Low-temperature-resistant conductive hydrogel and preparation method and application thereof
The conductive hydrogel with a dual-network structure solves the problems of freezing and water evaporation of hydrogels at low temperatures, achieving flexibility and self-healing ability under low-temperature conditions, making it suitable for wearable flexible sensors.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANDONG UNIV OF TECH
- Filing Date
- 2023-12-01
- Publication Date
- 2026-06-12
AI Technical Summary
Hydrogels are prone to freezing or water evaporation at low temperatures, which affects their flexibility and performance, making them difficult to adapt to changes in daily use conditions.
The conductive hydrogel employs a dual-network structure, including physical cross-linking of gelatin and guar gum via hydrogen bonding and dynamic covalent cross-linking of guar gum and borax via borate esters. Combined with liquid gallium and choline chloride, it enhances conductivity and low-temperature resistance.
It maintains flexibility and self-healing ability at low temperatures, can monitor deformation and temperature changes in real time, and has high sensitivity and stability, making it suitable for wearable flexible sensors.
Smart Images
Figure CN117659720B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of conductive hydrogel technology, specifically to a low-temperature resistant conductive hydrogel, its preparation method, and its application. Background Technology
[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.
[0003] The advent of the 5G era has made wearable devices the most exciting material in the smart era. In the future, flexible sensors will play an even more important role in the smart era and will bring tremendous changes to our daily lives. Flexible sensors overcome the shortcomings of traditional rigid sensors, which are hard and brittle. They possess flexibility, excellent fit, and high sensitivity, allowing them to perfectly conform to irregularly shaped dynamic surfaces, meeting the demands of modern electronic devices for portability, miniaturization, and intelligence. Flexible sensors can convert external dynamic deformations, temperature, humidity, and other factors into visible electrical signals, enabling applications in multiple fields.
[0004] Hydrogels are soft materials with a three-dimensional network structure and tunable physicochemical properties. They possess skin-like softness, elastic resilience, and good biocompatibility, making them ideal materials for fabricating multifunctional flexible sensors. However, hydrogels contain a large amount of water. High temperatures and prolonged storage at room temperature cause the water molecules inside the gel to evaporate, while low temperatures cause the water molecules in the gel to freeze, making the hydrogel hard and losing its flexibility. This severely affects the performance of hydrogels, making them difficult to cope with changes in daily use conditions when applied to flexible sensors. Summary of the Invention
[0005] To overcome the above problems, the present invention provides a low-temperature resistant conductive hydrogel, its preparation method and application.
[0006] To achieve the above technical objectives, the present invention adopts the following technical solution:
[0007] In a first aspect, the present invention provides a low-temperature resistant conductive hydrogel, the low-temperature resistant conductive hydrogel comprising gelatin, guar gum, borax, conductive material and modifier;
[0008] The conductive hydrogel has a dual-network structure, which includes: the hydrogen bonds inside gelatin and guar gum and the hydrogen bonds between gelatin and guar gum forming a first network of physical cross-linking; and the boronic acid ester dynamic covalent bonds formed between guar gum and borax and the boronic acid ester dynamic covalent bonds formed between gelatin and borax forming a second network of chemical cross-linking.
[0009] The conductive material is liquid gallium; the modifier is choline chloride.
[0010] Hydrogen bonds within gelatin, guar gum, and between gelatin and guar gum form the first physical cross-linking network. Dynamic covalent bonds of borate esters formed between guar gum and borax, and between gelatin and borax, form the second chemical cross-linking network. This dual-network structure of the conductive hydrogel maintains its excellent mechanical properties while enhancing its self-healing ability. Liquid gallium enhances the hydrogel's conductivity and flexibility, improving its sensitivity to deformation and temperature. Choline chloride effectively lowers the freezing point of water and raises its boiling point, thereby inhibiting freezing and water evaporation, and improving the hydrogel's low-temperature resistance.
