Flexible sensor with photoresponse and preparation method thereof

Abstract

The invention belongs to the technical field of flexible sensors, and particularly relates to a flexible sensor with light response and a preparation method thereof. PVA and the modified carbon dots are dissolved in a deionized water solution to be heated, then a borax solution is added, heating continues to be conducted, full mixing is conducted, then the mixture is injected into a mold to be subjected to multiple times of freeze thawing, then the mixture is soaked and washed in a sodium polyacrylate solution and a copper sulfate solution in sequence, and the flexible sensor is obtained. The flexible sensor provided by the invention has good mechanical properties and optical properties, the maximum bearable stress reaches 4MPA in a tensile state, strain visualization can be realized through the fluorescence effect of the carbon dots, and meanwhile, the preparation process is simple and pollution-free to the environment is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible sensors, and in particular relates to a flexible sensor with light response and a preparation method thereof. Background Art

[0002] With the advancement of science and technology, as human-computer interaction scenarios continue to increase, and as intelligent medical sensor systems are gradually becoming an important part of the medical field, the market demand for flexible sensors is increasing. Traditional rigid electronic sensors, due to their poor softness, bring discomfort to users and limit sensing performance. Therefore, it is urgent to develop new materials.

[0003] Hydrogel is a hydrophilic polymer material with a three-dimensional network structure that can hold a large amount of water without dissolving. With the continuous expansion of human-computer interaction scenarios and the continuous development of the medical rehabilitation field, the requirements for the performance of hydrogels used in this field are constantly increasing. Traditional hydrogel materials often have disadvantages such as non-conductivity, poor mechanical properties, and non-visual stretching. However, to be used in flexible electronic sensors, they are required to have good biocompatibility, sensing sensitivity, mechanical properties, optical properties, etc. Summary of the invention

[0004] The object of the present invention is to provide a flexible sensor with light response and a preparation method thereof, wherein the flexible sensor has excellent mechanical and optical properties, can withstand large stress and realize visualization of strain.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A flexible sensor with light response, the preparation method is as follows: a solution of PVA and modified carbon dots dissolved in deionized water is heated, then a borax solution is added and continued to be heated and fully mixed, then injected into a mold for multiple freeze-thaws, and then soaked and washed in a salt solution and a metal salt solution in turn to obtain the flexible sensor with light response.

[0007] The mass ratio of PVA: modified carbon dots: deionized water is preferably 2-6: 0.02-0.08: 12-25.

[0008] Heating was performed in a water bath at 80-90°C for 20-90 min.

[0009] The concentration of the borax solution is 0.005-0.008 mol / L; the mass ratio of PVA to the borax solution is 2-6:5.

[0010] After adding the borax solution, continue heating for 20-90 minutes.

[0011] The number of freeze-thaw cycles is preferably 1-5 times; the freezing time for each freeze-thaw cycle is 4-20 hours, and the melting time is 4-8 hours.

[0012] The salt solution is preferably a sodium polyacrylate solution, and the mass concentration of the sodium polyacrylate solution is 45-60%, and the soaking time is 10-120 minutes.

[0013] The metal salt solution is a copper salt, iron salt or lead salt solution, the concentration of the metal salt solution is 0.05-0.8 mol / L, and the soaking time is 15-180s.

[0014] The metal salt solution is preferably a copper sulfate solution.

[0015] In the present invention, the selection of salt solution and the immersion time are very important improvements. The addition of salt solution can make the water molecules on the surface of the hydrogel interact with the COO- groups and be stripped off, forming a tough PVA surface with low water content on the surface of the hydrogel, which greatly enhances the mechanical properties of the hydrogel.

[0016] The modified carbon dots are added to the raw materials, and then soaked in a metal salt solution. The purpose is to utilize the fluorescence effect of carbon dots under ultraviolet light and the quenching effect of some metal cations on carbon dots through the photoinduced electron transfer mechanism (PET) to achieve the quenching of carbon dots within a certain range inside the hydrogel, and further realize strain visualization. In addition, the addition of carbon dots can greatly improve the toughness of the hydrogel. Selecting a suitable concentration of carbon dots can improve the toughness of the hydrogel while improving its tensile resistance. The selection of the concentration of the metal salt solution and the soaking time has a very important influence on the size of the area of ​​quenched carbon dots inside the hydrogel. With the increase of the concentration of the metal salt solution and the increase of the soaking time, the area of ​​quenched carbon dots in the hydrogel continues to expand, and the area of ​​unquenched carbon dots in the hydrogel continues to decrease. Therefore, choosing a suitable concentration for soaking and a suitable soaking time can ensure that the carbon dots inside the hydrogel are not quenched and the quenching area is appropriate, thereby achieving a dynamic response to ultraviolet light under stretching.

