A multimodal self-powered wearable plant sensor and a method of making the same

Abstract

The application discloses a kind of multi-modal self-powered wearable plant sensors and preparation method thereof, sensor includes sequentially laminated flexible conductive substrate, sensitive layer film, top electrode, flexible conductive substrate is composed of polymer film and conductive film;Sensitive layer film is PVA / KOH / TiO2 Composite Film;In preparation method, first, flexible conductive substrate is prepared, then PVA, KOH, TiO2 Blending solution is configured and is spin-coated on flexible conductive substrate to obtain PVA / KOH / TiO2 Composite Film, then top electrode is fixed on PVA / KOH / TiO2 Composite Film to obtain complete sensor.The sensor of the application realizes the perception of moisture and vibration information on a single device, and can convert the two into electrical energy, which can improve the utilization rate of energy and reduce the power consumption of the device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of plant sensors, in particular to a multi-modal self-powered wearable plant sensor and a preparation method thereof. BACKGROUND

[0002] The rapid development of intelligent robots, wearable devices and the like puts forward higher requirements for the performance of flexible sensors. The research of sensors gradually develops from single-parameter sensing to multi-modal integrated sensing. Integrating multiple single-function sensing units into a sensing system is an effective means to realize multi-modal sensing, but it is limited by system size and complex process. However, integrated flexible multi-modal sensors have the advantages of compact structure, simple process, and monitoring of multiple parameters at the same point, and have become a research hotspot at home and abroad in recent years. It is worth noting that current sensors mainly rely on external battery power supply, which has the problems of limited installation location, not widely used (especially in remote areas), and high system complexity and cost.

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

[0004] In the field of agriculture, global warming, increasing extreme weather and frequent droughts pose a great threat to crop growth. At present, China's agricultural production mode is changing 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 current sensors are designed for static data and have a large disturbance to plant growth. Remote and non-contact sensing technologies have the problems of low spatial and temporal resolution, discontinuous measurement, poor sensitivity and stability, and are difficult to accurately and continuously monitor plant growth, microenvironment and organ development. Although wearable plant sensors solve the compatibility problem with plant surfaces, the sensing method is single and the data support is not comprehensive, which cannot meet the demand of simultaneous detection of multiple environmental factors.

[0005] It is worth noting that the multi-modal self-powered wearable sensor can monitor various physiological indicators and environmental parameters of plants such as light, temperature, humidity, soil moisture, carbon dioxide concentration, etc. while solving the energy supply, reducing errors through data cross-validation, deeply studying the physiological process of plants, realizing comprehensive monitoring and precise management of crop growth, improving yield and quality, reducing resource waste, and better meeting the development needs of smart agriculture. SUMMARY

[0006] The application provides a multi-modal self-powered wearable plant sensor and a preparation method thereof to overcome the deficiencies of the prior art wearable plant sensor.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0008] The multi-modal self-powered wearable plant sensor comprises a flexible conductive substrate, a sensitive layer film and a top electrode.

[0009] The top electrode and the conductive film in the flexible conductive substrate form positive and negative electrodes, and the sensitive layer film forms a potential difference between the positive and negative electrodes to generate an electrical signal after absorbing water.

[0010] The flexible conductive substrate and the sensitive layer film form a single-electrode structure of a friction nanogenerator, and the top electrode does not participate in the working process when the friction nanogenerator works.

[0011] Further, the material of the polymer film is any one of PET, PI, PDMS and TPU.

[0012] Further, the material of the conductive film is any one of ITO, graphene and carbon nanotube.

[0013] Further, the PVA / KOH / TiO2 composite film is obtained by spin coating a PVA / KOH / TiO2 blend solution on the conductive film of the flexible conductive substrate.

[0014] Further, the top electrode is a zinc electrode.

[0015] A preparation method of the multi-modal self-powered wearable plant sensor is provided, comprising the following steps:

[0016] Step 1, a flexible conductive substrate is prepared, and whether to perform a plasma etching treatment on the conductive film on the flexible conductive substrate is selected 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, the surface of the conductive film is selected to be etched by plasma;

[0017] Step 2, a PVA solution of 50 mg / ml and a KOH solution of 300 mg / ml are configured, both solvents are deionized water, the PVA solution and the KOH solution are mixed according to the solute mass ratio 2:1 to obtain a mixed solution, wherein the KOH solution is added dropwise into the cooled PVA solution, and the PVA solution is stirred at the same time to mix the KOH and the PVA solution uniformly; then TiO2 is added to the mixed solution for stirring to obtain a PVA, KOH and TiO2 blended solution, wherein the concentration of TiO2 is 0.6 mg / ml; finally, the blended solution is spin-coated on the conductive film of the flexible conductive substrate, and then annealing treatment is performed to obtain a PVA / KOH / TiO2 composite film;

[0018] Step 3, the top electrode is fixed on the PVA / KOH / TiO2 composite film by using a PI tape.

