Preparation method of liquid metal electronic tattoo sensor for detecting plant humidity

Abstract

The invention relates to a preparation method of a liquid metal electronic tattooing sensor for detecting plant humidity, which comprises the following steps of: mixing liquid metal and a high polymer material PVA (Polyvinyl Alcohol) to form composite ink, printing the composite ink on a plant leaf to manufacture a required sensor circuit, and packaging a substrate of the sensor circuit by adopting a PVA-based packaging film. By adding a specific amount of PVA and liquid metal to form the composite ink, the problem of adhesiveness when the composite ink is directly printed on the surface of the blade is effectively solved, the composite ink is effectively attached to the surface of the blade, and the prepared sensor is quick in response to an electric signal of humidity change of the blade, high in sensitivity and good in stability. And the humidity of the leaves can be monitored in real time.

Description

Technical Field

[0001] The present invention relates to the technical fields of plant sensing detection, and in particular to a method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity. Background Art

[0002] Humidity is one of the important environmental factors that affect plant growth. Different plants have different requirements for humidity. Real-time understanding of plant humidity helps to better plant and maintain plants. Monitoring plant electrical signals through sensors can provide the moisture status of plants and the transpiration of plants. At present, plant humidity sensors use the principle that there is a gradient between the humidity of plant leaves and the humidity in the surrounding air, and moisture will evaporate from the surface of plant leaves into the air. The higher the humidity on the leaf surface, the faster the evaporation rate. Leaf humidity sensors usually consist of two key parts: humidity sensitive elements and measurement circuits. The humidity sensitive element is the core component of the sensor, which is usually made of a material with good hygroscopic properties, such as polymers or fiber materials. This material can absorb moisture on the surface of plant leaves and respond to changes in humidity. The measurement circuit is used to measure the resistance or capacitance changes of the humidity sensitive element, which is related to the humidity of the leaf surface. The sensor can use resistance measurement methods or capacitance measurement methods to detect changes in humidity sensitive elements. Highly adhesive, breathable and flexible electronic tattoos can be maintained on the surface of plants for a long time and stably, and can non-invasively and continuously monitor plant signals, playing an important role in humidity monitoring and plant etiology. Since liquid metal has high conductivity, good fluidity and low toxicity, it is expected to realize highly foldable and stable flexible circuits and realize circuit recycling. Traditional liquid metal electronic circuit manufacturing generally uses the template method to print liquid metal circuits. To achieve continuous and reliable printing of liquid metal, it is necessary to prepare a template. The printed pattern is cut or hollowed out to form a template by laser, chemical etching or motor etching. This method first requires the design of a pattern to make a photomask template, and then a photoresist is coated on the silicon wafer. The laser shines through the photomask to form a pattern on the photoresist. The cycle is long, the cost is high, and the number of uses of the manufactured template is limited. At present, there are few reports on the manufacture of ultra-micro liquid metal flexible electronic devices by 3D printers, and even fewer reports on their use for plant electrical signal monitoring. A few studies have reported the application of liquid metal on plant epidermis, but most of these works focus on simple contact measurement, and have not yet achieved real-time, non-invasive monitoring of complex physiological parameters of plants. The application of flexible liquid metal materials to plant electronic tattoos to achieve in-situ, non-destructive and long-term physiological monitoring is currently in the initial exploration stage, and its technical bottlenecks include integration issues such as adhesion, durability, sensitivity, and multi-function. Summary of the invention

[0003] Based on the above technical problems, the purpose of the present invention is to provide a method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity. By combining the flexibility of liquid metal and plant compatibility, a new type of sensor that can be directly attached to plants is designed to achieve continuous and dynamic monitoring of the in-situ physiological state of plants.

[0004] The purpose of the present invention is achieved through the following technical solutions: A method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity, characterized in that it comprises the following steps: S1, a composite ink formed by mixing liquid metal with polymer material PVA; S2. Print the composite ink onto plant leaves according to the designed circuit diagram to produce the required sensor circuit; S3. Use a PVA-based packaging film to encapsulate the substrate of the sensor circuit.

