Preparation method of hydrogen bond organic framework-poly eutectic solvent composite hydrogel

Abstract

The invention relates to a preparation method of hydrogen bond organic framework-poly eutectic solvent composite hydrogel. According to the method, HOFs are uniformly dispersed in a DES aqueous solution, and then the HOFs and PDES composite hydrogel is formed through a free radical polymerization method. The composite hydrogel obtained by the invention can effectively integrate the advantages of HOFs and PDES, and after DES is polymerized to form PDES, the problem of DES leakage is solved, and the tensile strength, toughness, compression strength and conductivity of the hydrogel are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrogel preparation, and specifically relates to a method for preparing a hydrogen bond organic framework (HOFs) and poly-deep eutectic solvent (PDES) composite hydrogel. Background Art

[0002] Wearable flexible strain sensors have shown great application potential in many fields such as human motion detection, human-computer interaction, and bioelectronics. Hydrogels are widely used in wearable flexible strain sensors due to their excellent biocompatibility and adjustable mechanical properties, but many hydrogels still have problems such as low tensile strength, poor toughness, and weak conductivity, and optimizing these properties may be challenging. Introducing conductive nanofillers into hydrogels is an effective way to simultaneously improve their tensile strength, toughness, and conductivity. Yu et al. (Y.Li, D.Yang, Z.Wu, F.Gao, H.Zhao, X.Li, Z.Yu, Self-adhesive, self-healing, biocompatible and conductive polyacrylamidenanocomposite hydrogels for reliable strain and pressure sensors, Nano Energy 2023, 109, 108324.) introduced polydopamine-modified carbon nanotubes into polyacrylamide hydrogels to prepare carbon nanotube composite hydrogels with an electrical conductivity of 2mS m -1 , tensile strength of 20 kPa, elongation at break of 800%, can be used as strain sensors to monitor human movement. Lai et al. (Y.Ni, X.Zang, J.Chen, T.Zhu, Y.Yang, J.Huang, W.Cai, Y.Lai, Flexible MXene-based hydrogel enables wearable human-computer interaction for intelligent underwater communication and sensing rescue. Adv. Funct. Mat. 2023, 33, 2301127.) introduced MXene into polyacrylamide hydrogel to prepare a composite hydrogel with a tensile strength of about 100 kPa and a toughness of 560 kJ m -3, elongation at break is 1224%, used for underwater strain sensing. Although the tensile strength is improved by introducing conductive nanofillers into polymer hydrogels, these nanoparticles have fewer active sites, uneven dispersion, discontinuous conductive networks, and other problems, which affect the tensile strength, toughness, and conductivity of the hydrogels, thus limiting the expansion of their application areas. Designing and synthesizing nanofillers and polymer composite hydrogels with rich organic groups is a necessary condition for improving tensile strength, toughness, and conductivity.

[0003] HOFs are porous crystalline supramolecular materials that are self-assembled by organic building blocks through hydrogen bonding. They have the advantages of high specific surface area, regular and ordered pores, adjustable structure, rich functional groups and good solution processability. Deep eutectic solvent (DES) is an emerging green solvent composed of hydrogen bond acceptors and hydrogen bond donors. It has the advantages of simple preparation, green environmental protection, adjustable performance and high ionic conductivity, and is widely used in the research of conductive hydrogel sensors. When HOFs are introduced into DES hydrogels, the rich organic functional groups on the surface of HOFs can form supramolecular interactions with polymers and DES, thereby improving the tensile strength and toughness of the hydrogels. The regular and ordered pores of HOFs can promote ion transport and improve ionic conductivity. However, due to the leakage of DES solvent in the hydrogel, the mechanical properties and conductivity of the hydrogel are seriously affected. Designing and synthesizing new hydrogel materials is the key to improving tensile strength, toughness and conductivity.

