a deformation sensing film.

5. The preparation method according to claim 4, characterized in that: The drying and curing temperature is 75-85°C.

6. The preparation method according to claim 4, characterized in that: The drying and curing time is 10 to 20 minutes.

7. The preparation method according to claim 4, characterized in that: In step (1), the gallium-based alloy includes at least one of a gallium-indium alloy and a gallium-indium-tin alloy.

8. The preparation method according to claim 4, characterized in that: In step (3), the stacking and bonding method comprises the following steps: The concave surface of the second polydimethylsiloxane mold layer is facing upwards, and the polydimethylsiloxane solution is used to coat the periphery of the second polydimethylsiloxane mold layer. Then, the concave surface of the first polydimethylsiloxane mold layer is facing downwards for stacking and bonding.

9. The preparation method according to claim 4, characterized in that: In step (5), the method for preparing the electrochromic hydrogel comprises the following steps: Ethyl viologen dibromide, potassium ferrocyanide and potassium ferrocyanide are added to a polyvinyl alcohol solution, and then mixed with a sodium tetraborate solution and stirred to prepare an electrochromic hydrogel.

10. Application of the deformation sensing film according to any one of claims 1 to 3 in the fields of wearable devices, electronic skin, and tactile perception.

Images