[0005] Furthermore, the liquid metal is a gallium-indium-tin alloy, and Ga and In metals are evenly mixed in a mass ratio of 7:3 to 7.5:2.5 to form a gallium-indium alloy liquid metal.

[0006] Furthermore, the composite ink is prepared by mixing liquid metal and polymer material in a mass ratio of 1:0.8-1 and then ultrasonically treating the mixture; the polymer material is polyvinyl alcohol (PVA), which is used as an emulsifying stabilizer for the liquid metal.

[0007] During the preparation of the composite ink, it was found that when the composite ink was printed on the blade surface, it had poor uniformity, was easily aggregated into droplets, and was difficult to adhere to the blade surface. In addition, the circuit conductivity was poorly uniform, the sensor test signal response sensitivity was poor, and the test results were inaccurate.

[0008] In the present invention, liquid metal and polymer material PVA are compounded in a specific ratio to form a composite ink, which effectively improves the adhesion performance of the ink on the blade surface. At the same time, PVA acts as an emulsifier for the liquid metal, which improves the dispersion uniformity of the liquid metal in the composite ink and improves the response sensitivity of the sensor.

[0009] Furthermore, the encapsulation is to mix glycerol, PVA and water in a mass ratio of 1:4 to 6:60 to form a mixed liquid, thinly apply the mixed liquid on the surface of the liquid metal circuit, and prepare a PVA-based film by curing at room temperature.

[0010] Most specifically, a method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity is characterized by comprising the following steps: S1. Mix Ga and In metals in a mass ratio of 7:3-7.5:2.5, and stir continuously for 25-35 minutes at a temperature of 55°C-65°C to form a gallium-indium alloy liquid metal. Ultrasonic mix the liquid metal with a polymer material PVA in a mass ratio of 1:0.8-1 to form a composite ink; S2. According to the designed circuit diagram, the composite ink is printed onto the plant leaves to produce the required sensor circuit. The printing pulse equivalent is 0.0072 mm, the pulse frequency is 200K, the dispensing time accuracy is controlled to be 1ms, and the acceleration is 2000 mm / s 2 , the reset speed is 10~100 mm / s; S3. Mix glycerol, PVA and deionized water in a mass ratio of 1:4 to 6:60, stir for 1 hour at 70°C to 80°C to form a mixed solution, apply the mixture thinly on the sensor circuit and cure it at room temperature for 5 hours to form a PVA encapsulation film.

[0011] Further preferably, when preparing the composite ink, the liquid metal is mixed with PVA and clay in a mass ratio of 1:0.8 to 1:0.1 to 0.2, and then ultrasonically treated to obtain the liquid metal-PVA-clay composite ink.

[0012] Adding a small amount of clay to the composite ink further improves the dispersion uniformity of the liquid metal in the composite ink, and can also improve the line uniformity of the ink during the printing process, thereby improving the response sensitivity of the sensor.

[0013] The present invention has the following technical effects: In the present invention, a specific amount of PVA is added to form a composite ink with liquid metal, which effectively solves the adhesion problem of the composite ink when it is directly printed on the leaf surface. The composite ink effectively adheres to the leaf surface, and the prepared sensor responds quickly to the electrical signal of the leaf humidity change and has high sensitivity, thereby realizing real-time monitoring of the leaf humidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 : Actual image and scanning electron microscope (SEM) image of the liquid metal-PVA composite ink prepared in Example 1.

[0015] Figure 2 : Energy dispersive spectroscopy (EDS) diagram of the liquid metal-PVA composite ink prepared in Example 1.

[0016] Figure 3 : (a) Cross-sectional view of the flexible plant sensor circuit printed with liquid metal-PVA composite ink prepared in Example 1; (b) Scanning electron microscope (SEM) image of the PVA-LM ink circuit fiber under an electron microscope. Figure 4 : Printing effects of different liquid metal-based inks on leaves.

