A method for preparing a tensile-responsive conductive hydrogel with high strength and high sensitivity

Abstract

The present invention relates to the field of polymer functions and conductive materials, and in particular to a method for preparing a tensile-responsive conductive hydrogel with high strength and high sensitivity; the raw materials include polyvinyl alcohol, boric acid solution, graphene oxide, ferric chloride hexahydrate, agar, etc.; the preparation method of the present invention utilizes the physical means of cyclic freeze-thaw to quickly improve the mechanical properties of the hydrogel; the immersion strategy is designed to effectively improve the mechanical and electrical properties; the dynamic crosslinking effect between polyvinyl alcohol and boroester bonds and the ionic bonds between graphene oxide and trivalent iron ions produce the characteristic of tensile responsiveness; the preparation method of the hydrogel of the present invention is very simple, has the characteristics of tensile response, ultra-high mechanical properties and excellent electrical properties, and has great application prospects in the fields of wearable sensing devices and soft robots.

Description

Technical Field

[0001] The present invention relates to the field of polymer functions and conductive materials, and in particular to a method for preparing a tensile-responsive conductive hydrogel with high strength and high sensitivity. Background Art

[0002] Conductive hydrogels are often used in strain sensors, biomedicine, flexible wearable electronic devices, soft robots and other fields, mainly because they can better overcome the rigidity generated by the conjugated system of conductive polymers and the green and harmless nature of synthetic materials, making hydrogels a biocompatible material with extremely high water content and high elasticity.

[0003] At present, the common method for improving the conductivity is to introduce conductive materials such as carbon nanomaterials, liquid metals, inorganic ions, conductive polymers, etc. into the hydrogel or to add a conductive layer on the surface of the hydrogel. However, in general, the hydrogels induced by salt immersion and polyelectrolyte have the disadvantages of low conductivity and small sensitivity factor. The use of carbon nanomaterials will reduce the tensile strain due to the introduction of rigid particles. It is difficult to achieve a balance between mechanical and electrical properties.

[0004] At present, the system with PVA as elastic substrate and nanocomposite material as filling has good tensile strain and conductivity, but in the application of actual scenes, such as the simulation of tendons, muscles and bones, a higher Young's modulus and stronger mechanical properties are usually required. In response to this demand, the mechanical properties have been improved through various means, and attempts have been made to introduce a variety of dynamic networks into the hydrogel, such as hydrogen bonds, organic polymers, inorganic ions and other cross-linking effects, so that the hydrogel has more energy "sacrificial domains" and energy dissipation mechanisms in the process of doing work, as well as the repair and response of the dynamic network, but it often leads to a significant decrease in the water content of the hydrogel, and the conductivity of the hydrogel is sacrificed in the pursuit of mechanical properties. Therefore, it is very necessary to develop a hydrogel that takes into account both mechanical and electrical properties and can maintain stability for a long time. Summary of the invention

[0005] The present invention aims to solve the problem that the existing hydrogels are difficult to withstand high-strength stretching for a long time and their own mechanical properties and electrical properties cannot be taken into account at the same time, and provides a method for preparing a tensile-responsive conductive hydrogel with both high strength and high sensitivity.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing a tensile-responsive conductive hydrogel with high strength and high sensitivity, comprising the following steps:

[0007] Step 1) firstly ultrasonically dissolve graphene oxide in deionized water until the graphene oxide is fully dissolved to form a graphene oxide solution;

[0008] Step 2) Weigh ferric chloride hexahydrate and dissolve it in deionized water, then mix it with polyvinyl alcohol and the graphene oxide solution in step 1), stir it at a constant speed in a nitrogen atmosphere, keep the temperature at 95° C., and continue for two hours;

[0009] Step 3) Add agar to the mixed solution of step 2) and stir for 0.5 hours while keeping the temperature constant;

[0010] Step 4) Prepare BB solution, add it into the mixed solution in step 3) and continue the reaction for 1 hour;

[0011] Step 5) Pour the reaction solution into a petri dish and let it stand at 80°C for 1 hour to eliminate bubbles;

[0012] Step 6) The solution was subjected to 5 freeze / thaw cycles to obtain PVA-BB / GO-Fe 3+ / agar hydrogel;

[0013] Step 7) PVA-BB / GO-Fe 3+ / agar hydrogels were immersed in potassium chloride solution for 0-10 hours.

