Humidity sensitive material, flexible humidity sensor and preparation method

Abstract

The present invention discloses a humidity sensitive material, a flexible humidity sensor and a preparation method for detecting humidity of the environment and the skin surface. The humidity sensitive material used in the present invention is based on a high molecular polymer and a carbon material. The processing method of the sensor comprises the following steps: preparing a metal layer on a flexible substrate by vacuum evaporation, electroplating or other coating methods, then preparing electrodes by batch processing, and aligning the electrodes by scraping or screen printing to prepare a humidity sensitive layer. The flexible sensor prepared by the present invention has the advantages of high sensitivity, wide response range, wearability, and non-toxicity. The present invention has low production cost and simple manufacturing process, and can be prepared in batches and mass-produced in industry.

Description

Technical Field

[0001] The present invention belongs to the field of flexible electronic devices, and in particular relates to a humidity sensitive material, a flexible humidity sensor and a preparation method thereof. Background Art

[0002] Humidity has important applications in many places and is also one of the important indicators of environmental parameters. Humidity is an essential measurement value in agriculture, industrial production, meteorology, and human health. Wearable humidity sensors are in great demand in the fields of the Internet of Things and human-computer interaction. They can be used to detect breathing rate and skin surface humidity, and can also be used for non-contact control.

[0003] In 2021, Lijun Lu et al. ultrasonically anchored multilayer graphene (MG) into electrospun polyamide (PA) 66 as a humidity sensor, with a maximum sensitivity of ΔR / R0 of 34.5% at 90% RH. In addition, the ultrasonic anchoring method after electrospinning used also has certain problems in mass production. Graphene has a large specific surface area, high electron mobility and excellent mechanical properties, but pure graphene-based humidity sensors have low sensitivity to humidity and need further modification to improve their sensitivity to humidity.

[0004] At present, the manufacturing process of resistive flexible humidity sensors is complicated, and the sensitive materials are mostly liquid. The composite methods of sensitive materials and electrodes, such as drop casting, spin coating, and ultrasonic anchoring, are not conducive to mass production and reliability of devices during manufacturing. During drop casting, the sensitive layer has more sensitive materials at the edge than inside due to the coffee ring effect, which affects the stability of electronic devices, while spin coating and ultrasonic anchoring are not conducive to industrial production. Summary of the invention

[0005] In order to solve the above technical problems, the main purpose of the present invention is to provide a humidity sensitive material, a flexible humidity sensor and a preparation method.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A humidity sensitive material is obtained by uniformly mixing the following raw materials, including: water, polyurethane, hydroxyethyl cellulose, xanthan gum, glycerin and graphene.

[0008] Optionally, the specific preparation includes:

[0009] First, water and polyurethane are mixed to obtain a polymer solution, wherein the volume ratio of water to polyurethane is (4-16):1;

[0010] According to the mass ratio, 15 parts of polymer solution, 0.3 parts of hydroxyethyl cellulose, 0.1 parts of xanthan gum, 0.3 parts of glycerol and 0.2 parts of graphene were mixed evenly to obtain a paste.

[0011] Preferably, the specific preparation includes:

[0012] First, water and polyurethane are mixed to obtain a polymer solution, and the volume ratio of water to polyurethane is 12:1;

[0013] According to the mass ratio, 15 parts of polymer solution, 0.3 parts of hydroxyethyl cellulose, 0.1 parts of xanthan gum, 0.3 parts of glycerol and 0.2 parts of graphene were mixed evenly to obtain a paste.

[0014] A flexible humidity sensor, wherein the electrodes of the flexible humidity sensor are coated with any humidity sensitive material described in the present invention.

[0015] Optionally, the flexible humidity sensor comprises a flexible substrate, a metal layer is deposited on the flexible substrate, and the metal layer is processed into a pattern electrode, and the sensitive material is scraped or screen-printed on the surface of the pattern electrode.

[0016] Optionally, the metal layer includes but is not limited to a single or multiple metal deposition layers of Cu, Cr and Au.

[0017] Optionally, the flexible substrate used includes but is not limited to PET, PI, PDMS and eco-flex.

[0018] Optionally, processing the metal layer into the pattern electrode specifically includes: depositing the metal layer on the substrate by vacuum evaporation, electroplating or magnetron sputtering and engraving it into a patterned customized electrode.