[0017] Figure 5 : The plant electrical signal changes corresponding to the plant sensors with two different circuit diagrams.

[0018] Figure 6 : The plant sensor resistance change graph is used to monitor the water loss changes of plant leaves over time. DETAILED DESCRIPTION The present invention is described in detail below through examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above-mentioned contents of the present invention.

[0019] Example 1 A method for preparing a liquid metal sensor for monitoring plant leaf humidity comprises the following steps: S1. Ga and In metals are mixed in a mass ratio of 7.55:2.45, and stirred continuously at 60° C. for 30 min to prepare gallium-indium alloy liquid metal, and the liquid metal is ultrasonically mixed with a polymer material PVA in a mass ratio of 1:1 to form a composite ink; S2. According to the designed circuit diagram, the composite ink is printed onto the plant leaves to produce the required sensor circuit. The printing pulse equivalent is 0.0072 mm, the pulse frequency is 200K, the dispensing time accuracy is controlled to be 1ms, and the acceleration is 2000 mm / s 2 , the reset speed is 20 mm / s; S3. Mix glycerol, PVA and deionized water in a mass ratio of 1:6:60, stir at 75°C for 1 hour to form a mixed solution, pre-connect copper wires at both ends of the sensor circuit, apply the mixture thinly on the sensor circuit, and cure at room temperature for 5 hours to form a PVA packaging film.

[0020] The physical image and scanning electron microscope image of the composite ink prepared by the present invention are as follows: Figure 1 As shown, it can be seen that the ink has excellent fluidity and uniformity. Figure 2 It can be seen that the liquid metal is evenly dispersed in the ink. Figure 3 As shown, in the printed circuit, the liquid metal sensor circuit is attached to the surface of the blade, and the in-situ attachment on the surface of the blade is achieved without damaging the blade. And the droplets formed by the liquid metal are evenly dispersed in the circuit.

[0021] The present invention attempts to use clay to replace PVA and liquid metal to form a nanoclay-liquid metal composite ink, pure liquid metal as ink, and LM-PVA-clay composite ink composed of liquid metal, PVA and clay in a mass ratio of 1:1:0.1, and print them on the blade surface according to the method in Example 1. The results are as follows: Figure 4 As shown, (a) is nanoclay-liquid metal composite ink; (b) the effect of nanoclay-liquid metal composite ink on the blade; it can be seen that the addition of clay causes the liquid metal to become viscous, and the nanoclay-liquid metal composite ink has poor adhesion to the blade and extremely poor bonding force; (c) and (d) are the effects of printing pure liquid metal ink on the blade; it can be seen that when the pure liquid metal ink is printed on the blade, the contact angle with the blade is large, the adhesion is extremely poor, and it cannot be fixed to the blade surface; (e) is the effect of printing liquid metal-PVA composite ink on the blade, it can be seen that the LM-PVA composite ink can adhere well to the blade, but the continuity and uniformity of the printed circuit are slightly lacking, and the LM-PVA-clay composite ink of the present invention is used for printing on the blade surface, as shown in Figure (f), a continuous and complete liquid metal ultrafine circuit is formed with excellent adhesion performance.