[0019] Further, in step 1, a rigid substrate is used, the material constituting the polymer film is configured into a solution and coated on the rigid substrate to form a polymer film, then the material constituting the conductive film is prepared on the polymer film to form a conductive film, and then the conductive film is subjected to a plasma etching treatment, thereby obtaining 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.

[0020] Further, in step 2, the spin-coating speed is 600 rpm and the spin-coating time is 60 s

[0021] Further, in step 2, the temperature of the annealing is 85 °C and the time is 30 min.

[0022] The present application provides a kind of based on PVA / KOH / TiO2 Composite Film Multi-mode self-powered wearable plant sensor and preparation method thereof, compared with existing sensor, not only realize the perception of multi-parameter information, but also can realize the collection of multiple energy and realize the supply of self electric energy, can effectively reduce the complexity of sensor circuit, reduce power consumption and improve the utilization efficiency of resources.

[0023] The sensor preparation method of the present application is simple, the cost of raw materials used is low and easy to obtain, and the entire preparation process does not require complex and expensive equipment and harsh experimental conditions, and is easy to be widely applied.

[0024] In the sensor, on one hand, when the PVA / KOH / TiO2 composite film contacts with moisture in the environment, hydrogen ions are ionized due to the water effect, the upper surface of the functional layer contacts with a large area of moisture in the environment, the concentration of the ionized hydrogen ions is high, the ion concentration difference occurs in the film, the directional movement of the ions occurs, the potential difference between the upper and lower electrodes occurs, and thus the electric signal is generated, the moisture information in the environment is monitored; on the other hand, the PVA / KOH / TiO2 composite film is a good dielectric triboelectric layer, when the film contacts with other materials (the tested object) as a friction layer, due to the different electron capture capacities between the two, the dielectric material surface has equal and opposite triboelectric charges in the periodic contact and separation process, the back electrode generates the opposite induced charges by electrostatic induction, the electrode is connected with an external circuit load, and the external circuit forms a periodic alternating electric signal under the electrostatic potential difference of the triboelectric charges, and thus the vibration information in the environment is perceived.

[0025] In the application, by adjusting the doping ratio of TiO2 in the PVA / KOH / TiO2 composite film, the micro morphology of the polymer film can be regulated, and the overall performance of the device is further optimized.

[0026] The sensor realizes the perception of moisture and vibration information on a single device, and can convert the two into electric energy, so that the energy utilization rate is improved and the device power consumption is reduced, and the sensor has a wide application prospect in the fields of energy collection and self-powered sensing. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a structural schematic diagram of the sensor of the embodiment of the application.

[0028] Figure 2 is a physical diagram of the sensor of the embodiment of the application.

[0029] Figure 3 is an SEM scanning electron microscope diagram of the PVA / KOH composite film of the embodiment of the application.

[0030] Figure 4 is an SEM diagram of the composite film after TiO2 nanoparticles are added in the PVA / KOH film of the embodiment of the application.

[0031] Figure 5 is a humidity response curve and a cycle stability curve of the sensor of the embodiment of the application.

[0032] Figure 6 is a real-time monitoring physical diagram of the sensor for plant microenvironment humidity and vibration information in the embodiment of the application. DETAILED DESCRIPTION

[0033] The application is further described below in combination with the drawings and embodiments.

[0034] As Figure 1 , Figure 2 shown, the embodiment discloses a multi-modal self-powered wearable plant sensor, comprising a flexible conductive substrate, a sensitive layer film, a top electrode, wherein:

[0035] 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, TPU, and the material of the conductive film 2 is any one of ITO, graphene, carbon nanotube.

[0036] The sensitive layer film 3 is a PVA / KOH / TiO2 composite film, which is obtained by spin coating a PVA / KOH / TiO2 blend 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.

[0037] The top electrode 4 adopts zinc electrode, and the zinc foil is cut into a certain size of sheet to form the zinc electrode as the top electrode 4, and the top electrode 4 is fixed on the PVA / KOH / TiO2 composite film by PI tape.

[0038] As Figure 2 shown, the sensor of the embodiment shows good mechanical flexibility.

[0039] In the embodiment, the top electrode 4 and the conductive film 2 in the flexible conductive substrate constitute positive and negative electrodes, and the sensitive layer film 3 forms a potential difference between the positive and negative electrodes to generate an electrical signal after absorbing water.

[0040] And in the embodiment, the flexible conductive substrate and the sensitive layer film 3 constitute a single-electrode structure of a friction nanogenerator, and the top electrode 4 does not participate in the working process when it is used as a friction nanogenerator. Through the charge transfer and accumulation in the contact and separation process of the sensitive layer film 3 and the test object, an electrical signal is generated to realize the perception of vibration information. The working principle of the nanogenerator is to induce charges through the contact and separation process of the external environment and the functional layer (for example, when our fingers and the functional layer are in contact and separation), generate electrical energy, and realize the collection of external mechanical energy. In this structure, as long as the contact and separation with the functional layer can generate electrical energy, the vibration mechanical energy can be realized, so the perception of vibration information can be realized.