[0014] PVA-BB / GO-Fe 3+ / agar hydrogel's full Chinese name is polyvinyl alcohol-boric acid solution / graphene oxide-trivalent iron ion / agar hydrogel.

[0015] The advantages of the present invention are: 1) the mechanical properties of the hydrogel are rapidly improved by the physical means of freeze-thaw cycles; 2) the mechanical and electrical properties are effectively improved by designing an immersion strategy; 3) the dynamic cross-linking between polyvinyl alcohol and boron ester bonds and the ionic bonds between graphene oxide and trivalent iron ions produce the characteristic of tensile responsiveness. The preparation method of this hydrogel is very simple and has the characteristics of tensile responsiveness, ultra-high mechanical properties and excellent electrical properties.

[0016] Furthermore, the mass concentration of the graphene oxide solution in step 1) is 0.4%.

[0017] Furthermore, the mass ratio of ferric chloride hexahydrate, polyvinyl alcohol and graphene oxide added in step 2) is 4-7:126:2; the volume ratio of deionized water added in step 2) to step 1) is 5:1.

[0018] Furthermore, the mass ratio of the amount of agar added in step 3) to the amount of graphene oxide added in step 1) is 3:1.

[0019] Furthermore, the BB solution in step 4) is a mixed solution of 0.04 mol borax and 0.04 mol boric acid, and the volume ratio of the added volume of the BB solution to the volume of the deionized water in step 2) is 6:1.

[0020] Furthermore, the freezing / freeze-thawing conditions in step 6) are freezing at -20°C for 16 hours and then thawing at room temperature for 8 hours.

[0021] Furthermore, the mass concentration of the potassium chloride solution in step 7) is 20%.

[0022] Prepared PVA-BB / GO-Fe 3+ The detection method of / agar hydrogel is as follows:

[0023] 1. PVA-BB / GO-Fe 3+ Mechanical properties test of agar hydrogel:

[0024] All mechanical tests were performed using the same universal testing machine (INSTRON LEGEND 2345). The hydrogels were cut into cuboids with a length of 10 mm, a width of 5 mm, and a thickness of 2 mm, and subjected to tensile and loading-unloading tests at a speed of 20 mm / min. The energy dissipation coefficient was calculated by calculating the area between the loading-unloading curves to estimate the energy dissipation and dividing the dissipated energy by the load curve.

[0025] 2. PVA-BB / GO-Fe 3+ Electrical properties of agar hydrogel:

[0026] All electrical properties were measured by the same electrochemical workstation (DH7000). The conductivity was measured by electrochemical impedance spectroscopy (EIS), usually by sandwiching a hydrogel between two platinum sheets, with a control test range of 0.1HZ to 1MHZ and a hydrogel area of ​​0.5cm 2 , with a thickness of 0.2 cm. The calculation equation for ionic conductivity (σ) is: σ =L / (R× S), where L is the thickness of the hydrogel, R is the resistance determined by the intersection of the impedance curve and the real axis, and S is the area of ​​the hydrogel.

[0027] In addition, the present invention also provides the application of the conductive hydrogel prepared by the above preparation method in the field of strain sensors. 3+ / agar hydrogel can maintain ultra-high mechanical and electrical performance and stability while also having the characteristic of tensile response. It can support the sensing requirements in most scenarios, such as being attached to the athlete's knees, elbows, soles of feet, etc., and can support and stably transmit electrical signals.

[0028] In addition, the present invention also provides applications of the conductive hydrogel prepared by the above-mentioned preparation method in the fields of wearable sensing devices and soft robots.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The method of the present invention prepares different Fe 3+ The PVA-BB / GO-Fe hydrogel with tensile responsiveness, high strength and sensitivity was obtained through a simple freeze-thaw and soaking strategy. 3+ / agar hydrogel. The dynamic cross-linking bonds between polyvinyl alcohol and boron ester bonds and the ionic bonds between graphene oxide and trivalent iron ions produce tensile responsiveness; a large number of hydrogen bonds, ionic bonds and salting-out effects in the system give it strong mechanical properties; K + , Cl - , Fe 3+ The introduction of ions provides higher conductivity. In addition, by changing the number and time of freeze-thaw cycles and the duration of immersion, systems with different mechanical strengths and conductivity can be flexibly prepared to adapt to different environments.

