Preparation method of eutectic solvent-MXene double-conductive filler composite hydrogel

Abstract

The invention relates to a preparation method of a deep eutectic solvent-MXene double-conductive filler composite hydrogel. The method comprises the following steps: firstly, carrying out surface modification on MXene by using tannic acid to prevent MXene from being oxidized, then uniformly dispersing the modified MXene and DES in a polymeric monomer solution, and forming the DES and MXene double-conductive filler composite hydrogel through a free radical polymerization method. The DES and MXene double-conductive filler composite hydrogel obtained by the invention solves the problem of low conductivity of hydrogel with a single conductive filler. Compared with a single DES composite hydrogel and a single MXene composite hydrogel, the strain sensing sensitivity of the DES and MXene double-conductive filler composite hydrogel obtained by the preparation method disclosed by the invention is improved under both small strain and large strain.

Description

Technical Field

[0001] The present invention belongs to the technical field of strain sensing, and particularly relates to a preparation method of a composite hydrogel of DES and MXene double conductive fillers. Background Art

[0002] With the rapid development of fields such as human-computer interaction, health monitoring, biomedicine, and intelligent robots, the demand for wearable electronic devices shows a rapid growth trend. Flexible strain sensors play an indispensable role in wearable electronic devices due to their high stretchability and adjustable modulus, etc., and have broad market prospects and application potential.

[0003] Deep eutectic solvents (DES) are low-melting mixtures formed by mixing hydrogen bond donors and hydrogen bond acceptors in a certain molar ratio, and have advantages such as adjustable components, high ionic conductivity, and low volatility. Introducing them as conductive fillers into polymer materials shows great application prospects in strain sensing. Zhou et al. (R. Zhou, Y. Jin, W. Zeng, H. Jin, L. Shi, L. Bai, X. Shang, Versatile quasi-solid ionic conductive elastomer inspired by desertification control strategy for soft iontronics, Adv. Funct. Mater. 2023, 33, 2301921.) reported a DES-polyurethane strain sensor. After the introduction of DES, the ionic conductivity of the material increased to 3.8×10 -3 S m -1 , the response time of strain sensing was 0.35 s, and the sensitivity was 0.76. Although the introduction of DES in the polymer increased the conductivity. However, due to the inability to form effective ion transport paths inside these materials under large strains, the response time under large strains becomes slower and the sensitivity is lower. Designing and synthesizing DES composite materials with continuous conduction paths in a wide strain range is a necessary condition for accelerating the response time and improving the strain sensing sensitivity.

[0004] MXene is a two-dimensional nanomaterial with excellent electronic conductivity, abundant surface organic functional groups, and excellent hydrophilicity. By integrating MXene with high electronic conductivity and DES with high ionic conductivity into the polymer hydrogel at the same time, the abundant surface organic functional groups on MXene can form supramolecular interactions with DES and the polymer, enhancing the interfacial compatibility between MXene, DES, and the polymer, and enabling MXene to be uniformly dispersed in the hydrogel. The uniformly distributed MXene nanosheets in the hydrogel matrix can form an electronic conductive network. Moreover, DES provides abundant electron transfer pathways, improving the electronic conductivity. At the same time, a large number of water molecules are bound to MXene in the form of hydrogen bond clusters, which is beneficial to the transport of ions in DES and increases the ionic conductivity. MXene with high electronic conductivity and DES with high ionic conductivity not only provide excellent conductivity themselves but also promote the advantages of ion or electron transport with each other, which is conducive to significantly improving the conductivity of the hydrogel. Also, under small strains, the MXene nanosheets in the composite hydrogel slide, but the nanosheets still remain in close contact. At this time, the free ion transport path in DES is extended, causing a change in resistance, which is beneficial to improving the sensing sensitivity under small strains. Under large strains, the MXene nanosheets in the composite hydrogel are separated and aligned directionally, resulting in an effective extension of the electron transport path and causing a change in resistance, which is beneficial to improving the sensing sensitivity under large strains. However, MXene is easily oxidized to TiO 2 in air, leading to a significant decrease in its conductive performance. Designing and synthesizing new strain sensing materials is the key to achieving rapid response and high-sensitivity sensing of sensors in a wide strain range.

