Multi-mode self-powered wearable plant sensor and preparation method thereof

Abstract

The invention discloses a multi-mode self-powered wearable plant sensor and a preparation method thereof. The sensor comprises a flexible conductive substrate, a sensitive layer film and a top electrode which are stacked in sequence, and the flexible conductive substrate is composed of a polymer film and a conductive film; the sensitive layer film is a PVA / KOH / TiO2 composite film; the preparation method comprises the following steps: firstly preparing the flexible conductive substrate, then preparing a PVA, KOH and TiO2 blending solution, spin-coating the PVA, KOH and TiO2 blending solution on the flexible conductive substrate to obtain a PVA / KOH / TiO2 composite film, and then fixing the top electrode on the PVA / KOH / TiO2 composite film to obtain the complete sensor. According to the sensor, moisture and vibration information can be sensed on a single device and can be converted into electric energy, the energy utilization rate can be increased, and the power consumption of the device can be reduced.

Description

Technical Field

[0001] The present invention relates to the field of plant sensors, and specifically to a multimodal self-powered wearable plant sensor and a preparation method thereof. Background Art

[0002] The rapid development of intelligent robots and wearable devices has put forward higher requirements for the performance of flexible sensors. The research of sensors has gradually developed from single-parameter sensing to multimodal integrated sensing. Integrating multiple single-functional sensing units into a sensing system is an effective means to achieve multimodal sensing, but it is limited by the system size and complex processes. However, the integrated flexible multimodal sensor has the advantages of a compact structure, simple process, and the ability to monitor multiple parameters at the same point. In recent years, it has become a research hotspot at home and abroad. It is worth noting that the current sensors mainly rely on external batteries for power supply, and there are problems such as limited installation locations, limited use (especially in remote areas), and high system complexity and costs.

[0003] Self-powered sensors can generate electrical energy using the conditions of the surrounding environment and achieve information sensing. For example, sensors based on triboelectric nanogenerators (TENG) can convert mechanical energy into electrical energy and can also monitor vibration information in the environment; self-powered humidity sensors can generate electrical energy using moisture and can also monitor moisture information. The development of self-powered sensing technology provides a new way to solve the power supply problem of sensors. Therefore, the preparation of multimodal self-powered wearable sensors provides a new method to solve the problems of power supply and single-parameter sensing existing in existing sensors, and provides a new direction for the development of flexible electronics.

[0004] In the agricultural field, problems such as global warming, increasing extreme weather, and frequent droughts pose a huge threat to crop growth. At present, China's agricultural production mode is transforming from traditional to efficient and sustainable smart agriculture, which requires advanced sensors to obtain plant growth data to achieve precise management and decision-making and ensure food security. However, most of the current sensors are for static data, which cause great interference to plant growth. Remote and non-contact sensing technologies have problems such as low spatial and temporal resolutions, discontinuous measurements, poor sensitivity and stability, and it is difficult to accurately and continuously monitor plant growth, microenvironment, and organ development. Although wearable plant sensors solve the problem of compatibility with the plant surface, the sensing method is single and the data support is incomplete, and they cannot meet the needs of simultaneous detection of multiple environmental factors.

[0005] It should be noted that while solving the energy supply problem, the multimodal self-powered wearable sensor can simultaneously monitor multiple physiological indexes and environmental parameters of plants, such as light, temperature, humidity, soil humidity, carbon dioxide concentration, etc. By cross-verifying data to reduce errors, it can deeply study the physiological processes of plants, achieve comprehensive monitoring and precise management of crop growth, improve yield and quality, reduce resource waste, and better meet the development needs of smart agriculture. Summary of the Invention

[0006] The present invention provides a multimodal self-powered wearable plant sensor and a preparation method thereof to overcome the deficiencies of existing wearable plant sensors.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows: The multimodal self-powered wearable plant sensor includes a flexible conductive substrate, a sensitive layer film, and a top electrode; the flexible conductive substrate is composed of a polymer film and a conductive film prepared on the polymer film; the sensitive layer film is a PVA / KOH / TiO 2 composite film, and the sensitive layer film is prepared on the conductive film of the flexible conductive substrate; the top electrode is prepared on the sensitive layer film; The top electrode and the conductive film in the flexible conductive substrate form positive and negative electrodes, and a potential difference is formed between the positive and negative electrodes after the sensitive layer film absorbs water to generate an electrical signal; And a triboelectric nanogenerator with a single-electrode structure is formed by the flexible conductive substrate and the sensitive layer film. When used as a triboelectric nanogenerator, the top electrode does not participate in the working process, and an electrical signal is generated through charge transfer and accumulation during the contact and separation process between the sensitive layer film and the object to be tested, realizing the perception of vibration information.