[0011] A second aspect of the present invention provides a method for preparing the above-mentioned low-temperature resistant conductive hydrogel, comprising the following steps:
[0012] (1) Dissolve metallic gallium in deionized water, and add gelatin, borax and choline chloride to the solution in sequence, and stir for the first time;
[0013] (2) After the first stirring is completed, add guar gum and stir a second time. After the second stirring is completed, let it stand at room temperature to obtain a conductive hydrogel.
[0014] A third aspect of the present invention provides the application of the above-mentioned low-temperature resistant conductive hydrogel in the field of wearable flexible sensors.
[0015] The beneficial effects of this invention are as follows:
[0016] (1) The low-temperature resistant conductive hydrogel provided by this invention comprises a first network of physical cross-linking formed by hydrogen bonds within gelatin, hydrogen bonds within guar gum, and hydrogen bonds between gelatin and guar gum. A second network of chemical cross-linking is formed by the dynamic covalent bonds of borate esters formed between guar gum and borax, and by the dynamic covalent bonds of borate esters formed between gelatin and borax. This dual-network structure enhances the self-healing ability of the hydrogel while maintaining its excellent mechanical properties. Liquid gallium enhances the conductivity and flexibility of the hydrogel, improving its sensitivity to deformation and temperature. Choline chloride effectively lowers the freezing point of water and raises its boiling point, thereby inhibiting freezing and water evaporation, and improving the low-temperature resistance of the hydrogel. The abundant amino, hydroxyl, and carboxyl groups in the conductive hydrogel can form non-covalent bonds with the surface of the substrate material, allowing it to adhere firmly to different material surfaces.
[0017] (2) By connecting conductive hydrogels with wires to form a flexible sensor, it can not only be attached to different parts of the human body to monitor strain during human movement, but also monitor changes in ambient temperature in real time. When the conductive hydrogel undergoes tensile strain, the porous structure inside the conductive hydrogel is compressed, the migration rate of ions slows down, the conductivity of the conductive hydrogel decreases, and the resistance increases; when the conductive hydrogel returns to its initial deformation, the resistance returns to its initial value, and the strain can be converted into a recognizable change in resistance value, exhibiting high sensitivity, repeatability, and stability. When the temperature rises, the molecular thermal motion in the conductive hydrogel intensifies, the migration rate of ions accelerates, the conductivity of the conductive hydrogel increases, and the resistance decreases. When it returns to the initial temperature, the resistance returns to its initial value, and the temperature change can be converted into a change in resistance value, exhibiting high sensitivity and stability to temperature. Attached Figure Description
[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0019] Figure 1 This is a schematic diagram illustrating the synthesis of the low-temperature resistant conductive hydrogel in this invention;
[0020] Figure 2 The image shown is a scanning electron microscope image of the low-temperature resistant conductive hydrogel in Example 1.
[0021] Figure 3 The stress-strain curves are those of the low-temperature conductive hydrogels a, b, and c obtained by changing the amount of gelatin in Example 2, and the low-temperature conductive hydrogel obtained in Example 1.
[0022] Figure 4 The stress-strain curves are shown for the low-temperature conductive hydrogels d, e, and f obtained by changing the amount of guar gum in Example 3, and the low-temperature conductive hydrogel obtained in Example 1.
[0023] Figure 5 The stress-strain curves are for the low-temperature conductive hydrogels g, h, i, and j obtained by changing the amount of gallium in Example 4, and the low-temperature conductive hydrogel obtained in Example 1.
[0024] Figure 6 The conductivity of the low-temperature conductive hydrogel after changing the amount of gallium in Example 4;
[0025] Figure 7 Images showing the low-temperature resistant conductive hydrogel obtained in Example 1 firmly adhering to different substrate surfaces;
[0026] Figure 8The stress-strain curves of the low-temperature resistant conductive hydrogel obtained in Example 1 are shown in the initial state at room temperature and at a low temperature of -20°C.
[0027] Figure 9 The graph shows the test results of the self-healing performance of the low-temperature conductive hydrogel, where a is the stress-strain curve of the conductive gel at different self-healing times, and b is the self-healing efficiency graph.