[0005] Currently, there are few reports on composite hydrogels that simultaneously use DES and MXene as conductive fillers in the field of strain sensing. Developing DES and MXene double-conductive filler composite hydrogels with high conductivity, fast response time, high sensitivity, simple preparation, and low cost has become an urgent problem to be solved for expanding the application of their strain sensors. Summary of the Invention

[0006] The object of the present invention is to provide a preparation method of a deep eutectic solvent-MXene double conductive filler composite hydrogel aiming at the limitations existing in the current technology. In this method, MXene is first surface-modified with tannic acid to prevent MXene from oxidation, and then the modified MXene and DES are uniformly dispersed in a polymer monomer solution. Through free radical polymerization, a hydrogel composite with DES and MXene double conductive fillers is formed. The DES and MXene double conductive filler composite hydrogel obtained by the present invention solves the problem of low conductivity of the hydrogel with a single conductive filler. The DES and MXene double conductive filler composite hydrogel obtained by the present invention has improved strain sensing sensitivity under both small and large strains compared with the separate DES composite hydrogel and the separate MXene composite hydrogel.

[0007] The technical solution of the present invention is as follows:

[0008] A preparation method of a deep eutectic solvent-MXene double conductive filler composite hydrogel, the method comprising the following steps:

[0009] Add MXene and tannic acid to deionized water. After stirring the obtained mixture for 0.5 to 24 hours, add a deep eutectic solvent; after stirring for 0.5 to 24 hours, add a polymer monomer and a crosslinking agent; stir for 0.1 to 3 hours, add an initiator, and finally stir for 1 to 10 minutes to obtain a dispersion; pour the dispersion into a polytetrafluoroethylene mold and heat at 25 to 60 °C for 0.01 to 6 hours to carry out free radical polymerization to obtain a deep eutectic solvent-MXene double conductive filler composite hydrogel;

[0010] Wherein, the mass ratio of the deep eutectic solvent to deionized water is 1:0.1 to 100; 0.001 to 1 g of MXene and 0.5 to 5 g of polymer monomer are added to every 2.5 g of deionized water; the mass of the crosslinking agent is 0.1 to 5 wt% of the mass of the dispersion; the mass of the initiator is 0.1 to 5 wt% of the mass of the dispersion; the mass ratio of tannic acid to MXene is 1:0.5 to 50;

[0011] The polymer monomer is any one or more of acrylic acid, methyl methacrylate, methacrylic acid, acrylamide, methacrylamide, N-isopropylacrylamide;

[0012] The crosslinking agent is N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate or trimethylolpropane trimethacrylate;

[0013] The initiator is potassium persulfate or ammonium persulfate;

[0014] The preparation method of the deep eutectic solvent comprises the following steps:

[0015] Mix a hydrogen bond donor and a hydrogen bond acceptor, and heat them at 25 - 100 °C for 5 - 60 minutes to obtain the DES;

[0016] Among them, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:0.1 - 10;

[0017] The hydrogen bond donor is any one or more of glycerol, 1,4 - butanediol, ethylene glycol, phytic acid, thiourea, and malonic acid;

[0018] The hydrogen bond acceptor is any one or more of choline chloride, tetramethylammonium chloride, and lithium bis(trifluoromethanesulfonyl)imide;

[0019] Application of the deep eutectic solvent - MXene double - conductive filler composite hydrogel obtained by the method for use as a strain sensor.

[0020] Specifically, it includes the following steps: Use the deep eutectic solvent - MXene double - conductive filler composite hydrogel as the intermediate layer of the strain sensor, and encapsulate it between two pieces of pressure - sensitive tape to form the strain sensor.

[0021] The substantial features of the present invention are:

[0022] In the present invention, MXene is first surface - modified with tannic acid to prevent MXene from oxidation, and then the modified MXene and DES are uniformly dispersed in the polymerization monomer solution. Through free - radical polymerization, a hydrogel composite of DES and MXene double - conductive fillers is formed; in this composite hydrogel, the high ionic conductivity of DES and the high electronic conductivity of MXene synergistically enhance the conductivity of the composite hydrogel. Under small strains, the MXene nanosheets in the composite hydrogel slide, but the nanosheets still remain in close contact. At the same time, the free ion transport path in DES is extended, and the resistance change at this time is mainly due to the increase in the ion transport path. Under large strains, the MXene nanosheets in the composite hydrogel are separated and aligned directionally, and the resistance change at this time is mainly due to the increase in the electronic transport path. The effective resistance changes under small and large strains improve the strain response speed and sensitivity of the composite hydrogel, which are superior to many existing strain sensors.

