A method for preparing a flexible pressure sensor

Abstract

The present invention relates to a method for preparing a flexible pressure sensor, which belongs to the field of sensor preparation, and comprises the following steps: step 1, preparing a flexible substrate; step 2, respectively forming an interdigital electrode layer and a conductive layer on the two flexible substrates obtained in step 1; step 3, preparing a flexible pressure sensor; making a portion of bubble-free PDMS, coating the PDMS on a thin film other than the interdigital electrode layer and the RGO patterned electrode of the conductive layer obtained in step 2, placing the flexible substrates of the interdigital electrode layer and the conductive layer opposite to each other so that the two layers are relatively attached, and then placing them in a constant temperature blast drying oven for drying and packaging to obtain the flexible pressure sensor.

Description

Technical Field

[0001] The present invention relates to the field of sensors, and specifically to a method for preparing a flexible pressure sensor. Background Art

[0002] Water stress refers to the phenomenon that the water loss of plants exceeds the water absorption, which causes the water content of their tissues to decrease and makes it impossible to carry out normal metabolic activities. In addition to water stress caused by soil water shortage, other adverse external environmental factors such as waterlogging, freezing and salinity may also cause water stress in plants. Among all external environmental factors, water stress caused by drought is the most common and one of the key factors affecting plant yield. According to statistics, the economic losses caused by water stress account for about 60%-70% of all natural disasters, and the losses caused by drought are the sum of other factors.

[0003] As mentioned above, water stress can cause many adverse effects on plants, hinder their normal growth and development, and ultimately lead to reduced crop yields and affect economic benefits. Therefore, in the actual production process, it is necessary to grasp the water status of plants in real time and water the plants in time to avoid the occurrence of water stress. In summary, the significance of detecting plant water stress is mainly reflected in the following two aspects:

[0004] (1) Ensure normal plant growth and increase crop yields;

[0005] (2) Achieve precise irrigation of plants and save agricultural water;

[0006] After the roots of plants absorb water, they need to transport the water from bottom to top. The way water is conducted in plants is as follows: water is absorbed by the root hairs, reaches the root cortex, then enters the protoplasm of the endodermal cells, and then transfers to the root xylem vessels through the cells of the vascular column; then it is transported longitudinally over long distances, and after reaching the xylem vessels of the stems, it is transported upwards and supplied to various cells along the way for normal physiological activities, and then reaches the leaf vein vessels, and is transported to the mesophyll cells through the ends of the leaf veins, and finally dissipated into the atmosphere in the form of water vapor through the stomata or cuticle. This process is the complete transportation process of water in plants. In the above-mentioned water transportation process, the process of water flowing upward through the stems is an important link in the water transportation in plants. The liquid flowing up from the inside of the plant stems is called stem flow, and the plant stem flow is closely related to the transpiration of plants. Since most of the water absorbed by the roots of plants will be released through transpiration, the strength of the plant transpiration can be judged by detecting the plant stem flow, so as to grasp the water status of the plant. In addition to detecting stem flow, the stem growth rate of plants is different under different water conditions. Under normal conditions, plants grow normally and the stem diameter increases; under water shortage conditions, plant growth is inhibited and the stem growth slows down. Therefore, the water condition of the plant can also be determined by detecting the change in the diameter of the plant stem.

[0007] Detection of plant stem diameter changes. The stem diameter of a plant is closely related to its water content. Under normal conditions, plants grow normally and their stem diameter increases; under water shortage conditions, plant growth is inhibited and stem growth slows down. Therefore, the water content in the plant can be reflected by detecting changes in the stem diameter of the plant. The method of using stem diameter changes as an indicator of plant water content has received widespread attention because it is simple to operate and does not harm the plant.

[0008] Currently, the commonly used instruments for measuring plant stem diameters include linear displacement sensors and laser diameter meters.

[0009] In summary, when using existing technology to detect plant moisture information, it is easy to destroy the plant structure and cause damage to the plant stems; the rigid sensor cannot accurately fit the plant stems and can only detect moisture in the plant's surroundings. The results of this indirect measurement have a certain lag.

