Preparation method and application of flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel

Abstract

The invention belongs to the technical field of polymer photoelectric materials, and particularly relates to a preparation method and application of a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel, and the preparation method comprises the following steps: preparing a mixed aqueous solution A of carboxymethyl cellulose and sodium lignin sulfonate; liquid metal is added into the mixed water solution A for ultrasonic treatment, and a solution B is obtained; adding acrylic acid into the solution B, uniformly stirring, and adding a cross-linking agent and an initiator to obtain a solution C; the solution C is introduced into a mold for in-situ polymerization, and hydrogel D is prepared; the hydrogel D is placed on the prepared polydimethylsiloxane elastomer film, copper electrodes are connected to the two sides of the hydrogel through conductive silver paste, then the polydimethylsiloxane elastomer film is used for wrapping, and the flexible strain sensor is obtained. The wearable strain sensor is high in adhesion to various substrates, very stable in conductivity, good in flexibility and stable in sensing of human motion.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer optoelectronic materials, and in particular relates to a preparation method and application of a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel. Background Art

[0002] Flexible wearable electronic devices are a cutting-edge research field, and flexible multifunctional wearable electronic devices are in great demand at present. Therefore, flexible wearable electronic devices with self-recovery, photothermal conversion ability and high sensitivity have attracted widespread attention and are expected to be used in disease diagnosis, human motion and health monitoring, and electronic skin. However, due to the high surface tension of liquid metal, it is difficult to disperse evenly inside the hydrogel, resulting in stress concentration, resulting in disadvantages such as low stretchability, inherent brittleness and low durability. Therefore, it is still very challenging to prepare a wearable strain sensor with high durability, high sensitivity and multifunctionality. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention provides a method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel and its application. The defects of low stretchability, inherent brittleness and low durability of the existing wearable strain sensors based on conductive hydrogel are solved. The prepared sensor has the advantages of self-recovery, adhesion and high sensing sensitivity, and also has good mechanical properties and durability.

[0004] The technical solution provided by the present invention is as follows:

[0005] The present invention provides a method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel, comprising the following steps: preparing a mixed aqueous solution A of carboxymethyl cellulose and sodium lignin sulfonate; Adding liquid metal to mixed aqueous solution A and subjecting it to ultrasonic treatment to obtain solution B; Add acrylic acid to solution B, stir evenly, then add a crosslinking agent and an initiator to obtain solution C; The solution C was introduced into the mold for in-situ polymerization to obtain the hydrogel D; preparing polydimethylsiloxane elastomer films; The hydrogel D was placed on the prepared polydimethylsiloxane elastomer film, copper electrodes were connected to both sides of the hydrogel D through conductive silver paste, and then wrapped with the polydimethylsiloxane elastomer film to obtain a flexible strain sensor.

[0006] Furthermore, the mass volume ratio of carboxymethyl cellulose, sodium lignin sulfonate and water in the mixed solution A is 0.05-0.125:0.02:16 g / g / mL.

[0007] Furthermore, the mass volume ratio of carboxymethyl cellulose, sodium lignin sulfonate and water in the mixed aqueous solution A is 0.1:0.02:16 g / g / mL.

[0008] Furthermore, the liquid metal is a gallium-indium alloy, the mass ratio of metal gallium to metal indium in the gallium-indium alloy is 75.5:24.5, and the added amount of the gallium-indium alloy is 0.3 g.

[0009] Furthermore, the power of the ultrasonic treatment in S2 is 450-500 W, and the treatment time is 80-90 min.

[0010] Furthermore, the amount of acrylic acid added is 4 g, and the crosslinking agent and initiator are N'N-methylenebisacrylamide and ammonium persulfate, respectively.

[0011] Furthermore, the preparation method of the polydimethylsiloxane elastomer film comprises: Weigh the polydimethylsiloxane solution, add the curing agent and stir thoroughly, apply the mixed solution dropwise on a glass sheet to make it level, and peel it off from the glass sheet after vacuum curing to obtain a film.

[0012] Furthermore, the amount of the polydimethylsiloxane solution added is 1 g to 2 g, the amount of the curing agent added is 0.1 g to 0.2 g, and the vacuum curing time is 40 to 60 min.

[0013] Furthermore, the curing agent is diphenylbutyl carbamate.

[0014] The present invention also provides the application of the flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel prepared by the above-mentioned preparation method in wearable flexible electronic devices.