[0031] PVA-BB / GO-Fe 3+ / agar hydrogel can maintain ultra-high mechanical and electrical performance and stability while also having the characteristic of tensile response. It can support sensing requirements in most scenarios, such as being attached to athletes' knees, elbows, soles of feet, etc., and can support and stably transmit electrical signals. It can have great application prospects in the field of strain sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 PVA-BB / GO-Fe 3+ Figure 1 shows the mechanical properties of the agar hydrogel. Figure a shows the tensile stress-strain curves of Examples 1, 2, 3, and 4 after immersion in KCl solution for 2 hours; Figure b shows the corresponding stress-strain bar graph; and Figure c shows the 50-cycle loading-unloading curve.

[0033] Figure 2 PVA-BB / GO-Fe 3+ Figure a is the Nyquist curve of Example 4 after immersion in KCl solution for 0, 1, 2, 3, and 10 hours, and Figure b is the specific conductivity diagram calculated based on the Nyquist curve. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with specific embodiments.

[0035] Example 1

[0036] A method for preparing a tensile-responsive conductive hydrogel with high strength and high sensitivity comprises the following steps:

[0037] Step 1) First, 0.1 g of graphene oxide is ultrasonically dissolved in 25 ml of deionized water until it is fully dissolved to form a graphene oxide solution.

[0038] Step 2) Weigh 0.20 g of ferric chloride hexahydrate and dissolve it in 5 ml of deionized water, pour it into a three-necked flask together with 6.3 g of polyvinyl alcohol and graphene oxide solution, stir at a constant speed in a nitrogen atmosphere, maintain the temperature at 95° C., and continue for two hours.

[0039] Step 3) Add 0.3 g of agar to the three-necked flask and stir for 0.5 hour while maintaining the temperature.

[0040] Step 4) Prepare 30 ml of BB solution (a mixed solution of 0.04 mol borax and 0.04 mol boric acid), add it into a three-necked flask and continue the reaction for 1 hour.

[0041] Step 5) Pour the reaction solution into a petri dish and let it stand at 80°C for 1 hour to eliminate bubbles.

[0042] Step 6) The solution was subjected to 5 freeze / thaw cycles (freezing at -20°C for 16 hours and then thawing at room temperature for 8 hours).

[0043] Step 7) Prepare potassium chloride solution (dissolve 25 g KCl in 100 ml deionized water) and soak the gel for 2 hours.

[0044] Example 2

[0045] A method for preparing a tensile-responsive conductive hydrogel with high strength and high sensitivity comprises the following steps:

[0046] Step 1) First, 0.1 g of graphene oxide is ultrasonically dissolved in 25 ml of deionized water until it is fully dissolved to form a graphene oxide solution.

[0047] Step 2) Weigh 0.25 g of ferric chloride hexahydrate and dissolve it in 5 ml of deionized water, pour it into a three-necked flask together with 6.3 g of polyvinyl alcohol and graphene oxide solution, stir at a constant speed in a nitrogen atmosphere, maintain the temperature at 95° C., and continue for two hours.

[0048] Step 3) Add 0.3 g of agar to the three-necked flask and stir for 0.5 hour while maintaining the temperature.

[0049] Step 4) Prepare 30 ml of BB solution (a mixed solution of 0.04 mol borax and 0.04 mol boric acid), add it into a three-necked flask and continue the reaction for 1 hour.

[0050] Step 5) Pour the reaction solution into a petri dish and let it stand at 80°C for 1 hour to eliminate bubbles.

[0051] Step 6) The solution was subjected to 5 freeze / thaw cycles (freezing at -20°C for 16 hours and then thawing at room temperature for 8 hours).

[0052] Step 7) Prepare potassium chloride solution (dissolve 25 g KCl in 100 ml deionized water) and soak the gel for 2 hours.