[0023] The beneficial effects of the present invention are:

[0024] (1) The present invention provides a preparation method for a composite hydrogel of DES and MXene double - conductive fillers. The high ionic conductivity of DES and the high electronic conductivity of MXene solve the problem of low conductivity of hydrogels with a single conductive filler, and provide an ideal platform for understanding the relationship between double - conductive hydrogels and strain - sensing performance.

[0025] (2) The composite hydrogel of DES and MXene double - conductive fillers provided by the present invention has an ionic conductivity of 0.509 S m-1 , the electronic conductivity is 0.00159 S m -1 , higher than that of the single DES composite hydrogel (ionic conductivity is 0.251 S m -1 , the electronic conductivity is 0.00105 S m -1 ) and the MXene composite hydrogel (ionic conductivity is 0.028 S m -1 , the electronic conductivity is 0.00096 S m -1 ).

[0026] (3) For the DES and MXene dual-conductive filler composite hydrogel provided by the present invention, when strain is applied, both the response time and the recovery time are 0.01 s.

[0027] (4) For the DES and MXene dual-conductive filler composite hydrogel provided by the present invention, the minimum strain monitoring value is 1%, while that of the single DES composite hydrogel and the MXene composite hydrogel is only 10%.

[0028] (5) For the DES and MXene dual-conductive filler composite hydrogel provided by the present invention, the sensitivity is 1.01 in the small strain range of 1% - 50%, and 1.10 in the large strain range of 50% - 150%, both of which are higher than those of the single DES composite hydrogel (sensitivity is 0.86 in the range of 10% - 50% and 0.54 in the range of 50% - 150%) and the MXene composite hydrogel (sensitivity is 0.77 in the range of 10% - 50% and 0.91 in the range of 50% - 150%). Description of the Drawings

[0029] Figure 1 Shows the ionic conductivity and electronic conductivity of the DES composite hydrogel in Comparative Example 1, the MXene composite hydrogel in Comparative Example 2, and the DES and MXene dual-conductive filler composite hydrogel in Example 1 of the present invention.

[0030] Figure 2 Shows the strain response time and recovery time of the DES and MXene dual-conductive filler composite hydrogel in Example 1 of the present invention.

[0031] Figure 3 Shows the curve of the relative current varying with strain and time of the DES composite hydrogel in Comparative Example 1 of the present invention.

[0032] Figure 4 Shows the strain sensing sensitivity of the DES composite hydrogel in Comparative Example 1 of the present invention.

[0033] Figure 5 Shows the curve of the relative current varying with strain and time of the MXene composite hydrogel in Comparative Example 2 of the present invention.

[0034] Figure 6 This is the strain sensing sensitivity of the MXene composite hydrogel in Comparative Example 2 of the present invention.

[0035] Figure 7 This is a graph showing the change of the relative current of the DES and MXene double conductive filler composite hydrogel in Example 1 of the present invention with strain (1% - 15%) over time.

[0036] Figure 8 This is a graph showing the change of the relative current of the DES and MXene double conductive filler composite hydrogel in Example 1 of the present invention with strain (25% - 150%) over time.

[0037] Figure 9 This is the strain sensing sensitivity of the DES and MXene double conductive filler composite hydrogel in Example 1 of the present invention. Detailed implementation manners

[0038] For a further understanding of the method of the present invention, specific descriptions are now made in the form of examples in conjunction with the accompanying drawings. The following examples are only the specific preparation methods of the present invention and do not limit the scope of the present invention.

[0039] The MXene described is titanium carbide (Ti 3 C 2 )), which is a well-known material. Its preparation method includes the following steps: Add lithium fluoride (1 g) to hydrochloric acid aqueous solution (20 mL 9M), stir for 5 minutes to fully dissolve it, then add aluminum titanium carbide (1 g), and under ice bath, stir at 35 °C for 24 hours. After that, the obtained mixture is centrifuged, washed with deionized water until the pH value of the supernatant reaches 6. Add the precipitate to deionized water (100 mL), ultrasonically treat it for 1 hour under a nitrogen atmosphere, then centrifuge it at 3500 rpm for 1 hour, and collect the obtained dark supernatant and freeze-dry it to obtain MXene. However, it is not limited to this.

[0040] Comparative Example 1

[0041] Stir choline chloride (3.23 g) and glycerol (4.27 g) at 80 °C for 30 minutes to obtain DES.