[0015] Beneficial Effects

[0016] 1. In conductive hydrogels, since it is difficult for conductive materials to be evenly dispersed in the hydrogel, stress concentration occurs, resulting in low stretchability, inherent brittleness and low durability, which hinders the practical application of wearable strain sensors based on conductive hydrogels. The present invention constructs a double-network conductive hydrogel with polyacrylic acid and carboxymethyl cellulose, and carboxymethyl cellulose can use the negatively charged carboxyl groups on its surface to evenly disperse the conductive liquid metal in the hydrogel matrix through electrostatic repulsion. This greatly improves the mechanical properties, toughness and conductive stability of the conductive hydrogel, and broadens the practical application range of wearable strain sensors based on conductive hydrogels.

[0017] 2. Self-adhesion is a very important property for wearable electronic devices. However, general wearable strain sensors based on conductive hydrogels do not have such properties, which also limits the practical application of wearable strain sensors based on conductive hydrogels. Due to the presence of a large number of catechol groups in the chemical structure of sulfonated lignin, sulfonated lignin can adhere to various substrates through non-covalent and covalent chemical bonding.

[0018] 3. The water retention capacity of the conductive hydrogel greatly affects its conductivity. Coating the carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel with a polydimethylsiloxane elastomer film can slow down the evaporation of water in the hydrogel and thus extend the service life of the wearable strain sensor based on the carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is based on the stress-strain curve of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel under tensile test;

[0020] Figure 2 It is based on the adhesion strength of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel to different substrates in adhesion and peel tests;

[0021] Figure 3 It is based on the output voltage curve of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel under simulated sunlight;

[0022] Figure 4 The wearable strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel is shown in photos at different finger bending angles (0°, 30°, 60° and 90°) and the current-time curve;

[0023] Figure 5 This is a photo of the wearable strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel when writing text and the current-time change curve;

[0024] Figure 6 The current-time variation curve of the wearable strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel transmitting Morse code through long and short presses. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings. The following examples are used to more clearly illustrate the technical solution of the present invention, but are not intended to limit the protection scope of the present invention.

[0026] The embodiment of the present invention provides a method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel, comprising the following steps: preparing a mixed aqueous solution A of carboxymethyl cellulose and sodium lignin sulfonate; Adding liquid metal to mixed aqueous solution A and subjecting it to ultrasonic treatment to obtain solution B; Add acrylic acid to solution B, stir evenly, then add a crosslinking agent and an initiator to obtain solution C; The solution C was introduced into the mold for in-situ polymerization to obtain the hydrogel D; preparing polydimethylsiloxane elastomer films; The hydrogel D was placed on the prepared polydimethylsiloxane elastomer film, copper electrodes were connected to both sides of the hydrogel D through conductive silver paste, and then wrapped with the polydimethylsiloxane elastomer film to obtain a flexible strain sensor.

[0027] In this embodiment, the mass volume ratio of carboxymethyl cellulose, sodium lignin sulfonate and water in the mixed solution A is 0.05-0.125:0.02:16 g / g / mL.

[0028] Preferably, the mass volume ratio of carboxymethyl cellulose, sodium lignin sulfonate and water in the mixed aqueous solution A is 0.1:0.02:16 g / g / mL.

[0029] In this embodiment, the liquid metal is a gallium-indium alloy, the mass ratio of metal gallium to metal indium in the gallium-indium alloy is 75.5:24.5, and the amount of the gallium-indium alloy added is 0.3 g.

[0030] In this embodiment, the power of the ultrasonic treatment in S2 is 450-500 W, preferably 500 W, and the treatment time is 80-90 min, preferably 90 min.

[0031] In this embodiment, the amount of acrylic acid added is 4 g, and the crosslinking agent and initiator are N'N-methylenebisacrylamide and ammonium persulfate, respectively.

[0032] In this embodiment, the method for preparing the polydimethylsiloxane elastomer film includes: Weigh the polydimethylsiloxane solution, add the curing agent and stir thoroughly, apply the mixed solution dropwise on a glass sheet to make it level, and peel it off from the glass sheet after vacuum curing to obtain a film.

[0033] In this embodiment, the amount of the polydimethylsiloxane solution added is 1 g to 2 g, the amount of the curing agent added is 0.1 g to 0.2 g, and the vacuum curing time is 40 to 60 min.

[0034] In this embodiment, the curing agent is diphenylbutyl carbamate.

[0035] The embodiments of the present invention also provide the application of the flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel prepared by the above-mentioned preparation method in wearable flexible electronic devices.