[0017] In addition, in the invention, the hydrogel is first soaked in a salt solution and then in a metal salt solution. It is found through research that the tough PVA surface with a low water content formed after soaking in the salt solution can inhibit the swelling of the hydrogel in water to a certain extent, thereby inhibiting the swelling of the hydrogel during soaking in the metal salt solution, thereby avoiding the degradation of mechanical properties caused by swelling during the quenching process.

[0018] The carbon dots can be obtained by, but not limited to, the following method: heating a mixture of citric acid and l-glutathione at 140°C for 30 minutes, then increasing the heating temperature to 180°C and adding polyethylene polyamine, then reacting at 180°C for 1 hour and cooling to 25-30°C, purifying and separating to obtain the modified carbon quantum dots; wherein the mass ratio of citric acid to l-glutathione is 3:1, and the mass ratio of l-glutathione to polyethylene polyamine is 1:10.

[0019] The present invention prepares a photoresponsive hydrogel sensor, which simultaneously utilizes the fluorescence effect of carbon dots under ultraviolet light and the quenching of carbon dots by copper ions, lead ions or iron ions through a photoinduced electron transfer mechanism (PET), thereby realizing visualization of the stretching degree of the hydrogel; in addition, the hydrogel sensor of the present invention also has good mechanical properties and can withstand a tensile stress of 4MPa without breaking.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The present invention provides a flexible sensor with good mechanical and optical properties. In a stretched state, the maximum stress it can withstand is 4 MPA, and the strain can be visualized through the fluorescence effect of carbon dots. The preparation process is simple and does not pollute the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the stress-strain diagram of the sensor stretched corresponding to Example 23. At a strain of 1400%, the sensor can withstand a maximum tensile stress of about 4 MPa, and has excellent mechanical properties;

[0023] Figure 2 Schematic diagram of the sensor corresponding to Example 12 being stretched under ultraviolet light; it can be seen that under ultraviolet light irradiation, the brightness of the area where the carbon dots inside the hydrogel are not quenched is higher, and the brightness of the area where the carbon dots are quenched is lower; in addition, when the degree of stretching increases, the brightness changes, indicating that the strain is visualized;

[0024] Figure 3 The strain coefficient (ie, strain sensitivity factor) of the sensor of Example 3 was tested, and the results showed that the hydrogel of the present invention has excellent strain sensing sensitivity. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is described below with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0026] In the following examples and comparative examples, the experimental methods used are conventional methods unless otherwise specified, and the materials, reagents, etc. used are all commercially available unless otherwise specified, and the brands, etc. have no effect on the experimental results.

[0027] The carbon dots used in the following examples were obtained by the following method:

[0028] The mixture of citric acid and l-glutathione is heated at 140°C for 30 minutes, then the heating temperature is increased to 180°C, polyethylene polyamine (PEPA) is added to the molten liquid and heated and stirred at 180°C for 1 hour; after naturally cooling to 25-30°C, the modified carbon dots are purified and separated; wherein the mass ratio of citric acid to l-glutathione is 3:1, and the mass ratio of l-glutathione to polyethylene polyamine is 1:10.

[0029] Example 1

[0030] Weigh 2g PVA and 25mg modified carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 5g 0.01mol / L borax solution (the same below) and stir, continue heating for 20min, inject into the mold after eliminating bubbles, freeze and thaw 3 times, freeze for 4h each time, thaw for 4h, take out and soak in 50% sodium polyacrylate solution for 10min, take out and wash, soak in 0.5mol / L copper sulfate solution for 2min, take out and wash, and the flexible sensor can withstand a maximum tensile stress of 0.2MPa.

[0031] Example 2

[0032] Weigh 3g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to 80℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 8h each time, thaw for 4h, then take out, soak in 45% sodium polyacrylate solution for 20min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 0.3MPa.

[0033] Example 3

[0034] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 1.5MPa.

[0035] Example 4

[0036] Weigh 5g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 60min, inject into the mold after eliminating bubbles, freeze and thaw 4 times, freeze for 16h each time, thaw for 6h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and obtain the flexible sensor. The maximum tensile stress can reach 2.0MPa.

[0037] Example 5

[0038] Weigh 6g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 90min, eliminate bubbles and inject into the mold, freeze and thaw 5 times, freeze for 20h each time, thaw for 8h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 2.4MPa.

[0039] Example 6

[0040] Weigh 4g PVA and 20mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 60min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 2.6MPa.

[0041] Example 7

[0042] Weigh 4g PVA and 50mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 0.8MPa.