[0053] Example 3

[0054] A method for preparing a tensile-responsive conductive hydrogel with high strength and high sensitivity comprises the following steps:

[0055] Step 1) First, 0.1 g of graphene oxide is ultrasonically dissolved in 25 ml of deionized water until it is fully dissolved to form a graphene oxide solution.

[0056] Step 2) Weigh 0.30 g of ferric chloride hexahydrate and dissolve it in 5 ml of deionized water, pour it into a three-necked flask together with 6.3 g of polyvinyl alcohol and graphene oxide solution, stir at a constant speed in a nitrogen atmosphere, maintain the temperature at 95° C., and continue for two hours.

[0057] Step 3) Add 0.3 g of agar to the three-necked flask and stir for 0.5 hour while maintaining the temperature.

[0058] Step 4) Prepare 30 ml of BB solution (a mixed solution of 0.04 mol borax and 0.04 mol boric acid), add it into a three-necked flask and continue the reaction for 1 hour.

[0059] Step 5) Pour the reaction solution into a petri dish and let it stand at 80°C for 1 hour to eliminate bubbles.

[0060] Step 6) The solution was subjected to 5 freeze / thaw cycles (freezing at -20°C for 16 hours and then thawing at room temperature for 8 hours).

[0061] Step 7) Prepare potassium chloride solution (dissolve 25 g KCl in 100 ml deionized water) and soak the gel for 2 hours.

[0062] Example 4

[0063] A method for preparing a tensile-responsive conductive hydrogel with high strength and high sensitivity comprises the following steps:

[0064] Step 1) First, 0.1 g of graphene oxide is ultrasonically dissolved in 25 ml of deionized water until it is fully dissolved to form a graphene oxide solution.

[0065] Step 2) Weigh 0.35 g of ferric chloride hexahydrate and dissolve it in 5 ml of deionized water, pour it into a three-necked flask together with 6.3 g of polyvinyl alcohol and graphene oxide solution, stir at a constant speed in a nitrogen atmosphere, maintain the temperature at 95° C., and continue for two hours.

[0066] Step 3) Add 0.3 g of agar to the three-necked flask and stir for 0.5 hour while maintaining the temperature.

[0067] Step 4) Prepare 30 ml of BB solution (a mixed solution of 0.04 mol borax and 0.04 mol boric acid), add it into a three-necked flask and continue the reaction for 1 hour.

[0068] Step 5) Pour the reaction solution into a petri dish and let it stand at 80°C for 1 hour to eliminate bubbles.

[0069] Step 6) The solution was subjected to 5 freeze / thaw cycles (freezing at -20°C for 16 hours and then thawing at room temperature for 8 hours).

[0070] Step 7) Prepare potassium chloride solution (dissolve 25 g KCl in 100 ml deionized water) and soak the gel for 0, 1, 2, 3, and 10 hours respectively.

[0071] PVA-BB / GO-Fe 3+ / agar hydrogel detection:

[0072] 1) PVA-BB / GO-Fe 3+ Mechanical properties of agar hydrogels

[0073] Mechanical tests were performed using the same universal testing machine (INSTRON LEGEND 2345). The hydrogel was cut into cuboids with a length of 10 mm, a width of 5 mm, and a thickness of 2 mm, and subjected to tensile and loading-unloading tests at a speed of 20 mm / min. The energy dissipation coefficient was calculated by calculating the area between the loading-unloading curves to estimate the energy dissipation and dividing the dissipated energy by the load curve. Figure 1 This is the mechanical properties test of PVA-BB / GO-Fe3+ / agar hydrogel. Figure 1 a is the tensile stress-strain curve of Examples 1, 2, 3, and 4 after being immersed in KCl solution for 2 hours; Figure 1 b is the bar graph of the corresponding stress-strain; Figure 1 c is the 50-time loading-unloading cycle curve. It can be seen intuitively from the figure that when Fe 3+ When the addition amount is 0.35g, the mechanical properties reach the maximum value, and the tensile stress is 3.05Mpa, which is higher than that of Fe 3+ When the addition amount was 0.2g, it increased by 3.35 times, indicating that Fe 3+ The content has a great influence on the mechanical properties; in addition, it can be found that after 50 cycles, the maximum tensile stress increases from 1.467Mpa to 1.927Mpa, which fully illustrates the characteristics of the mechanical response and the ultra-high mechanical properties.