[0041] The embodiment also discloses a preparation method of the above-mentioned multi-modal self-powered wearable plant sensor, comprising the following steps:

[0042] Step 1, using a rigid substrate, preparing a flexible conductive substrate on the rigid substrate, and selecting 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 low and cannot be spin-coated with a sensitive layer, the surface of the conductive thin film is subjected to plasma etching treatment. The specific process is as follows:

[0043] In this embodiment, the polymer thin film material is PDMS, and the conductive thin film material is Ag NW.

[0044] Glass or silicon wafer is used as the rigid substrate, and the size of the rigid substrate is 2.5 cm x 2.5 cm.

[0045] The rigid substrate is cleaned: the rigid substrate is ultrasonically cleaned in acetone, isopropanol and deionized water for 5-10 min, and then dried with nitrogen for standby. The cleaned rigid substrate is subjected to surface treatment, and the surface treatment process is: first, plasma treatment for 5-10 min, and then octadecyl octyltrichlorosilane (OTS) treatment for about 20 min. The OTS treatment process is: mix OTS and toluene in a clean petri dish according to a certain volume ratio, then put it into the substrate to be treated, heat and fumigate for about 20 min, take out the treated sample, rinse with toluene and isopropanol, and dry with nitrogen for standby. The rigid substrate is cleaned and surface treated to facilitate the later peeling of the rigid substrate and reduce the deformation damage.

[0046] The PDMS stock solution is mixed with the crosslinking agent at a mass ratio of 10:1, stirred uniformly, vacuumed to remove bubbles, and then placed for standby. On the cleaned and surface-treated rigid substrate, the PDMS solution is coated by spin coating or blade coating process, and after vacuum annealing at 60°C for 12 hours, the PDMS film as a polymer thin film is obtained.

[0047] A 5 mg / ml silver nanowire (Ag NW) stock solution is prepared by diluting the Ag NW stock solution with isopropanol. The mixture volume ratio of the Ag NW stock solution to isopropanol is 1:20. Then adjust the distance between the needle and the nozzle of the spray gun, place the rigid substrate coated with the polymer thin film on the 80°C heating table for preheating, spray the spray solution on the surface of the polymer thin film, and perform annealing treatment after spraying to improve the conductivity. The annealing temperature is 115°C, and the annealing time is 5 min. Thus, the Ag NW film as a conductive thin film is obtained.

[0048] In this embodiment, the conductive thin film is Ag NW film, and the sensitive layer solution can be well coated on its surface, so no plasma etching treatment is needed.

[0049] Step 2, configure PVA, KOH, TiO2 blend solution, prepare PVA / KOH / TiO2 composite film as sensitive layer film, the process is as follows:

[0050] Take 300 mg of polyvinyl alcohol (PVA) powder, add 5.5 ml of deionized water, heat and stir at 85 °C for 3 h until the solute is completely dissolved to obtain a PVA solution, and cool it down.

[0051] Take 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.

[0052] Take 0.5 ml of KOH solution and add it dropwise to the cooled 5.5 ml PVA solution, stir until uniform, to obtain a PVA / KOH mixed solution with a blend solute mass ratio of 2:1, at this time the PVA concentration in the mixed solution is 50 mg / ml and the KOH concentration is 25 mg / ml.

[0053] Take 3.6 mg of TiO2 nanoparticles and add it to 6 ml of the mixed and uniform PVA / KOH mixed solution, then magnetically stir for 6 hours to obtain a PVA, KOH, TiO2 blend solution, at this time the concentration of TiO2 in the mixed solution is 0.6 mg / ml.

[0054] Figure 3 This is a scanning electron microscope image of the PVA / KOH composite film of the present embodiment, the film surface has relatively sparse holes and the hole diameter is relatively large.

[0055] Take 0.5 ml of PVA / KOH blend solution and spin coat it on the conductive film of the pre-processed flexible conductive substrate, the spin coating speed is 600 rpm and the spin coating time is 60 s, then place the spin-coated film on a high-temperature heating platform at 85 °C for annealing for 30 min to obtain a PVA / KOH composite film.

[0056] Take 0.5 ml of PVA, KOH, TiO2 blend solution and spin coat it on the conductive film of the pre-processed flexible conductive substrate, the spin coating speed is 600 rpm and the spin coating time is 60 s, then place the spin-coated film on a high-temperature heating platform at 85 °C for annealing for 30 min to obtain a PVA / KOH / TiO2 composite film.