[0028] Figure 10 This is a schematic diagram of the flexible sensor structure;
[0029] Figure 11 This is a curve showing the strain-resistance change rate of a flexible sensor.
[0030] Figure 12 The strain-resistance rate curve of a flexible sensor after being frozen at -20°C for 48 hours.
[0031] Figure 13 The graph shows the time-resistance change rate of a flexible sensor under 300 cycles of continuous loading-unloading at 100% strain.
[0032] Figure 14 A time-resistance change rate curve for monitoring when the finger is bent at different angles;
[0033] Figure 15 A graph showing the rate of change of resistance during movement while the knee is bent.
[0034] Figure 16 A graph showing the motion time versus rate of change of electrical resistance during blinking.
[0035] Figure 17 A graph showing the motion time versus rate of change of electrical resistance monitored during pulse vibration at the wrist.
[0036] Figure 18 A graph showing the motion time versus rate of change of electrical resistance during smiling activities;
[0037] Figure 19 The graph shows the time-resistance change rate of a finger when it is bent at different angles after the flexible sensor has been frozen at -20°C for 48 hours.
[0038] Figure 20 This is a temperature-resistance rate curve for a flexible sensor.
[0039] Figure 21 A graph showing the rate of change of resistance when a flexible sensor monitors different temperature variations. Detailed Implementation
[0040] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0041] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.
[0042] A first typical embodiment of the present invention provides a low-temperature resistant conductive hydrogel, the conductive hydrogel comprising gelatin, guar gum, borax, conductive materials and modifiers;
[0043] The conductive hydrogel has a dual-network structure, which includes: the hydrogen bonds inside gelatin and guar gum and the hydrogen bonds between gelatin and guar gum forming a first network of physical cross-linking; and the boronic acid ester dynamic covalent bonds formed between guar gum and borax and the boronic acid ester dynamic covalent bonds formed between gelatin and borax forming a second network of chemical cross-linking.
[0044] The conductive material is metallic gallium; the modifier is choline chloride.
[0045] In one or more embodiments, the mass ratio of gallium, gelatin, borax, choline chloride, and guar gum is 0.00025–0.0115:0.35–1.55:0.1–0.15:1.5–2.0:0.15–0.40, preferably 0.008:1.08:0.12:1.815:0.3.
[0046] A second typical embodiment of the present invention provides a method for preparing the above-mentioned low-temperature resistant conductive hydrogel, comprising the following steps:
[0047] (1) Dissolve metallic gallium in deionized water, and add gelatin, borax and choline chloride to the solution in sequence, and stir for the first time;
[0048] (2) After the first stirring is completed, add guar gum and stir a second time. After the second stirring is completed, let it stand at room temperature to obtain a low-temperature resistant conductive hydrogel.
[0049] In one or more embodiments, the mass ratio of gallium, deionized water, gelatin, borax, choline chloride, and guar gum is:
[0050] 0.00025~0.0115:3.5~4.5:0.35~1.55:0.1~0.15:1.5~2.0:0.15~0.40, preferably 0.008:4:1.08:0.12:1.815:0.3.
[0051] In one or more embodiments, the temperature at which the metallic gallium dissolves in deionized water is 30–35°C, preferably 30°C.
[0052] In one or more embodiments, the temperature of the first stirring is 35-45°C, preferably 40°C; the stirring time for the first stirring is 0.5-1.5 hours, preferably 1 hour.
[0053] In one or more embodiments, the temperature of the second stirring is 35-45°C, preferably 40°C; the time of the second stirring is 1.5-2.5 hours, preferably 2 hours.
[0054] In one or more embodiments, the standing time at room temperature is 10 to 14 hours, preferably 12 hours.
[0055] A third typical embodiment of the present invention provides the application of the above-mentioned low-temperature resistant conductive hydrogel in the field of wearable flexible sensors.
[0056] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.
