Organic hydrogel with environmental stability and conductivity as well as preparation method and application of organic hydrogel

Abstract

The invention belongs to the field of sensors, and discloses organic hydrogel with environmental stability and electrical conductivity as well as a preparation method and application of the organic hydrogel. The preparation method comprises the following steps: (1) adding poly (3, 4-ethylenedioxythiophene)-polystyrolsulfon acid into water, and uniformly stirring to obtain a dispersion liquid A; (2) adding polyethyleneimine, acrylamide and [2-(methylacryloyloxy) ethyl] dimethyl-(3-sulfonic acid propyl) ammonium hydroxide into the dispersion liquid A, uniformly stirring, and performing ultrasonic dispersion to obtain dispersion liquid B; (3) adding a cross-linking agent and an initiator into the dispersion liquid B, uniformly stirring, ultrasonically dispersing, deoxidizing in vacuum, and carrying out free radical polymerization reaction to obtain conductive hydrogel; and (4) soaking the conductive hydrogel in a low-volatility organic solvent for solvent replacement to prepare the organic hydrogel. The organic hydrogel prepared by the invention is applied as a sensor in flexible wearable electronic equipment. The organic hydrogel prepared by the invention has high stretchability, environmental stability and high conductivity.

Description

Technical Field

[0001] The invention belongs to the field of sensors, and in particular relates to an organic hydrogel having both environmental stability and electrical conductivity, and a preparation method and application thereof. Background Art

[0002] In the medical field, temperature sensors are indispensable. Monitoring human body temperature is one of the important bases for diagnosing diseases. Traditional mercury thermometers require a long time to measure and cannot achieve real-time monitoring. Although infrared temperature guns are fast, they need to be close to the object being measured and have obvious shortcomings in accuracy. Although thermocouples have a wide measurement range, their accuracy in the low temperature range is low and requires complex compensation circuits. Therefore, it is necessary to design an instrument that can monitor body temperature for a long time.

[0003] As a highly flexible material, hydrogel is developing rapidly in the field of wearable electronic devices. Hydrogel has good biocompatibility and skin affinity, and can fit closely to human skin, reducing discomfort when wearing. This property makes hydrogel perform well in wearable electronic devices such as electronic skin and health monitoring equipment. The flexibility and stretchability of hydrogel enable it to adapt to the movement and deformation of the human body, without being damaged by bending or stretching, and can quickly respond to changes in human movement or physiological signals. In addition, the ions in the hydrogel will migrate when the temperature changes, causing its conductivity to change. For example, hydrogels containing ions with larger radii are very sensitive to temperature changes, and the movement of ions increases with increasing temperature, thereby changing the conductivity of the hydrogel. This property can be used to develop highly sensitive temperature sensors.

[0004] Based on traditional hydrogels, organic hydrogels can be prepared by introducing low-volatile organic solvents (such as ethylene glycol and glycerol), and they show good environmental stability and antifreeze and anti-drying properties. The principle is that organic solvents form strong hydrogen bonds with water molecules, inhibiting ice crystal formation and reducing water evaporation. However, the addition of organic solvents reduces the conductivity of hydrogels, limiting their application in flexible wearable sensors. Therefore, the development of synthetic hydrogels that have both environmental stability and high conductivity is of great significance in the field of high-performance flexible sensors. Summary of the invention

[0005] In order to solve the shortcomings of the prior art hydrogels that cannot have both environmental stability and electrical conductivity, the purpose of the present invention is to provide an organic hydrogel having both environmental stability and electrical conductivity, and a preparation method and application thereof.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A method for preparing an organic hydrogel having both environmental stability and electrical conductivity, comprising the following steps: (1) Add poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid into water and stir evenly to obtain dispersion A; (2) Add polyethyleneimine, acrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium hydroxide to the dispersion A obtained in step (1), stir evenly and then disperse by ultrasonication to obtain dispersion B; (3) adding a crosslinking agent and an initiator to the dispersion B obtained in step (2), stirring evenly, ultrasonically dispersing, vacuum deoxygenating, and obtaining a conductive hydrogel through a free radical polymerization reaction; (4) Soaking the conductive hydrogel obtained in step (3) in a low-volatile organic solvent for solvent replacement to obtain an organic hydrogel having both environmental stability and conductivity.