[0057] Figure 4The SEM image of the PVA / KOH / TiO2 composite film after adding TiO2 nanoparticles in the PVA / KOH film of the present embodiment is shown in the figure. It can be seen that the addition of titanium dioxide nanoparticles increases the holes in the film and makes them more fine and dense, which is more conducive to the absorption and dissociation of water. In addition, more hole structures are conducive 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.

[0058] Figure 5 The humidity response curve and cycle stability curve of the device prepared by the PVA / KOH / TiO2 film of the present embodiment are shown in the figure. The results show that the device has good sensor performance (output voltage ~ 900 mV, response time 21 s, recovery time 18 s) and cycle stability. The response / recovery curve waveforms of five times are similar, and no obvious fluctuations occur.

[0059] Step 3, use polyimide (PI) high-temperature tape to fix the zinc electrode with a size of 0.2*1 cm on the PVA / KOH / TiO2 film to obtain a top electrode.

[0060] Copper wires are drawn from the conductive film and the top electrode, and the rigid substrate is peeled off from the flexible conductive substrate to obtain a multi-modal self-powered wearable plant sensor based on the PVA / KOH / TiO2 composite film.

[0061] The sensor of the present embodiment can realize real-time monitoring of the humidity and vibration information of the plant microenvironment, as shown in Figure 6 After the plant micro-sensing system is built, the prepared PVA / KOH / TiO2 composite film multi-modal self-powered wearable sensor is fixed on the back of the plant leaf with biocompatible tape, connected to the embedded system through copper wires, and the mobile terminal is opened to connect the Bluetooth module to start receiving data for monitoring the humidity and vibration information in the plant microenvironment.

[0062] The preferred embodiments of the present application are described in detail above with reference to the accompanying drawings. The embodiments described in the present application are only a description of the preferred embodiments of the present application, and do not limit the concept and scope of the present application. In the above specific embodiments, each specific technical feature described above can be combined in any appropriate manner without contradiction. Such a combination, as long as it does not deviate from the spirit of the present application, should also be considered as disclosed by the present disclosure. In order to avoid unnecessary repetition, the present application does not further describe various possible combinations.

[0063] The present application is not limited to the specific details of the above-described embodiments, and various modifications and improvements to the technical solutions of the present application made by those skilled in the art within the technical concept of the present application and without departing from the design idea of the present application shall fall within the protection scope of the present application, and the technical content of the present application claimed for protection has been entirely recorded in the claims.

Claims

1. A multimodal self-powered wearable plant sensor, characterized in that, The device 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 / TiO2 composite film, prepared on the conductive film of the flexible conductive substrate. The top electrode is prepared on the sensitive layer film. The positive and negative electrodes are formed by the top electrode and the conductive film in the flexible conductive substrate. After the sensitive layer film absorbs water, a potential difference is formed between the positive and negative electrodes to generate an electrical signal. The triboelectric nanogenerator, consisting of a flexible conductive substrate and a sensitive thin film, is a single-electrode structure. When used as a triboelectric nanogenerator, the top electrode does not participate in the working process. The electrical signal is generated through charge transfer and accumulation during the contact separation process between the sensitive thin film and the test object, thereby realizing the sensing of vibration information.

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

3. The multimodal self-powered wearable plant sensor according to claim 1, characterized in that, The conductive film is made of any one of ITO, graphene, or 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 PVA, KOH, and TiO2 blend solution onto a conductive film on 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 fabricating a multimodal self-powered wearable plant sensor as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Prepare a flexible conductive substrate, and select 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 too low to spin-coat the sensitive layer, plasma etching is selected to be performed on its surface. Step 2: Prepare a 50 mg / ml PVA solution and a 300 mg / ml KOH solution, both using deionized water as the solvent. Mix the PVA solution and KOH solution at a solute mass ratio of 2:1 to obtain a mixed solution. The KOH solution is added dropwise to the cooled PVA solution while stirring to ensure uniform mixing. Next, add TiO2 to the mixed solution and stir to obtain a PVA, KOH, and TiO2 blended solution with a TiO2 concentration of 0.6 mg / ml. Finally, spin-coat the blended solution onto a conductive film on a flexible conductive substrate and then perform a heat annealing treatment to obtain a PVA / KOH / TiO2 composite film. Step 3: Fix the top electrode onto the PVA / KOH / TiO2 composite film using PI tape.

7. The method for fabricating a multimodal self-powered wearable plant sensor according to claim 6, characterized in that, In step 1, a rigid substrate is used. The materials constituting the polymer film are prepared into a solution and coated onto the rigid substrate to form a polymer film. Then, the materials constituting the conductive film are prepared on the polymer film to form a conductive film. The conductive film is then subjected to plasma etching 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 fabricating a 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 fabricating a multimodal self-powered wearable plant sensor according to claim 6, characterized in that, In step 2, the temperature for heating and annealing is 85 °C and the time is 30 min.

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