[0036] Example 1

[0037] Step 1, preparation of a carboxymethyl cellulose-liquid metal nanocomposite suspension, i.e., solution B, comprises the following specific steps: (1) Weigh 0.05 g of carboxymethyl cellulose and add it to 16 mL of an aqueous solution containing 0.02 g of sodium lignin sulfonate, and stir and mix the mixture with a magnetic stirrer at 65°C to obtain a mixed aqueous solution A; (2) Slowly add 0.3 g of liquid metal to the solution in (1) and pretreat for a certain period of time to obtain a carboxymethyl cellulose-liquid metal nanocomposite suspension.

[0038] Step 2, preparation of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid suspension, i.e., solution C, comprises the following specific steps: Add 4 g of acrylic acid to the carboxymethyl cellulose-liquid metal nanocomposite suspension prepared in step 1, stir for 3-5 min, and then add 0.02 g of N'N-methylenebisacrylamide and 0.05 g of ammonium persulfate to form a carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid suspension.

[0039] Step 3, preparation of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel, i.e., hydrogel D, the specific method steps of which include: The carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-acrylic acid suspension prepared in step 2 is introduced into a mold and in-situ polymerized at 25-30° C. to obtain a carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel.

[0040] Step 4, preparation of polydimethylsiloxane elastomer film, the specific method steps include: (1) Weigh 1-2 g of polydimethylsiloxane solution, add 0.1-0.2 g of curing agent (butyl diphenyl carbamate), stir the mixture thoroughly with a magnetic stirrer, and leave it for 30-40 min; (2) Weigh 1-2 g of the mixed solution prepared in step (1) and apply it on a glass sheet to make it level. Place it in a vacuum oven to cure for 40-60 min, and peel it off from the glass sheet to obtain a thin film of polydimethylsiloxane elastomer. Use the same method to prepare another piece of polydimethylsiloxane elastomer.

[0041] Step 5, preparation of the flexible strain sensor, the specific method steps include: The carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel prepared in step 3 is placed on the polydimethylsiloxane elastomer film prepared in step 4, two copper electrodes are connected to both sides of the carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel through conductive silver paste, and the above system is then wrapped with a polydimethylsiloxane elastomer film to obtain a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel.

[0042] Example 2

[0043] Step 1, preparation of a carboxymethyl cellulose-liquid metal nanocomposite suspension, i.e., solution B, comprises the following specific steps: (1) Weigh 0.075 g of carboxymethyl cellulose and add it to 16 mL of an aqueous solution containing 0.02 g of sodium lignin sulfonate, and stir and mix with a magnetic stirrer at 65°C to obtain a mixed aqueous solution A; (2) Slowly add 0.3 g of liquid metal to the solution in (1) and pretreat for a certain period of time to obtain a carboxymethyl cellulose-liquid metal nanocomposite suspension.

[0044] Step 2, preparation of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid suspension, i.e., solution C, comprises the following specific steps: Add 4 g of acrylic acid to the carboxymethyl cellulose-liquid metal nanocomposite suspension prepared in step 1, stir for 3-5 min, and then add 0.02 g of N'N-methylenebisacrylamide and 0.05 g of ammonium persulfate to form a carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid suspension.

[0045] Step 3, preparation of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel, i.e., hydrogel D, the specific method steps of which include: The carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-acrylic acid suspension prepared in step 2 is introduced into a mold and in-situ polymerized at 25-30° C. to obtain a carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel.

[0046] Step 4, preparation of polydimethylsiloxane elastomer film, the specific method steps include: (1) Weigh 1-2 g of polydimethylsiloxane solution, add 0.1-0.2 g of curing agent (butyl diphenyl carbamate), stir the mixture thoroughly with a magnetic stirrer, and leave it for 30-40 min; (2) Weigh 1-2 g of the mixed solution prepared in step (1) and apply it on a glass sheet to make it level. Place it in a vacuum oven to cure for 40-60 min, and peel it off from the glass sheet to obtain a thin film of polydimethylsiloxane elastomer. Use the same method to prepare another piece of polydimethylsiloxane elastomer.

[0047] Step 5, preparation of the flexible strain sensor, the specific method steps include: The carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel prepared in step 3 is placed on the polydimethylsiloxane elastomer film prepared in step 4, two copper electrodes are connected to both sides of the carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel through conductive silver paste, and the above system is then wrapped with a polydimethylsiloxane elastomer film to obtain a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel.