[0004] At present, there is no report on the application of PDES and HOFs composite hydrogel in the field of wearable flexible strain sensors. The development of PDES and HOFs composite hydrogel with high strength, good toughness, strong conductivity, simple preparation and low cost has become an urgent problem to be solved in expanding the application of wearable flexible strain sensors. Summary of the invention

[0005] The present invention mainly aims at the problems existing in the hydrogels currently used in wearable flexible strain sensors, provides a method for preparing a HOFs and PDES composite hydrogel, and applies it to strain sensors. The method uniformly disperses HOFs in a DES aqueous solution, and then forms a HOFs and PDES composite hydrogel by free radical polymerization. The composite hydrogel obtained by the present invention can effectively integrate the advantages of HOFs and PDES, and after polymerizing DES to form PDES, the problem of DES leakage is solved, and the tensile strength, toughness, compressive strength and conductivity of the hydrogel are improved. Compared with the single PDES hydrogel, the composite hydrogel obtained by the present invention has a tensile strength increased by 4.5 times, a toughness increased by 4.5 times, a compressive strength increased by 2.6 times, and a conductivity increased by 1.2 times.

[0006] The technical solution of the present invention is:

[0007] A method for preparing a hydrogen-bonded organic framework-poly-deep eutectic solvent composite hydrogel, the method comprising the following steps:

[0008] HOFs and DES are added to deionized water, stirred for 1 to 24 hours, and then polyethyleneimine aqueous solution is added, stirred for 2 to 15 minutes, and then an initiator is added, stirred for 0.1 to 3 minutes to obtain a hydrogen-bonded organic framework-poly-low eutectic solvent composite hydrogel;

[0009] The mass of HOFs is 0.01-30% of the mass of DES; the mass of deionized water is 10-300% of the mass of DES; the mass of polyethyleneimine is 0.1-50% of the mass of DES; the mass of initiator is 0.03-10% of the mass of DES;

[0010] The concentration of the polyethyleneimine aqueous solution is 100-3000 mg / mL;

[0011] The initiator is potassium persulfate or sodium persulfate;

[0012] The preparation method of HOFs comprises the following steps:

[0013] The building block is added to a first organic solvent, stirred at 25 to 120° C. for 0.5 to 48 hours, cooled to room temperature, and then a second organic solvent is added, stirred for 0.1 to 24 hours, and the synthesized solid is centrifuged, washed, Soxhlet extracted, and dried to obtain HOFs;

[0014] The volume ratio of the first organic solvent to the second organic solvent is 1:1-100; 0.1-30 mg of the building block is added to every 1 mL of the first organic solvent; the first organic solvent is N,N-dimethylformamide, ethanol or tetrahydrofuran; the second organic solvent is any one or both of ethanol and ethyl acetate;

[0015] The building blocks are 1,3,6,8-tetracarboxypyrene, 1,3,6,8-tetra(4-carboxyphenyl)pyrene, 1,3,6,8-tetra(6-carboxy-2-naphthyl)pyrene, 4,4',4",4"'-(pyrene-1,3,6,8-tetrayl)tetra(2-fluorobenzoic acid), 4,4',4",4"'-(pyrene-1,3,6,8-tetrayl)tetra(2-aminobenzoic acid), 4,4',4",4"'-(pyrene-1,3,6,8-tetrayl)tetra(2-methylbenzoic acid)aldehyde or 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine.

[0016] The preparation method of DES comprises the following steps:

[0017] 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;

[0018] The molar ratio of hydrogen bond donor to hydrogen bond acceptor is 1:0.1-5;

[0019] The hydrogen bond donor is an olefinic substance, or a mixture of an olefinic substance and a non-olefinic substance;

[0020] The olefinic substance is any one or more of acrylamide, acrylic acid, and hydroxyethyl methacrylate, and the non-olefinic substance is any one or more of glycerol, urea, benzoic acid, malonic acid, and 1,4-butanediol;

[0021] The hydrogen bond acceptor is any one or more of choline chloride, ammonium chloride, choline fluoride, betaine, lithium bis(trifluoromethanesulfonyl)imide, glycine, histidine, and alanine;

[0022] The hydrogen-bonded organic framework-poly-low eutectic solvent composite hydrogel obtained by the method is used as an intermediate layer of a wearable strain sensor. The specific steps are as follows:

[0023] The poly-low eutectic solvent-hydrogen bond organic framework composite gel is used as the middle layer of the wearable strain sensor, and copper wires are wrapped around both ends. It is fixed between two pieces of tape to assemble into a strain sensor; and it is adhered to the skin including the wrist joints, finger joints, and pulse points. A 1-3V voltage is connected to both ends of the gel to monitor the resistance changes of the hydrogels in these parts during human movement.