[0008] Further, the material of the polymer film is any one of PET, PI, PDMS, and TPU.

[0009] Further, the material of the conductive film is any one of ITO, graphene, and carbon nanotubes.

[0010] Further, the PVA / KOH / TiO 2 composite film is obtained by spin-coating a PVA, KOH, TiO 2 blended solution on the conductive film of the flexible conductive substrate.

[0011] Further, the top electrode is a zinc electrode.

[0012] A preparation method of the above multimodal self-powered wearable plant sensor includes the following steps: Step 1: Prepare a flexible conductive substrate, and select whether to perform plasma etching on the conductive thin film on the flexible conductive substrate according to the material and surface characteristics of the conductive thin film. When the surface energy of the conductive thin film is too low to spin-coat the sensitive layer, select to perform plasma etching on its surface; Step 2: Prepare a 50 mg / ml PVA solution and a 300 mg / ml KOH solution. The solvent for both is deionized water. Mix the PVA solution and the KOH solution according to the solute mass ratio of 2:1 to obtain a mixed solution. The KOH solution is added dropwise to the cooled PVA solution while stirring the PVA solution to make the KOH and the PVA solution mix evenly; Then add TiO 2 to the mixed solution and stir to obtain a PVA, KOH, TiO 2 blended solution, where the concentration of TiO 2 is 0.6 mg / ml; Finally, spin-coat the blended solution on the conductive thin film of the flexible conductive substrate and then perform heat annealing treatment to obtain a PVA / KOH / TiO 2 composite film; Step 3: Fix the top electrode on the PVA / KOH / TiO 2 composite film with PI tape.

[0013] Furthermore, in Step 1, use a rigid substrate. After configuring the material constituting the polymer thin film into a solution, coat it on the rigid substrate to form a polymer thin film, and then prepare the material constituting the conductive thin film on the polymer thin film to form a conductive thin film, and then perform plasma etching on the conductive thin film to obtain a flexible conductive substrate; In Step 3, after the top electrode is fixed on the PVA / KOH / TiO 2 composite film, peel the rigid substrate from the flexible conductive substrate.

[0014] Furthermore, in Step 2, the spin-coating speed during spin-coating is 600 rpm, and the spin-coating time is 60 s Furthermore, in Step 2, the temperature during heat annealing is 85 °C, and the time is 30 min.

[0015] The present invention provides a multimodal self-powered wearable plant sensor based on a PVA / KOH / TiO 2 composite film and a preparation method thereof. Compared with existing sensors, it not only realizes the perception of multi-parameter information, but also can realize the collection of multiple energies and the supply of its own electric energy, which can effectively reduce the complexity of the sensor circuit, reduce power consumption and improve the utilization efficiency of resources.

[0016] The preparation method of the sensor of the present invention is simple, the raw materials used have low cost and are easy to obtain, and the whole preparation process does not require complex and expensive equipment and harsh experimental conditions, and is easy to be popularized and applied on a large scale.

[0017] In the sensor of the present invention, on the one hand, when the PVA / KOH / TiO 2 composite film contacts with the moisture in the environment, due to the hydrovoltaic effect, hydrogen ions will be ionized. The contact area between the upper surface of the functional layer and the moisture in the environment is large, resulting in a relatively high concentration of ionized hydrogen ions, causing an ion concentration difference inside the film and the directional movement of ions, resulting in a potential difference between the upper and lower electrodes, thereby generating an electrical signal and realizing the monitoring of moisture information in the environment; on the other hand, the PVA / KOH / TiO 2 composite film is a good dielectric triboelectric layer. When it contacts with other materials (test objects) as the friction layer, due to the different electron capture capabilities between the two, during the periodic contact and separation process, the surface of the dielectric material is charged with equal amounts of opposite triboelectric charges, and the back electrode generates opposite induced charges by electrostatic induction. Connecting the electrode to the external circuit load, the external circuit will form a periodically alternating electrical signal under the electrostatic potential difference of the triboelectric charges, thereby realizing the perception of vibration information in the environment.

[0018] In the present invention, by adjusting the doping ratio of TiO 2 in the PVA / KOH / TiO 2 composite film, the microscopic morphology of the polymer film can be regulated, and the overall performance of the device can be further optimized.

[0019] The sensor of the present invention realizes the perception of moisture and vibration information on a single device, and can convert the two into electrical energy, which can improve the energy utilization rate and reduce the device power consumption, and has broad application prospects in the fields of energy harvesting and self-powered sensing. Description of the Drawings

[0020] Figure 1 is a schematic structural diagram of the sensor in the embodiment of the present invention.