[0057] Example 1
[0058] according to Figure 1 The above-described synthesis diagram illustrates the specific steps involved in synthesizing the conductive hydrogel:
[0059] (1) At 30°C, add 8 mg of gallium to 4 mL of deionized water and stir at 700 rpm for 20 minutes until the gallium is completely dissolved; add 1.08 g of gelatin, 0.12 g of borax and 1.815 g of choline chloride to the solution in sequence and stir at 700 rpm for 1 hour at 40°C until completely dissolved.
[0060] (2) Add 0.3g of guar gum to the solution in step (1) and stir at 700 rpm for 2 hours at 40°C until completely dissolved. After standing at room temperature for 12 hours, a low-temperature resistant conductive hydrogel is obtained.
[0061] Example 2
[0062] The difference from Example 1 is that the amount of gelatin was changed to 0.35g, 0.77g, and 1.55g, respectively, resulting in conductive hydrogels a, b, and c.
[0063] Example 3
[0064] The difference from Example 1 is that the content of guar gum was changed to 0.15g, 0.2g and 0.4g, respectively, and the resulting low-temperature resistant conductive hydrogels were d, e and f, respectively.
[0065] Example 4
[0066] The difference from Example 1 is that the content of metallic gallium was changed to 0g, 0.0025g, 0.005g and 0.115g, and the resulting low-temperature resistant conductive hydrogels were g, h, i and j, respectively.
[0067] Example 5
[0068] This embodiment characterizes the low-temperature resistant conductive hydrogels obtained in Examples 1 to 4.
[0069] Figure 2 Here is a scanning electron microscope image of the low-temperature resistant conductive hydrogel obtained in Example 1, as shown below. Figure 2 As shown, the conductive hydrogel has a three-dimensional network-like porous structure, which can provide channels for ion migration while maintaining the gel's flexibility and stretchability.
[0070] Figure 3 The stress-strain curves are those of the low-temperature conductive hydrogels a, b, and c obtained by changing the amount of gelatin in Example 2, and the low-temperature conductive hydrogel obtained in Example 1. Figure 4 The stress-strain curves are shown for the low-temperature conductive hydrogels d, e, and f obtained by changing the amount of guar gum in Example 3, and the low-temperature conductive hydrogel obtained in Example 1. Figure 5 The stress-strain curves are shown for the low-temperature resistant conductive hydrogels g, h, i, and j obtained by varying the amount of gallium in Example 4, and the conductive hydrogel obtained in Example 1. Figure 6 To improve the conductivity of the low-temperature conductive hydrogel after changing the amount of gallium in Example 4, combined with... Figures 3-6 The results show that the optimal mass ratio of raw materials in conductive hydrogels can be determined.
[0071] Figure 7 Images showing the low-temperature resistant conductive hydrogel obtained in Example 1 firmly adhering to different substrate surfaces, such as... Figure 7 As shown, because conductive hydrogels have functional groups such as amino, hydroxyl and carboxyl groups, they can adhere firmly to the surfaces of pigskin, foam, glass, metal, plastic, paper, wood, leaves and rubber.
[0072] Figure 8 The figures show the stress-strain curves of the low-temperature conductive hydrogel obtained in Example 1 under the initial state at room temperature and at a low temperature of -20°C. Figure 8The low-temperature conductive hydrogel obtained in Example 1 can maintain good flexibility and tensile properties at -20°C. This is because choline chloride can effectively lower the freezing point of water and raise the boiling point of water, thereby inhibiting the freezing and evaporation of water in the conductive hydrogel and improving the low-temperature stability of the conductive hydrogel.
[0073] To verify the self-healing properties of the low-temperature resistant conductive hydrogel obtained in Example 1, the low-temperature resistant conductive hydrogel was divided into two halves, and its self-healing performance was tested. The results are as follows: Figure 9 As shown, the self-healing efficiency of the conductive hydrogel can reach 98% after 9 hours. This is because the conductive hydrogel with a dual-network structure maintains the excellent mechanical properties of the hydrogel while improving its self-healing ability through the synergistic effect of multiple hydrogen bonds and dynamic borate ester covalent bonds.