[0024] The essential features of the present invention are:

[0025] The present invention uniformly disperses HOFs in a DES aqueous solution, and prepares a HOFs and PDES composite hydrogel by a free radical polymerization method; in the composite hydrogel, organic functional groups on the surface of HOFs form supramolecular interactions with PDES, thereby enhancing the tensile strength, toughness and compressive strength of the hydrogel; the regular and orderly pores of HOFs are conducive to promoting ion transmission, thereby improving the conductivity of the hydrogel, which is superior to many existing hydrogel strain sensors.

[0026] The beneficial effects of the present invention are:

[0027] (1) The present invention provides a method for preparing a HOFs and PDES composite hydrogel. The clear structures of HOFs and PDES provide an ideal platform for understanding the relationship between hydrogel structure and strain sensing performance.

[0028] (2) The HOFs and PDES composite hydrogel provided by the present invention benefits from the supramolecular effect formed between HOFs and PDES and the crystal structure of HOFs, and has a tensile strength of 135.23 kPa. Compared with the single PDES hydrogel (30.22 kPa), the tensile strength of the composite hydrogel is increased by 4.5 times.

[0029] (3) The HOFs and PDES composite hydrogel provided by the present invention has a toughness of 2.69 MJ m -3 , compared with the PDES hydrogel alone (0.6 MJ m -3 ), the toughness of the composite hydrogel increased by 4.5 times.

[0030] (4) The HOFs and PDES composite hydrogel provided by the present invention has a strength of 0.89 MPa under 80% compression. Compared with the single PDES hydrogel (0.34 MPa), the compressive strength of the composite hydrogel is increased by 2.6 times.

[0031] (5) The HOFs and PDES composite hydrogel provided by the present invention has a conductivity of 4.33±0.02S m -1 , compared with the PDES hydrogel alone (3.53 ± 0.07 S m -1 ), the conductivity of the composite hydrogel increased by 1.2 times.

[0032] (6) The HOFs and PDES composite hydrogel provided by the present invention is assembled into a strain sensor and adhered to the skin including wrist joints, finger joints, and pulse beats to monitor the relative resistance changes of the hydrogel strain sensors in these parts during exercise in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 1 and 2 are the tensile stress-strain curves of the composite hydrogel and PDES hydrogel obtained in Example 1 and Comparative Example 1.

[0034] Figure 2 1 is the compression stress-strain curve of the composite hydrogel and PDES hydrogel obtained in Example 1 and Comparative Example 1.

[0035] Figure 3 It is the ionic conductivity of the composite hydrogel and PDES hydrogel obtained in Example 1 and Comparative Example 1.

[0036] Figure 4 Schematic diagram of the strain sensor.

[0037] Figure 5The composite hydrogel sensor obtained in Example 1 is pasted on the wrist joint to monitor the relative resistance change curve during 19 cycles of the wrist from straightening, downward bending to upward bending.

[0038] Figure 6 The composite hydrogel sensor obtained in Example 1 is pasted on the finger joint to monitor the relative resistance change curve during the bending process of the finger from straightening to bending downward 45° for 10 cycles and then from straightening to bending downward 90° for 13 cycles.

[0039] Figure 7 The composite hydrogel sensor obtained in Example 1 is pasted on the pulse beat to monitor the relative resistance change curve during the pulse beat. DETAILED DESCRIPTION

[0040] In order to further understand the method of the present invention, the following examples are specifically described in conjunction with the accompanying drawings. The following examples are only specific preparation methods of the present invention, and do not limit the scope of the present invention.

[0041] Comparative Example 1

[0042] Acrylamide (1.8 g, 0.025 mol), acrylic acid (1.78 g, 0.025 mol) and choline chloride (3.49 g, 0.025 mol) were stirred at 80°C for 15 minutes to obtain DES.

[0043] DES (7.07 g) was added to deionized water (7 mL), polyethyleneimine (0.5 g) was added, and the mixture was stirred for 5 min, followed by potassium persulfate (0.021 g) and stirred for 0.5 min to obtain PDES hydrogel;

[0044] Example 1

[0045] 4,4',4",4"'-(pyrene-1,3,6,8-tetrayl)tetrakis(2-fluorobenzoic acid) (200 mg) was added to N,N-dimethylformamide (10 mL), heated and stirred at 120°C for 30 minutes, cooled to room temperature, and ethyl acetate (200 mL) was added. After stirring for 12 hours, the synthesized solid was centrifuged, washed, Soxhlet extracted, and dried to obtain HOFs;

[0046] Acrylamide (1.8 g, 0.025 mol), acrylic acid (1.78 g, 0.025 mol) and choline chloride (3.49 g, 0.025 mol) were stirred at 80°C for 15 minutes to obtain DES.