[0048] Example 3

[0049] Step 1, preparation of a carboxymethyl cellulose-liquid metal nanocomposite suspension, i.e., solution B, comprises the following specific steps: (1) Weigh 0.1 g of carboxymethyl cellulose and add it to 16 mL of an aqueous solution containing 0.02 g of sodium lignin sulfonate, and stir and mix the mixture with a magnetic stirrer at 65°C to obtain a mixed aqueous solution A; (2) Slowly add 0.3 g of liquid metal to the solution in (1) and pretreat for a certain period of time to obtain a carboxymethyl cellulose-liquid metal nanocomposite suspension.

[0050] Step 2, preparation of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid suspension, i.e., solution C, comprises the following specific steps: Add 4 g of acrylic acid to the carboxymethyl cellulose-liquid metal nanocomposite suspension prepared in step 1, stir for 3-5 min, and then add 0.02 g of N'N-methylenebisacrylamide and 0.05 g of ammonium persulfate to form a carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid suspension.

[0051] Step 3, preparation of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel, the specific method steps of which include: The carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-acrylic acid suspension prepared in step 2 is introduced into a mold and in-situ polymerized at 25-30° C. to obtain a carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel.

[0052] Step 4, preparation of polydimethylsiloxane elastomer film, the specific method steps include: (1) Weigh 1-2 g of polydimethylsiloxane solution, add 0.1-0.2 g of curing agent (butyl diphenyl carbamate), stir the mixture thoroughly with a magnetic stirrer, and leave it for 30-40 min; (2) Weigh 1-2 g of the mixed solution prepared in step (1) and apply it on a glass sheet to make it level. Place it in a vacuum oven to cure for 40-60 min, and peel it off from the glass sheet to obtain a thin film of polydimethylsiloxane elastomer. Use the same method to prepare another piece of polydimethylsiloxane elastomer.

[0053] Step 5, preparation of the flexible strain sensor, the specific method steps include: The carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel prepared in step 3 is placed on the polydimethylsiloxane elastomer film prepared in step 4, two copper electrodes are connected to both sides of the carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel through conductive silver paste, and the above system is then wrapped with a polydimethylsiloxane elastomer film to obtain a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel.

[0054] Example 4

[0055] Step 1, preparation of a carboxymethyl cellulose-liquid metal nanocomposite suspension, i.e., solution B, comprises the following specific steps: (1) Weigh 0.125 g of carboxymethyl cellulose and add it to 16 mL of an aqueous solution containing 0.02 g of sodium lignin sulfonate, and stir and mix with a magnetic stirrer at 65°C to obtain a mixed aqueous solution A; (2) Slowly add 0.3 g of liquid metal to the solution in (1) and pretreat for a certain period of time to obtain a carboxymethyl cellulose-liquid metal nanocomposite suspension.

[0056] Step 2, preparation of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid suspension, i.e., solution C, comprises the following specific steps: Add 4 g of acrylic acid to the carboxymethyl cellulose-liquid metal nanocomposite suspension prepared in step 1, stir for 3-5 min, and then add 0.02 g of N'N-methylenebisacrylamide and 0.05 g of ammonium persulfate to form a carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid suspension.

[0057] Step 3, preparation of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel, i.e., hydrogel D, the specific method steps of which include: The carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-acrylic acid suspension prepared in step 2 is introduced into a mold and in-situ polymerized at 25-30° C. to obtain a carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel.

[0058] Step 4, preparation of polydimethylsiloxane elastomer film, the specific method steps include: (1) Weigh 1-2 g of polydimethylsiloxane solution, add 0.1-0.2 g of curing agent (butyl diphenyl carbamate), stir the mixture thoroughly with a magnetic stirrer, and leave it for 30-40 min; (2) Weigh 1-2 g of the mixed solution prepared in step (1) and apply it on a glass sheet to make it level. Place it in a vacuum oven to cure for 40-60 min, and peel it off from the glass sheet to obtain a thin film of polydimethylsiloxane elastomer. Use the same method to prepare another piece of polydimethylsiloxane elastomer.

[0059] Step 5, preparation of the flexible strain sensor, the specific method steps include: (1) The carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel prepared in step 3 is placed on the polydimethylsiloxane elastomer film prepared in step 4, two copper electrodes are connected to both sides of the carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel through conductive silver paste, and the above system is then wrapped with a polydimethylsiloxane elastomer film to prepare a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel.