[0074] Example 6
[0075] like Figure 10 As shown, a flexible sensor can be obtained by directly connecting the low-temperature resistant conductive hydrogel prepared in Example 1 to a conductive material, and the performance of the obtained flexible sensor is tested.
[0076] The two ends of the flexible sensor are connected to a universal tensile testing machine and connected to a data acquisition device via wires to record the flexible sensor's response to strain.
[0077] Strain sensitivity is an important performance parameter characterizing the sensitivity of a sensor to strain. The calculation formula is: GF=[(R-R0) / R0] / ε, where R is the resistance under applied strain, R0 is the resistance without applied strain, and ε is the strain. Figure 11 This describes the resistance change rate of a flexible sensor within the strain range of 0–2100%. The sensitivity is 2.25 within the strain range of 0–1000%, 3.17 within the strain range of 1000–1600%, and 5.53 within the strain range of 1600–2100%.
[0078] Furthermore, to test the stability of the flexible sensor, it was frozen at -20°C for 48 hours, and its strain sensitivity was then measured. The results are as follows: Figure 12 As shown, the sensitivity of the hydrogel flexible sensor to strain does not change much after freezing. In the ranges of 0–1000%, 1000–1600%, and 1600–2100%, the sensitivities are 2.01, 2.98, and 5.14, respectively.
[0079] To test the stability and durability of the flexible sensor, its resistance change rate curve was measured after 300 consecutive load-unload cycles under 100% strain. The results are as follows: Figure 13As shown, the resistance change rate curves at the initial, intermediate, and final stages of the test did not show significant changes, indicating that the flexible sensor has high stability and excellent durability.
[0080] Experiment Example 1: Applying Flexible Sensors to Monitor Human Movement and Physiological Activities
[0081] Flexible sensors are attached to different parts of the human body, including fingers, knees, corners of the eyes, wrists, and corners of the mouth, to monitor deformations that occur during human movement. Figure 14 The graph shows the motion time versus rate of change of resistance when the finger is bent at different angles, as shown in the figure. Figure 14 As shown, when the finger bending angle increases from 0° to 90°, the flexible sensor displays a clear and distinguishable change in resistance, indicating that the flexible sensor of the present invention can monitor the finger bending angle. Figure 15 A graph showing the motion time versus rate of change of electrical resistance during knee flexion, such as... Figure 15 As shown, the flexible sensor has a fast and stable response to knee flexion, indicating that it can record the joint flexion and extension states during human exercise. Figure 16 This is a graph showing the motion time versus rate of change of electrical resistance during blinking. Figure 17 This is a graph showing the motion time versus rate of change of electrical resistance monitored during pulse vibration at the wrist. Figure 18 This is a graph showing the motion time versus rate of change of electrical resistance during smiling activities. Figures 16-18 The image shows the flexible sensor's response to human physiological activities such as blinking, pulse, and smiling. This demonstrates that the flexible sensor of this invention can record changes in human physiological activities in real time.
[0082] To further test the stability of the flexible sensor, the sensor was frozen at -20°C for 48 hours, and the finger bending movements were monitored. The results are as follows: Figure 19 As shown, the flexible sensor can still quickly and accurately monitor finger bending movements after being frozen at -20℃ for 48 hours, demonstrating good low-temperature resistance.
[0083] Example 2: Applying a flexible sensor to temperature monitoring
[0084] Temperature coefficient of resistance is an important parameter characterizing the temperature sensitivity of a sensor. The formula for calculation is: TCR = [(R...] t -R0)×100% / R0] / ΔT, where R0 is the resistance of the sensor at 25℃, R t It is the resistance of the sensor at the measurement temperature, and ΔT is the temperature difference between the measurement temperature and 25℃. Figure 20This refers to the change in resistance of the sensor with temperature within the range of 0–100℃. The temperature coefficient of resistance is -3.973% / ℃ within the range of 0–25℃. Within the range of 25–100℃, the temperature coefficient of resistance is -0.6508% / ℃.