[0021] Figure 2 is a physical diagram of the sensor in the embodiment of the present invention.

[0022] Figure 3 is a SEM scanning electron micrograph of the PVA / KOH composite film in the embodiment of the present invention.

[0023] Figure 4 is a SEM image of the composite film after adding TiO 2 nanoparticles to the PVA / KOH film in the embodiment of the present invention.

[0024] Figure 5It is the humidity response curve and cyclic stability curve of the sensor in the embodiment of the present invention.

[0025] Figure 6 It is a physical diagram of the sensor for real-time monitoring of the humidity and vibration information of the plant microenvironment in the embodiment of the present invention. Specific embodiments

[0026] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0027] As Figure 1 、 Figure 2 shown, this embodiment discloses a multi-modal self-powered wearable plant sensor, including a flexible conductive substrate, a sensitive layer film, and a top electrode, wherein: The flexible conductive substrate is composed of a polymer film and a conductive film 2 prepared on the polymer film 1. The material of the polymer film 1 is any one of PET, PI, PDMS, and TPU, and the material of the conductive film 2 is any one of ITO, graphene, and carbon nanotubes.

[0028] The sensitive layer film 3 is a PVA / KOH / TiO 2 composite film. This PVA / KOH / TiO 2 composite film is obtained by spin-coating a PVA, KOH, TiO 2 blended solution on the conductive film 2 of the flexible conductive substrate. The sensitive layer film 3 is prepared on the conductive film of the flexible conductive substrate.

[0029] The top electrode 4 uses a zinc electrode. A zinc foil is cut into thin slices of a certain size to form the zinc electrode as the top electrode 4. The top electrode 4 is fixedly adhered to the PVA / KOH / TiO 2 composite film with a PI tape.

[0030] As Figure 2 shown, the sensor in this embodiment exhibits good mechanical flexibility.

[0031] In this embodiment, the top electrode 4 and the conductive film 2 in the flexible conductive substrate form positive and negative electrodes. After the sensitive layer film 3 absorbs water, a potential difference is formed between the positive and negative electrodes to generate an electrical signal.

[0032] In this embodiment, a triboelectric nanogenerator with a single - electrode structure is composed of a flexible conductive substrate and a sensitive - layer thin film 3. When used as a triboelectric nanogenerator, the top electrode 4 does not participate in the working process. An electrical signal is generated through the charge transfer and accumulation during the contact - separation process between the sensitive - layer thin film 3 and the object to be tested, realizing the perception of vibration information. The working principle of the nanogenerator is to induce charges through the contact - separation process between the external environment and the functional layer (for example, when our finger contacts and separates from the functional layer), generating electrical energy and realizing the collection of external mechanical energy. In this structure, as long as the contact - separation with the functional layer can be achieved, electrical energy can be generated, and vibration, as a form of mechanical energy, can be realized, so the perception of vibration information can be achieved.

[0033] This embodiment also discloses a preparation method of the above - mentioned multimodal self - powered wearable plant sensor, including the following steps: Step 1: Use a rigid substrate, prepare a flexible conductive substrate on the rigid substrate, and select whether to perform plasma etching treatment on the conductive thin film on the flexible conductive substrate according to the material and surface characteristics of the conductive thin film. When the surface energy of the conductive thin film is too low to spin - coat the sensitive layer, select to perform plasma etching treatment on its surface. The specific process is as follows: In this embodiment, the polymer - film material is PDMS, and the conductive - film material is Ag NW.

[0034] Use glass or silicon wafer as the rigid substrate, and the size of the rigid substrate is 2.5 cm×2.5 cm.

[0035] Clean the rigid substrate: Ultrasonically clean the rigid substrate in acetone, isopropyl alcohol, and deionized water for 5 - 10 minutes respectively, and then dry it with nitrogen for standby. Perform surface treatment on the cleaned rigid substrate. The surface - treatment process is as follows: First, perform plasma treatment for 5 - 10 minutes, and then treat it with octadecyltrichlorosilane (OTS) for about 20 minutes. The process of using OTS is as follows: Mix OTS and toluene in a certain volume ratio in a clean petri dish, put the substrate to be treated in it, heat and fumigate for about 20 minutes, take out the treated sample, rinse it with toluene and isopropyl alcohol respectively, and dry it with nitrogen for standby. Cleaning and surface - treating the rigid substrate is to facilitate the later peeling of the rigid substrate and reduce deformation damage.