[0010] At present, there are many problems and limitations in the traditional plant water information detection method. In view of the problems existing in the existing technology, it is necessary to study a new detection device to achieve accurate and efficient detection of plant water information, so as to accurately and in real time grasp the water status in the plant body, avoid water stress on the plant, and ensure the normal growth and development of the plant. In the face of more and more special signals and special environments, the development trends of new sensor technology are as follows: develop new materials, new processes and new sensors; realize the integration and intelligence of sensors; realize the miniaturization of sensor technology hardware systems and components; and integrate sensors with other disciplines. Sensors are also required to be transparent, flexible, extensible, freely bendable and foldable, easy to carry, and wearable. Summary of the invention

[0011] In order to solve the problems existing in the background technology, the present invention aims to provide a method for preparing a flexible pressure sensor, which uses the flexible sensor to detect water stress on flexible plants. The flexible pressure sensor is mainly used to measure the stems of the plants. When the stems of the plants are sufficiently watered, the stems are full and swollen, and the greater the pressure felt by the flexible pressure sensor; when the stems of the plants are under water stress, the stems are shrunken and contracted, and the smaller the pressure felt by the flexible pressure sensor.

[0012] Solutions for solving problems

[0013] A method for preparing a flexible pressure sensor, the method comprising:

[0014] Step 1, preparing a flexible substrate;

[0015] Step 2: forming an interdigital electrode layer and a conductive layer respectively on the two flexible substrates obtained in step 1;

[0016] Step 3: Preparation of flexible pressure sensor;

[0017] Prepare a portion of bubble-free PDMS, apply the PDMS on the thin film outside the RGO patterned electrode of the interdigital electrode layer and the conductive layer obtained in step 2, place the flexible substrate of the interdigital electrode layer and the conductive layer opposite to each other so that the two layers are relatively fitted, and then place them in a constant temperature forced air drying oven for drying and packaging to obtain the flexible pressure sensor.

[0018] Furthermore, the step 1 of preparing the flexible substrate specifically comprises:

[0019] First, the main agent and the curing agent are mixed in a mass ratio of 10:1 and stirred evenly, then poured into a disposable round culture dish with a diameter of 10 mm, the internal bubbles are extracted in a vacuum drying oven, and the film is cured at 65°C in an oven to obtain a PDMS thin film substrate, i.e., a flexible substrate PDMS.

[0020] Further, the step 2 specifically includes:

[0021] 2mg·mL -1 The graphene oxide (GO) solution is poured on the two flexible substrates obtained in step 1 respectively and dried at room temperature. After it is completely dried, a GO film is formed on the PDMS film substrate, one part of which serves as the interdigitated electrode layer on the substrate and the other part as the conductive layer on the substrate.

[0022] Furthermore, the step 2 further comprises:

[0023] Place two flexible substrates forming GO films flat under a laser engraving machine, set the engraving power to 20% and the engraving depth to 10, engrave the set patterned electrodes on the GO films, then import the electrode patterns drawn by computer software into the control software of the laser engraving machine, and adjust the focus and starting position of the laser; laser induction uses a 450nm semiconductor laser diode in an air environment, the laser power is 3.85W, and the scanning rate is maintained at 200mm / s to obtain the final required laser engraved reduced graphene oxide RGO patterned electrode; connect the wires on the RGO patterned electrode with silver paste, and dry it at 65°C in a constant temperature forced air drying oven to form a scaly interdigitated electrode layer and a conductive layer.

[0024] Beneficial effects:

[0025] The beneficial effects of the above technical solution are:

[0026] The flexible pressure sensor adopts a double-layer structure. The sensor is divided into an interdigital electrode layer and a conductive layer. The sensing unit is composed of laser engraved reduced graphene oxide, which is then assembled into a flexible substrate graphene pressure sensor. The corresponding electrical and mechanical performance tests are carried out. It has the characteristics of high sensitivity, ultra-thin and ultra-light, good air permeability, anti-aging and strong applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a scaly image of laser engraved reduced graphene oxide RGO of the present invention;

[0028] Figure 2 This is a diagram of connecting wires with silver paste on RGO patterned electrodes;

[0029] Figure 3 is a diagram of sensor test data. DETAILED DESCRIPTION

[0030] The specific implementation mode of the present invention is described below in conjunction with embodiments:

[0031] It should be noted that the structures, proportions, sizes, etc. shown in this specification are only used to match the contents disclosed in the specification so that people familiar with this technology can understand and read them, and are not used to limit the conditions under which the present invention can be implemented. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0032] At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0033] Embodiment 1:

[0034] The flexible pressure sensor with a double-layer structure is divided into an interdigitated electrode layer and a conductive layer. The sensing unit is composed of laser-engraved reduced graphene oxide, which is then assembled into a flexible substrate graphene pressure sensor and subjected to corresponding electrical and mechanical performance tests. It has the characteristics of high sensitivity, ultra-thin and ultra-light, good air permeability, anti-aging and strong applicability.

