A method for preparing a hydrogel film humidity sensor
By preparing a PVA/CA@TA/AgNPs composite film, the challenges of miniaturization and stability of hydrogel films were overcome, resulting in a highly sensitive and recyclable humidity sensor suitable for skin moisture detection in wearable devices.
Patent Information
- Application Number
- CN202211465460.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-11-22
- Publication Date
- 2026-02-13
- Estimated Expiration
- 2042-11-22
AI Technical Summary
Existing hydrogel films face challenges in miniaturization and stability, particularly in mechanical properties and interfacial crosslinking. Furthermore, the lack of stretchability in traditional humidity sensing materials limits their application in stretchable and wearable electronic devices.
A hydrogel film humidity sensor was prepared using polyvinyl alcohol (PVA) as a substrate, citric acid (CA) and tannic acid (TA) as reducing agents, and reduced silver nanoparticles (AgNPs) as conductive components through in-situ reduction and solvent casting techniques. Combining the hygroscopicity and recyclability of PVA and CA, a PVA/CA@TA/AgNPs composite film was formed.
The prepared hydrogel film has controllable thickness, stretchability, transparency and environmental stability, high humidity response sensitivity and biocompatibility, can be reused, is suitable for skin moisture detection, and has high sensitivity and stability.
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Figure CN115808446B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of hydrogel sensors, in particular to a preparation method of a hydrogel film humidity sensor. BACKGROUND
[0002] Electrically conductive hydrogels have an effective combination of mechanical stretchability and electrical conductivity, and are one of the most widely studied materials in the field of flexible and stretchable electronics, showing considerable application potential in wearable / portable electronics, energy storage devices, artificial intelligence, biomedical and other fields. In particular, hydrogels can be used to prepare various sensors to detect strain / pressure, temperature, humidity and gas by converting these external stimuli into detectable electrical signals (resistance or capacitance changes). Despite the intriguing stretchability, flexibility and transparency in the manufacture of wearable electronics, the mechanical properties, miniaturization and stability of hydrogel-based devices still need to be improved for practical applications. To this end, considerable efforts have been devoted to improving and optimizing the electromechanical properties and functions of hydrogels, such as introducing multiple networks, adding nanofillers and modifying functional groups. Equally important is the miniaturization of hydrogels, which is necessary for the future development of miniature intelligent electronic products. Therefore, stable and stretchable hydrogel films with minimal thickness must be prepared to develop high-performance and miniaturized devices. However, some challenges have seriously hindered the development of hydrogel films. First, the cross-linking at the interface of the hydrogel is usually poor, and the micron-scale defects generated on the surface lead to a sharp deterioration of the mechanical properties of the hydrogel film as the thickness of the hydrogel decreases.
[0003] Humidity detection has practical significance in our lives. For example, human skin is a typical source of humidity; therefore, high-precision detection of the humidity field around it is expected to realize a non-contact human-machine control system, which helps to solve the inevitable wear, pollution and virus transmission problems caused by traditional contact sensing. In addition, the humidity of exhaled air is closely related to human health; therefore, the development of high-precision humidity sensors can play an important role in real-time monitoring of human health. At present, various humidity sensors based on graphene and its derivatives, metal oxides or sulfides and conductive polymers have been developed according to the changes in electrical properties. Although the function of detection has been achieved, the lack of stretchability of these sensing materials limits their application in stretchable and wearable electronics, so the development of stretchable humidity sensor materials is an urgent problem to be solved. SUMMARY
[0004] In order to overcome the defects in the prior art, the application provides a preparation method of a hydrogel film humidity sensor, which is developed by using polyvinyl alcohol (PVA) as a substrate, citric acid (CA) and tannic acid (TA) as reducing agents, and reduced silver nanoparticles (AgNPs) as a conductive component through simple in-situ reduction and solvent casting technology, and the sensor has the functions of flexibility, transparency and recyclability.
[0005] Technical scheme
[0006] The application provides a preparation method of a hydrogel film humidity sensor, and specifically comprises the following steps.
[0007] In step one, tannic acid solid and citric acid solid are added into 20ml water for dissolution, 5ml silver nitrate solution is added and stirred uniformly, and then the mixture is subjected to hydrothermal reaction at 20-40 DEG C for 30-60min to obtain a TA@CA / Ag precursor solution.