[0007] Preferably, the dosage ratio of the raw materials is poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid: acrylamide: [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide: water = (0.67-1.6) g: (1.6-2.8) g: (1.6-2.8) g: 8 mL; the dosage of polyethyleneimine is 2-3% as a percentage of the total mass of acrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide; the molar dosage of the crosslinking agent is 0.01-0.05% as a percentage of the total molar dosage of acrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide, and the molar dosage of the initiator is 0.4-0.8%. Poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid itself is a solution and is directly added to the dispersion A. The present invention preferably uses poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid with a solid content of 1.3-1.7wt%. The present invention preferably uses polyethyleneimine with a weight average molecular weight of 70,000-75,000, which can be directly added to the dispersion A or added to the dispersion A in the form of an aqueous solution, as long as the amount of polyethyleneimine is within the range of 2-3%.

[0008] Preferably, the crosslinking agent is N,N'-methylenebisacrylamide, and the initiator is azobisisobutyronitrile.

[0009] Preferably, in step (1), the stirring time is 1 to 2 hours; in step (2), the stirring time is 15 minutes to 1 hour, and the ultrasonic dispersion time is 30 minutes to 1 hour; in step (3), the stirring time is 10 minutes to 15 minutes, and the ultrasonic dispersion time is 10 minutes to 15 minutes.

[0010] Preferably, in step (3), the temperature of the free radical polymerization reaction is 50-60° C. and the time is 10-24 h.

[0011] Preferably, in step (4), the low volatility organic solvent is 1,2-propylene glycol, ethylene glycol or glycerol.

[0012] Preferably, in step (4), the weight of the low-volatile organic solvent is 5 to 12 times the weight of the conductive hydrogel, and the immersion time is 1 to 6 hours.

[0013] An organic hydrogel prepared by the preparation method having both environmental stability and conductivity.

[0014] The environmentally stable and conductive organic hydrogel is used as a sensor in flexible wearable electronic devices.

[0015] Preferably, the sensor is a temperature sensor or a strain sensor.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The preparation method of the present invention is simple to operate and has low cost. The prepared organic hydrogel uses a network composed of polyethyleneimine / co-acrylamide-[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonate propyl)ammonium hydroxide / poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid as the basic skeleton, which significantly improves the tensile strength and elongation at break of the hydrogel, making it show higher stability and reliability in complex application environments. The intrinsic conductive polymer poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid in the system has good electronic properties. Conductivity, and the sulfonic acid group can ionize anions, as well as the thiophene cations ionized in poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid, which release free-moving ions in water, giving it a certain ionic conductivity. Finally, the low-volatile organic solvent has good hygroscopicity, can absorb water and keep the system moist, and is a highly efficient solvent and humectant. The low-volatile organic solvent is used as a solvent to improve the environmental stability of the gel to replace some water molecules in the matrix and introduce it into the system, so that the gel has excellent adhesion and environmental stability; (2) The organohydrogel prepared by the present invention has excellent mechanical properties, the tensile length can reach about 8 times of the original length, and the breaking strength can reach 225.7 kPa; (3) The organic hydrogel prepared by the present invention has excellent environmental stability and still has excellent sensing stability at -30°C to 60°C; (3) The present invention proposes an innovative hydrogel flexible matrix - polyethyleneimine / poly(acrylamide-co-[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonatepropyl)ammonium hydroxide) / poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate composite organic hydrogel. The matrix is ​​prepared in water and soaked in a low-volatile organic solvent. It has excellent adhesion and can be firmly adhered to the skin without the need for additional medical tape. (4) The organic hydrogel prepared by the present invention has excellent sensing stability and long-term cycle stability in a wide sensing response range; (5) The organic hydrogel prepared by the present invention has high stretchability, environmental stability and high conductivity, and can be used for strain sensors and temperature sensors. Due to its unique structural design and excellent performance, it has broad application prospects in the sensor field. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : Schematic diagram and mechanism diagram of the preparation process of the organohydrogel of the present invention.

[0018] Figure 2 : Stress-strain curves of the hydrogels PMSP, MS, PMS and MSP obtained in Example 1 and Comparative Examples 1 to 3.

[0019] Figure 3 : Time-resistance change rate response curves of the sensor made of the hydrogel PMSP obtained in Example 1 under different large strain conditions (50%, 100%, 200%, 400%, 600%).

[0020] Figure 4 : Time-resistance change rate response curve of the sensor made of the hydrogel PMSP obtained in Example 1 under different small strain conditions (0.1%, 0.3%, 0.5%, 1%, 3%).

[0021] Figure 5 : Long-term cycle stability test curve of the sensor made of the hydrogel PMSP obtained in Example 1 under a strain of 200%.

[0022] Figure 6 : Temperature test curve of the sensor made from the hydrogel PMSP obtained in Example 1.