[0035] The laser engraved reduced graphene oxide flexible pressure sensor prepared by this double-layer structure uses polydimethylsiloxane, namely PDMS, as a flexible substrate. First, the main agent and the curing agent are mixed and stirred evenly in a mass ratio of 10:1, and then poured into a disposable round culture dish with a diameter of 10 mm. The internal bubbles are extracted in a vacuum drying oven, and the film is cured in an oven at 65°C. Then, a bubble-free PDMS is prepared in the same way for later use.

[0036] After PDMS was solidified into a thin film, 2 mg mL -1 The graphene oxide (GO) solution is poured onto the PDMS film and dried at room temperature. After it is completely dried, a GO film is formed on the PDMS film substrate. The GO film is divided into two parts, one as the interdigital electrode layer and the other as the conductive layer. When making a piezoresistive pressure sensor, the two parts are combined into one, which can greatly increase the contact area, thereby making the double-layer structure flexible pressure sensor have higher sensitivity.

[0037] Place the above materials flat under the laser engraving machine and attach the GO film tape to a 8×8cm 2On the PET substrate, avoid the generation of bubbles during the attachment process, so that the GO film is flatly attached to the PET substrate to prevent the GO film from warping during the laser process. Set the engraving power to 20%, the engraving depth to 10, and engrave the set patterned electrode on the GO film. Then import the electrode pattern drawn by the computer software into the control software of the laser engraving machine, and debug the focus and starting position of the laser. Then import the electrode pattern drawn by the computer software into the control software of the laser engraving machine, and debug the focus and starting position of the laser. Laser induction uses a 450nm semiconductor laser diode in an air environment. The laser power is 3.85W and the scanning rate is maintained at 200mm / s. The final required laser engraved reduced graphene oxide (RGO for short) is obtained. Use silver paste to connect the wires on the RGO patterned electrodes and dry them at 65°C in a constant temperature blower drying oven. Figure 1 and Figure 2 shown.

[0038] As shown in Figure 3, (a) the resistance response change of the double-layer flexible pressure sensor with increasing strain when the strain stretching rate is 0 to 100%; (b) under 25% strain, the electrical response and input strain change of the double-layer flexible pressure sensor with time.

[0039] In the strain range of 0-10%, the sensitivity GF of the sensor is 97.6, which increases slowly with the increase of strain. This is mainly because under small strain, the reduced graphene oxide sheets gradually produce microcracks, which causes the destruction of the sensing material network. With the slow increase of uniaxial tensile strain (strain: 0%-10%), the crack gap and crack density increase, and the conductivity slowly decreases. When the uniaxial tensile strain increases to (strain: 10%-40%), ΔR / Ro increases rapidly, and GF is 563.6. This may be because under the action of strain, the adjacent stacked reduced graphene oxide sheets slip, the overlapping area decreases, and the connection between some PDMS is gradually disconnected, and the conductivity decreases. When the applied strain is greater than 40%, due to the significant increase in microcrack gaps and crack density and the broken connection between a large number of reduced graphene oxide sheets, the conductive path is greatly reduced, and ΔR / Ro increases sharply.

[0040] The pangolin scales were simulated to reduce the strain of graphene oxide sheets. The RGO composite sensing layer was prepared by spreading a few layers of GO solution on the elastomer matrix. Due to the expansion of microcracks and the increase of crack spacing and the reversible sliding of overlapping RGO sheets, the scale-like layered stacking microstructure not only broadened the strain detection range, but also greatly improved the sensitivity of the device.

[0041] This structural design combines the crack propagation mechanism with the slip mechanism, allowing the overlapping RGO sheets to change their overlapping area through reversible sliding, resulting in a change in contact resistance, achieving excellent sensing performance. In addition, the sensitivity and strain detection range can be adjusted by regulating the proportion of the RGO sheets, thereby sensing the loss and replenishment of water in leaf stems.