[0008] In step two, polyvinyl alcohol solid is added into 20ml water for dissolution at 100 DEG C, then the solution temperature is reduced to 30-50 DEG C, the TA@CA / Ag precursor solution prepared in step one is added, and the stirring reaction is continued for 60-120min to obtain a PVA / CA@TA / Ag solution.
[0009] In step three, the PVA / CA@TA / Ag solution prepared in step two is poured into an evaporation dish, and then evaporated into a film under a set temperature and humidity, and finally a PVA / CA@TA / AgNPs film is obtained.
[0010] Further, the mass of the tannic acid solid in step (1) is 0.1-0.4g, the mass of the citric acid solid in step (1) is 2-3g, and the concentration of the silver nitrate solution is 2-5%.
[0011] Further, the polyvinyl alcohol solid in step (2) is added into 20ml water for dissolution, and the mass concentration of the dissolved polyvinyl alcohol solution is 5-15%.
[0012] Further, the set temperature and humidity in step (3) are as follows: the temperature is 30-40 DEG C, the humidity is 40%-70%, and the crosslinking time is 12-24h.
[0013] The application has the following beneficial effects:
[0014] The conductive hydrogel film is controllable in thickness, stretchable, transparent, has good environmental stability and very high response sensitivity to humidity; the remolded sensor made of the recycled PVA / CA@TA / AgNPs composite material by the dissolution shaping treatment has excellent mechanical and sensing performances even after multiple recycling; due to the hygroscopicity of PVA, TA and CA, the prepared sensor has very high humidity sensitivity and stability, and thus can be used as a skin moisture detector; the PVA / CA / AgNPs composite film has very strong biocompatibility and can be recycled, so it is friendly to human skin and environment;
[0015] By means of simple in-situ reduction and solvent casting technology, a flexible, transparent and recyclable sensor with humidity sensing function is developed by taking polyvinyl alcohol (PVA) as a substrate, citric acid (CA) and tannic acid (TA) as reducing agents and reduced silver nanoparticles (AgNPs) as a conductive component. BRIEF DESCRIPTION OF DRAWINGS
[0016] Figure 1 SEM of the hydrogel film humidity sensor of the present application;
[0017] Figure 2 Humidity sensing performance diagram of the present application;
[0018] Figure 3 Stress-strain curve diagram of the present application before and after remolding;
[0019] Figure 4 Comparison diagram of sensing performance after remolding of the present application;
[0020] Figure 5 Resistance change rate when detecting moisture of human body of the present application. DETAILED DESCRIPTION
[0021] In order to better illustrate the content of the present application, the following will be described in conjunction with the drawings and examples:
[0022] As shown in the figure, the present application discloses a preparation method of a hydrogel film humidity sensor, which specifically comprises the following steps: Figures 1-5
[0023] Step one, dissolve tannic acid solid and citric acid solid in 20ml water, add 5ml silver nitrate solution and stir uniformly, and then hydrothermally react at 20-40℃ for 30-60min to obtain TA@CA / Ag precursor solution;
[0024] Step two, at 100℃, polyvinyl alcohol solid is dissolved in 20ml water, then the solution temperature is reduced to 30-50℃, and the TA@CA / Ag precursor solution prepared in step one is added, and the reaction is continued for 60-120min to obtain a PVA / CA@TA / Ag solution;
[0025] Step three, the PVA / CA@TA / Ag solution prepared in step two is poured into an evaporating dish, and evaporated into a film under a set temperature and humidity, and finally a PVA / CA@TA / AgNPs film is obtained.
[0026] Further, the mass of the tannic acid solid in step (1) is 0.1-0.4g.
[0027] Further, the mass of the tannic acid solid in step (1) is 0.1-0.4g.
[0028] Further, the polyvinyl alcohol solid in step (2) is dissolved in 20ml water: the mass concentration of the polyvinyl alcohol solution after dissolution is 5-15%.
[0029] Further, the set temperature and humidity in step (3) are: the temperature is 30-40℃, the humidity is 40%-70%, and the crosslinking time is 12-24h.