[0023] Figure 7 : Actual application signal curve of the sensor made from the hydrogel PMSP obtained in Example 1. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the described embodiments, all other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the present invention.

[0025] Example 1

[0026] A method for preparing an organic hydrogel, a schematic diagram of the preparation process and a mechanism diagram are shown in Figure 1 As shown, the preparation steps are as follows: (1) Add 1.6 g of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (solid content 1.5 wt%) into 8 g of deionized water and stir magnetically for 1 h to obtain dispersion A; (2) Add 0.16 g of 50 wt% aqueous solution of polyethyleneimine (weight average molecular weight of polyethyleneimine is 70,000), 1.6 g of acrylamide and 1.6 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium hydroxide to the dispersion A obtained in step (1), stir magnetically for 1 h, and disperse ultrasonically for 45 min using a cell crusher to obtain dispersion B; (3) Add 0.028 g of azobisisobutyronitrile to the dispersion B obtained in step (2), and then add 0.13 mL of a 1 wt% N,N'-methylenebisacrylamide aqueous solution, stir magnetically for 15 min, and disperse ultrasonically for 15 min using a cell crusher. After vacuum deoxygenation, free radical polymerization was performed at 60°C for 12 h to obtain a conductive hydrogel. (4) The conductive hydrogel obtained in step (3) was immersed in 1,2-propylene glycol (10 times its own weight) for 3 hours for solvent replacement to obtain the target product organic hydrogel, which was labeled as PMSP.

[0027] Comparative Example 1 The difference from Example 1 is that poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid) is not added in step (1), and polyethyleneimine is not added in step (2); the rest is the same as Example 1.

[0028] The obtained products were labeled as MS.

[0029] Comparative Example 2 The difference from Example 1 is that poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid is not added in step (1); the rest is the same as Example 1.

[0030] The obtained product was labeled as PMS.

[0031] Comparative Example 3 The difference from Example 1 is that polyethyleneimine is not added in step (2); the rest is the same as Example 1.

[0032] The obtained product was labeled as MSP.

[0033] Performance Testing (i) The hydrogels PMSP, MS, PMS and MSP obtained in Example 1 of the present invention and Comparative Examples 1 to 3 were respectively fixed on an electronic universal testing machine for relevant tensile tests.

[0034] Figure 2 The stress-strain curves of the hydrogels PMSP, MS, PMS and MSP obtained in Example 1 and Comparative Examples 1 to 3 are shown in FIG. Figure 2 It can be seen that with the addition of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid and polyethyleneimine, the elongation at break of the hydrogel increases, the tensile strength increases, and its mechanical properties are effectively improved. The PMSP stretching length of the hydrogel can reach about 8 times the original length, and the fracture strength can reach 225.7 kPa; this is attributed to the fact that in the PMSP organic hydrogel system, polyethyleneimine and poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid form an interfacial reinforcement phase through amino-sulfonic acid ionic bonds, and the synergistic effect of the two forms a more stable multi-level network, with the highest tensile strength and high toughness.

[0035] (ii) Sensor preparation: Carbon cloth is attached to both ends of the hydrogel PMSP obtained in Example 1 of the present invention using conductive tape, and the carbon cloth is led out with a wire to obtain a sensor.

[0036] (2.1) Fix the sensor on the electronic universal testing machine, connect the other end of the wire to the CHI660E electrochemical workstation, and start the relevant tensile test. At the same time, use the CHI660E electrochemical workstation to record the output signals at both ends of the sensor in real time.

[0037] Figure 3 The time-resistance change rate response curve of the sensor made of the hydrogel PMSP obtained in Example 1 under different large strain conditions (50%, 100%, 200%, 400%, 600%). Figure 3 It can be seen that there is a stable resistance change rate and similar peak value under the same strain condition, which proves that the hydrogel PMSP has excellent strain sensing stability under larger strain conditions.

[0038] Figure 4 The time-resistance change rate response curve of the sensor made of the hydrogel PMSP obtained in Example 1 under different small strain conditions (0.1%, 0.3%, 0.5%, 1%, 3%). Figure 4It can be seen that there is a stable resistance change rate and similar peak value under the same strain condition, which proves that the hydrogel PMSP has excellent strain sensing stability under smaller strain conditions.

[0039] Figure 5 This is a long-term cycle stability test curve of the sensor made from the hydrogel PMSP obtained in Example 1 under a strain of 200%. Figure 5 It can be seen that under 200% strain, the hydrogel PMSP can maintain excellent sensing signal stability and reproducibility in 20,000 cycles of loading-unloading tests.