[0047] HOFs (18 mg) and DES (7.07 g) were added to deionized water (6 mL), and after stirring for 12 hours, polyethyleneimine aqueous solution (500 mg / mL, 1 mL) was added and stirred for 5 minutes, and then potassium persulfate (0.021 g) was added and stirred for 0.5 minutes to obtain a hydrogen-bonded organic framework-poly-low eutectic solvent composite hydrogel;

[0048] Figure 1 In the experiment, the tensile stress-strain curves of the composite hydrogel and PDES hydrogel were obtained by using a material tensile testing machine (CMT 6104). The maximum stress of the tensile stress-strain curve is the tensile strength, and the area enclosed by the stress-strain curve and the horizontal axis is the toughness. The tensile strength of the HOFs and PDES composite hydrogel is 135.23 kPa, which is 4.5 times higher than that of the single PDES hydrogel (30.22 kPa). The toughness of the HOFs and PDES composite hydrogel is 2.69 MJ m -3 , compared with the PDES hydrogel alone (0.6 MJ m -3 ), the toughness of the composite hydrogel increased by 4.5 times.

[0049] Figure 2 In the experiment, the compressive stress-strain curves of the composite hydrogel and PDES hydrogel were obtained by using a material tensile testing machine (CMT 6104). The maximum stress of the compressive stress-strain curve is the compressive strength. The strength of the HOFs and PDES composite hydrogel is 0.89MPa at 80% compression. Compared with the single PDES hydrogel (0.34MPa), the compressive strength of the composite hydrogel is increased by 2.6 times.

[0050] Figure 3 The ionic conductivity of the composite hydrogel and PDES hydrogel was measured by electrochemical impedance spectroscopy using an electrochemical workstation (CHI 760E). The conductivity of the HOFs and PDES composite hydrogel was 4.33 ± 0.02 S m -1 , compared with the PDES hydrogel alone (3.53 ± 0.07 S m -1 ), the conductivity of the composite hydrogel increased by 1.2 times.

[0051] Figure 4 In the experiment, the composite gel was used as the middle layer of the wearable strain sensor, copper wires were wrapped around both ends, and they were fixed between two pieces of tape to assemble into a strain sensor.

[0052] Figure 5 In the experiment, the composite hydrogel sensor was pasted on the wrist joint to monitor the relative resistance change curve during 19 cycles of the wrist from straightening, bending downward to bending upward.

[0053] Figure 6 In the experiment, the composite hydrogel sensor was pasted on the finger joints, and the relative resistance change curve was monitored during the bending process of the finger from straightening to bending downward 45° for 10 cycles and then from straightening to bending downward 90° for 13 cycles.

[0054] Figure 7 In the figure, the composite hydrogel sensor is pasted on the pulse beat, and the relative resistance change curve of the strain sensor is monitored during the pulse beat.

[0055] Example 2

[0056] 1,3,6,8-tetrakis(4-carboxyphenyl)pyrene (210 mg) was added to N,N-dimethylformamide (31.5 mL), stirred at 25°C for 24 hours, cooled to room temperature, added with ethanol (174.3 mL), stirred for 10 minutes, and the synthesized solid was centrifuged, washed, Soxhlet extracted, and dried to obtain HOFs;

[0057] Glycerol (4.6 g, 0.05 mol), acrylic acid (1.78 g, 0.025 mol) and choline chloride (3.49 g, 0.025 mol) were stirred at 80°C for 20 minutes to obtain DES.

[0058] HOFs (0.99 mg) and DES (9.87 g) were added to deionized water (28.6 mL), and after stirring for 1 hour, a polyethyleneimine aqueous solution (100 mg / mL, 1 mL) was added, and stirred for 2 minutes, and then sodium persulfate (0.011 g) was added and stirred for 0.1 minute to obtain a hydrogen-bonded organic framework-poly-low eutectic solvent composite hydrogel;

[0059] Example 3

[0060] 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine (100 mg) was added to ethanol (100 mL), stirred at 90°C for 48 hours, cooled to room temperature, added with ethanol (200 mL), stirred for 10 minutes, and the synthesized solid was centrifuged, washed, Soxhlet extracted, and dried to obtain HOFs;

[0061] Acrylamide (1.48 g, 0.025 mol), acrylic acid (1.78 g, 0.025 mol) and ammonium chloride (1.34 g, 0.025 mol) were stirred at 60°C for 30 minutes to obtain DES.