[0043] Example 8

[0044] Weigh 4g PVA and 80mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 0.5MPa.

[0045] Example 9

[0046] Weigh 4g PVA and 25mg carbon dots, add them to 12ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 2MPa.

[0047] Example 10

[0048] Weigh 4g PVA and 25mg carbon dots, add them to 25ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 1.6MPa.

[0049] Embodiment 11

[0050] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.005mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 0.5MPa.

[0051] Example 12

[0052] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.02mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 60min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 3.0MPa.

[0053] Example 13

[0054] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.04mol / L borax solution and stir, continue heating for 60min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 2.8MPa.

[0055] Embodiment 14

[0056] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.08mol / L borax solution and stir, continue heating for 90min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and obtain the flexible sensor. The maximum tensile stress can reach 2.4MPa.

[0057] Embodiment 15

[0058] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 45% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 0.5MPa.

[0059] Example 16

[0060] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 55% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 1.4MPa.

[0061] Embodiment 17

[0062] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 60% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 1.2MPa.

[0063] Embodiment 18

[0064] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.05mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 1.5MPa.

[0065] Embodiment 19

[0066] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.3mol / L copper sulfate solution for 1min, take out, wash, and obtain the flexible sensor. The maximum tensile stress can reach 1.6MPa.

[0067] Embodiment 20

[0068] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.8mol / L copper sulfate solution for 30s, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 1.7MPa.

[0069] Embodiment 21

[0070] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.02mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 2.2MPa.

[0071] Embodiment 22

[0072] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.01mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 60min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 3MPa.

[0073] Embodiment 23

[0074] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.02mol / L borax solution and stir, continue heating for 30min, inject into the mold after eliminating bubbles, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 90min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 4MPa.

[0075] Embodiment 24

[0076] Weigh 4g PVA and 40mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.02mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 50% sodium polyacrylate solution for 30min, wash, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and make the flexible sensor. The maximum tensile stress can reach 2.0MPa.

[0077] Comparative Example 1

[0078] Weigh 4g PVA, add it to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.02mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take it out, soak it in a 50% sodium polyacrylate solution for 90min, wash it, soak it in a 0.5mol / L copper sulfate solution for 2min, take it out, wash it, and make the flexible sensor. The maximum tensile stress can reach 1.8MPa, and it does not have light response ability.

[0079] Comparative Example 2

[0080] Weigh 4g PVA and 25mg carbon dots, add them to 16ml deionized water, transfer the solution to a 90℃ water bath for heating, add 0.02mol / L borax solution and stir, continue heating for 30min, eliminate bubbles and inject into the mold, freeze and thaw 3 times, freeze for 10h each time, thaw for 4h, then take out, soak in 0.5mol / L copper sulfate solution for 2min, take out, wash, and the flexible sensor is obtained. The maximum tensile stress can reach 20kPa. The mechanical properties are poor.

Claims

1. A method for preparing a flexible sensor with light response, characterized in that: The solution of PVA and modified carbon dots dissolved in deionized water is heated, and then a borax solution is added and continued to be heated and fully mixed, and then injected into a mold for multiple freeze-thaw cycles, and then soaked and washed in a salt solution and a metal salt solution in turn to obtain the light-responsive flexible sensor.

2. The method for preparing a flexible sensor with light response according to claim 1, characterized in that: The mass ratio of PVA: modified carbon dots: deionized water is 2-6: 0.02-0.08: 12-25.

3. The method for preparing a flexible sensor with light response according to claim 1, characterized in that: Heating was performed in a water bath at 80-90°C for 20-90 min.

4. The method for preparing a flexible sensor with light response according to claim 1, characterized in that: The concentration of the borax solution is 0.005-0.08 mol / L; the mass ratio of PVA to the borax solution is 2-6:

5.

5. The method for preparing a flexible sensor with light response according to claim 4, characterized in that: After adding the borax solution, continue heating for 20-90 minutes.

6. The method for preparing a flexible sensor with light response according to claim 1, characterized in that: The salt solution is a sodium polyacrylate solution, and the mass concentration of the sodium polyacrylate solution is 45-60%, and the immersion time is 10-120 minutes.

7. The method for preparing a flexible sensor with light response according to claim 1, characterized in that: The metal salt solution is a copper salt, iron salt or lead salt solution, the concentration of the metal salt solution is 0.05-0.8 mol / L, and the soaking time is 15-180s.

8. The method for preparing a flexible sensor with light response according to claim 1, characterized in that: The number of freeze-thaw cycles is 1-5; the freezing time for each freeze-thaw cycle is 4-20 hours, and the melting time is 4-8 hours.

9. A flexible sensor with light response obtained by any preparation method of claims 1-8.

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