[0036] Blend the PDMS stock solution and the cross - linker evenly at a mass ratio of 10:1, evacuate to remove air bubbles, and then let it stand for standby. On the rigid substrate that has been cleaned and surface - treated, coat the PDMS solution by spin - coating or blade - coating process, and anneal it at 60 °C in vacuum for 12 hours to obtain the PDMS thin film as the polymer film.

[0037] Using a stock solution of silver nanowires (i.e., Ag NW) at 5 mg / ml, the Ag NW stock solution was diluted and mixed with isopropanol to obtain a spraying solution. The mixing volume ratio of the Ag NW stock solution to isopropanol was 1:20. Then, the distance between the spray gun thimble and the nozzle was adjusted, and the rigid substrate coated with the polymer film was placed on an 80 °C heating table for preheating. The spraying solution was sprayed on the surface of the polymer film. After spraying, annealing treatment was carried out to improve the conductivity. The annealing temperature was 115 °C and the annealing time was 5 min, thereby obtaining an Ag NW film as the conductive film.

[0038] In this embodiment, the conductive film is an Ag NW film, and the sensitive layer solution can be well coated on its surface, so no plasma etching treatment is required.

[0039] Step 2: Prepare a PVA, KOH, TiO 2 blended solution to prepare a PVA / KOH / TiO 2 composite film as the sensitive layer film, and the process is as follows: Weigh 300 mg of polyvinyl alcohol (PVA) powder, add 5.5 ml of deionized water, and heat and stir at 85 °C for 3 h until the solute is completely dissolved to obtain a PVA solution, and let it stand and cool.

[0040] Weigh 1200 mg of potassium hydroxide (KOH) powder, add 4 ml of deionized water to obtain a KOH solution with a concentration of 300 mg / ml.

[0041] Take 0.5 ml of the KOH solution and add it dropwise to the cooled 5.5 ml of the PVA solution, and stir evenly to obtain a PVA / KOH mixed solution with a blended solute mass ratio of 2:1. At this time, the concentration of PVA in the mixed solution is 50 mg / ml, and the concentration of KOH is 25 mg / ml.

[0042] Weigh 3.6 mg of TiO 2 nanoparticles, add them to 6 ml of the uniformly mixed PVA / KOH mixed solution, and then magnetically stir for 6 hours to obtain a PVA, KOH, TiO 2 blended solution. At this time, the concentration of TiO 2 in the mixed solution is 0.6 mg / ml.

[0043] Figure 3 This is the scanning electron microscope image of the PVA / KOH composite film in this embodiment. There are relatively sparse holes on the film surface, and the pore diameter is relatively large.

[0044] Take 0.5 ml of the PVA / KOH blend solution and spin-coat it on the conductive film of the pretreated flexible conductive substrate. The spin-coating speed during spin-coating is 600 rpm, and the spin-coating time is 60 s. Then, place the spin-coated film on a high-temperature heating table at 85 °C and anneal it for 30 min to obtain a PVA / KOH composite film.

[0045] Take 0.5 ml of PVA, KOH, and TiO 2 The blend solution is spin-coated on the conductive film of the pretreated flexible conductive substrate. The spin-coating speed during spin-coating is 600 rpm, and the spin-coating time is 60 s. Then, place the spin-coated film on a high-temperature heating table at 85 °C and anneal it for 30 min to obtain a PVA / KOH / TiO 2 Composite film.

[0046] Figure 4 For the PVA / KOH film in this example, after adding TiO 2 nanoparticles, the SEM image of the composite film PVA / KOH / TiO 2 is shown. It can be seen from the figure that after adding titanium dioxide nanoparticles, the pores in the film increase and become finer, which is more conducive to the absorption and dissociation of moisture. In addition, more pore structures are beneficial to increasing the surface roughness and thus increasing the contact area, which helps to improve the vibration sensing performance of the device as a TENG.

[0047] Figure 5 For the device corresponding to the PVA / KOH / TiO 2 film prepared in this example, the humidity response curve and the cyclic stability curve are shown. The results show that the device has good sensor performance (output voltage ~900 mV, response time is 21 s, and recovery time is 18 s) and cyclic stability. The waveforms of the five response / recovery curves are similar, and no obvious fluctuations occur.

[0048] Step 3: Use a polyimide (PI) high-temperature tape to fix a zinc electrode with a size of 0.2×1 cm on the PVA / KOH / TiO 2 film to obtain a top electrode.

[0049] Lead out copper wires from the conductive film and the top electrode, and peel off the rigid substrate from the flexible conductive substrate to obtain a multimodal self-powered wearable plant sensor based on the PVA / KOH / TiO 2 composite film.