[0060] Figure 1 In the tensile test, the tensile stress-strain curve of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel shows that as the amount of carboxymethyl cellulose added increases from 0g to 0.125g, the tensile strength of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel increases first and then decreases. When the amount of carboxymethyl cellulose added reaches 0.1g, carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel has the best mechanical strength, with an elongation at break of 331% and a tensile strength of 101.96kPa, indicating that a certain amount of carboxymethyl cellulose can be used as a reinforcing phase to greatly improve the mechanical properties of the hydrogel. Figure 2 It is the adhesion strength value of carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel on different substrates, indicating that the hydrogel has high adhesion strength to many substrates and is suitable for application in wearable flexible electronic devices. Figure 3 It is carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid under simulated sunlight (100mW cm -2) irradiation, the output voltage curve shows that the continuous voltage output can remain stable under irradiation conditions of more than 10,000 seconds, indicating that the hydrogel has excellent photothermal to electric conversion ability and can stabilize the output voltage (3mV). Figure 4 The flexible strain sensor monitors the movement of human finger joints. The graph of the current variation over time at different finger bending angles (30°, 60° and 90°) shows that the sensor has good sensing sensitivity, stability and repeatability. Figure 5 The flexible strain sensor monitors the fingers' writing. For the complex and tiny movements of the fingers when writing, the flexible strain sensor can also quickly respond to the current signal, indicating the repeatable and stable current response capability of the flexible strain sensor. Figure 6 The flexible strain sensor transmits Morse code through long press and short press. The flexible strain sensor can also quickly respond to current signals, indicating that the flexible strain sensor can be used in different sensing fields.

[0061] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above-mentioned implementation mode, but also include technical solutions composed of any combination of the above-mentioned technical features. The above is only a preferred implementation mode of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also considered as the protection scope of the present invention.

Claims

1. A method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel, characterized in that: The following steps are involved: preparing a mixed aqueous solution A of carboxymethyl cellulose and sodium lignin sulfonate; Adding liquid metal to mixed aqueous solution A and subjecting it to ultrasonic treatment to obtain solution B; Add acrylic acid to solution B, stir evenly, then add a crosslinking agent and an initiator to obtain solution C; The solution C was introduced into the mold for in-situ polymerization to obtain the hydrogel D; preparing polydimethylsiloxane elastomer films; The hydrogel D was placed on the prepared polydimethylsiloxane elastomer film, copper electrodes were connected to both sides of the hydrogel D through conductive silver paste, and then wrapped with the polydimethylsiloxane elastomer film to obtain a flexible strain sensor.

2. The method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel according to claim 1, characterized in that: The mass volume ratio of carboxymethyl cellulose, sodium lignin sulfonate and water in the mixed solution A is 0.05-0.125:0.02:16 g / g / mL.

3. The method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel according to claim 1, characterized in that: The mass volume ratio of carboxymethyl cellulose, sodium lignin sulfonate and water in the mixed aqueous solution A is 0.1:0.02:16 g / g / mL.

4. The method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel according to claim 1, characterized in that: The liquid metal is a gallium-indium alloy, the mass ratio of metal gallium to metal indium in the gallium-indium alloy is 75.5:24.5, and the added amount of the gallium-indium alloy is 0.3 g.

5. The method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel according to claim 1, characterized in that: The power of the ultrasonic treatment in S2 is 450-500 W, and the treatment time is 80-90 min.

6. The method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel according to claim 1, characterized in that: The amount of acrylic acid added is 4 g, and the crosslinking agent and initiator are N'N-methylenebisacrylamide and ammonium persulfate respectively.

7. The method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel according to claim 1, characterized in that: The preparation method of the polydimethylsiloxane elastomer film comprises: Weigh the polydimethylsiloxane solution, add the curing agent and stir thoroughly, apply the mixed solution dropwise on a glass sheet to make it level, and peel it off from the glass sheet after vacuum curing to obtain a film.

8. The method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel according to claim 7, characterized in that: The amount of the polydimethylsiloxane solution added is 1 g to 2 g, the amount of the curing agent added is 0.1 g to 0.2 g, and the vacuum curing time is 40 to 60 minutes.

9. The method for preparing a flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel according to claim 7, characterized in that: The curing agent is diphenyl butyl carbamate.

10. Application of the flexible strain sensor based on carboxymethyl cellulose-liquid metal-sodium lignin sulfonate-polyacrylic acid hydrogel prepared by the preparation method according to any one of claims 1 to 9 in wearable flexible electronic devices.

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