[0019] A method for preparing a flexible humidity sensor comprises the following steps:

[0020] S1: A metal layer is deposited on a flexible substrate by vacuum evaporation, electroplating or magnetron sputtering, and then the metal layer is etched by laser direct writing or photolithography to obtain an electrode with a customized pattern;

[0021] S2: performing plasma etching on the electrode obtained in step S1 to modify the electrode surface, and then using a scraper coating or screen printing process to apply the humidity sensitive material of the present invention to the electrode surface.

[0022] Optional, S1: directly printing metal electrodes on the flexible substrate using a screen printing process.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention improves the hydrophilicity of carbon materials to water molecules by compounding multiple polymers with carbon materials. At the same time, the hygroscopic expansion properties of the polymers further promote the improvement of sensor sensitivity.

[0025] (2) The preparation process of the sensitive material of the present invention is simple and efficient. Based on the sensitive material, a flexible humidity sensor with high sensitivity and mass production can be prepared.

[0026] (3) The flexible humidity sensor includes sensitive materials made of a variety of polymers and carbon materials, customized electrodes made by vacuum coating and laser direct writing, and a bendable flexible substrate. Its flexible properties can add more application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are part of this application and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute improper limitations of the present invention. In the accompanying drawings:

[0028] Figure 1 The figure is a process flow chart of the preparation of the flexible humidity sensor;

[0029] Figure 2 It is a dot-line graph of the responsiveness of the flexible humidity sensor from 0 to 100% RH;

[0030] Figure 3 For selection Figure 2 The responsivity dot-line graph in the range of 0-90%RH;

[0031] Figure 4 This is the time-response diagram of the skin humidity field test of the flexible humidity sensor prepared in Example 3;

[0032] Figure 5 This is the time-response diagram of the skin environment test of the flexible humidity sensor prepared in Example 3. DETAILED DESCRIPTION

[0033] The present invention is described in detail below in conjunction with embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, some adjustments and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0034] The humidity sensitive material of the present invention uses materials including water, polyurethane, hydroxyethyl cellulose, xanthan gum, glycerol and graphene, wherein the polyurethane is water-based polyurethane, which is a commercially available product. The specific preparation includes: firstly mixing water and polyurethane to obtain a polymer solution, wherein the volume ratio of water to polyurethane is (4-16):1; taking 15 parts of the polymer solution, 0.3 parts of hydroxyethyl cellulose, 0.1 parts of xanthan gum, 0.3 parts of glycerol and 0.2 parts of graphene by mass ratio, and mixing them evenly to obtain a paste.

[0035] Preferably, the specific preparation includes: first mixing water and polyurethane to obtain a polymer solution, wherein the volume ratio of water to polyurethane is 12:1; according to the mass ratio, taking 1.5g of the polymer solution, 0.03g of hydroxyethyl cellulose, 0.01g of xanthan gum, 0.03g of glycerol and 0.02g of graphene and mixing them evenly to obtain a paste.

[0036] The flexible humidity sensor of the present invention is prepared by modulating a sensitive material composited with a polymer and a carbon material, and innovatively printing it on an electrode by screen printing. The flexible humidity sensor includes a sensitive material made of a variety of polymers and carbon materials, a customized electrode made by vacuum coating and laser direct writing, and a bendable flexible substrate. By using the method of screen printing and scraping, a paste-like sensitive material with a certain viscosity is compounded with an electrode, so that controllable and large-scale production can be achieved. The prepared sensitive material has good fit and controllability with the electrode, and can be quickly dried and combined with the electrode at room temperature. The prepared humidity sensor has good humidity resolution, a simple sensor manufacturing process, controllable thickness, and can be produced on a large scale and efficiently. The flexible sensor prepared by the present invention has the advantages of high sensitivity, wide response range, wearable, and non-toxic. The present invention has low production cost and simple manufacturing process, and can be mass-produced in industry for large-scale production.

[0037] The flexible substrates used include but are not limited to PET, PI, PDMS, eco-flex, etc.

[0038] The metal electrodes processed on the flexible substrate use vacuum evaporation, electroplating or other metals to deposit a metal layer on the substrate and use laser direct writing and photolithography to process it into a patterned customized electrode. Gold includes but is not limited to single or multiple metal deposition layers of Cu, Cr, and Au.

[0039] Combination Figure 1 The processing method of the flexible humidity sensor of the present invention comprises the following steps:

[0040] S1: Put the polymer compound and the carbon material into deionized water, disperse them ultrasonically, and then stir and mix them evenly with a magnetic stirrer to obtain a paste-like sensitive material.