[0042] Add DES (7.5 g) to deionized water (2.5 g); after stirring for 12 hours, add acrylic acid (2.25 g), acrylamide (2.25 g) and N,N'-methylenebisacrylamide (0.025 g); after stirring for 0.5 hours, add potassium persulfate (0.02 g), and finally stir for 2 minutes. Pour the obtained dispersion into a polytetrafluoroethylene mold and heat it at 60 °C for 1 hour to carry out free radical polymerization to obtain a DES composite hydrogel.

[0043] Comparative Example 2

[0044] MXene (0.048 g) and tannic acid (0.012 g) were added to deionized water (10 g). After stirring the resulting mixture for 12 hours, acrylic acid (2.25 g), acrylamide (2.25 g), and N,N’-methylenebisacrylamide (0.025 g) were added. After stirring for 0.5 hour, potassium persulfate (0.02 g) was added, and finally, it was stirred for 2 minutes. The obtained dispersion was poured into a polytetrafluoroethylene mold, and free radical polymerization occurred at 25 °C for 20 minutes to obtain the MXene composite hydrogel.

[0045] Example 1

[0046] Choline chloride (3.23 g) and glycerol (4.27 g) were stirred at 80 °C for 30 minutes to obtain DES.

[0047] MXene (0.048 g) and tannic acid (0.012 g) were added to deionized water (2.5 g). After stirring the resulting mixture for 3 hours, DES (7.5 g) was added. After stirring for 12 hours, acrylic acid (2.25 g), acrylamide (2.25 g), and N,N’-methylenebisacrylamide (0.025 g) were added. After stirring for 0.5 hour, potassium persulfate (0.02 g) was added, and finally, it was stirred for 2 minutes. The obtained dispersion was poured into a polytetrafluoroethylene mold, and free radical polymerization occurred at 25 °C for 1 minute to obtain the deep eutectic solvent-MXene double conductive filler composite hydrogel.

[0048] Figure 1 Among them, an electrochemical workstation (CHI 760E) was used to measure the change of the DC voltage acting on the hydrogel with time under a constant current, so as to obtain the electronic conductivity. Through the electrochemical workstation (CHI 760E), the electrochemical impedance spectrum was measured in the range of 1×10 6 Hz to obtain the ionic conductivity. For the deep eutectic solvent-MXene double conductive filler composite hydrogel, the ionic conductivity was 0.509 S m -1 , and the electronic conductivity was 0.00159 S m -1 , which was higher than that of the single DES composite hydrogel (ionic conductivity was 0.251 S m -1 , and the electronic conductivity was 0.00105 S m -1 ) and the MXene composite hydrogel (ionic conductivity was 0.028 S m -1 , and the electronic conductivity was 0.00096 S m -1 ).

[0049] Figure 2In this case, a eutectic solvent-MXene double conductive filler composite hydrogel is used as the intermediate layer of the strain sensor, which is encapsulated between two pieces of pressure-sensitive tape to form a strain sensor. Among them, copper wires are connected to both ends of the composite hydrogel, and then the copper wires at both ends are connected to an electrochemical workstation (CHI 760E). At the same time, both ends of the strain sensor are connected to a material tensile testing machine (CMT 6104). By controlling the material tensile testing machine to apply deformation, the electrochemical workstation can measure the corresponding current in real time, calculate the relative current change, and draw a curve of the relative current versus strain and time. For the DES and MXene double conductive filler composite hydrogel, when strain is applied, both the response time and the recovery time are 0.01 s.

[0050] Figure 3 In this case, for the DES composite hydrogel, the minimum strain monitoring value is 10%.

[0051] Figure 4 In this case, according to the relative current change-strain diagram, linear fitting is performed, and the slope of the straight line is the strain sensing sensitivity. For the DES composite hydrogel, the sensitivity is 0.86 in the range of 10% - 50% and 0.54 in the range of 50% - 150%.

[0052] Figure 5 In this case, for the MXene composite hydrogel, the minimum strain monitoring value is 10%.

[0053] Figure 6 In this case, for the MXene composite hydrogel, the sensitivity is 0.77 in the range of 10% - 50% and 0.91 in the range of 50% - 150%.

[0054] Figure 7 In this case, for the DES and MXene double conductive filler composite hydrogel, the minimum strain monitoring value is 1%.

[0055] Figure 8 In this case, for the DES and MXene double conductive filler composite hydrogel, it is a curve of the relative current versus strain and time in the strain monitoring range of 25% - 150%.

[0056] Figure 9 In this case, for the DES and MXene double conductive filler composite hydrogel, the sensitivity is 1.01 in the small strain range of 1% - 50% and 1.10 in the large strain range of 50% - 150%.