[0085] Figure 21 The display shows that the flexible sensor can monitor the resistivity change when the temperature changes. The sensor can output different resistance change rate curves at different temperatures, and can accurately monitor changes in external temperature.
[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A low-temperature resistant conductive hydrogel, characterized in that, The low-temperature resistant conductive hydrogel includes gelatin, guar gum, borax, conductive materials, and modifiers. The low-temperature resistant conductive hydrogel has a dual-network structure. The hydrogen bonds inside gelatin and guar gum, as well as the hydrogen bonds between gelatin and guar gum, constitute the first network of physical cross-linking. The dynamic covalent bonds of borate esters formed by guar gum and borax, as well as the dynamic covalent bonds of borate esters formed between gelatin and borax, constitute the second network of chemical cross-linking. The conductive material is liquid gallium; the modifier is choline chloride. The conductive hydrogel has a porous internal structure.
2. The low-temperature resistant conductive hydrogel as described in claim 1, characterized in that, The mass ratio of metallic gallium, gelatin, borax, choline chloride, and guar gum is: 0.00025~0.0115:0.35~1.55:0.1~0.15:1.5~2.0:0.15~0.
40.
3. The low-temperature resistant conductive hydrogel as described in claim 2, characterized in that, The mass ratio of gallium, gelatin, borax, choline chloride, and guar gum was 0.008:1.08:0.12:1.815:0.
3.
4. The method for preparing the low-temperature resistant conductive hydrogel according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Dissolve metallic gallium in deionized water, and add gelatin, borax and choline chloride to the solution in sequence, and stir for the first time; (2) After the first stirring is completed, add guar gum and stir a second time. After the second stirring is completed, let it stand at room temperature to obtain a low-temperature resistant conductive hydrogel.
5. The method for preparing the low-temperature resistant conductive hydrogel as described in claim 4, characterized in that, The temperature at which the metallic gallium dissolves in deionized water is 30~35 ℃.
6. The method for preparing the low-temperature resistant conductive hydrogel as described in claim 5, characterized in that, The temperature at which the metallic gallium dissolves in deionized water is 30 °C.
7. The method for preparing the low-temperature resistant conductive hydrogel as described in claim 4, characterized in that, The temperature for the first stirring is 35~45 ℃; the stirring time for the first stirring is 0.5~1.5 h.
8. The method for preparing the low-temperature resistant conductive hydrogel as described in claim 7, characterized in that, The temperature for the first stirring was 40 ℃; the stirring time for the first stirring was 1 h.
9. The method for preparing the low-temperature resistant conductive hydrogel as described in claim 4, characterized in that, The temperature for the second stirring is 35~45 ℃; the stirring time for the second stirring is 1.5~2.5 h.
10. The method for preparing the low-temperature resistant conductive hydrogel as described in claim 9, characterized in that, The temperature for the second stirring was 40 ℃; the stirring time for the second stirring was 2 h.
11. The method for preparing the low-temperature resistant conductive hydrogel as described in claim 4, characterized in that, The time for standing at room temperature is 10~14 h.
12. The method for preparing the low-temperature resistant conductive hydrogel as described in claim 11, characterized in that, The time for standing at room temperature was 12 hours.
13. The method for preparing the low-temperature resistant conductive hydrogel as described in claim 4, characterized in that, The mass ratio of gallium, deionized water, gelatin, borax, choline chloride, and guar gum is as follows: 0.00025~0.0115:3.5~4.5:0.35~1.55:0.1~0.15:1.5~2.0:0.15~0.40。 14. The method for preparing the low-temperature resistant conductive hydrogel as described in claim 13, characterized in that, The mass ratio of gallium, deionized water, gelatin, borax, choline chloride, and guar gum is 0.008:4:1.08:0.12:1.815:0.
3.
15. The application of the low-temperature resistant conductive hydrogel according to any one of claims 1 to 3 or the conductive hydrogel according to any one of claims 4 to 14 prepared by the preparation method of the low-temperature resistant conductive hydrogel in the field of wearable flexible sensors.