[0041] S2: Vacuum evaporation, magnetron sputtering and other methods are used to deposit metal layers of different thicknesses on the flexible substrate, and laser direct writing, photolithography and other methods are used to write the metal layer to obtain electrodes with customized patterns. Or the electrodes are directly printed by screen printing.

[0042] Plasma etching is performed on the flexible electrode prepared in step S1 to modify the surface of the flexible electrode, and then the sensitive material prepared in S2 is applied to the electrode surface by a scraping or screen printing process.

[0043] In the following examples, unless otherwise specified, the materials used are all common materials in the art, and the methods used are all conventional methods in the art.

[0044] Embodiment 1:

[0045] Processing of flexible electrodes: First, a 10nm chromium metal layer is deposited on the flexible substrate by vacuum evaporation, and then a 50nm gold metal layer is deposited. The evaporation rate is controlled at 0.1-1.0Å / s, and the vacuum degree in the device cavity should be 1×10 -3 After the metal layer is processed, the electrode pattern is customized using design software, and the laser direct writing equipment is used to process it into a customized pattern electrode with a laser power of 20W and a wavelength of 1064nm;

[0046] Preparation of sensitive material: deionized water and polyurethane are prepared into a mixed solution in a ratio of 4:1, 1.5 g of the mixed solution of deionized water and polyurethane, 0.02 g of graphene, 0.03 g of hydroxyethyl cellulose, 0.01 g of xanthan gum, and 0.03 g of glycerol are taken, and stirred at a rate of 500 rpm with a magnetic stirrer for 1 hour to mix them evenly, and a paste-like sensitive material is obtained after stirring.

[0047] Bonding the sensitive material to the electrode: The prepared sensitive material is bonded to the electrode by scraping, and a flexible humidity sensor is obtained after natural drying.

[0048] Embodiment 2:

[0049] Processing of flexible electrodes: First, a 10nm chromium metal layer is deposited on the flexible substrate by vacuum evaporation, and then a 50nm gold metal layer is deposited. The evaporation rate is controlled at 0.1-1.0Å / s, and the vacuum degree in the device cavity should be 1×10 -3 After the metal layer is processed, the electrode pattern is customized using design software, and the laser direct writing equipment is used to process it into a customized pattern electrode with a laser power of 20W and a wavelength of 1064nm;

[0050] Preparation of sensitive materials: deionized water and polyurethane are prepared into a mixed solution in a ratio of 8:1, 1.5 g of the mixed solution of deionized water and polyurethane, 0.02 g of graphene, 0.03 g of hydroxyethyl cellulose, 0.01 g of xanthan gum, and 0.03 g of glycerol are taken, and stirred with a magnetic stirrer at a rate of 500 rpm for 1 hour to mix them evenly, and a paste-like sensitive material is obtained after stirring.

[0051] Bonding the sensitive material to the electrode: The prepared sensitive material is bonded to the electrode by scraping, and a flexible humidity sensor is obtained after natural drying.

[0052] Embodiment 3:

[0053] Preparation of substrate electrode:

[0054] Processing of flexible electrodes: First, a 10nm chromium metal layer is deposited on the flexible substrate by vacuum evaporation, and then a 50nm gold metal layer is deposited. The evaporation rate is controlled at 0.1-1.0Å / s, and the vacuum degree in the device cavity should be 1×10 -3 After the metal layer is processed, the electrode pattern is customized using design software, and the laser direct writing equipment is used to process it into a customized pattern electrode with a laser power of 20W and a wavelength of 1064nm;

[0055] Preparation of sensitive material: deionized water and polyurethane are prepared into a mixed solution in a ratio of 12:1, 1.5 g of the mixed solution of deionized water and polyurethane, 0.02 g of graphene, 0.03 g of hydroxyethyl cellulose, 0.01 g of xanthan gum, and 0.03 g of glycerol are taken, and stirred at a rate of 500 rpm with a magnetic stirrer for 1 hour to mix them evenly, and a paste-like sensitive material is obtained after stirring.

[0056] Bonding the sensitive material to the electrode: The prepared sensitive material is bonded to the electrode by scraping, and a flexible humidity sensor is obtained after natural drying.