[0057] Example 2

[0058] Mix tetraethylammonium chloride (1 g) and ethylene glycol (1.5 g) and stir at 60 °C for 60 minutes to obtain DES.

[0059] MXene (0.096 g) and tannic acid (0.024 g) were added to deionized water (7.5 g). After stirring the resulting mixture for 12 hours, DES (2.5 g) was added; after stirring for 12 hours, methyl methacrylate (2.25 g), methacrylic acid (2.25 g), and ethylene glycol dimethacrylate (0.025 g) were added; after stirring for 1 hour, ammonium persulfate (0.02 g) was added, and finally, it was stirred for 1 minute. The obtained dispersion was poured into a polytetrafluoroethylene mold, and free radical polymerization occurred at 25 °C for 0.5 minutes to obtain a deep eutectic solvent-MXene double conductive filler composite hydrogel.

[0060] Example 3

[0061] Lithium bis(trifluoromethanesulfonyl)imide (2 g), thiourea (2 g), and ethylene glycol malonate (1 g) were stirred at 80 °C for 15 minutes to obtain DES.

[0062] MXene (0.096 g) and tannic acid (0.048 g) were added to deionized water (5 g). After stirring the resulting mixture for 24 hours, DES (5 g) was added; after stirring for 24 hours, N-isopropylacrylamide (5 g), methacrylic acid (5 g), and trimethylolpropane trimethacrylate (0.05 g) were added; after stirring for 1 hour, ammonium persulfate (0.04 g) was added, and finally, it was stirred for 10 minutes. The obtained dispersion was poured into a polytetrafluoroethylene mold, and free radical polymerization occurred at 25 °C for 1 minute to obtain a deep eutectic solvent-MXene double conductive filler composite hydrogel.

[0063] Matters not covered by this invention are well-known techniques.

Claims

1. A method for preparing a low eutectic solvent-MXene dual conductive filler composite hydrogel, characterized in that: The method comprises the following steps: MXene and tannic acid are added to deionized water, and the resulting mixture is stirred for 0.5 to 24 hours, and then a low eutectic solvent is added; after stirring for 0.5 to 24 hours, a polymerization monomer and a cross-linking agent are added; after stirring for 0.1 to 3 hours, an initiator is added, and finally stirred for 1 to 10 minutes to obtain a dispersion; the dispersion is poured into a polytetrafluoroethylene mold, and heated at 25 to 60° C. for 0.01 to 6 hours to obtain a low eutectic solvent-MXene dual conductive filler composite hydrogel; The mass ratio of the low eutectic solvent to deionized water is 1:0.1-100; 0.001-1g of MXene and 0.5-5g of polymerization monomer are added to every 2.5g of deionized water; the mass of the crosslinking agent is 0.1-5wt% of the mass of the dispersion; the mass of the initiator is 0.1-5wt% of the mass of the dispersion; the mass ratio of tannic acid to MXene is 1:0.5-50; The polymerizable monomer is any one or more of acrylic acid, methyl methacrylate, methacrylic acid, acrylamide, methacrylamide, and N-isopropylacrylamide.

2. The method for preparing the deep eutectic solvent-MXene dual conductive filler composite hydrogel according to claim 1, characterized in that: The crosslinking agent is N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate or trimethylolpropane trimethacrylate.

3. The method for preparing the deep eutectic solvent-MXene dual conductive filler composite hydrogel according to claim 1, characterized in that: The initiator is potassium persulfate or ammonium persulfate.

4. The method for preparing the deep eutectic solvent-MXene dual conductive filler composite hydrogel according to claim 1, characterized in that: The method for preparing the deep eutectic solvent comprises the following steps: The hydrogen bond donor and the hydrogen bond acceptor are mixed and heated at 25 to 100° C. for 5 to 60 minutes to obtain a DES; Wherein, the molar ratio of hydrogen bond donor to hydrogen bond acceptor is 1:0.1-10; The hydrogen bond donor is any one or more of glycerol, 1,4-butanediol, ethylene glycol, phytic acid, thiourea, and malonic acid; The hydrogen bond acceptor is any one or more of choline chloride, tetramethylammonium chloride and lithium bis(trifluoromethanesulfonyl)imide.

5. Application of the deep eutectic solvent-MXene dual conductive filler composite hydrogel obtained by the method of claim 1, characterized in that: As the middle layer of strain sensor.

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