[0042] After obtaining the above-mentioned semi-finished product after drying, the previously retained undried PDMS is coated on the film outside the RGO patterned electrode of the interdigital electrode layer and the conductive layer, and the two layers are bonded together. At this time, the viscosity of the PDMS itself will stick the two layers together, and then put them in a constant temperature forced air drying oven to dry the PDMS to obtain a complete RGO flexible pressure sensor.

[0043] By collecting pressure data from a double-layer flexible pressure sensor, it is possible to identify whether crops are experiencing water stress. Sensor data from a cluster of cherry trees is obtained. Each tree has four double-layer flexible pressure sensors, which are placed on the top leaf stem, bottom leaf stem, sun-facing leaf stem, and shaded leaf stem. If water is transported sufficiently within the plant, the leaf stem will swell. If water is insufficient within the plant, the leaf stem will shrink.

[0044] Comprehensively determine the water industry of a tree and generate the following results.

[0045] The more water the plant loses, the greater the stem shrinkage and the smaller the SD (diameter difference) (negative value). There is a very significant linear correlation between the diameter difference and the stem water content θ, and θ passed the significance test at the 0.01 level.

[0046] Tomato, tomato, θ≥30%; water stress level not reached; double-layer flexible pressure sensor conversion value is stem difference -30*10 -2 mm<β<30*10 -2 mm.

[0047] Tomato, tomato, θ≥30%; water stress level not reached; the flexible pressure sensor with double-layer structure senses β<-30*10 -2 mm or β>30*10 -2 mm, and adjust the drip irrigation water volume according to the threshold.

Claims

1. A method for preparing a flexible pressure sensor, characterized in that: The method comprises: Step 1, preparing a flexible substrate; Step 2: forming an interdigital electrode layer and a conductive layer respectively on the two flexible substrates obtained in step 1; Step 3: Preparation of flexible pressure sensor; Prepare a portion of bubble-free PDMS, apply the PDMS on the thin film outside the interdigital electrode layer and the RGO patterned electrode of the conductive layer obtained in step 2, place the flexible substrate of the interdigital electrode layer and the conductive layer opposite to each other so that the two layers are relatively attached, and then place them in a constant temperature blast drying oven for drying and packaging to obtain the flexible pressure sensor; The step 2 specifically includes: 2mg·mL -1 The graphene oxide GO solution is poured on the two flexible substrates obtained in step 1 respectively and dried at room temperature. After it is completely dried, a GO film is formed on the PDMS film substrate, one portion of which is used as an interdigital electrode layer on the substrate, and the other portion is a conductive layer on the substrate; The step 2 also includes: Two flexible substrates forming GO films are placed flat under a laser engraving machine, the engraving power is set to 20%, the engraving depth is set to 10, and patterned electrodes are engraved on the GO films. Subsequently, the electrode pattern drawn by the computer software is imported into the control software of the laser engraving machine, and the focus and starting position of the laser are adjusted. Laser induction uses a 450nm semiconductor laser diode in an air environment, the laser power is 3.85W, and the scanning rate is maintained at 200mm / s to obtain the final required laser-engraved reduced graphene oxide RGO patterned electrode; the RGO patterned electrode is composed of stacked RGO sheets; the RGO patterned electrode is connected to the wire with silver paste, and dried at 65°C in a constant temperature forced air drying oven to form a scaly interdigitated electrode layer and a conductive layer, the scaly interdigitated electrode layer and the conductive layer are designed with a layered structure imitating the pangolin scale, the stacked RGO sheets produce microcracks, and the crack extension and slip mechanism are combined to improve the sensitivity and strain detection range of the sensor, and the reversible sliding of the RGO sheets changes the contact resistance, thereby optimizing the sensing performance.

2. The method for preparing a flexible pressure sensor according to claim 1, characterized in that: The step 1 of preparing a flexible substrate specifically comprises: First, PDMS and curing agent are mixed in a mass ratio of 10:1 and stirred evenly, then poured into a disposable round culture dish with a diameter of 10 mm, the internal bubbles are extracted using a vacuum drying oven, and the film is cured at 65°C in an oven to obtain a PDMS thin film substrate, i.e., a flexible substrate PDMS.

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