[0062] HOFs (0.1 g) and DES (4.92 g) were added to deionized water (4 mL). After stirring for 24 h, an aqueous solution of polyethyleneimine (2000 mg / mL, 1 mL) was added and stirred for 15 min. Potassium persulfate (0.05 g) was then added and stirred for 3 min to obtain a hydrogen-bonded organic framework-poly-eutectic solvent composite hydrogel.

[0063] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing a hydrogen-bonded organic framework-poly-deep eutectic solvent composite hydrogel, characterized in that: The method comprises the following steps: HOFs and DES are added to deionized water, stirred for 1 to 24 hours, and then polyethyleneimine aqueous solution is added, stirred for 2 to 15 minutes, and then an initiator is added, stirred for 0.1 to 3 minutes to obtain a hydrogen-bonded organic framework-poly-low eutectic solvent composite hydrogel; The mass of HOFs is 0.01-30% of the mass of DES; the mass of deionized water is 10-300% of the mass of DES; the mass of polyethyleneimine is 0.1-50% of the mass of DES; the mass of initiator is 0.03-10% of the mass of DES; The concentration of the polyethyleneimine aqueous solution is 100-3000 mg / mL.

2. The method for preparing the hydrogen-bonded organic framework-poly-deep eutectic solvent composite hydrogel according to claim 1, characterized in that: The initiator is potassium persulfate or sodium persulfate.

3. The method for preparing the hydrogen-bonded organic framework-poly-deep eutectic solvent composite hydrogel according to claim 1, characterized in that: The preparation method of HOFs comprises the following steps: The building block is added to a first organic solvent, stirred at 25 to 120° C. for 0.5 to 48 hours, cooled to room temperature, and then a second organic solvent is added, stirred for 0.1 to 24 hours, and the synthesized solid is centrifuged, washed, Soxhlet extracted, and dried to obtain HOFs; The volume ratio of the first organic solvent to the second organic solvent is 1:1-100; 0.1-30 mg of the building block is added to every 1 mL of the first organic solvent; the first organic solvent is N,N-dimethylformamide, ethanol or tetrahydrofuran; the second organic solvent is one or both of ethanol and ethyl acetate; The building blocks are 1,3,6,8-tetracarboxypyrene, 1,3,6,8-tetra(4-carboxyphenyl)pyrene, 1,3,6,8-tetra(6-carboxy-2-naphthyl)pyrene, 4,4',4",4"'-(pyrene-1,3,6,8-tetrayl)tetra(2-fluorobenzoic acid), 4,4',4",4"'-(pyrene-1,3,6,8-tetrayl)tetra(2-aminobenzoic acid), 4,4',4",4"'-(pyrene-1,3,6,8-tetrayl)tetra(2-methylbenzoic acid)aldehyde or 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine.

4. The method for preparing the hydrogen-bonded organic framework-poly-deep eutectic solvent composite hydrogel according to claim 1, characterized in that: The preparation method of DES 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; The molar ratio of hydrogen bond donor to hydrogen bond acceptor is 1:0.1-5; The hydrogen bond donor is an olefinic substance, or a mixture of an olefinic substance and a non-olefinic substance; The olefinic substance is any one or more of acrylamide, acrylic acid, and hydroxyethyl methacrylate, and the non-olefinic substance is any one or more of glycerol, urea, benzoic acid, malonic acid, and 1,4-butanediol; The hydrogen bond acceptor is any one or more of choline chloride, ammonium chloride, choline fluoride, betaine, lithium bis(trifluoromethanesulfonyl)imide, glycine, histidine, and alanine.

5. Application of the hydrogen-bonded organic framework-poly-deep eutectic solvent composite hydrogel obtained by the method according to claim 1, characterized in that: Used as an intermediate layer for wearable strain sensors.

6. The use according to claim 5, characterized in that: The steps include: The poly-low eutectic solvent-hydrogen bond organic framework composite gel is used as the middle layer of the wearable strain sensor, copper wires are wrapped around both ends, and they are fixed between two pieces of tape to assemble into a strain sensor.

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