[0050] The sensor in this example can realize the real-time monitoring of the humidity and vibration information of the plant microenvironment. As Figure 6 shown, after completing the construction of the plant micro-sensing system, the prepared PVA / KOH / TiO 2The biocompatible tape for the composite film multimodal self-powered wearable sensor is fixed on the back of the plant leaf, connected to the embedded system through a copper wire, and the mobile phone terminal is turned on. The Bluetooth module is connected to start receiving data for monitoring the humidity and vibration information in the plant microenvironment.

[0051] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. The embodiments described in the present invention are only descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. Among the various specific technical features described in the above specific embodiments, they can be combined in any suitable manner without contradiction. As long as such a combination does not violate the idea of the present invention, it should also be regarded as the content disclosed in the present disclosure. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0052] The present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention and without departing from the design idea of the present invention, various modifications and improvements made by those skilled in the art to the technical solution of the present invention should fall within the protection scope of the present invention. The technical content claimed by the present invention has been fully recorded in the claims.

Claims

1. Multimodal self-powered wearable plant sensor, characterized in that, It comprises a flexible conductive substrate, a sensitive layer film, and a top electrode; the flexible conductive substrate is composed of a polymer film and a conductive film prepared on the polymer film; the sensitive layer film is a PVA / KOH / TiO2 composite film, and the sensitive layer film is prepared on the conductive film of the flexible conductive substrate; the top electrode is prepared on the sensitive layer film; The top electrode and the conductive film in the flexible conductive substrate form positive and negative electrodes, and after the sensitive layer film absorbs water, a potential difference is formed between the positive and negative electrodes to generate an electrical signal; A friction nanogenerator with a single electrode structure is composed of a flexible conductive substrate and a sensitive layer film. When used as a friction nanogenerator, the top electrode does not participate in the working process. An electrical signal is generated through the charge transfer and accumulation during the contact and separation process between the sensitive layer film and the tested object, thereby realizing the perception of vibration information.

2. The multimodal self-powered wearable plant sensor according to claim 1, characterized in that: The material of the polymer film is any one of PET, PI, PDMS and TPU.

3. The multimodal self-powered wearable plant sensor according to claim 1, characterized in that: The material of the conductive film is any one of ITO, graphene and carbon nanotubes.

4. The multimodal self-powered wearable plant sensor according to claim 1, characterized in that: The PVA / KOH / TiO2 composite film is obtained by spin coating a mixed solution of PVA, KOH and TiO2 on a conductive film of a flexible conductive substrate.

5. The multimodal self-powered wearable plant sensor according to claim 1, characterized in that: The top electrode is a zinc electrode.

6. A method for preparing a multimodal self-powered wearable plant sensor according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1, preparing a flexible conductive substrate, and selecting whether to perform plasma etching on the conductive film on the flexible conductive substrate according to the material and surface characteristics of the conductive film. When the surface energy of the conductive film is low and the sensitive layer cannot be spin-coated, plasma etching is selected on the surface of the conductive film; Step 2, prepare 50 mg / ml PVA solution and 300 mg / ml KOH solution, both of which are deionized water solvents, and mix the PVA solution and KOH solution according to the solute mass ratio of 2:1 to obtain a mixed solution, wherein the KOH solution is added dropwise to the cooled PVA solution, and the PVA solution is stirred while dropping to make the KOH and PVA solutions evenly mixed; then TiO2 is added to the mixed solution and stirred to obtain a PVA, KOH, TiO2 blended solution, wherein the concentration of TiO2 is 0.6 mg / ml; finally, the blended solution is spin-coated on a conductive film of a flexible conductive substrate, and then heated and annealed to obtain a PVA / KOH / TiO2 composite film; Step 3: Fix the top electrode on the PVA / KOH / TiO2 composite film with PI tape.

7. The method for preparing the multimodal self-powered wearable plant sensor according to claim 6, characterized in that: In step 1, a rigid substrate is used, and the material constituting the polymer film is configured into a solution and then coated on the rigid substrate to form a polymer film, and then the material constituting the conductive film is prepared on the polymer film to form a conductive film, and then the conductive film is plasma etched to obtain a flexible conductive substrate; in step 3, after the top electrode is fixed on the PVA / KOH / TiO2 composite film, the rigid substrate is peeled off from the flexible conductive substrate.

8. The method for preparing the multimodal self-powered wearable plant sensor according to claim 6, characterized in that: In step 2, the spin coating speed is 600 rpm and the spin coating time is 60 s.

9. The method for preparing the multimodal self-powered wearable plant sensor according to claim 6, characterized in that: In step 2, the temperature during heating annealing is 85 °C and the time is 30 min.

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