[0057] Embodiment 4:

[0058] Processing of flexible electrodes: First, a 10nm chromium metal layer is deposited on the flexible substrate by vacuum evaporation, and then a 50nm gold metal layer is deposited. The evaporation rate is controlled at 0.1-1.0Å / s, and the vacuum degree in the device cavity should be 1×10 -3 After the metal layer is processed, the electrode pattern is customized using design software, and the laser direct writing equipment is used to process it into a customized pattern electrode with a laser power of 20W and a wavelength of 1064nm;

[0059] Preparation of sensitive material: deionized water and polyurethane are prepared into a mixed solution in a ratio of 16:1. 1.5 g of the mixed solution of deionized water and polyurethane, 0.03 g of hydroxyethyl cellulose, 0.01 g of xanthan gum, and 0.03 g of glycerol are taken and stirred with a magnetic stirrer at a rate of 500 rpm for 1 hour to mix them evenly. After stirring, a paste-like sensitive material is obtained.

[0060] Bonding the sensitive material to the electrode: The prepared sensitive material is bonded to the electrode by scraping, and a flexible humidity sensor is obtained after natural drying.

[0061] The sensor was then tested for humidity response. The humidity sensor was placed in a cavity of about 5 cubic centimeters. Dry synthetic air was first passed through for 200 seconds to remove the humid air in the cavity. The dry synthetic air was then passed through saturated salt solutions of different salts to fill the cavity with synthetic air with stable relative humidity for 120 seconds. The resistance change of the flexible humidity sensor was measured using a digital source meter, and the sensitivity of the flexible humidity sensor was calculated according to formula (1).

[0062]

[0063] Where R0 is the initial resistance value, R is the resistance value at a certain humidity, and ΔR is the resistance change value.

[0064] The flexible humidity sensor prepared in Example 3 was subjected to a skin humidity field test. The sensor measured the finger three times at a distance of 5 mm from the humidity sensor and at distances of 4 mm, 3 mm, 2 mm, and 1 mm from the humidity sensor.

[0065] Figure 2 The responsivity dot-line graphs of the humidity sensors prepared in Examples 1-4 at different humidity levels are given, indicating that Example 3 has the highest humidity responsivity relative to the other examples.

[0066] Figure 3 For selection Figure 2 From the response dotted line graph in the range of 0-90%RH, it can be seen that in the low humidity part, the humidity response value of Example 3 is still greater than that of the other examples.

[0067] Figure 4 This is the time-response diagram of the skin humidity field test of the flexible humidity sensor prepared in Example 3. It can be seen that the responsiveness changes with the distance between the skin and the sensor.

[0068] Figure 5 This is the time-response diagram of the skin environment test of the flexible humidity sensor prepared in Example 3. The left Y-axis is the responsivity and the right Y-axis is the environmental humidity value. It can be seen that the sensor responsivity changes consistently with the environmental humidity.

[0069] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A flexible humidity sensor, characterized in that: The electrodes of the flexible humidity sensor are coated with humidity sensitive material; The humidity sensitive material is obtained by uniformly mixing the following raw materials, including: water, polyurethane, hydroxyethyl cellulose, xanthan gum, glycerin and graphene; The specific preparation includes: First, water and polyurethane are mixed to obtain a polymer solution, and the volume ratio of water to polyurethane is 12:1; According to the mass ratio, 15 parts of polymer solution, 0.3 parts of hydroxyethyl cellulose, 0.1 parts of xanthan gum, 0.3 parts of glycerol and 0.2 parts of graphene were mixed uniformly to obtain a paste; The flexible humidity sensor comprises a flexible substrate, a metal layer is deposited on the flexible substrate, and the metal layer is processed into a pattern electrode, and the sensitive material is scraped or screen-printed on the surface of the pattern electrode; The metal layer includes but is not limited to single or multiple metal deposition layers of Cu, Cr and Au; The flexible substrates used include, but are not limited to, PET, PI, PDMS, and eco-flex; Processing the metal layer into a patterned electrode specifically includes: A metal layer is deposited on a substrate by vacuum evaporation, electroplating or magnetron sputtering and then etched into a patterned customized electrode.

2. A method for preparing a flexible humidity sensor, characterized in that: The flexible humidity sensor is the flexible humidity sensor according to claim 1, comprising the following steps: S1: Depositing a metal layer on a flexible substrate by vacuum evaporation, electroplating or magnetron sputtering, and then engraving the metal layer by laser direct writing or photolithography to obtain electrodes with customized patterns; or directly printing metal electrodes on a flexible substrate by screen printing; S2: performing plasma etching on the electrode prepared in step S1 to modify the electrode surface, and then using a scraper coating or screen printing process to apply the humidity sensitive material to the electrode surface.

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