[0030] Example 1
[0031] A preparation method of a hydrogel film humidity sensor, specifically comprising the following steps:
[0032] Step one, 0.1g of tannic acid and 2g of citric acid are dissolved in 20ml of water, and 5ml of 2% silver nitrate solution is added and stirred uniformly, and then hydrothermal reaction is carried out at 20℃ for 30min to obtain a TA@CA / Ag precursor solution;
[0033] Step two, at 100℃, 1g of polyvinyl alcohol is dissolved in 20ml of water, then the polyvinyl alcohol solution temperature is reduced to 30℃, and the TA@CA / Ag precursor solution prepared in step one is added, and the reaction is continued for 120min to obtain a PVA / CA@TA / Ag solution;
[0034] Step three, the PVA / CA@TA / Ag solution prepared in step two is poured into an evaporating dish, and evaporated into a film under a set temperature and humidity, and finally a PVA / CA@TA / AgNPs film is obtained.
[0035] From Figure 1As can be seen, the cross-section of the hydrogel has a large number of wrinkles, and the strong interaction between TA and the polymer usually leads to the formation of a condensed layer on the surface of the polymer. This structure can effectively release the interfacial stress and expand the specific surface area to improve the mechanical properties and mechanical deformation ability of the flexible and stretchable sensor.
[0036] Example 2
[0037] A preparation method of a hydrogel film humidity sensor, specifically comprising the following steps:
[0038] Step one, 0.16g tannic acid and 2.6g citric acid are added to 20ml water to dissolve, and 5ml of 3% silver nitrate is added to stir uniformly, and hydrothermal reaction is carried out at 20℃ for 30min, to obtain TA@CA / Ag precursor solution;
[0039] Step two, 2.5g polyvinyl alcohol is added to 20ml water to dissolve at 100℃, then the solution temperature is reduced to 35℃, and then the TA@CA / Ag precursor solution prepared in step one is added, and the stirring reaction is continued for 120min, to obtain PVA / CA@TA / Ag solution;
[0040] Step three, the PVA / CA@TA / Ag solution prepared in step two is poured into an evaporation dish, and under the set conditions: temperature is 30℃, humidity is 40%, and crosslinking is carried out for 16h, to evaporate into a film, and finally PVA / CA@TA / AgNPs film is obtained.
[0041] Due to the hygroscopicity of CA and PVA, the moisture resistance of the PVA / CA / AgNPs composite film is also sensitive to humidity changes, making it a potential humidity sensor. The mechanism of the PVA / CA / AgNPs humidity sensor can be explained as follows: CA and PVA are easy to absorb water and retain water due to their rich hydrophilic groups, Figure 2 (Left) The accuracy of the sensor is calibrated with standard saturated salt solutions, showing accurate measurement of environmental humidity, Figure 2 (Right) shows the electrical signal test in the relative humidity range of 11-30% to evaluate the detection range of the humidity sensor, and it is observed that the relative humidity of 11% can still cause a response of the resistance; this indicates that the sensor has an ultra-high humidity sensing detection range.
[0042] Example 3
[0043] A preparation method of a hydrogel film humidity sensor, specifically comprising the following steps:
[0044] Step one, 0.2g tannic acid and 2g citric acid are added to 20ml water to dissolve, and 5ml of 4% silver nitrate is added to stir uniformly, and hydrothermal reaction is carried out at 40℃ for 30min, to obtain TA@CA / Ag precursor solution;
[0045] Step 2: Dissolve 2g of polyvinyl alcohol in 20ml of water at 100℃. Then, lower the solution temperature to 30℃ and add the TA@CA / Ag precursor solution prepared in Step 1. Continue stirring and reacting for 100min to obtain PVA / CA@TA / Ag solution.
[0046] Step 3: Pour the PVA / CA@TA / Ag solution obtained in Step 2 into an evaporating dish and crosslink it for 12 hours under the set conditions: temperature 30℃, humidity 50%, to allow it to evaporate into a film, and finally obtain the PVA / CA@TA / AgNPs film.
[0047] Since the prepared PVA / CA / AgNPs hydrogel film is composed of fully physical cross-linking, it is reproducible. The damaged hydrogel film can be redissolved by placing it in water at 40°C. After going through the above preparation process again, the damaged hydrogel film can be remade into a new sensor, and the mechanical properties of the film remain unchanged before and after remodeling. The PVA / CA@TA / AgNPs sensor can be considered a green electronic device, which provides great potential for reducing waste electronic products.
[0048] Example 4
[0049] A method for preparing a hydrogel film humidity sensor specifically includes the following steps:
[0050] Step 1: Dissolve 0.3g tannic acid and 3g citric acid in 20ml water, add 5ml of 4% silver nitrate and stir until homogeneous. Perform hydrothermal reaction at 20℃ for 30min to obtain TA@CA / Ag precursor solution.