[0040] (2.2) Place the sensors in different temperature environments and connect the other end of the wire to the CHI660E electrochemical workstation. Use the CHI660E electrochemical workstation to record the output signals at both ends of the sensor in real time.

[0041] Figure 6 This is the temperature test curve of the sensor made based on the hydrogel PMSP obtained in Example 1. Figure 6 It can be seen that as the temperature rises from -30℃ to 60℃, the relative resistance of the hydrogel PMSP decreases significantly, showing that the hydrogel has a negative temperature coefficient behavior; in the temperature range of -30℃~10℃, the temperature coefficient of resistance (TCR) of the hydrogel PMSP is -5.3℃ -1 ; In the temperature range of 10℃~60℃, the temperature coefficient of resistance (TCR) of PMSP organohydrogel is 0.07℃ -1 .

[0042] (2.3) Place the sensor on the volunteer’s forehead and use an infrared thermal imaging camera to record the instantaneous temperature, reflecting the changes in the volunteer’s body temperature during fever and fever reduction.

[0043] Figure 7 This is the actual application signal curve of the sensor made based on the hydrogel PMSP obtained in Example 1. Figure 7 It can be seen that when the temperature of the volunteer increased from 36.8℃ to 39.7℃, the resistance change rate decreased from -0.65 to -0.72, and when the temperature of the volunteer decreased from 39.7℃ to 36.5℃, the resistance change rate decreased from -0.72 to -0.63, which shows that its performance is effective in collecting human body temperature data. This is a suitable solution for human body temperature detection.

Claims

1. A method for preparing an organic hydrogel having both environmental stability and electrical conductivity, characterized in that: Here are the steps: (1) Add poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid into water and stir evenly to obtain dispersion A; (2) Add polyethyleneimine, acrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium hydroxide to the dispersion A obtained in step (1), stir evenly and then disperse by ultrasonication to obtain dispersion B; (3) adding a crosslinking agent and an initiator to the dispersion B obtained in step (2), stirring evenly, ultrasonically dispersing, vacuum deoxygenating, and obtaining a conductive hydrogel through a free radical polymerization reaction; (4) Soaking the conductive hydrogel obtained in step (3) in a low-volatile organic solvent for solvent replacement to obtain an organic hydrogel having both environmental stability and conductivity.

2. The method for preparing an organic hydrogel having both environmental stability and electrical conductivity as claimed in claim 1, characterized in that: The solid content of the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid is 1.3-1.7wt%, and the dosage ratio of the raw materials is poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid: acrylamide: [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide: water = (0.67-1.6) g: (1.6-2.8) g: (1.6-2.8) g: 8 mL; the dosage of polyethyleneimine is 2-3% in terms of the percentage of the total mass of acrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide; the molar dosage of the crosslinking agent is 0.01-0.05% in terms of the percentage of the total molar dosage of acrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide, and the molar dosage of the initiator is 0.4-0.8%.

3. The method for preparing an organic hydrogel having both environmental stability and electrical conductivity as claimed in claim 1, characterized in that: The cross-linking agent is N,N'-methylenebisacrylamide, and the initiator is azobisisobutyronitrile.

4. The method for preparing an organic hydrogel having both environmental stability and electrical conductivity as claimed in claim 1, characterized in that: In step (1), the stirring time is 1 to 2 hours; in step (2), the stirring time is 15 minutes to 1 hour, and the ultrasonic dispersion time is 30 minutes to 1 hour; in step (3), the stirring time is 10 minutes to 15 minutes, and the ultrasonic dispersion time is 10 minutes to 15 minutes.

5. The method for preparing an organic hydrogel having both environmental stability and electrical conductivity as claimed in claim 1, characterized in that: In step (3), the temperature of the free radical polymerization reaction is 50-60° C. and the time is 10-24 h.

6. The method for preparing an organic hydrogel having both environmental stability and electrical conductivity as claimed in claim 1, characterized in that: In step (4), the low volatility organic solvent is 1,2-propylene glycol, ethylene glycol or glycerol.

7. The method for preparing an organic hydrogel having both environmental stability and electrical conductivity as claimed in claim 1, characterized in that: In step (4), the weight of the low-volatile organic solvent is 5 to 12 times the weight of the conductive hydrogel, and the immersion time is 1 to 6 hours.

8. An organic hydrogel having both environmental stability and electrical conductivity prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the environmentally stable and conductive organic hydrogel as claimed in claim 8 as a sensor in a flexible wearable electronic device.

10. The use of the environmentally stable and electrically conductive organic hydrogel according to claim 9, characterized in that: The sensor is a temperature sensor or a strain sensor.

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