[0022] According to the method of Example 1, two sensors with different circuit patterns were prepared on the leaf surface, and their applications in monitoring plant leaf humidity and electrical signals are as follows: Figure 5 As shown in the figure, (a) and (b) are two different printed flexible plant sensors, and the curves of the plant sensor current changing with the applied voltage. The magnitude of the current (I) is equal to the voltage (U) divided by the resistance (R), that is, I=U / R. From the linear relationship between current and voltage, it can be concluded that: (1) the conductivity of the plant sensor after pressurization was tested, and the plant sensor circuit prepared by PVA-LM conductive ink has conductivity; (2) the resistance of the plant sensor will not change at the same time, and the resistance of different plant sensors is different. When different voltages are applied to the sensor of the plant leaf, its current signal changes accordingly and shows a positive correlation. Example 2 A method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity comprises the following steps: S1. Ga and In metals were mixed in a mass ratio of 7.55:2.45, and stirred continuously for 30 minutes at a temperature of 60° C. to prepare gallium-indium alloy liquid metal, and the liquid metal was ultrasonically mixed with polymer materials PVA and clay in a mass ratio of 1:1:0.1 to form a composite ink; S2. According to the designed circuit diagram, the composite ink is printed onto the plant leaves to produce the required sensor circuit. The printing pulse equivalent is 0.0072 mm, the pulse frequency is 200K, the dispensing time accuracy is controlled to be 1ms, and the acceleration is 2000 mm / s 2 , the reset speed is 20 mm / s; S3. Mix glycerol, PVA and deionized water in a mass ratio of 1:6:60, stir at 75°C for 1 hour to form a mixed solution, pre-connect copper wires at both ends of the sensor circuit, apply the mixture thinly on the sensor circuit, and cure at room temperature for 5 hours to form a PVA packaging film.

[0023] like Figure 6 As shown, the present invention explores the electrical signal response of plant sensors on leaves. In order to eliminate the potential influence of the sensor's own resistance, a blank control experiment was set up with paper as the test object. The experiment was carried out in a stable temperature and humidity environment. The experimental results show that the sensor resistance value on the paper remains stable over a period of time, which proves that the resistance of the plant sensor itself is constant. However, when applied to plant leaves, as time increases (0~50h), when the leaves gradually become withered, water is lost, the humidity of the leaves decreases, and the electrical signal value of the plant sensor changes significantly, which is manifested as an increase in resistance value and an acceleration in the rate of increase. This change shows that the plant sensor can effectively reflect the water content state of the plant by monitoring the change in resistance. The larger the resistance, the lower the water content of the leaves; when the resistance is very small, the water content of the plant leaves is higher. In the sensor test of Example 1, as the humidity of the plant leaves decreases, the sensor resistance value changes significantly. At the beginning, the leaf humidity is the highest, and the resistance value at this time is the sensor's own resistance. After 50 hours, the leaf humidity reaches the lowest, and the sensor resistance reaches 23Ω at this time. Compared with Example 1, the resistance value of the sensor in Example 2 changes more significantly when the same leaf has the same humidity change, that is, the sensor has a higher electrical signal responsiveness, and the sensor has better sensitivity in the process of testing plant leaf humidity changes.

[0024] In the process of preparing composite inks, we tried composite inks prepared with different proportions of liquid metal and PVA and found that if the PVA and clay content were too low, the adhesion performance of the composite ink on the blade surface would deteriorate, while too much PVA and clay would reduce the response sensitivity of the circuit.

[0025] Example 3 A method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity comprises the following steps: S1. Ga and In metals are mixed in a mass ratio of 7:3, and stirred continuously for 25 minutes at a temperature of 65° C. to form a gallium-indium alloy liquid metal. The liquid metal and the polymer material PVA are ultrasonically mixed in a mass ratio of 1:0.8 to form a composite ink; S2. According to the designed circuit diagram, the composite ink is printed onto the plant leaves to produce the required sensor circuit. The printing pulse equivalent is 0.0072 mm, the pulse frequency is 200K, the dispensing time accuracy is controlled to be 1ms, and the acceleration is 2000 mm / s 2 , the reset speed is 100 mm / s; S3. Mix glycerol, PVA and deionized water in a mass ratio of 1:4:60, stir at 80°C for 1 hour to form a mixed solution, apply the mixture thinly on the sensor circuit and cure at room temperature for 5 hours to form a PVA encapsulation film.

[0026] The prepared liquid metal sensor circuit has excellent adhesion to the leaf surface and excellent bonding strength with the leaves. During the test of plant leaf humidity changes, as the plant leaf humidity decreases, the sensor resistance value changes significantly. At the initial stage, the leaf humidity is the highest, and the resistance value at this time is the sensor's own resistance. At 50h, the leaf humidity reaches the lowest, and the sensor resistance reaches 24Ω.