[0051] Step 2: Dissolve 1.5g of polyvinyl alcohol in 20ml of water at 100℃. Then, lower the solution temperature to 30℃ and add the TA@CA / Ag precursor solution prepared in Step 1. Continue stirring and reacting for 180min to obtain PVA / CA@TA / Ag solution.
[0052] Step 3: Pour the PVA / CA@TA / Ag solution obtained in Step 2 into an evaporating dish and crosslink it for 18 hours under the set conditions: temperature 30℃, humidity 60%, to allow it to evaporate into a film, and finally obtain the PVA / CA@TA / AgNPs film.
[0053] Due to the good water solubility of PVA, TA, and CA, the PVA / CA@TA / AgNPs sensor exhibits excellent recyclability. The broken composite film is re-dissolved to form a homogeneous suspension, then reshaped using a procedure similar to that used to prepare the original composite film. The recovered composite film is then assembled into a sensor, which still possesses excellent sensing capabilities for external stimuli. Figure 4 As shown, the humidity sensing performance of the recycled sensor is comparable to that of the original sensor.
[0054] Example 5
[0055] A method for preparing a hydrogel film humidity sensor specifically includes the following steps:
[0056] Step 1: Dissolve 0.4g tannic acid and 3g citric acid in 20ml of water, add 5ml of 5% silver nitrate and stir until homogeneous. Perform hydrothermal reaction at 20℃ for 30min to obtain TA@CA / Ag precursor solution.
[0057] Step 2: Dissolve 3g of polyvinyl alcohol in 20ml of water at 100℃. Then, lower the solution temperature to 60℃ and add the TA@CA / Ag precursor solution prepared in Step 1. Continue stirring and reacting for 120min to obtain PVA / CA@TA / Ag solution.
[0058] Step 3: Pour the PVA / CA@TA / Ag solution obtained in Step 2 into an evaporating dish and crosslink it for 20 hours under the set conditions: temperature 30℃, humidity 60%, to allow it to evaporate into a film, and finally obtain the PVA / CA@TA / AgNPs film.
[0059] like Figure 5 As shown, leveraging the advantages of PVA / CA@TA / AgNPs composite films such as conductivity, flexibility, tensile strength, humidity sensing performance, and long-term stability, this sensor is used to simulate the function of skin moisture content. The film's high sensitivity and low strain detection limit make it suitable for use as a humidity sensor to accurately identify real-time changes in human body moisture content. Figure 5 The resistance response of the sensor integrated into the skin under different stimuli was recorded. When the skin was washed with water, the water content of the skin increased significantly, and the resistance change rate of the hydrogel film also increased accordingly. Even after the skin was moisturized with cosmetics, the hydrogel film sensor could still accurately reflect the change in the water content of the skin.
[0060] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the same; although the technical solutions of the present application are described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some of the technical features thereof can be replaced by equivalent features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.
Claims
1. A method for preparing a hydrogel thin film humidity sensor, characterized by, The method comprises the following steps: Step one, dissolve tannic acid solid and citric acid solid in 20ml water, and add 5ml silver nitrate solution and stir evenly, then hydrothermal reaction at 20-40℃ for 30-60min, to obtain TA@CA / Ag precursor solution; Step two, dissolve polyvinyl alcohol solid in 20ml water at 100℃, then reduce the solution temperature to 30-50℃, and then add the TA@CA / Ag precursor solution prepared in step one, continue to stir for 60-120min, to obtain PVA / CA@TA / Ag solution; Step three, pour the PVA / CA@TA / Ag solution prepared in step two into an evaporation dish, evaporate it into a film under the set temperature and humidity, and finally obtain PVA / CA@TA / AgNPs film.
2. The method of claim 1, wherein the method further comprises: The mass of the tannic acid solid in step (1) is 0.1-0.4g.
3. The method of claim 1, wherein the method further comprises: The mass of the citric acid solid in step (1) is 2-3g.
4. The method of claim 1, wherein the method further comprises: The concentration of the silver nitrate solution in step (1) is 2-5%.
5. The method of claim 1, wherein the method further comprises: In step (2), the polyvinyl alcohol solid is dissolved in 20ml water: the mass concentration of the dissolved polyvinyl alcohol solution is 5-15%.
6. The method of claim 1, wherein the method further comprises: In step (3), the set temperature and humidity: the temperature is 30-40℃, the humidity is 40%-70%, and the crosslinking time is 12-24h.