[0074] 2) PVA-BB / GO-Fe 3+ Electrical properties of Mg / agar hydrogels

[0075] The electrical properties were measured by the same electrochemical workstation (DH7000). The conductivity was measured by electrochemical impedance spectroscopy (EIS), usually by sandwiching a hydrogel between two platinum sheets, with a control test range of 0.1HZ to 1MHZ and a hydrogel area of ​​0.5cm 2 , thickness is 0.2cm. The calculation equation of ionic conductivity (σ) is: σ = L / (R×S), where L is the thickness of the hydrogel, R is the resistance determined by the intersection of the impedance curve and the real axis, and S is the area of ​​the hydrogel. Figure 2 a is the Nyquist curve of Example 4 after immersion in KCl solution for 0, 1, 2, 3, and 10 hours, Figure 2 b is the specific conductivity diagram calculated based on the Nyquist curve. It can be seen from the figure that the overall trend is first increasing and then decreasing. When the immersion time is 2 hours, it reaches the highest value of 20.6 S / m, which is 7.4 times higher than 2.8 S / m without immersion, indicating that the immersion strategy can effectively improve the conductivity of the system.

Claims

1. A method for preparing a tensile-responsive conductive hydrogel having both high strength and high sensitivity, characterized in that: The following steps are involved: Step 1) firstly ultrasonically dissolve graphene oxide in deionized water until the graphene oxide is fully dissolved to form a graphene oxide solution; Step 2) Weigh ferric chloride hexahydrate and dissolve it in deionized water, then mix it with polyvinyl alcohol and the graphene oxide solution in step 1), stir it at a constant speed in a nitrogen atmosphere, keep the temperature at 95° C., and continue for two hours; wherein the mass ratio of ferric chloride hexahydrate, polyvinyl alcohol and graphene oxide is 4-7:126:2; Step 3) Add agar to the mixed solution of step 2) and stir for 0.5 hours while keeping the temperature constant; Step 4) preparing a BB solution, adding it to the mixed solution in step 3) and continuing the reaction for 1 hour; the BB solution is a mixed solution of 0.04 mol borax and 0.04 mol boric acid, and the volume ratio of the added BB solution to the deionized water in step 2) is 6:1; Step 5) Pour the reaction solution into a petri dish and let it stand at 80°C for 1 hour to eliminate bubbles; Step 6) The solution was subjected to 5 freeze / thaw cycles to obtain PVA-BB / GO-Fe 3+ / agar hydrogel; Step 7) PVA-BB / GO-Fe 3+ / agar hydrogels were immersed in potassium chloride solution for 1-10 hours.

2. The method for preparing a high-strength and high-sensitivity tension-responsive conductive hydrogel according to claim 1, characterized in that: The mass concentration of the graphene oxide solution in step 1) is 0.4%.

3. The method for preparing a high-strength, high-sensitivity tension-responsive conductive hydrogel according to claim 1, characterized in that: The volume ratio of the deionized water added in step 2) to that added in step 1) is 5:

1.

4. The method for preparing a high-strength, high-sensitivity tension-responsive conductive hydrogel according to claim 1, characterized in that: The mass ratio of the amount of agar added in step 3) to the amount of graphene oxide added in step 1) is 3:

1.

5. The method for preparing a high-strength, high-sensitivity tension-responsive conductive hydrogel according to claim 1, characterized in that: Step 6) The freezing / freeze-thawing conditions are freezing at -20°C for 16 hours and then thawing at room temperature for 8 hours.

6. The method for preparing a high-strength, high-sensitivity tension-responsive conductive hydrogel according to claim 1, characterized in that: The mass concentration of the potassium chloride solution in step 7) is 20%.

7. Application of the conductive hydrogel prepared by the preparation method according to any one of claims 1 to 6 in the field of strain sensors.

8. Application of a conductive hydrogel prepared by the preparation method according to any one of claims 1 to 6 in the fields of wearable sensing devices and soft robots.

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