[0027] Example 4 A method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity comprises the following steps: S1. Ga and In metals are mixed in a mass ratio of 7.5:2.5, and stirred continuously for 35 minutes at a temperature of 55° C. to form a gallium-indium alloy liquid metal. The liquid metal and the polymer material PVA are ultrasonically mixed in a mass ratio of 1:0.9 to form a composite ink; S2. According to the designed circuit diagram, the composite ink is printed onto the plant leaves to produce the required sensor circuit. The printing pulse equivalent is 0.0072 mm, the pulse frequency is 200K, the dispensing time accuracy is controlled to be 1ms, and the acceleration is 2000 mm / s 2 , the reset speed is 10 mm / s; S3. Mix glycerol, PVA and deionized water in a mass ratio of 1:5:60, stir at 70°C for 1 hour to form a mixed solution, apply the mixture thinly on the sensor circuit and cure at room temperature for 5 hours to form a PVA encapsulation film.

[0028] The prepared liquid metal sensor circuit has excellent adhesion to the leaf surface and excellent bonding strength with the leaves. During the test of plant leaf humidity changes, as the plant leaf humidity decreases, the sensor resistance value changes significantly. At the initial stage, the leaf humidity is the highest, and the resistance value at this time is the sensor's own resistance. At 50h, the leaf humidity reaches the lowest, and the sensor resistance reaches 22Ω.

Claims

1. A method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity, characterized in that: The steps include: S1. A composite ink formed by mixing liquid metal and polymer material; S2. Print the composite ink onto plant leaves according to the designed circuit diagram to produce the required sensor circuit; S3. Use a PVA-based packaging film to encapsulate the substrate of the sensor circuit.

2. The method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity according to claim 1, characterized in that: The composite ink is prepared by mixing liquid metal and polymer material in a mass ratio of 1:0.8-1 and then ultrasonically treating the mixture; the polymer material is polyvinyl alcohol (PVA).

3. A method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity as claimed in claim 1 or 2, characterized in that: The liquid metal is a gallium-indium-tin alloy, and Ga and In metals are mixed evenly in a mass ratio of 7:3 to 7.5:2.5 to form a gallium-indium alloy liquid metal.

4. A method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity according to any one of claims 1 to 3, characterized in that: The encapsulation comprises mixing glycerol, PVA and water in a mass ratio of 1:4 to 6:60 to form a mixed liquid, thinly coating the mixed liquid on the surface of the liquid metal circuit, and curing the mixed liquid at room temperature to prepare a PVA-based film.

5. A method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity, characterized in that: The steps include: S1. Mix Ga and In metals in a mass ratio of 7:3-7.5:2.5, and stir continuously for 25-35 minutes at a temperature of 55°C-65°C to form a gallium-indium alloy liquid metal. Ultrasonic mix the liquid metal with a polymer material PVA in a mass ratio of 1:0.8-1 to form a composite ink; S2. According to the designed circuit diagram, the composite ink is printed onto the plant leaves to produce the required sensor circuit. The printing pulse equivalent is 0.0072 mm, the pulse frequency is 200K, the dispensing time accuracy is controlled to be 1ms, and the acceleration is 2000 mm / s 2 , the reset speed is 10~100 mm / s; S3. Mix glycerol, PVA and deionized water in a mass ratio of 1:4 to 6:60, stir for 1 hour at 70°C to 80°C to form a mixed solution, apply the mixture thinly on the sensor circuit and cure it at room temperature for 5 hours to form a PVA encapsulation film.

6. A method for preparing a liquid metal electronic tattoo sensor for detecting plant humidity according to any one of claims 1 to 5, characterized in that: When preparing the composite ink, the liquid metal, PVA and clay are mixed in a mass ratio of 1:0.8-1:0.1-0.2, and then ultrasonically treated to obtain the liquid metal-PVA-clay composite ink.

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